WO2014089069A1

WO2014089069A1 - Multi-site operation in shared spectrum

Info

Publication number: WO2014089069A1
Application number: PCT/US2013/072860
Authority: WO
Inventors: Rocco Digirolamo; Debashish Purkayastha; Jean-Louis Gauvreau; Yuying Dai
Original assignee: InterDigital Patent Holdings Inc
Current assignee: InterDigital Patent Holdings Inc
Priority date: 2012-12-03
Filing date: 2013-12-03
Publication date: 2014-06-12
Anticipated expiration: 2015-06-03

Abstract

Procedures enable multi-site aggregation (MSA) for a wireless transmit/receive unit (WTRU). MSA may be initiated by a macro cell or a small cell. A small cell evaluation procedure may be triggered at a WTRU based on information from a serving macro cell, which may include a list of available small cells within a coverage area of the macro cell. A WTRU may receive discovery signals from one or more small cells, and may perform inter-frequency measurements on the frequencies associated with the small cells in order to rank small cells. Procedures may enable a WTRU to transition between IDLE mode and Connected mode with MSA enabled. Other procedures support MSA including radio resource control (RRC) connection establishment and re-establishment in multi-layer operation, WTRU speed determination, connection request, admission control and resource negotiation, initial access, adding radio bearers across a small cell, and small cell and macro cell handovers.

Description

MULTI-SITE OPERATION IN SHARED SPECTRUM

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application

No. 61/732,659, filed December 3, 2012, the contents of which are hereby incorporated by reference herein.

BACKGROUND

[0002] According to Third Generation Partnership Project (3GPP) Long

Term Evolution (LTE) Release 10 (R10), Radio Resource Control (RRC) connection establishment may be used to make the transition from RRC IDLE mode to RRC Connected mode. A wireless transmit/receive unit (WTRU) may make the transition to RRC Connected mode before transferring any application data, or completing any signaling procedures.

[0003] The RRC connection establishment procedure may be initiated by the WTRU but may be triggered by either the WTRU or the network. For example, the WTRU may trigger RRC connection establishment if the end-user starts an application to browse the internet, or to transmit an email. Similarly, the WTRU may trigger RRC connection establishment if the WTRU moves into a new Tracking Area (TA) and has to complete the Tracking Area Update (TAU) signaling procedure. The network may trigger the RRC connection establishment procedure by transmitting a Paging message to the WTRU. This may be used to allow the delivery of an incoming SMS or notification of an incoming voice call.

[0004] The RRC Connection Request message may be transmitted as part of the Random Access procedure. It may correspond to the initial Layer 3 message. For example, it may be transferred using signaling radio bearer (SRB)

0 on the Common Control Channel (CCCH) in the case where neither SRB 1 nor a Dedicated Control Channel (DCCH) have been setup at this point. The uplink

Resource Block allocation for the RRC Connection Request message may be signaled within the Random Access Response message. The RRC Connection

Request message may include a WTRU identity and an establishment cause. [0005] The WTRU may monitor the physical downlink control channel

(PDCCH) for a downlink allocation addressed to its cell radio network temporary identifier (C-RNTI). The PDCCH may specify the set of physical downlink shared control channel (PDSCH) Resource Blocks used to transfer the RRC Connection Setup message. The RRC Connection Setup message may be transferred using SRB 0 on the CCCH. The RRC Connection Setup message may contain configuration information for SRB 1. This may allow subsequent signaling to use the DCCH logical channel. SRB 2 may be configured after security activation.

[0006] The RRC Connection Setup message may also define configuration information for the PDSCH, physical uplink control channel (PUCCH) and physical uplink shared control channel (PUSCH) physical channels. It may also include information regarding uplink power control, channel quality indicator (CQI) reporting, the Sounding Reference Signal, antenna configuration and scheduling requests. Subsequently using Dedicated Control Channel, WTRU and evolved NodeB (eNB) proceed to setup data radio bearers.

SUMMARY

[0007] Procedures enable multi-site aggregation (MSA) for a wireless transmit/receive unit (WTRU). MSA may be initiated by a macro cell or a small cell. A small cell evaluation procedure may be triggered at a WTRU based on information from a serving macro cell, which may include a list of available small cells within a coverage area of the macro cell. A WTRU may receive discovery signals from one or more small cells, and may perform inter-frequency measurements on the frequencies associated with the small cells in order to rank small cells. Procedures may enable a WTRU to transition between IDLE mode and Connected mode with MSA enabled. Other procedures support MSA including radio resource control (RRC) connection establishment and re- establishment in multi-layer operation, WTRU speed determination, connection request, admission control and resource negotiation, initial access, adding radio bearers across a small cell, and small cell and macro cell handovers. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:

[0009] FIG. 1A is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented;

[0010] FIG. IB is a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A;

[0011] FIG. 1C is a system diagram of an example radio access network and an example core network that may be used within the communications system illustrated in FIG. 1A;

[0012] Figure 2 is a flow diagram of an example X2 based small cell handover procedure;

[0013] Figure 3 is a diagram of an example deployment environment that may be used for multi-site aggregation (MSA);

[0014] Figure 4 is a diagram of an example deployment environment where a wireless transmit/receive unit (WTRU) is not in the vicinity of the small cells;

[0015] Figure 5 is a flow diagram of an example procedure for gathering small cell information for an IDLE mode WTRU;

[0016] Figure 6 is a flow diagram of an example procedure for gathering small cell information for a Connected Mode WTRU;

[0017] Figure 7 is a flow diagram of an example procedure for small cell measurement and ranking in IDLE mode, performed by a WTRU;

[0018] Figures 8A and 8B are examples of measurement event triggers as measured quantities over time;

[0019] Figure 9 is a flow diagram of an example procedure for system information change on a small cell based on a paging message;

[0020] Figures 10 and 11 are flow diagrams of example procedures for a successful and an unsuccessful Radio Resource Control Connection Reestablishment, respectively; [0021] Figure 12 is a flow diagram of an example procedure of an RRC connection re-establishment failure in multi-layer operation fall back to small cell standalone mode;

[0022] Figure 13 is a flow diagram of an example procedure for WTRU speed determination in Connected Mode;

[0023] Figure 14 is a flow diagram of an example procedure for a WTRU transitioning from IDLE mode to Connected Mode with MSA enabled;

[0024] Figure 15 is a flow diagram of an example procedure for a connection request;

[0025] Figure 16 is a flow diagram of an example connection request procedure;

[0026] Figure 17 is a flow diagram of an example admission control and resource negotiation procedure;

[0027] Figure 18 is a flow diagram of an example Initial Access Procedure on a small cell;

[0028] Figure 19 is a flow diagram of an example procedure for adding a data radio bearr (DRB) across a small cell;

[0029] Figure 20 is a flow diagram of an example procedure for adding a

DRB across a small cell;

[0030] Figure 21 is a flow diagram of an example macro cell initiated MSA procedure;

[0031] Figure 22 is a flow diagram of an example small cell initiated MSA procedure;

[0032] Figure 23 is a flow diagram of an example small cell layer handover procedure;

[0033] Figure 24 is a flow chart of an example macro cell handover procedure where the small cell is unchanged;

[0034] Figure 25 is a flow diagram of an example macro cell handover procedure with small cell change;

[0035] Figure 26 is an example protocol architecture for MSA with the macro cell as the anchor node; [0036] Figure 27 is an example protocol architecture for MSA with the serving gateway (S-GW) as the anchor node; and

[0037] Figure 28 is an example of a protocol stack in a WTRU with a split medium access control (MAC) entity.

DETAILED DESCRIPTION

[0038] FIG. 1A is a diagram of an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like.

[0039] As shown in FIG. 1A, the communications system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d may be configured to transmit and/or receive wireless signals and may include user equipment (WTRU), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like. [0040] The communications systems 100 may also include a base station

114a and a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the core network 106, the Internet 110, and/or the networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements.

[0041] The base station 114a may be part of the RAN 104, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and/or the base station 114b may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station 114a may employ multiple -input multiple output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell.

[0042] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0043] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

[0044] In another embodiment, the base station 114a and the WTRUs

102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and/or LTE- Advanced (LTE-A).

[0045] In other embodiments, the base station 114a and the WTRUs 102a,

102b, 102c may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0046] The base station 114b in FIG. 1A may be a wireless router, Home

Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the core network 106.

[0047] The RAN 104 may be in communication with the core network 106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (V oIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 and/or the core network 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may be utilizing an E-UTRA radio technology, the core network 106 may also be in communication with another RAN (not shown) employing a GSM radio technology.

[0048] The core network 106 may also serve as a gateway for the WTRUs

102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and/or other networks 112. The PSTN 108 may include circuit- switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks 112 may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks 112 may include another core network connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0049] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities, i.e., the

WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links.

For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellular -based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0050] FIG. IB is a system diagram of an example WTRU 102. As shown in FIG. IB, the WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad 128, non-removable memory 106, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals 138. It will be appreciated that the WTRU 102 may include any subcombination of the foregoing elements while remaining consistent with an embodiment.

[0051] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit/receive element 122. While FIG. IB depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0052] The transmit/receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals.

[0053] In addition, although the transmit/receive element 122 is depicted in FIG. IB as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0054] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit/receive element 122 and to demodulate the signals that are received by the transmit/receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example.

[0055] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 106 and/or the removable memory 132. The non-removable memory 106 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0056] The processor 118 may receive power from the power source 134, and may be configured to distribute and/or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like.

[0057] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location- determination method while remaining consistent with an embodiment.

[0058] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like.

[0059] FIG. 1C is a system diagram of the RAN 104 and the core network

106 according to an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106.

[0060] The RAN 104 may include eNode-Bs 140a, 140b, 140c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 140a, 140b, 140c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 140a, 140b, 140c may implement MIMO technology. Thus, the eNode-B 140a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0061] Each of the eNode-Bs 140a, 140b, 140c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in FIG. 1C, the eNode-Bs 140a, 140b, 140c may communicate with one another over an X2 interface.

[0062] The core network 106 shown in FIG. 1C may include a mobility management gateway (MME) 142, a serving gateway 144, and a packet data network (PDN) gateway 146. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0063] The MME 142 may be connected to each of the eNode-Bs 142a,

142b, 142c in the RAN 104 via an Si interface and may serve as a control node. For example, the MME 142 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 142 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0064] The serving gateway 144 may be connected to each of the eNode Bs

140a, 140b, 140c in the RAN 104 via the Si interface. The serving gateway 144 may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102c. The serving gateway 144 may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0065] The serving gateway 144 may also be connected to the PDN gateway 146, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0066] The core network 106 may facilitate communications with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit- switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the core network 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network 106 and the PSTN 108. In addition, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0067] The operation of local-area access may include local-area nodes creating cells of their own, while operating stand-alone and relatively independently of the overlaid macro layer. In such a case, the low-power nodes may transmit all the signals associated with a cell, including cell- specific reference signals and synchronization signals, and the full set of system information. Furthermore a mobile device may communicate with either a single local-area node or a single macro node.

[0068] A stand-alone node may operate regardless of the presence of a wide-area layer. However, in scenarios where basic coverage is already available from the wide-area layer, benefits may be achieved by operating the wide-area and local-area layers in a more integrated manner where the terminal is connected to both of the layers.

[0069] A node (e.g. a WTRU) may have dual connectivity: (1) to the wide- area layer through an anchor carrier used for system information, basic radio- resource control (RRC) signaling and possible low-rate/high-reliability user data; and (2) to the local-area layer through a booster carrier used for large amounts of high-rate user data. The booster-carrier transmissions may be ultra-lean with the minimum possible amount of overhead including no cell- specific reference signals and no system information. This may also be referred to as New Carrier Type (NCT). In essence, there may be booster carrier transmissions only in subframes in which there are information to transmit to a terminal.

[0070] As part of LTE Dynamic Spectrum Management (DSM), methods and procedures may support the activation of multi-site aggregation in LTE Connected mode, where aggregation may be across a macro cell and/or a dynamic and/or shared spectrum small cell.

[0071] Small cells may operate in a different band than the one used by the macro cells, for example, using the 3.5 Gigahertz (GHz) band. In the United States, the 3550-3650 MHz band may be used by US Military Navy Radar systems. However, regulations may be put in place which will allow small cells to operate on this band. More generally, a President's Council of Advisors on Science and Technology (PCAST) report has discussed the notion of a Spectrum Access System (SAS) that may give incentive to federal primary users to share their spectrum with Tier 2 users, such as Operators, and Tier 3 users, such as Wi-Fi.

[0072] A number of other sources of dynamic and shared spectrum exist.

For example, as a result of the transition from analog to digital television (TV) transmissions in the 470-862 Megahertz (MHz) frequency band, certain portions of the spectrum may no longer be used for TV transmissions, though the amount and exact frequency of unused spectrum varies from location to location. These unused portions of spectrum may be referred to as TV White Space (TVWS). The

FCC has opened up these TVWS frequencies for a variety of unlicensed uses. The

470-790 MHz band may be exploited by secondary users for any radio communication, provided that this communication does not interfere with other incumbent/primary users of the band. As a result, the use of LTE and other cellular technologies within the TVWS bands has recently been considered, notably in standards bodies such as The European Telecommunications Standards Institute (ETSI) Reconfigurable Radio Systems (RRS) group. Use of LTE in other unlicensed bands such aa industrial, scientific and medical (ISM) radio bands may therefore also be possible.

[0073] TVWS cells may have specific power limitations, for example the

FCC allows 100 Milliwatts (mW) for portable devices on an available channel, or 40mW on a channel adjacent to the operating channel of primary user. As a consequence of the limited power, it may be that the coverage radius of a TVWS cell may be smaller than a typical licensed Macro cell.

[0074] In a Dynamic Shared Spectrum (DSS), the LTE system may need to dynamically change from one unlicensed frequency to another, for example, because of the presence of interference and/or potentially primary users in the unlicensed bands. For example, a strong interference, such as a microwave or cordless phone, may make a particular channel in the ISM band unusable for data transmission. IN another example of dealing with TVWS channels as the unlicensed channels, a user of these channels may need to evacuate the channel upon the arrival of a system which has exclusive rights to use that channel, such as a TV broadcast or wireless microphone in the case of TVWS. Furthermore, the nature of unlicensed bands and the increase in the number of wireless systems that may make use of these bands may inherently result in the relative quality of channels within the licensed band changing dynamically. In order to handle to this, an LTE system in DSS may be able to dynamically change from one unlicensed channel to another or to reconfigure itself in order to operate on a different frequency.

[0075] According to LTE R10, a WTRU may only be connected to a single eNB at any one time. If, while connected to a macro cell, the WTRU finds a small cell as part of its intra-frequency or inter-frequency measurements, the WTRU may monitor this small cell and transmit associated measurement reports to the macro cell. In response to these measurement reports, the macro cell may then initiate a handover to the small cell. [0076] Figure 2 is a flow diagram of an example X2 based small cell handover procedure 200. The example handover procedure 200 may be used in LTE R10. The entities in the system include a WTRU 201, a macro cell 202, a small cell 204, an MME 204, a serving gateway (S-GW) 205 and a packet data network (PDN) gateway (P-GW) 206. According to handover procedure 200, the macro cell 202 may send an RRC measurement configuration message, 210. For example, the RRC measurement configuration message, 210, may allow the WTRU to obtain the neighbor cell list from the macro cell, as well as the measurement configuration information. The WTRU may configure intra and inter-frequency measurements, 212, based on the RRC measurement configuration message, 210. The WTRU may measure intra-frequency and inter- frequency cells, 214, in order to monitor small cell(s), including small cell 203.

[0077] A handover may occur if at some point, the WTRU 201 triggers a measurement event for the small cell 203. The WTRU 201 may transmit an RRC measurement report, 216, to macro cell 202. The macro cell 202 may decide whether to initiate a handover to the small cell 203, 218. If a handover is triggered, the macro cell 202 may initiate a HANDOVER Request, 220, to the small cell 203. If the small cell 203 accepts the handover, it may prepare the configuration details for the WTRU 201 (i.e. for operation over the small cell 203) and may transmit this information to the WTRU 201, by transmitting a container that is transported in the HANDOVER Request acknowledgment (Ack), 220, from small cell 203 to macro cell 202, and through a HANDOVER command, 226, from the macro cell 202 to the WTRU 201. During this process, the X2 bearer may be established, 224.

[0078] The WTRU 201 may disconnect from the macro cell 202 and may start synchronization over a Random Access Channel (RACH), 228, on the small cell 203. The RACH may be a non- contention RACH (with a dedicated preamble). If RACH is successful, the small cell 203 may provide the timing advance information to the WTRU 201, as well as an uplink (UL) allocation, 230.

The WTRU 201 may send an RRC HANDOVER confirm message, 232, to the small cell 203. In response to the HANDOVER confirm message, 232, the small cell 203 may begin a PATH SWITCH procedure, 235, to tell the S-GW 205 to transfer the Radio Access Bearers from the macro cell 202 to the small cell 203. The PATH SWITCH procedure, 235, may include: a path switch request, 234, from small cell 203 to MME 204; a modify bearer request, 236, from MME 204 to S-GW 205; a modify bearer request, 238, from S-GW 205 to P-GW 206; a modify bearer response, 240, from P-GW 206 to S-GW 205; a modify bearer response, 242, from S-GW 205 to MME 204; and a path switch request ack, 244, from MME 204 to small cell 203.

[0079] Following the PATH SWITCH PROCEDURE, 235, the small cell

203 may inform the macro cell 202 that the handover has been completed by transmitting a WTRU Context Release message, 246, so that the macro cell 202 may remove the WTRU context.

[0080] An eNB may have neighbor intra-frequency cells, neighbor inter- frequency cells, and neighbor inter-RAT cells. The eNB may maintain neighbor relations with these cells through knowledge of some operational details including, but not limited to, the frequency of operation of a neighbor inter- frequency cell, and/or the RAT type of a neighbor inter-RAT cell. The eNB may use the neighbor relation information to assist a WTRU in cell reselection and handover. This assistance may be through neighbor cell lists broadcast in system information or through dedicated signaling.

[0081] The eNB may build its neighbor relations through either manual configuration and through some Operation and Maintenance (OAM) assistance or through Automatic Neighbor Relation (ANR) functionality. In the ANR case, the eNB may continue to rely on OAM assistance, but replace the manual configuration with WTRU assistance to help find the neighbors. The eNBs may exchange cell information through the X2 interface. For example, eNBl may inform eNB2 about an activated or modified cell through an ENB CONFIGURATION UPDATE message. This provides eNB2 with the details about the cell controlled by eNBl.

[0082] An anchor node/entity may be a node or entity at which aggregation may occur and where the data may be routed to the different sites involved in the aggregation. An umbrella macro cell may be a macro cell that has a number of small cells in its coverage area. These small cells and the umbrella macro cell may communicate over an X2 interface, modified X2 interface, or some other interface. Planned small cells may be planned small cells having some structure, for example, a linear structure along a highway. Unplanned small cells may be randomly located and may be installed by different parties. An example of an unplanned cell may be in a hotspot. Clustered small cells may be clustered cells that are a grouping of cells that have some overlap. Non-clustered cells may have limited or no overlap. WTRU state information may be information related to the WTRU including, but not limited to, a speed indication, and/or a power status, for example.

[0083] As described above, small cells may operate in a different band thanthe one used by the macro cells, for example, the 3.5GHz band. Regulations may be put in place, which may allow small cells to share the the 3550-3650 MHz band with the Navy Radar system. Moreover, Spectrum Access System (SAS) may give incentive to federal primary users to share their spectrum with Tier 2 users (e.g. Operators) and Tier 3 users (e.g. Wi-Fi). The operation as a Tier 2 user may be impacted compared to licensed spectrum usage.

[0084] A small cell operating in DSS may be under umbrella coverage of a macro cell. The deployment of these DSS small cells may be clustered, either in some area in a planned organized manner or in some unplanned sporadic manner. The configuration and operating details (for example, frequency, UL/DL format, RACH format, and coexistence mechanism) of these cells may be very dynamic or much more dynamic than that of licensed cells.

[0085] Examples of problems that may arise if these small cells are to use

DSS and allow for multi-site aggregation (MSA) mode include the following. In an first example, the spectrum usage of the DSS small cells may be more dynamic as the incumbent may move back in some spectrum segments, which may force the DSS small cells to change operating frequency. The assignment of spectrum to a DSS small cell may vary from one location to another, making discovery and mobility handling more challenging. Multiple operators deploying DSS small cells may also share the same band potentially using the same frequencies, which may lead to multiple public land mobile networks (PLMNs) overlapping.

[0086] In another example, neighbor relations between the macro cells and the small cells may be very dynamic. The maintenance of these neighbor relations may either imply a heavy signaling load on the X2 interface between the small cell and macro cell, or an excessive burden on the WTRUs to assist in ANR. For example, a frequency change affecting a number of clustered small cells may result in a high signaling load towards the macro cell, as all these small cells inform the macro of the neighbor relation change.

[0087] In another example, when WTRUs use intra and inter frequency measurements, the WTRUs may be continuously looking for DSS small cells, which may lead to additional processing and poor battery utilization. In an example scenario, a WTRU may be unnecessarily looking for DSS small cells where there are none in the vicinity.

[0088] In another example, in the case where the WTRU has an indication that small cells are present in a locality, the size and number of DSS bands may make small cell discovery slow, as the WTRU may be required to scan through the complete spectrum in order to discover the small cells. Scanning through the whole bandwidth may burden the processor, drain battery life and reduce throughput for introducing system wide gap to measure inter frequency small cells.

[0089] In another example, DSS small cells may be used especially for offloading, and these small cells may rely on the macro cells for control signaling.

This use case may apply both to new emerging operators with no licensed spectrum, as well as to established operators providing services outside of their home regulatory domains (for example, Verizon providing service in Canada). In these cases, the foreign operator may establish agreements with the local operators who own the licensed spectrum, and who agree to provide the control signaling to roaming WTRUs, provided that these WTRUs are offloaded as quickly as possible to the DSS small cells, so as not to interfere with the non- roaming WTRUs. Two such scenarios where this offload may need to be quick are when moving from IDLE to connected mode with MSA enabled, and when performing a macro cell handover to a cell with DSS small cells. Certain RRC and network procedures may not allow for these two scenarios. For example, the connection establishment procedure may not be capable of starting a multi-site aggregation session for an IDLE mode WTRU.

[0090] In another example, a first cell may have has no means to request the start of multi-site aggregation for a connected mode WTRU with a second cell. A multi-site aggregation procedure may not be defined to manage the transfer of radio access bearers between the first cell and the second cell. In another example, the macro cell may have no procedure to determine when to start multi-site aggregation. This procedure may be different from the one used for handover decisions, which is based mostly on RF signal quality.

[0091] In another example, the addition of TVWS channels in a MSA mode may not work using Release 10 LTE procedures. IDLE mode measurement, RACH procedures, Radio bearer addition, Radio bearer reconfiguration procedures may need modification. Radio bearers of a WTRU may no longer be tied to a single medium access control (MAC) and/or physical (PHY) layer. The protocol stack may require enhanced MAC and radio link control (RLC) protocols to handle multiple data flows, coordinated silent periods, sudden change in cell availability, among other things.

[0092] In another example, Radio Access Bearers (RABs) from a serving gateway (S-GW) to a given WTRU may no longer be destined to a single eNB. The S-GW may need a new segregation functionality to route RABs to the different cells involved in the multi-site aggregation.

[0093] Procedures and techniques described below may manage the activation of multi-site aggregation, particularly in DSS. A procedure may perform DSS small cell discovery based on GPS, markers, a reserved discovery frequency, and/or an order from the macro cell. An MSA activation procedure may allow the transfer of some RABs from the macro cell to the small cell.

According to the MSA activation procedure, the WTRU may use the MSA Activation Command to set up the secondary MAC and PHY for the DSS small cell, to initiate the radio bearers that were transferred to the small cell, and to release the transferred radio bearers from the macro cell.

[0094] According to an RRC Connection establishment procedure, a WTRU in IDLE may transition directly to Connected Mode with MSA enabled. This may include connection request procedure from IDLE mode providing an MSA status information element (IE) that may include details for a ranked list of DSS small cells. For example the details may include some operator identification. An admission control and resource negotiation procedure, may involve the MME holding off the dedicated evolved packet system (EPS) bearer creation until it receives confirmation from the small cell that it has accepted or refused the MSA activation request. A connection setup may include the macro cell providing the WTRU with the details for the MSA activation across both the macro cell and the small cell. An initial access procedure on the small cell may perform timing using.

[0095] According to another procedure, the anchor aggregation node may route traffic to a WTRU based on the RAB identity. For example, some RABs may go to the macro cell and others may go to the small cell. This anchor aggregation node may be the macro cell eNB, the S-GW or some interworking gateway.

[0096] Procedures may manage the neighbor relations with small cells using DSS including exchange of new information such as discovery signal configuration, and/or type of small cell, including planned versus unplanned, and/or clustered versus non-clustered. Such procedures may done over an X2 exchange, or relying on a centralized repository that may push information to macro cells.

[0097] A MAC functionality may associate radio bearers to either the primary or secondary MAC and/or PHY layers. Small cell evaluation procedures may be initiated in IDLE mode for Connected Mode operation. An MSA activation algorithm at the macro cell eNB may be based on the availability of resources, and/or may be based on any of the following: WTRU speed, band support, and/or deployment characteristic of small cell.

[0098] A procedure may perform WTRU speed determination based on

GPS information of the WTRU, GPS information of the serving cell, and/or number of cell change events, which may include (combined) IDLE mode events and/or Connected Mode events. A WTRU autonomous control procedure may allow the WTRU to refuse to start MSA related procedures.

[0099] Measurement configuration and reporting procedures for Connected

Mode WTRUs may provide the WTRU with information particular to a DSS small cell and may configure the WTRU to generate DSS small cell specific reports, including for example a ranked list repport. A PATH SWITCH procedure may transfer the bearers at the S-GW.

[0100] Figure 3 is a diagram of an example deployment environment 300 that may be used for MSA. The example deployment environment 300 includes macro cells 301 and 302 and several small cells, shown by small circles, including small cells 305 and 312. The macro cells 301 and/or 302 may operate on a frequency (e.g. frequency fl) and may act as an umbrella or parent cell to a number of small cells. The small cells, which may operate in DSS, may not be expected to have the same operating frequency and configuration as the macro cells 301 and/or 302. Small cells within a macro cell may be grouped according to some common characteristic. For example, the grouping may be based on the deployment of the small cells, such as clustered, non-clustered, random, or planned. Clustered may be a number of small cells in close vicinity. Non- clustered may be isolated or sporadic deployment of cells. Random may be small cells with no deployment structure, For example as one found in hot spot setting. Planned may be small cells with a deployment structure, For example along a highway. Examples of small cell groupings are illustrated in Figure 3, including a random and clustered group 306, a non-clustered group 308, and a planned and clustered group 310, which is shown as being along a road or highway.

[0101] The following assumptions may be used here in for illustration purposes. The macro cell may be assumed to be in the licensed band and the small cells that provide multi-site aggregation may be in DSS, for example, tier 2 users in shared spectrum. The WTRU may be in macro cell umbrella coverage. Macro cell and the small cell may be operated by the same operator or by different operators. The WTRU may capable and allowed to operate in both macro cells and small cells when two different operators are involved. The WTRU may operate one or more radios. For example, the WTRU may have two independent radios that may run simultaneously. For example, one radio may be for the licensed carrier on the macro cell and a second radio may be for the booster carrier on the MSA capable small cell.

[0102] In a multi-site shared spectrum scenario, the configuration of the small cells may change dynamically. For example, the operating frequency of each small cell may depend on the available spectrum in an area. If this frequency is shared between multiple systems, a higher priority system may force an operating frequency change in the small cell. Other configuration aspects of the small cell may also change dynamically. For example, this may include coexistence mechanism, and/or uplink (UL) and/or downlink (DL) configuration for a TDD small cell.

[0103] When a small cell changes its configuration, the neighbor macro cells may need to be informed in order to generate the appropriate neighbor cell list. In the case of multi-site aggregation, the neighbor macro cells may refer to the overlay or umbrella cells, as shown in Figure 3. Two methods are described below for updating the macro cell: the X2 interface method; and the shared spectrum repository method.

[0104] According to the X2 interface method, the small cell may transmit a configuration update message to the neighbor (umbrella) macro cell to provide the updated configuration. For example, this may be based on an enhanced ENB

CONFIGURATION UPDATE message or a small cell equivalent ENB

CONFIGURATION UPDATE message. The information may include, but is not limited to, the following list of configuration elements: an indication that cell is a small cell; the operating frequency of the small cell; the coexistence mechanism used in the small cell; the UL/DL configuration used in the small cell; the load in the small cell; the geolocation of the small cell; whether the cell is clustered or not; whether the cluster is random or not; and identification of the umbrella macro cell.

[0105] The information may be divided into group information that is common to a group of small cells (for example, with a common operating frequency, UL/DL configuration, and/or small cell deployment) and into cell- specific information that may be independently managed for each small cell, for example, based on a coexistence mechanism, or load. The small cell eNBs that are part of a group may designate one small cell eNB as the master of the group, which may be referred to as the Small Cell eNB Group Master. When an item in the group information changes, the Small Cell eNB Group Master may send the configuration update message to the umbrella macro cell.

[0106] Alternatively, the information may be divided in primary information that the umbrella macro cell eNB may need to be immediately informed, or secondary information that may not be as urgent. The ENB CONFIGURATION UPDATE message may be transmitted for all small cell configuration changes to primary information. In addition, the ENB CONFIGURATION UPDATE message may be transmitted periodically to inform the macro umbrella cell about the changes in the secondary information, for example, to make sure that the macro cell is aware of small cells that are no longer in service. The small cell eNB configuration information may be carried to the umbrella macro cell eNB in a DSSSmallCelllnfo IE.

[0107] According to the shared spectrum repository method, the small cells may transmit their operating information to a shared repository that may reside in the evolved packet core or some third party entity. For example, the shared repository may reside in a small cell GW, in the MME, and/or in an Oracle Access Manager (OAM) server. Every time a configuration element changes, the small cells may update the shared repository with the new configuration. The small cell eNBs may send the new configuration using a configuration update message. The shared repository may build a table for each macro umbrella cell. Upon reception of a configuration update message, the shared repository may update the table entry for the impacted umbrella macro cell.

[0108] When needed, the macro cell may query the shared repository to get the latest view of small cell deployment. Alternatively, the shared repository may push this information to the impacted macro cells. The repository may perform any of the following: push this information as a result of an event, for example, a small cell frequency change; push this information periodically; or have some information pushed periodically while other information is pushed as a result of an event.

[0109] The rules for group information, cell-specific information, primary information, and secondary information may also apply to this method. As the configuration elements from multiple small cells may be centralized, the repository may combine or fuse the information before sending to the macro cell, thereby reducing the signaling load to the macro cells.

[0110] Small cell discovery procedures may be used to search for small cells to enable MSA. In order to setup a radio bearer with small cell, it may be useful determine which small cell may best serve the WTRU. Small cell availability may not always be guaranteed. The cells may be in small or large clusters in either a planned way or an unplanned way. It may not be beneficial for a WTRU to constantly monitor for small cells, which may involve scanning the complete band and performing frequent intra/inter frequency measurements, which may quickly drain the WTRU's battery. Procedures described below may be used to assist a WTRU in knowing the availability of small cell without wasting battery power.

[0111] Figure 4 is a diagram of an example deployment environment 400 where a WTRU is not in the vicinity of the small cells. WTRU 406 is within macro cell 402 but is far away from planned small cell cluster 404. Accordingly, in the example deployment environment 400, the WTRU 406 may benefit from not searching for small cells.

[0112] According to a macro cell assisted small cell discovery procedure, the WTRU may trigger a small cell evaluation procedure based on information from the umbrella macro cell. A macro cell may gather information about small cells operating within its coverage area using the mechanisms described above.

[0113] LTE System Information may be updated to include a possible list of small cells available within the coverage of the macro cell. Table 1 is an example of advanced information relative to small cells.

Information oment

SmallCelllnformationList (l...n) of

Celllnfo

• Cell ID

• PLMN ID, Operator ID

• TVWS Band identifier

• Channel, frequency information

• Discovery signal configuration

(periodicity, frequency)

• Type of small cell (planned vs

unplanned, clustered vs non- clustered)

• Geolocation (center, range)

• Coexistence mechanism

TABLE 1

[0114] Table 1 shows a SmallCelllnformationList IE, that may contain any of the following elements: cell identification (ID), PLMN ID, operation ID, TVWS band identifier, channel information, frequency information, discovery signal configuration (including periodicity and frequency), type of small cell, geolocation information, and/or coexistence mechanism information. The SmallCelllnformationList IE shown in Table 1 may be contained in the master information block (MIB), system information block 1(SIB1) or system information block 2 (SIB2), for example.

[0115] Upon determining the system information in a cell, for example, due to a handover or from a cell reselection, a WTRU may determine if the cell encompasses any small cells. For example, after a cell reselection to a macro cell, or a handover to a macro cell, whose system information contains a non-empty Small Cell Information List IE, the WTRU may start a small cell evaluation procedure.

[0116] According to a geolocation based small cell discovery procedure, the

WTRU may rely on location information to trigger a small cell evaluation procedure, which may include searching and/or monitoring for small cells to enable multi-site aggregation.

[0117] According to an embodiment, the WTRU may rely on GPS information to trigger a small cell evaluation procedure, which may be its own GPS location information and/or the GPS location information of the small cells. Fro example, the WTRU may determine the distance between itself and the closest small cell and may begin a small cell search or a small cell evaluation procedure if the distance is below a pre-configured threshold. The WTRU may rely on additional small cell information to estimate the coverage range of a small cell and determine whether to start a small cell search. For example, the WTRU may use the small cell transmitted power, GPS location, and/or pathloss model to estimate the coverage contour of a small cell, and only trigger a small cell evaluation procedure if within this contour.

[0118] According to another embodiment, the WTRU may rely on macro cell markers and/or indications to trigger small cell evaluation procedure. For example, in the case that small cells are used to increase the cell edge coverage, the small cells may be found in areas where macro cell coverage overlaps.

WTRUs in these overlap regions may be able to detect all or a subset of the overlapped macro cells. The detection of these overlapped macro cells, for example during normal intra-frequency measurements, may be used as a location indication, and may trigger the WTRU to start a small cell evaluation procedure. The marker and/or indication information may be pre-configured in the WTRU. In these examples, the pre-configuration information may come from an umbrella macro-cell, for example through system information, or through dedicated signaling, or from a OAM procedure. [0119] According to an embodiment where small cells may use a second known frequency band, the small cells may broadcast a heartbeat or discovery signal in a second frequency (f2), which may be different than the small cell operating frequency (fl). The signal on the second frequency may become a form of beacon to indicate proximity to a small cell. Alternatively, the same cells may be grouped in a cluster, which may use a common frequency to broadcast the discovery signal, although cells in that cluster may use different operating frequencies. In this scenario, the discovery signal may signal a form of cluster ID. The same frequency may be used by all small cells of a given cluster to transmit the discovery signal. Small cells may transmit the discovery signal continuously or periodically, for example N sub-frames every frame or 1 sub- frame every N frames.

[0120] The discovery signal may encode identification information related to the small cell. The identification information may include, but is not limited to, any of the following: an indication that the cell is a small cell; an indication that the cell is an MSA capable small cell; an indication as to the frequency used in the small cell, for example the band of operation, the center frequency of operation, the offset between the frequency of operation and/or the discovery frequency; an indication of the operator of the small cell, for example, the PLMN ID or some other operator identification; a cell identification, for example the physical cell ID (PCI) or the Cell global ID (ECGI); and/or an indication as to the type of small cell (e.g. planned vs unplanned, clustered vs non-clustered). This information may be used to reduce discovery time by the WTRU. Some or all of the small cells may transmit the discovery signal on the second frequency using various orthogonal codes.

[0121] The WTRUs may know the second frequency through some pre- configuration or through system information provided from the macro cell. The

WTRU may synchronize to the discovery signals on the second frequency, and may determine the encoded cell identification information, for example, the Cell

ID and/or PLMN ID. The WTRU may perform Inter- Frequency measurements on this second frequency every N milliseconds, which may be set to long periodicity. In addition, the WTRU may perform the measurement once when it attaches to the network and immediately before radio bearer setup due to a service request or a page. As all small cells may be using the same second frequency, the WTRU may find multiple discovery signals and determine that it is in the vicinity of multiple small cells.

[0122] The WTRU may rely on a metric to rank these small cells. For example, the metric may be based on the quality of the discovery and/or the information contained in the cell identification. Once the WTRU has found one or more discovery signals, it may select one from among those found, for example based on quality or PLMN-ID, and may start the small cell evaluation procedure on the operating frequency of the small cell.

[0123] According to an embodiment, the second frequency used to transmit the discovery signal may correspond to the operating frequency of the umbrella macro cell. In this scenario, a small cell operating on frequency fl, possibly in shared spectrum, may transmit a discovery signal on the macro licensed frequency to assist the WTRU in determining proximity to a small cell. The small cell may limit the transmission of the discovery signal on the macro cell frequency to reduce the interference caused to the macro cell. The WTRU may not be required to perform inter-frequency measurements to find the discovery signal and determine the small cell identification. Rather, these may be determined through intra-frequency measurements taken as part of IDLE mode, for example, for cell reselection, or as part of Connected Mode, for example, for mobility handover.

[0124] The discovery signal broadcast by the small cell may include a modified primary synchronization signal (PSS) and/or secondary synchronization signal (SSS). The PSS/SSS may be re-designed to encode the identification information described above. The encoding may replace that used in the Release 10 PSS/SSS, where the PSS/SSS encode a FDD/TDD indication and the Physical Cell ID (PCI). The WTRU may use the identification information to determine that the intra-frequency cell is a MSA capable small cell, and start a small cell evaluation procedure. [0125] According to a small cell discovery procedure involving a direct order from the umbrella macro cell, the macro cell may transmit an order to signal the WTRUs to start a small cell evaluation procedure. The macro cell may transmit this order for any number of reasons. For example, the macro cell may determine that it wants to initiate MSA to relieve congestion. In another example, the WTRU may have transmitted a measurement report that suggests to the macro cell that the WTRU is close to a small cell. For example, the macro cell may broadcast a cell wide order to inform all capable WTRUs to start the small cell evaluation procedure. This may be carried in the cells system information. In another example, the macro cell may transmit a targeted order to specific capable WTRUs to start the small cell evaluation procedure. The order may be transmitted through a new RRC message, through a new MAC control element (CE), or through some PHY layer signaling.

[0126] Any of the following techniques may be used as part of the small cell evaluation procedure. The discovery signal may carry enough information to allow the WTRU to begin measuring and ranking the small cells. For example, the discovery signal may provide the frequency of operation of the small cell as well as other configuration details of the small cell. Alternatively, the discovery signal may provide only limited information or the discovery signal may be absent and the WTRU may rely on R10 cell search information. In either case, the WTRU may not have enough information to begin measuring and ranking the small cells. In such a case, the WTRU may query the macro cell in order to determine the remaining information, including possibly the advanced information described in Table 1.

[0127] Figure 5 is a flow diagram of an example procedure 500 for gathering small cell information for an IDLE mode WTRU. Figure 5 shows a

WTRU 502, a macro cell 504 operating on frequency f3 and a small cell 506 operating on frequencies fl and f2. For example, small cell 506 may perform

LTE UL and/or DL operation, 520, on frequency fl. Small cell 506 may send a discovery signal, for example a beacon signal, on frequency f2, 508. The WTRU

502 may search for the discovery signal on frequency f2, 510. As part of the small cell discovery procedure, the WTRU 502 may find the discovery signal through inter-frequency measurements if frequency f2 is different from frequency f3 or through intra-frequency measurements if frequency f2 is the same as frequency f3.

[0128] The detection of the discovery signal, 512, may cause the WTRU

502 to start an RRC Connection request to determine the rest of the small cell information. The WTRU 502 may start with a R10 RACH procedure on the macro cell 504: sending random access preamble, 514, and receiving random access response, 516.

[0129] In its scheduled transmission, 518, the WTRU 502 may transmit an

RRC message, for example SmallCellEnquiryReq, to the macro cell 504, asking for additional configuration information for the small cell 506 it has found. It may include the cell identification information of the small cell 506, so that the macro cell may tailor its response to configuration details of only the small cell 506. The macro cell 504 may transmit the small cell details to the WTRU 502 as part of contention resolution, 522, through an RRC SmallCellEnquiryResp message. The WTRU 502 may then start measuring and ranking the small cell 506, 524.

[0130] Figure 6 is a flow diagram of an example procedure 600 for gathering small cell information for a Connected Mode WTRU. Figure 6 shows a WTRU 602, a macro cell 604 operating on frequency f3 and a small cell 606 operating on frequencies fl and f2. For example, small cell 606 may perform LTE UL and/or DL operation, 620, on frequency fl. Small cell 606 may send a discovery signal, for example a beacon signal, on frequency f2, 608. The WTRU 602 may search for the discovery signal on frequency f2, 610.

[0131] The detection of the discovery signal, 612, through inter-frequency or intra-frequency measurements, may result in an RRC exchange between the WTRU and the macro cell: transmitting RRC message SmallCellEnquiryReq, 618, to the macro cell 604, and receiving RRC message SmallCellEnquiryResp, 622, back from the macro cell 604. The details of this exchange may be similar to those described for IDLE mode WTRUs in Figure 5. The WTRU 602 may then start measuring and ranking the small cell 606, 624.

[0132] Once the WTRU has knowledge of the small cell configuration, it may begin to measure and rank these small cells in order to eventually start a MSA session. In IDLE mode, the WTRU may: synchronize to the small cells, determine some operator identification of the small cell (since it is possible that more than one operator is using the same frequency and cell ID); and measure the signal quality of the small cell.

[0133] According to an embodiment that may be used for LTE, the synchronization may be done through a PSS and/or SSS mechanism, which may allow the WTRU to determine the physical cell ID and as a result the location of the reference signals and measure the small cell Reference Signal Received

Power (RSRP) and Reference Signal Received Quality (RSRQ). The WTRU may also read the system information to determine the PLMN ID. The WTRU may store this information and keep a ranking of the found small cells. The WTRU may keep this small cell information separate from the measurement information for the macro cells used for cell reselection. The WTRU may not consider the MSA small cells for cell reselection and may not use any measurement rules on these small cells. For example, unlike inter-frequency and inter-RAT cells on licensed carriers, the WTRU may measure and rank the small cells even if the quality of the serving macro cell is very good.

[0134] Figure 7 is a flow diagram of an example procedure 700 for small cell measurement and ranking in IDLE mode, performed by a WTRU. If it is determined the serving cell is a macro cell, 702, the WTRU may perform a cell evaluation procedure, such as the procedure descripted in 3GPP Technical

Standard (TS) 36.304. The WTRU may perform synchronization, 714, measurements, 716, and rank operations, 718, on the intra-frequency cell(s).

The WTRU may perform a condition check by determining if the macro cell quality is poor, 720. If the macro cell quality is poor, then the WTRU may perform synchronization, 722, measurements, 724, and rank operations, 726, on inter-frequency and/or inter-RAT cells. Based on the intra and/or inter- frequency and inter-RAT macro cells ranking, The WTRU may performs cell reselection evaluation operations, 728, by evaluating the cell reselection criteria. If the cell is not a macro cell, 702, but is for example an MSA small cell, the WTRU may perform a procedure for MSA small cells, 704. The WTRU may perform any of the following: synchronization to inter-frequency small cells, 706; determine operator identification of small cell, 708; perform inter-frequency small cell measurements operation, 710; and inter-frequency small cell ranking operation, 712, which may occur regardless if the quality of the serving macro cell is very good. The WTRU may keep this small cell information separate from the measurement information for the macro cells and may not consider the MSA small cells for cell reselection and may not use any measurement rules on these small cells.

[0135] In Connected mode, the WTRU may be configured with measurement objects for each of the small cells for which MSA is possible. The WTRU may synchronize to these cells, read the operator identification, take measurements of signal quality, and transmit measurement reports in response to the configured measurement objects.

[0136] Procedures for MSA mode over DSS small cells may include measurement reporting and configuration for DSS small cells. Small cell measurements and reporting may be used to trigger both the setup and the teardown of multi-site aggregation. A macro cell eNB may configure a WTRU to start small cell measurements using, for example, a measConfig IE carried in the RRCConnectionReconfiguration message. In addition to the R10 measurement configuration details such as carrier frequency to measure and allowed measurement bandwidth, the configuration information may also provide coexistence information to the WTRU so that the WTRU may only take measurements when the DSS small cell is used by the LTE system for DL transmissions.

[0137] The macro cell eNB may provide the worst case coexistence gap duty cycle for all the small cells that the WTRU is asked to measure. For example, this may include all the small cells on a specific DSS frequency or all the small cells in the vicinity of the WTRU. The macro cell eNB may know the coexistence duty cycles of all the small cells. It may determine the small cell with the lowest duty cycle (i.e. least time spent in LTE) and signal this duty cycle to the WTRUs.

[0138] Alternatively, the macro cell eNB may provide the coexistence gap information on a per small cell basis. The macro cell eNB may also provide a speed restriction indication for a group of small cells sharing a DSS frequency or for a specific small cell. This information may be conveyed to the WTRU in a measObjectEUTRA IE, which may be carried in measConfig IE. Table 2 shows an example of a measObjectEUTRA IE that includes the following IEs: coexistenceGapConfig-rXX, speedRestriction-rXX, cellCoexistenceGapConfig- rXX, and cellSpeedRestriction-rXX. The remainder of the elements in Table 2 may be as described in the LTE RIO standard, for example in 3GPP TS 36.331, which is incorporated herein by reference.

TABLE 2

[0139] For example, the CoexistenceGapConfig-rXX IE may indicate the coexistence duty cycles of the small cells. It may have ten values, including for example: a value "low" indicating, during predefined duty cycle, that the small cell is operating at LTE mode most of the time, and only small portion of the time is left for other RATs; and a value "high: indicating that the small cell is operating in LTE mode for a small portion of the time, and large portion is left for other RATs. In another example, the SpeedRestriction-rXX IE may be a flag to indicate if the WTRU may set up inter-frequency measurements for the small cell. If speedRestriction-rXX is set to TRUE and the WTRU is in high mobility state, the WTRU may not set up inter-frequency measurements for the small cell. Otherwise, it may set up inter-frequency measurements for the small cell.

[0140] The WTRU may continuously monitor its speed state to determine if it is a "high", "medium", or "low" moving WTRU. Upon reception of the a MeasObjectEUTRA measurement object, as shown in Table 2, the WTRU may set-up inter-frequency measurements for this frequency if: speedRestriction-rXX IE is set to FALSE, or if speedRestriction-rXX IE is set to TRUE and the WTRU is not in the high mobility state.

[0141] Additionally, any time a WTRU changes its mobility state, it may re-assess its inter-frequency measurements for a DSS frequency. For example, if a MeasObjectEUTRA measurement object, as shown in Table 2, has speedRestriction-rXX set to TRUE and a WTRU determines that its mobility state has changed to "high", the WTRU may stop performing inter-frequency measurements on that frequency and stop sending measurement reports for that frequency. In contrast, if a MeasObjectEUTRA measurement object has speedRestriction-rXX set to TRUE and a WTRU determines that its mobility state has changed from "high" to either "medium" or "low", it may begin performing inter-frequency measurements and reporting measurements for this DSS frequency.

[0142] The network may optionally setup a new reporting event to gauge the quality of the small cell in an effort to maximize the data offload potential.

Figures 8A and 8B show examples of measurement event triggers as measured qualities over time. The measured quality is shown on vertical axis, and time on the horizontal axis. Figure 8A shows examples of measured signal quality over time for: a neighbor macro celll (dashed line), a neighbor macro cell2 (dotted line), and a neighbor small cell (solid line). At time tO, the macro celll measured quality may exceeds the threshold, and at time tl, the macro cell2 measured quality may exceeds the threshold. At time t2, the small cell measured quality exceeds the threshold (specified as a8-threshold-rXX in Table 3 below) and event

A8 may be triggered following a time-to-trigger. Event A8 may consider only neighbor small cells, excluding the serving and neighbor macro cells (i.e. neighbor macros celll and cell2).

[0143] The WTRU may inform the network through event A8 when the quality of the small cell exceeds the threshold for a time period, referred to as a time-to-trigger. The network may then enable MSA to maximize the data offload potential to the small cell.

[0144] In addition, owing to mobility, a WTRU may move out of the coverage area of small cells. In this case, the multi-site aggregation should be terminated for this WTRU, and the radio bearers on the small cell brought back (repatriated) to the macro cell. To facilitate the decision for this WTRU, the macro cell eNB may need to know the quality of the serving small cell, the neighbor small cells, and the macro cell eNB. In an effort to reduce the measurement signaling load on the macro cell, a new event-triggered reporting criteria, referred to as event A7, may be defined, which may be triggered when the macro cell becomes better than all small cells, by a preconfigured offset, as illustrated in Figure 8B. Figure 8B shows examples of measured signal quality over time for: a macro cell (dashed line), a neighbor small celll (dotted line), a neighbor small cell2 (dash-dotted line), and a serving small cell (solid line). At time tO, the macro signal quality may exceed the measurement quality of the serving small cell. At time tl, the macro cell signal quality may exceed the quality of all the small cells by at least an offset quantity (specified as a7-Offset- rXX in Table 3 below). This may continue for time period, referred to as a Time- to-Trigger, until time t2, at which point the WTRU may send a measurement report announcing Event A7.

TABLE 3

[0145] The details of events A7 and A8, shown in Figures 8A and 8B, may be specified in the ReportConfigEUTRA IE shown in Table 3. Table 3 shows an example of a ReportConfigEUTRA IE that may include the following IEs: eventA7-rXX; a7-Offset-rXX; eventA8-rXX; and a8-Threshold-rXX. The remainder of the elements in Table 3 may be as described in the LTE RIO standard, for example in 3GPP TS 36.331.

[0146] The a3-Offset/a6-Offset/a7-Offset offset values may be used in E-

UTRA measurement reports triggering conditions for event a3/a6/a7, respectively. The actual value may be IE value times 0.5 dB. For RSRP measurements, the ThresholdEUTRA IE may be the RSRP based threshold for event evaluation, and the actual value may be IE value - 140 dBm. For RSRQ, the ThresholdEUTRA IE may be the RSRQ based threshold for event evaluation. The actual value may be (IE value - 40)/2 dB.

[0147] Small cells operating in MSA mode may dynamically change configuration parameters including, but not limited to: operating frequency, coexistence mechanism, UL/DL TDD configuration, and/or transmit and/or receive power settings. WTRUs using these small cells in MSA mode may need to be informed about the changes in small cell parameters so that the WTRU may take certain actions based on the updated information. WTRUs in MSA mode may be informed through dedicated signaling or by reading the new system information, as described below.

[0148] For example, the Small Cell eNB may generate an X2 message, for example SMALL CELL RRC message, that may include a transparent container to carry RRC messages from the small cell eNB to the WTRU, via the signaling radio bearer terminating at the Macro Cell eNB. The Small cell eNB may forward the RRCConnectionReconfiguration Message, with the new configuration, to the Macro cell eNB in this transparent container. For example, the X2 message may indicate any of the following: the destination WTRU or list of WTRUs that are to receive this RRC message, and/or the identification of the small cell.

[0149] In another example, the Small Cell eNB may inform the Macro Cell eNB about the change in small cell eNB configuration, for example through an ENB CONFIGURATION UPDATE message. For example, the X2 message may indicate any of the following: the destination WTRU or list of WTRUs that are to receive this RRC message, and/or the identification of the small cell as discussed above.

[0150] In another example, the Small Cell eNB may end an X2 message, for example a SMALL CELL PAGE message, that may indicate that a system information change has occurred. The Small Cell eNB may begin broadcasting the modified system information that includes the new cell configuration. The X2 message may indicate the identification of the small cell, for example. [0151] Upon reception of the message from the Small Cell eNB, the macro cell eNB perform any of the following procedures. For example, the macro cell eNB may unpack the RRC message contained in the transparent container and send it to the targeted WTRUs. The macro cell eNB may obtain the information about the targeted WTRUs from the received X2 message if this information is contained in this message, or by keeping track of which WTRUs have MSA mode enabled for the small cell eNB that has changed its configuration. The macro cell eNB may maintain a list of small cell eNBs that are active in MSA mode, as well as the WTRUs using these small cell eNBs for MSA.

[0152] In another example, the macro cell eNB may generate an RRC message containing the new configuration of the small cell eNB and may send this RRC message to the targeted WTRUs. In another example, the macro cell eNB may generate an RRC Paging message to inform WTRUs that have MSA mode active with the modified small cell eNB, to read the system information of the small cell eNB and to obtain the new configuration. The Paging message may contain an indication that the system information of a small cell has been changed and may provide an ID of the small cell.

[0153] Upon reception of the RRC message from the Macro cell eNB, the

WTRU may perform any of the following procedures. For example, if receiving a dedicated RRC message, the WTRU act on the reconfiguration message. For example, the WTRU may change the operating frequency of the booster carrier, and/or the coexistence mechanism, and/or the UL/DL TDD configuration, among other things.

[0154] In another example, if receiving a Paging message, the WTRU may check whether the WTRU has MSA enabled with the small cell eNB being changed. If the WTRU has MSA enabled, the WTRU may read the system information of the small cell eNB and act on the reconfiguration. For example, the WTRU may change the operating frequency of the booster carrier, and/or the coexistence mechanism, and/or the UL/DL TDD configuration, among other things. [0155] In the above example procedures, the small cell eNB may schedule a change in configuration at some future system frame number (SFN). The WTRUs may be told the SFN when the configuration will be changed. This may help ensure a more seamless re- configuration.

[0156] Figure 9 shows a flow diagram of an example procedure 900 for system information change on a small cell based on a paging message. Figure 9 shows a WTRU 902, a macro cell 904 and a small cell 906. In the example of Figure 9, it may be assumed that a user powers ON the WTRU 902 in order to synchronize or download a big media file. It may also be assumed the WTRU 902 is in the coverage of a Macro cell 904, which may operate on a licensed band, and small cell(s) 906, which may operate on unlicensed band and/or shared spectrum.

[0157] The small cell 906 in MSA mode may change is operating parameters triggering an SIBl update, 908, to be sent to the macro cell 904. The small cell 906 eNB may provide the updated information in an SIBl broadcast message, 910.

[0158] The macro cell 904 eNB may send a trigger to the WTRU 902 to read updated SIBl from the small cell 906. It may send the trigger by sending an RRC paging message, 912, to trigger the WTRU 902 to read about the SIBl change in the small cell 906. The RRC paging message 912 may be sent from the E-UTRAN to the WTRU 902 on the PCCH logical channel, for example.

[0159] The WTRU in MSA mode may read the updated SIBl from small cell, 914, after receiving the paging message, 912, which may have msa- systemlnfoModification-rXX IE set to TRUE, for example. The presence of the msa-systemlnfoModification-rXX IE may indicate to the WTRU that SIBl from a small cell has changed, and that it needs to be read. The WTRU can then proceed with the WTRU reconfiguration, 916, based on the SIBl.

TABLE 4

[0160] An example of the paging message, 912, is shown in Table 4. Table

4 shows an example of a Paging message that may include the following new IEs: msa-systemlnfoModification-rXX and physCellld-rxx. The remainder of the elements in Table 4 may be as described in the LTE R10 standard, for example in 3GPP TS 36.331. The msa-systemlnfoModification-rXX IE may be a flag to indicate to the WTRU that SIBl from a small cell has changed, and that it needs to be read.

[0161] An RRC connection establishment procedure with MSA enabled may be used during a WTRU transition from IDLE mode to Connected mode. According to an example use case, a user may power ON the WTRU in order to synch/download a big media file. The user may be in the coverage area of a macro cell and small cells. Macro umbrella coverage may be present, as in a HetNet deployment, for example. Macro cell and small cells may be operated by the same operator or by different operators. The WTRU may be capable and allowed to operate in both macro and small cells when two different operators are involved. The small cell may manage the User Plane in a break-and-then- make fashion if the WTRU goes out of coverage, which may apply to background traffic, for example.

[0162] According to an RRC connection establishment procedure with MSA enabled, the WTRU may move from IDLE mode directly to Connected Mode with MSA mode enabled. This may allow significant reduction in call setup times for WTRUs relying on the DSS small cells for data offload. These WTRUs may not have to do any of the following actions: connect to the macro cell eNB, be configured for measurements, send measurement events, wait for the macro cell eNB decision and/or be eventually reconfigured for MSA operation over small cells. Instead, these WTRUs may be sent to MSA enabled mode as part of the RRC Connection Request procedure.

[0163] While in IDLE mode, the WTRU perform any of the following procedures. While in IDLE mode, the WTRU may read the system information of the macro cell to determine the DSS small cell operating frequencies and operator IDs, such as the PLMNJD, of the operators controlling these small cells. This information may be included, for example, in a msa-plmn-list IE, carried in SIB1. Table 5 shows an example of an S1B1 message including the msa-plmn-list information element. The description of the msa-plmn-list IE in addition to the other IEs may be found in the LTe R10 standard, for example in 3GPP TS 36.331. For example, a WTRU may perform IDLE mode inter- frequency measurements on the DSS frequencies, if the desired operator is on this msa-plmn-list.

OPTIO:

TABLE 5

[0164] The plmn-IdentityList IE may list PLMN identities. The first listed

PLMN-Identity may be the primary PLMN. The msa-plmn-list IE may list the small cell PLMN identities. The listed PLMN-Identity may be the desired and/or allowed small PLMN.

[0165] Multiple operators may share the same DSS frequency. As part of the system information, the WTRU may obtain a list of physical cell IDs that belong to a specific operator. For example, a plmn-Identity IE may be included in the InterFreqNeighCelllnfo IE, shown in Table 6, which may be carried in SIB5.

[0166] The WTRU may perform inter-frequency measurements on the frequencies that have a small cell belonging to the desired operator, for example with a given PLMN ID. Upon finding a cell operating on the inter-frequency, the WTRU may need to determine operator specific details of the small cell to make sure that the cell belongs to the desired operator. If some operator ID is encoded in the PSS/SSS, the WTRU may be able to determine this information after synchronization. Alternatively, the WTRU may read the system information of the inter-frequency cell to determine the operator ID (e.g. the PLMN ID). Alternatively, if the system information broadcasts the PLMN ID associated with each cell ID, the WTRU may maintain a look-up table to cross-reference the found cell (and its physical cell ID) and to determine the operator (e.g. through PLMNJD).

[0167] The WTRU may take measurements on DSS inter-frequency cells belonging to the desired operator. The WTRU may rank these inter-frequency cells but may not consider them for IDLE mode cell reselection. Upon the need for a RRC connection, the WTRU may send an indication to the network that it would prefer to be moved to Connected Mode with MSA enabled. This indication information may be included in an MSA-status IE, as shown in Table 7. The MSA-status IE may include a ranked list of DSS small cells and PLMNJD to the network. The WTRU may also include an indication of the quality of each of the found small cells (RSRP or RSRQ measurement) and an indication of the WTRU speed.

TABLE 7

[0168] The physCellld IE may be used to indicate the physical layer identity of the ranked small cells. The one listed first may have the highest rank. The PLMNId IE may indicate the PLMN identity of the ranked small cell. The rsrpResult IE may be the measured RSRP result of the ranked small cell. The rsrqResult IE may be the measured RSRQ of the ranked small cell. The ue- speed IE may be used to indicate the WTRU speed when MSA-status is sent, and may have three values, for example, low, medium or high.

[0169] The WTRU may send the above information autonomously and without having measurement objects configured, using one of the following mechanisms. For example, the WTRU may provide this information as part of the RRCConnectionRequest message that would assist the macro cell in evaluating if the connection should be established with MSA enabled. The WTRU may provide a MSA- status IE, for example the one in Table 7, which may include an indication of the WTRU speed and the ranked small cell list. The small cell list may include the physical cell ID and PLMN ID for each cell in the list.

[0170] In another example, the WTRU may indicate to the macro cell that it wants to send an MSA-status IE. This indication may come through coding in the preamble selection. For example, some preambles may be reserved for signaling the need to send the MSA- status IE, and WTRU may select from these reserved preambles to notify the macro cell. Alternatively, the WTRU may signal the need for an additional assignment in the RRCConnectionRequest message through a new EstablishmentCause (for instance EstablishmentCause == MSAActivation) or through an MSA-trigger IE, as shown in Table 8.

MSA-trir^er ENUMERATED {true, false

TABLE 8

[0171] Upon receiving this indication, the macro cell eNB may allocate a subsequent UL grant. The WTRU may send the MSA- status IE on this new grant, through a new RRCConnectionRequest2 message.

[0172] Alternatively, the WTRU may include the MSA-status IE in the

RRCConnectionSetupComplete message or in a new RRCConnectionMSA message sent after the WTRU has transmitted the RRCConnectionSetupComplete message.

[0173] The network may take the reception of and MSA-status IE as a request to enable MSA with a preferred DSS small cell. The network may enable MSA mode without configuring the WTRU for measurements, and may send an RRCConnectionReconfiguration message. WTRU may activate MSA based on the received configuration. [0174] An RRC Connection Re-establishment may be achieved in MSA mode. A WTRU may initiate an RRC Connection Re-establishment procedure when any of the following conditions are met in MSA operation: upon detecting radio link failure on the macro cell connection; upon macro cell handover failure; upon mobility from E-UTRA failure; upon integrity check failure indication from lower layers; and/or upon an RRC connection reconfiguration on the macro cell failure.

[0175] When a WTRU performs a re-establishment procedure with MSA mode enabled, the small cell operation may not be impacted by the re- establishment procedure done at the macro cell layer. Figure 10 is a flow diagram of an example procedure 1000 for a successful RRC Connection Re- establishment. In the example call flow, WTRU 1002 may perform packet data transfer, 1008, with the serving macro cell 1004 and the packet data transfer, 1010, with the MSA small cell 1006. At one point, when the WTRU 1002 may detect radio link failure, 1012, with the serving macro cell 1004, it may initiate cell selection procedure, 1014, to find the best suitable macro cell to re-establish the RRC connection. And at the same time, WTRU 1002 may maintain the protocol stack on the small cell layer and continue communicating via this layer. In the example of Figure 10, the best suitable macro cell after cell selection procedure, 1014, may be the original serving macro cell 1004, such that the WTRU 1002 may initiate synchronization, 1016, with the macro cell 1004. The macro cell 1004 may respond back the UL grant and Timing Alignment information, 1018, for the WTRU 1002 to re-establish the RRC connection in operation. The WTRU 1002 may send RRC-Connection-Reestablishment-Request message, 1020, to the macro cell 1004. Upon reception of message, 1020, the macro cell 1004 may reset the MAC layer, re-establish PDCP and RLC layer for SRB1, 1022, and respond with RRC-Connection-Reestablishment message, 1024. Upon reception of RRC-Connectio-Reestablishment message from macro cell 1004, 1024, the WTRU 1002 may re-establish the PDCP and RLC layer for SRB1 and perform Radio Bear reconfiguration, 1026, for those RBs associated with the macro cell 1004. The WTRU 1002 may respond the macro cell 1004 with RRC- Connection-Reestablishment-Complete message, 1028.

[0176] Figure 11 is a flow diagram of an example procedure 1100 for a unsuccessful RRC Connection Re-establishment to an unprepared cell. The WTRU 1102 may perform packet data transfer, 1108, with the serving macro cell 1104 and the packet data transfer, 1110, with the MSA small cell 1106. At one point, when the WTRU 1002 may detect radio link failure, 1112, with the serving macro cell 1104, the macro cell 1104 may also detect the radio link failure (RLF), 1114, and the WTRU may initiate a cell selection procedure, 1116, to find the best suitable macro cell to re-establish the RRC connection. In the example of Figure 11, the best suitable macro cell after cell selection procedure, 1116, may be the macro cell 1107, such that the WTRU 1102 may initiate synchronization, 1118, with the macro cell 1107. The macro cell 1107 may respond back the UL grant and Timing Alignment information, 1120, for the WTRU 1102 to reestablish the RRC connection in operation. The WTRU 1102 may send RRC- Connection-Reestablishment-Request message, 1122, to the macro cell 1107. Upon reception of message, 1122, the macro cell 1107 may send an RRC- Connection-Reestablishment-Reject message, 1124, which may cause the WTRU to go into idle mode and release resources on both stacks, 1126.

[0177] When the source macro cell 1104 may detect the radio link failure from the WTRU 1102, 1114, it may start a timer to wait for the WTRU 1102 to re-establish the RRC connection. At expiry of this timer, the macro cell 1104 may release the resources, 1132, for the WTRU 1102 and may send an X2 message, for example a WTRU CONTEXT RELEASE message, 1128, to the small cell 1106 to inform it to release the resources, 1130, associated with the WTRU 1102.

[0178] In the event of a re-establishment failure in MSA mode, the WTRU may fall back to the small cell standalone mode. This may be useful in DSS cases, as the macro cell may not be capable of handling the load from the WTRU, since this WTRU may have been admitted to the network only because its user- plane traffic is offloaded to the DSS small cells. In these cases, rather than returning to IDLE mode, the WTRU should preferably transfer its signaling radio bearers to the small cell and communicate only via the small cell.

[0179] Figure 12 is a flow diagram of an example procedure 1200 of an

RRC connection re-establishment failure in multi-layer operation fall back to small cell standalone mode. The procedure 1200 may involve WTRU 1202, macro cell 1204, small cell 1206, and MME/S-GW 1207. The WTRU 1202 may communicate packet data with the small cell 1206, 1208, and may communicate packet data with the macro cell 1204, 1210. The WTRU 1202 may initiate an RRC connection reestablishment procedure, 1212, when one of the conditions is met, such as the conditions discussed above. The WTRU 1202 may start the cell selection procedure, 1214, to find the best suitable cell with which to reestablish the connection.

[0180] For example, a re-establishment failure may be from the expiry of timer T311, 1215, or the reception of an RRCConnectionReestablishmentReject (not shown). Following a re-establishment failure, 1215, the WTRU may send an RRCConnectionReestablishmentRequest to the small cell eNB, which may indicate as the ReestablishmentCause an MSAMacroCellFailure, 1216. Table 9 shows an example of a RestablishmentCause IE.

l!!iii!llll!!!!!!!!!!!!!!!!!!!!!!!

TABLE^" 9

[0181] As part of the RRCConnectionReestablishmentRequest message,

1216, the WTRU may also provide an indication of the cell ID of the original macro cell that was handling its SRBs, for example.

[0182] Alternatively, the WTRU may decide to send the

RRCConnectionReestablishmentRequest to the small cell eNB without waiting for a RRC Connection reestablishment failure from the macro cell. For example, the WTRU may always try to re-establish the RRC on the small cell, or it may make this decision after selecting a cell that is no longer the original macro cell, or if the cell selection ranking shows that the small cell is significantly better than the macro cell.

[0183] With reference to Figure 12, upon reception of the

RRCConnectionReestablishmentRequest message, 1216, the small cell 1206 eNB may request the original macro cell 1204 for the AS security parameters and SRB configuration information for the WTRU 1202. This may be achieved by sending an X2 message, for example a WTRUContextRequest message, 1218. An example of a WTRUContextRequest message is shown in Table 10. The macro cell eNB may respond with the AS security parameters and SRB information, which may be encapsulated in an X2 message, for example a WTRUContextRequestAck message, 1220, as shown in Table 11. Definitions of Presence, Range Criticality, Assigned Criticality and other IEs may be found in 3GPP TS 36.413 and 3GPP TS 36.423, which are incorporated herein by reference.

[0184] With reference to Figure 12, the small cell 1206 eNB may establish the PDCP/RLC for the SRBl, 1222, with the configuration information from the macro cell 1204 eNB. The small cell 1206 eNB may send the RRCConnectionReestablishment message, 1224, with the AS security parameters from the macro cell 1204 eNB to the WTRU 1202. Upon receiving the RRCConnectionReestablishment message, 1225, the WTRU may shut down its macro cell protocol stack and may release the associated resource. The WTRU may re-establishe the PDCP/RLC for the SRBl, 1234, on the small cell stack and may send back RRCConnectionReestablishmentComplete, 1226, to the small cell 1206.

[0185] The small cell 1206 eNB may send a path switch request, 1228, to the MME/S-GW 1207 for path switching the EPS endpoint from the macro cell 1204 to small cell 1206. The MME/S-GW 1207 may send a path switch ack message, 1230, to the small cell 1206.

[0186] After the path switch is complete, the small cell 1206 may send a

WTRU Context Release message, 1232, to the macro cell 1204, which may then release the resource, 1236. [0187] WTRU speed may be determined in small cells. A WTRU may monitor its speed state when in Connected Mode based on any one or more of the following methods: frequency of the number of handovers and cell reselections; change in its monitored location such as instance through GPS; and/or change in location of the serving MSA small cell, for example through GPS coordinates of the small cell or some other location designation. Figure 13 is a flow diagram of an example procedure 1300 for WTRU speed determination in Connected Mode.

[0188] According to procedure 1300, a WTRU may first determine if it is capable of using a GPS for speed determination, 1302. If yes, the WTRU may determine its speed based on a sampling of GPS position data, 1304. The WTRU may then compare calculated speed to thresholds to establish a speed state, 1306. For example, the following speed states may be used: fast (e.g. highway travel), slow (e.g. bike travel), very slow (e.g. walking), and/or stationary.

TABLE 10

Message Type M YES Reject

Macro eNB WTRU M Allocated at the YES Reject

X2AP ID macro eNB.

Small Cell eNB WTRU M Allocated at the small YES Ignore

X2AP ID cell eNB.

GUMMEI M This IE indicates the YES Reject

MME serving the UE

WTRU Context YES Reject

Information:

>MME WTRU S1AP M MME WTRU S1AP

ID ID allocated at the

MME

>WTRU Security M - -

Capabilities

>AS Security M

Information

>WTRU Aggregate M

Maximum Bit Rate

>Subscriber Profile ID 0

for RAT/Frequency

priority

WTRU History M YES Ignore

Information:

>RRC Context M Includes the RRC

Handover

Preparation

Information message

TABLE 11

[0189] If the GPS cannot be used for speed determination, the WTRU may determine if it is aware of the location of the MSA serving cell, 1308, for example the center of the serving cell. If yes, it may determine its speed based on the change in location of the MSA serving cell, 1310. The WTRU may then compare calculated speed to thresholds to establish a speed state, 1312. If the WTRU is not aware of the location of the MSA serving cell, it may monitor a number of cell transition events over macro cells, 1314. It may monitor a number of cell transition events over small cells, 1316. The WTRU may then compare a number of cell transition events over a moving window to some thresholds to establish a speed state, 1318.

[0190] A WTRU may autonomously refuse MSA activation, for example via an RRC Connection Reconfiguration Reject message. For example, a WTRU may autonomously decide that it is not willing to partake in MSA to save battery power. In such a case, the WTRU may decide to ignore the triggers to start evaluating and/or measuring DSS small cells or the RRCConnectionReconfiguration message from the macro cell that enables MSA.

[0191] The WTRU may base this refusal decision on one or more parameters. For example, the refusal decision may be based on the state of the WTRU, such as the speed of the WTRU. For example, a fast moving WTRU may decide it would not be useful to start MSA. Another such parameter may be the available power of the WTRU. For example, a WTRU may decide to conserve power in order to maintain a minimum connection with the macro cell.

[0192] Another example of a parameter may be the type of small cell in the vicinity. A macro cell may inform the WTRU about some characteristic of the small cells under its umbrella coverage area that may make these cells unsuitable for MSA. For example, the small cells may belong to a closed subscriber group to which the WTRU does not belong, or the small cells may be unplanned and non-clustered. Another example of a parameter may be the type of applications running in the WTRU. For example, the WTRU may decide that based on its active radio bearers, it would prefer to stay in Connected Mode on the macro cell.

[0193] Upon determining that it is not willing to initiate MSA, the WTRU may notify the macro cell eNB through an RRCConnectionReconfigurationReject message. This message may contain a cause for the rejection, which may include, but is not limited to: power, WTRU speed, interference on frequency, and/or unsuitable small cell type. For those radio bearers mapped to the DSS small cell, the network may decide to move these radio bearers back to the macro cell, or delete the radio bearers.

[0194] An IDLE mode WTRU may not camp on an MSA enabled small cell, but may measure and rank these cells to facilitate any transition to Connected Mode with MSA enabled. While in IDLE mode, the WTRU may only need to discover and measure these cells. The example scenario in Figure 14 highlights the following procedures: Modified Admission Control at the macro cell; Modified Connection Request; MSA Activation Algorithm; Modified Admission Control and Resource Negotiation Procedure; Modified Connection Setup; and Initial Access Procedure on the small cell.

[0195] Figure 14 is a flow diagram of an example procedure 1400 for a

WTRU transitioning from IDLE mode to Connected Mode with MSA enabled. The WTRU 1402 may, as part of a R10 LTE procedure, power on and attach to LTE macro cell 1404, 1408. The WTRU may perform small cell discovery, 1410, to discover small cell 1406. The WTRU 1402 may then perform a R10 LTE connection establishment procedure and may transmit a RB setup REQUEST message, 1412, to macro cell 1404. The WTRU 1402 may inform the macro cell 1404 about available small cell 1406 through a connection establishment request message, 1414. The macro cell 1404 may decide to setup a booster, 1416, then perform an admission control and resource negotiation procedure, 1418, with small cell 1406. The macro cell 1404 may provide initial access information for small cell 1406, 1420, to the WTRU 1402. Then, WTRU 1402 may perform a (non contention) RACH and radio bearer setup procedure, 1422, with small cell 1406 via macro cell 1404. The procedures summarized in Figure 14 are described in further detail below.

[0196] The WTRU may be powered on and may follow a R10 LTE procedure to camp on the LTE macro cell. For example, the macro cell may have information about the small cells under its coverage based on the procedures described above, and may package some or all of this information in its neighbor cell list. The macro cell may broadcast some small cell information as part of the System Information. The WTRU may read this System Information to obtain the macro cell related information as well as small cell related information, which may include the details of the discovery signal used for the Small Cell Discovery Procedure.

[0197] As part of the R10 LTE ATTACH procedure, admission control may occur at the macro cell. The core network may set up a default EPS bearer for the WTRU. In addition to the existing load in the macro cell and the QoS requirements of the requested EPS bearer, the macro cell may rely on any of the following factors in accepting or rejecting the request: the WTRU capability for MSA; the presence of MSA small cells under the macro cell coverage; and the number of MSA small cells and the status of these small cells such as load, and/or deployment type. For example, the macro cell may not have enough resources to admit a WTRU, but may still accept the default EPS bearer request, because the WTRU may be MSA capable and the macro cell may have a dense deployment of small cells under its coverage area.

[0198] Alternatively, the macro cell may accept the default bearer setup, but this may trigger the macro cell to free resources. For example, the macro cell may use the trigger to find radio bearers from other MSA capable WTRUs, and to request a radio bearer transfer of these radio bearers to appropriate MSA small cells.

[0199] The WTRU may start the small cell discovery procedure. For example, the small cell discovery procedure, may be based on geolocation information, System Information, and/or the detection of a discovery signal. The WTRU may obtain certain small cell identification information such as Cell ID and PLMN ID.

[0200] The WTRU may initiate a Small Cell Evaluation Procedure for

IDLE mode, which may be broken down into a system information based procedure and a discovery signal method. In a System Information based procedure, the WTRU 1402 may be able to perform inter-frequency measurements to create a ranked list of small cells based on RSRP and/or RSRQ measurement.

[0201] In the discovery signal method, the WTRU may not have enough information to start measuring and ranking small cells. In either case, if the

WTRU 1402 does not have enough information about the small cells, it needs to first retrieve this information from the macro cell. As part of a Connection

Request, The WTRU may send a MSA-Status IE to the macro cell eNB.

[0202] Alternatively, if the WTRU does not have a ranked cell list, or if it has an outdated cell list, it may perform a new ranking. The WTRU may provide a request for the small cell information as part of the connection setup message.

This may be based on the detected discovery signal. Figure 15 is a flow diagram of an example procedure 1500 for a connection request. The WTRU 1502 may perform a connection establishment procedure by transmitting a small cell information request to the macro cell 1504 as part of a Connection Setup message, 1508. The macro cell 1504 may respond with small cell details, 1510, such as the small cell operating band, operating channel and frequency. The WTRU may perform small cell inter-frequency measurements, 1512, on those frequencies and it may create the ranked small cell list based on RSRP/RSRQ measurements. The WTRU may transmit the small cell measurement results, 1514, for example in a MSA-Status IE to the macro cell 1504.

[0203] Figure 16 is a flow diagram of an example connection request procedure 1600. The macro cell 1604 eNB may communicate with the MME 1607 by forwarding a NAS service request and/or attach request, 1608, which may include the WTRU credentials. The MME 1607 may authenticate the WTRU through standard security mode command procedure, 1610. The MME 1607 may inform the macro cell 1604 eNB about the bearer allowed QOS profile and may activate the dedicated EPS bearer, 1612. The acceptance of the service request may depend on the following metrics: required bearer QoS, the load in the macro cell 1604, the MSA capability of the WTRU, and the potential for offloading the bearer to the MSA small cell. For example, the macro cell 1604 may accept the service request if the WTRU is MSA capable and in vicinity of a MSA small cell that is willing to accept the bearer.

[0204] As part of an MSA Activation Algorithm, the macro cell 1604 eNB may evaluate whether or not to initiate MSA for the WTRU by evaluating the required QoS, 1614. For example, the macro cell 1604 eNB may base this evaluation on a number of inputs, including but not limited to: the number of users currently serviced, the available radio resources at its disposal, the WTRU frequency bands supported, the WTRU speed, and the deployment characteristic of the small cells.

[0205] Based on this evaluation, the macro cell 1604 eNB may decide to move the WTRU to MSA enabled Connected Mode, by setting up a booster carrier for the WTRU through a small cell. The macro cell 1604 eNB may use the ranked list sent by the WTRU and the information it has about a Preferred PLMN list, 1616, in order to to select the small cell for radio bearer set up. The macro cell 1604 eNB may inform the MME 1607 not to establish the bearer with the S-GW immediately, 1618. Rather, the MME 1607 may wait to hear either from macro cell 1605 eNB or from the selected small cell.

[0206] Figure 17 is a flow diagram of an example admission control and resource negotiation procedure 1700. The macro cell 1704 may select a small cell 1706, 1708, to enable MSA. For an admission control and resource negotiation procedure 1700, once the macro cell 1704 eNB has established that it wishes to enable MSA for a particular WTRU, it may need to negotiate the details of the MSA with the selected small cell 1706.

[0207] The macro cell 1704 eNB may communicate with the selected small cell 1706 performing resource negotiation and admission control, 1710, in order to find out if the small cell 1706 has available resources to setup a booster carrier. For example, the small cell 1706 may be provided with the WTRU ID, requested QOS profile for the booster carrier, measurements by the WTRU, and/or WTRU speed. If the small cell 1706 agrees to setup the booster carrier, it may provide the macro cell 1704 eNB with the initial access information for the WTRU, 1712, which may include, but is not limited to PRACH configuration on the small cell and/or preamble information to be used for initial access. This information may be carried in a container between the small cell 1706 and the macro cell 1704 eNB.

[0208] According to example 1714, upon confirmation that the small cell

1706 is willing to be set up as a booster cell, the macro cell 1704 eNB may inform the MME 1707 to redirect the EPS bearer towards the selected small cell, 1716. The macro cell 1704 eNB may provide the small cell identification to the MME 1707. The MME 1707 may then set up the EPS bearer between the small cell and the S-GW, 1718, and transmit the dedicated EPS bearer setup, 1720, to the small cell 1706.

[0209] According to example 1722, the small cell 1706 may inform MME

1707 about the WTRU and the requested QOS via a service request for the WTRU, 1724. The MME 1707 may cross-reference the WTRU identity and determine that this a pending request. In response it may cancel the pending request, transmit an acknowledgement to the small cell 1706 and inform the S- GW to setup a bearer, 1726, which may support the requested QOS profile, and transmit the dedicated EPS bearer setup, 1728, to the small cell 1706.

[0210] According to a Connection Setup, the WTRU may be informed that the connection request has been granted and that MSA has been enabled for this connection. The macro cell eNB may respond to the Connection Request by transmitting Initial Access information for the small cell to the WTRU. This may be transmitted as part of the RRC Connection Setup messages, for example. This message may have configuration information for the PHY and MAC layer to be used on the small cell. This may be referred to as the secondary PHY and MAC layer to distinguish it from the primary PHY and MAC layer used from macro cell communication. The macro cell eNB may also update RLC and PDCP configuration to support multi-site aggregation. The WTRU may start secondary PHY layer configuration based on this information. Assuming there are two radios, the WTRU may power on the second radio for establishing contact with the small cell.

[0211] A small cell may carry PDCCH for DL assignments. The WTRU may perform a non-contention RACH procedure over the small cell for timing alignment. The WTRU may start reading the PDCCH of the small cell in order to read the PDSCH assignment. Figure 18 is a flow diagram of an example Initial Access Procedure 1800 on a small cell.

[0212] The WTRU 1802 may use the small cell PRACH configuration and

Preamble information provided by the macro cell eNB, 1808. The WTRU 1802 may transmit the RACH preamble, 1810, to the small cell 1806 on the PRACH.

The WTRU 1802 may receive a random access response message, 1812, which may provide resource allocation information and which may contain radio bearer setup information, and/or a temporary C-RNTI, which may be different than the one provided by macro cell and may be used by the WTRU 1802 to communicate with small cell 1806. The WTRU 1802 may use the resource allocation information and timing adjustment information to setup a radio bearer, 1814. Alternatively, there may be no PDDCH on the small cell, and the PDCCH on the macro cell may inform the WTRU about DL assignments in the PDSCH of the small cell.

[0213] The WTRU may complete radio bearer setup and communicate through MSA. For the media download service example, the WTRU may begin actively downloading data through the small cell.

[0214] For the addition of a data radio bearer (DRB) to inactive Connected

Mode WTRU, it may be assumed that the WTRU is in connected mode, but inactive and not involved in any active data session. The SRB1 and SRB2 may be established with macro cell. The WTRU may initiate a data download in an area where small cells may be available.

[0215] Figure 19 is a flow diagram of an example procedure 1900 for adding a DRB across a small cell. Procedure 1900 may be used while the WTRU 1902 is in Connected Mode with SRB1 and SRB2. There may be no active DRBs or very little activity on these DRBs.

[0216] The WTRU 1902 in connected mode may, as part of a R10 LTE procedure, establish a connection with the macro cell 1904, 1908. The WTRU 1902 may detect and discover small cell 1906, measure its quality, and report the small cell quality through an RRC message, 1910, to the macro cell 1904 in order to discover small cell 1406. The WTRU 1902 may transmit a SERVICE REQUEST message, 1912, to macro cell 1404. The macro cell may decide to setup a booster carrier, 1914, and then perform admission control and resource negotiation, 1916, with the small cell 1906. The macro cell 1904 may provide initial access information for small cell 1906, 1918, to the WTRU 1902. The WTRU 1902 may perform a RACH procedure and radio bearer setup, 1920, with the small cell 1906 via the macro cell 1904. According to procedure 1900, the WTRU may use the established SRB for obtaining small cell detection trigger, and/or small cell frequency information for discovery.

[0217] After a WTRU has discovered small cell, it may transmit the small cell measurement report through RRC messages to the MACRO. [0218] For the addition of DRB to an active Connected Mode WTRU, it may be assumed that the WTRU is in connected mode and active. For example, the WTRU may have SRB1, SRB2 and one or more DRBs with the macro cell. The WTRU may have an existing DRB with small cell. The WTRU may initiate a new data session or the network may decide to offload traffic to small cell.

[0219] Figure 20 is a flow diagram of an example procedure 2000 for adding a DRB across a small cell. Procedure 1900 may be used while the WTRU 1902 is in Connected Mode with SRB and DRBs with significant activity.

[0220] The WTRU 2002 in connected mode may, as part of a R10 LTE procedure, establish a connection with the macro cell 2004, 2008. The WTRU 2002 may detect and discover small cell 2006, measure its quality, and report the small cell quality through an RRC message, 2010, to the macro cell 2004 in order to discover small cell 2006. The WTRU 2002 may transmit a SERVICE REQUEST message, 2012, to macro cell 2004. Alternatively, the macro cell 2004 may decide on its own to add a DRB with small cell 2006. The macro cell may decide to setup an additiaonl DRB with the small cell 2006, 2014, and then perform radio bearer reconfiguration, 2016. The macro cell 2004 may reconfigure a radio bearer after it decides to establish an additional DRB with small cell 2006.

[0221] The macro cell 2004 may perform admission control and resource negotiation, 2018, with the small cell 2006. The macro cell 2004 may provide initial access information for small cell 2006, 2020, to the WTRU 2002. The WTRU 2002 may perform a RACH procedure and radio bearer setup, 2022, with the small cell 2006 via the macro cell 2004. According to procedure 2000, the WTRU may use the established SRB for obtaining small cell detection trigger, and/or small cell frequency information for discovery.

[0222] A WTRU in connected mode may start multi-site aggregation for any number of reasons including, for example, addition of a DRB due to WTRU mobility (e.g. WTRU coming in vicinity of an MSA small cell), or due to some macro cell decision to free resources. A macro cell initiated method for MSA and a small cell initiated method for MSA are described below. [0223] Figure 21 is a flow diagram of an example macro cell initiated MSA procedure 2100. The macro cell initiated MSA procedure 2100 performs the following functions: WTRU speed determination, WTRU autonomous MSA control , measurement configuration and reporting, MSA Activation, MSA Request between macro cell 2104 eNB and small cell 2106, reception of MSA Activation Command, transmission of MSA Activation Confirm, and/or PATH SWITCH.

[0224] The steps to initiate MSA are described below for WTRU 2102.

WTRU 2102 may be connected to the macro cell 2104 and may perform a small cell discovery procedure, 2108.

[0225] Once triggered by the small cell discovery procedure, 2108, the

WTRU 2102 may begin the small cell evaluation procedure, 2112. As a part of small cell evaluation procedure, 2112, the WTRU 2102 may apply a measurement configuration, 2110, and reporting mechanism, 2114, for the MSA capable small cell(s) 2106.

[0226] The measurement configuration, 2110, may be tailored for MSA capable small cells. For example, the network may define new trigger events for small cells that may be based on the RF quality of the small cells, in addition to the parameters listed in the WTRU 2102 autonomous MSA control procedure. The measurement configuration, 2110, may provide details about the small cell 2106 operation, for example by including the coexistence mechanism used in the small cell 2106 and/or measurement gap information for the small cell 2106 operating frequency.

[0227] Alternatively, the macro cell 2104 may configure a measurement to return a ranked cell list, targeting MSA capable small cells. This may be configured as a periodic measurement report or based on some specified event.

For example, the WTRU 2102 may transmit the ranked cell list when the quality of at least one of the monitored small cells exceeds a threshold.

[0228] Once a configured event is triggered, the WTRU 2102 may transmit an measurement report, 2114, to the macro cell 2104. The measurement report,

2114, for MSA small cells may include additional information compared to R10 LTE. The additional information may include, but is not limited to additional small cell identification such as Physical cell ID, cell global ID, and/or PLMN identity. The measurement report, 2114, may also include some WTRU 2102 state information, for example, WTRU 2102 speed.

[0229] The MSA Activation Procedure, 2116, includes the following procedures. The macro cell 2104 eNB may evaluate the benefits of starting MSA for each WTRU it is serving in order to decide to initiate MSA, 2118, with a particular WTRU 2102. This may be continuously done as the macro cell 2104 eNB receives measurement reports, 2114. The evaluation may use an MSA activation algorithm.

[0230] If the macro cell 2104 eNB decides to start MSA, 2118, it may select the best small cell 2106 and the RABs it wishes to transfer to the small cell 2106. The macro cell 2104 eNB may use the X2 interface to transmit an MSA Request to this small cell. The MSA Request, 2120, which may include a list of RABs that need to be transferred to the small cell 2106, and which may include the QoS information for these RABs.

[0231] The small cell 2106 may evaluate whether to accept the RAB transfer or not, 2122. This decision may be based on the current load in the small cell 2106, as well as WTRU 2102 details. If the small cell 2106 accepts to transfer some or all of the RABs, 2122, it may transmit an MSA Request Ack message, 2124, to the macro cell 2104. This message may include the new RAB information, the MAC, PHY information of the small cell 2106, the C-RNTI to use in the small cell 2106, the Cell_ID of the small cell 2106, the RACH resource to use in the small cell 2106, and other small cell 2106 related information, such as information related to the MAC configuration and PHY configuration in the small cell 2106. This information may be transmitted to the macro cell 2104 eNB and an X2 bearer is established between the two cells, 2126. The small cell 2106 may also create a new signaling radio bearer to the WTRU 2102, for RRC signaling between the small cell 2106 and the WTRU 2102.

[0232] Macro cell 2104 may transmit an MSA Activation Command (RRC message), 2128, on SRB1 to the WTRU 2102, which may include the information received from the small cell 2106. Macro cell 2104 may transmit an SN Status Transfer message, 2132, to the small cell 2106 for the effected RABs.

[0233] For reception of MSA Activation Command, 2128, the WTRU 2102 may reestablish the targeted RBs, 2130, which are being transferred to the small cell 2106. Other RBs may remain in the macro cell 2104. The WTRU 2102 may also configure a MAC and PHY entity for communication over the small cell 2106, which may be referred to as secondary MAC and secondary PHY. This may include setting up CQI reporting, SRS transmission, and/or measurement gaps on the small cell 2106 frequency. Unlike a handover procedure, the WTRU 2102 may not reset the primary MAC and PHY layers associated with the macro cell 2104. In addition, the WTRU 2102 may modify its MAC and PHY procedures on the macro cell 2106 to account for the transferred radio bearers. For example, it may reduce the reporting of CQI and SRS.

[0234] The WTRU 2102 may perform a RACH in the small cell 2106 over secondary MAC and PHY layers, and may perform synchronization, 2134, to the small cell 2106. Following the reception of an UL allocation, 2136, from the small cell, 2106, the WTRU 2102 may transmit an RRC MSA Activation Confirm message, 2138, to the macro cell 2104 eNB. In response, the macro cell 2104 eNB may transmit a Path Switch request message, 2140, to the MME 2107 for the effected E-RABs to request that the S-GW 2107 transfer the bearers from the macro cell 2104 to the small cell 2106. The MME 2107 may perform a PATH

SWITCH procedure, 2142, and send a Path Switch Request Ack message 2144, to the msall cell 2106. Alternatively, the macro cell 2104 may transmit a MSA

Request Confirm message to the small cell 2106, and have it initiate the PATH

SWITCH procedure, 2142. The small cell 2106 may send a WTRU Context

Release message, 2146, to the macro cell 2104 for the affected RABs.

[0235] Figure 22 shows a flow diagram of an example small cell initiated

MSA procedure 2200. The small cell initiated MSA procedure 2200 is similar to the macro-cell initiated MSA procedure 2100 in Figure 21, but with a modified

MSA Activation Procedure, 2225, and may include the following functions: Small

Cell Discovery Procedure, WTRU speed determination, and/or WTRU autonomous MSA control procedure. The WTRU 2202 may not have the capability for WTRU autonomous control for MSA, or if it does, the WTRU 2202 may accept to allow MSA.

[0236] Once triggered by the small cell discovery procedure, 2208, the

WTRU may begin a small cell evaluation procedure, 2212, where the WTRU may apply a measurement configuration, 2210, and reporting mechanism for the MSA capable small cells. For Measurement Configuration, 2210, and Reporting, once a configured event is triggered, the WTRU 2202 may decide not to transmit a measurement report to the macro cell 2206 eNB. Rather, the WTRU 2202 may transmit an RRC message to the small cell 2206 and then rely on the small cell 2206 to contact the macro cell 2204 eNB.

[0237] According to MSA Activation Procedure, 2225, the WTRU 2202 may read the system information of the small cell 2106. The WTRU 2202 may obtain the common system information to initiate a RACH and perform a RACH in the small cell 2206 using secondary MAC and PHY, in order to perform synchronization, 2214, to the small cell 2206. The small cell 2206 may provide an UL allocation, 2216, to the WTRU 2202 on the small cell 2206. As part of the RACH process, the WTRU 2202 may use a RACH message, for example RACH message 3, to transmit an RRC MSA Activation Req message, 2218, to the small cell 2206. The RRC MSA Activation Req message, 2218, may include any of the following: an indication as to the radio bearers that are currently active in the WTRU 2202, the cell ID of the WTRU's 2202 serving macro cell 2204, and/or the state of the WTRU 2202.

[0238] In response, the small cell 206 may first evaluate if it is able to support the RABs, 2220, of the WTRU 2202. If it can support the RABs of the WTRU 2202, the small cell 2206 may contact the macro cell 2204 eNB, using a MSA Request message, 2222, over the X2 interface. The small cell 2206 may forward the information provided by the WTRU 2202.

[0239] Upon receiving the MSA Request message, 2222, the macro cell

2204 eNB may evaluate the benefits of starting MSA, 2224, for this particular

WTRU 2202 it is serving. The evaluation may use an MSA activation algorithm. If the macro cell 2204 eNB decides to start MSA, 2224, it may respond to the small cell 2206 with an MSA Request Ack message, 2226. The MSA Request Ack message, 2226, may include a list of RABs that are to be transferred to the small cell 2206, and may include the QoS information for these RABs.

[0240] If the small cell 2206 accepts to transfer some or all of the RABs, it may transmit an MSA Request Conf message, 2230, to the macro cell 2204, which may include the new RAB information, the MAC and PHY information of the small cell 2206, the C-RNTI to use in the small cell 2206, the CellJD of the small cell 2206, the RACH resource to use in the small cell 2206, and other small cell 2206 related information, such as information related to the MAC configuration and PHY configuration in the small cell 2206. This information may be transmitted to the macro cell 2204 eNB and an X2 bearer may be established between the two cells. The small cell 2206 may also create a new signaling radio bearer to the WTRU 2202 for RRC signaling between the small cell 2206 and the WTRU 2202.

[0241] The macro cell 2204 may transmit an RRC MSA Activation

Command message, 2232, to the WTRU 2202, on SRB1 including the information received from the small cell 2206. The macro cell 2204 may transmit an SN Status Transfer message, 2234, to the small cell 2206 for the affected RABs.

[0242] For Reception of MSA Activation Command, 2232, the WTRU 2202 may reestablish the targeted RBs, 2236, that are being transferred to the small cell 2206. Other RBs may remain in the macro cell 2204. The WTRU 2202 may also configure a MAC and PHY entity for communication over the small cell 2206, which may be referred to as secondary MAC and secondary PHY. For example, this may include setting up CQI reporting, SRS transmission, and/or measurement gaps on the small cell 2206. Unlike a handover procedure, the WTRU 2202 may not reset the primary MAC and PHY associated with the macro cell 2204. The WTRU 2202 may modify its MAC and PHY procedures on the macro cell 2204 to account for the transferred radio bearers. For example, it may reduce the reporting of CQI and SRS. [0243] The WTRU 2202 may transmit an RRC MSA Activation Confirm message, 2238, to the macro cell 2204 eNB. In response, the macro cell 2204 eNB may transmit a Path Switch request message, 2240, to the MME 2207 to request that the S-GW 2207 transfer the bearers from the macro cell 2204 to the small cell 2206. The MME 2207 may perform a PATH SWITCH procedure, 2242, and transmit a Path Switch Request Qck message, 2246, to the small cell 2206. The small cell 2206 may transmit a WTRU Context Release message, 2248, to the macro cell. Alternatively, the macro cell 2204 may transmit a MSA Request Confirm message to the small cell 2206 and have it initiate the PATH SWITCH procedure, 2242.

[0244] As a WTRU in MSA Connected Mode moves, handover may happen at the macro cell layer or the small cell layer. When the WTRU stays in the same macro cell while moving through small cells, it may cause a Small Cell layer handover. When the WTRU reaches a macro cell border, it may handover to a new macro cell resulting in a Macro Cell layer handover. The WTRU may fall within the same small cell, a new small cell, or no small cell. A handover procedure described below may be used to take care of the MSA function during the handover.

[0245] Figure 23 shows a flow diagram of an example small cell layer handover procedure 2300. The small cell layer handover procedure 2300 may include any of the following function: a Handover Procedure; a simplified Handover Request message; an X2AP message to trigger SN Status Transfer from source small cell to target small cell; an X2AP message to trigger handover from source small cell to target small cell; and/or Modified Random Access Response Message from target small cell to WTRU with no UL Grant.

[0246] With reference to Figure 23, the WTRU 2302 may engage in packet data communication, 2308, with small cell 2306 and may engage in packet data communication, 2310, with the macro cell 2304. WTRU 2302 may detect and/or discover small cells, 2312, perform Small Cell Evaluation, 2314, and may send Measurement Reports, 2316, to macro cell 2304 on a periodic or event triggered basis. The measurement reports, 2316, may include both macro cell 2304 and small cell 2305, 2306 information.

[0247] According to an example handover procedure, 2317, the macro cell

2304 may make a handover decision from small cell 2306 (SC#1) to small cell

2305 (SC#2) based on the measurements. It may transmit a Handover Request message, 2318, to small cell 2305 through X2. The Handover Request message, 2318, may include the e-RABs to be set up at the target small cell 2305. Since the small cell handover only involves DRBs that are to be transferred from small cell 2306 to small cell 2305, the SRBs that exist at macro cell 2304 may not be touched. The SRB information may not be needed to be transferred to target small cell 2305. Upon receiving the Handover Request message, 2318, from the macro cell 2304, the target small cell 2305 may perform admission control, 2320, and may accept the e-RABs by sending Handover Request Ack message, 2322, to the macro cell 2304. The macro cell 2304 may transmit an RRC Connection Reconfig message, 2324, to the WTRU 2302. Macro cell 2304 may transmit a X2 AP SN Status Trigger message, 2326, to inform the source small cell 2306 to transfer the uplink and downlink PDCP SN and a hyper frame number (HFN) receiver status to target small cell 2305. The small cell 2306 may complete the transfer by sending an SN Status Transfer message, 2328, to the target small cell 2305.

[0248] According to another example handover procedure, 2330, the macro cell 2304 may transmit a X2 AP SCHandoverTrigger message, 2332, to inform small cell 2306 to initiate a handover to small cell 2305. The source small cell

2306 may transmit a Handover Request message, 2334, to target small cell 2305, which may respond with a Handover Request Ack message 2338 to admit the e- RABs, following an admission control, 2336. The source small cell 2306 may respond to macro cell 2304 with an X2 AP SCHandoverTriggerAck message, 2340, to inform the admitted e-RABs. The macro cell 2304 may send an RRCConnectionReconfig message, 2342, to the WTRU 2302 and the small cell 2306 may complete the transfer by sending an SN Status Transfer message, 2344, to the target small cell 2305. [0249] The macro cell 2304 may transmit an

RRCConnectionReconfiguration message, 2342, acting as a handover command to the WTRU 2302 with the impacted DRB list and the target small cell 2305 information. The WTRU 2302 may reestablish the DRBs, 2348, that are involved in the small cell handover, after which data forwarding, 2346, from the source small cell 2306 to the target small cell 2305 may occur. The WTRU 2302 may start synchronization, 2350, with the target small cell 2305.

[0250] The target small cell 2305 may transmit a random access response

(RAR) with timing adjustment, 2352 for the WTRU 2302. The RAR, 2352, may not carry an UL grant. The WTRU 2302 may wait for an UL grant, 2354, from macro cell 2304 and may transmit an RRCConnectionReconfigurationComplete message, 2356, to macro cell 2304 as a handover confirmation. The macro cell 2304 may transmit the WTRU Context Release message, 2358, to source small cell 2306.

[0251] If an aggregation anchor is at S-GW 2307, then the macro cell 2304 may need to inform the MME/S-GW 2307 to switch the path for the e-RABs from source small cell 2306 to target small cell 2306. This may be done by the exchange of a Path Switch Request message, 2360, and a Path Switch Request Ack message, 2362, between the macro cell 2304 and the MME/S-GW 2307. At the end of the small cell layer handover procedure 2300, the WTRU 2302 may perform packet data communication, 2364, with the target small cell 2305 and perform packet data communication, 2366, with the macro cell 2304.

[0252] Figure 24 shows a flow chart of an example macro cell handover procedure 2400, where the small cell is unchanged. The macro cell handover procedure 2400 includes the following functionality: a Handover Procedure, a HandoverRequest message including the SC/e-RAB information to a target macro cell, and a X2AP message MSA-MC- Change-Request to inform the small cell of the change of macro cell.

[0253] The WTRU 2402 may engage in packet data communication, 2408, with small cell 2406 and may engage in packet data communication, 2410, with the macro cell 2404. The macro cell 2404 may make a handover decision from macro cell 2404 to macro cell 2405, 2414, based on the measurements reports, 2412, and may transmit a Handover Request message, 2416, to macro cell 2405 through X2. The Handover Request message, 2416, may include only the e-RABs to be set up at the target macro cell 2405. It may also transfer the small cell 2406 and corresponding e-RABs information to the target macro cell 2405 in the HandoverRequest message, 2416.

[0254] The target macro cell 2405 may perform admission control, 2418, and may accept the e-RABs by transmitting a HandoverRequestAck message, 2420, to source macro cell, 2404. Source macro cell, 2404, may transmit an RRCConnectionReconfiguration message, 2422, to the WTRU 2402 with the impacted MC-RB list and the target macro cell 2405 information. The source macro cell 2404 may transmit a SN Status Transfer message, 2424, which may include only the e-RABs on the macro cell 2404 to the target macro cell 2405 and start forwarding the DL data, 2426, from macro cell e-RABs.

[0255] The WTRU 2402 may reestablish the DRBs, 2428, involved in the macro cell handover. The WTRU 2402 may start synchronization, 2430, with the target macro cell 2405. The target macro cell 2405 may transmit an UL Grant and RAR message, 2432, with timing adjustment (TA) for the WTRU 2402. The WTRU 2402 may transmit a RRCConnectionReconfigurationComplete message, 2434, to the target macro cell 2405 to confirm the handover. The target macro cell 2405 may transmit a Path Switch Request, 2436, to the MME/S-GW 2407, which may respond with a Path Switch Request Ack message, 2440, for path switching of macro cell e-RABs. Target macro cell may transmit a X2AP MSA- MC- Change-Request message, 2438, to the small cell 2406 to inform it of the macro cell change. The small cell 2406 may respond with a MSA-MC-Change- Complete message, 2442. The target macro cell 2405 may transmit a WTRU Context Release message, 2446, to the source macro cell 2404. At the end of the macro cell layer handover procedure 2400, the WTRU 2402 may perform packet data communication, 2446, with the target macro cell 2405 and perform packet data communication, 2448, with the small cell 2406. [0256] Figure 25 is a flow diagram of an example macro cell handover procedure 2500 with small cell change. The macro cell handover procedure 2500 may include any of the following functions: a handover procedure; separate macro cell and small cell e-RABs in HandoverRequest message; target small cell included in the HandoverRequest message; MSA Request/ACK procedure with target small cell; target macro cell admission control performed with the feedback from small cell admission control to determine if it may admit the SC- eRABs that rejected by the Small Cell; separate MC and SC-eRABs in SN status Transfer message; and/or separate MC and SC-RBs in an RRC HandoverCommand message.

[0257] With reference to Figure 25, the WTRU 2502 may engage in packet data communication, 2508, with small cell 2306 and may engage in packet data communication, 2510, with the macro cell 2504. The WTRU 2502 may send Measurement Reports, 2512, to the macro cell 2504.

[0258] The source macro cell 2504 may make a Handover Decision, 2514, to the target macro cell 2504 based on the measurements reports, 2512. The source macro cell 2504 may transmit a Handover Request message, 2516, to target macro cell 2503. The Handover Request message, 2516, may include the macro cell and small cell e-RABs to be set up at the target macro cell 2503 and the target small cell 2505, if available. The target macro cell 2503 may decide whether to perform MSA or non-MSA, 2518, with the target small cell 2505 based on, for example, the WTRU 2502 speed, macro cell 2503 capacity and other factors.

[0259] The target macro cell 2503 may transmit an MSA request message,

2520, to target small cell 2505 if the MSA decision, 2518, is made.

[0260] The target small cell 2505 may perform admission control, 2522, to decide where to accept the e-RABs or not, and transmit back an MSA Request

Ack or Reject message, 2524, to the target macro cell 2503. Upon receiving target small cell's 2505 response, the target macro cell may perform admission control, 2526, to check the e-RABs it may accept, including the e-RABs from the source macro cell 2504 and the source small cell 2506. The target macro cell 2503 may respond to the source macro cell 2504 with the admitted e-RABs at macro cell 2503 and target small cell 2505, if applicable, in a HandoverRequesetAck message, 2528.

[0261] The source macro cell 2504 may transmit a

RRCConnectionReconfiguration message, 2530, to the WTRU 2502 with the MC- RB list, target small cell 2505 information and SC-RB list, if applicable. The source macro cell, 2504, may transmit an SN Status Transfer message, 2534, which may include the admitted e-RABs on the macro cell and small cell, if applicable, to the target small cell 2505 and may start data forwarding, 2538, the DL data. Upon receiving the SN Status transfer message, 2534, the target macro cell 2503 may forward the part of the SN Status transfer message, 2536, for small cell to the target small cell 2505.

[0262] The WTRU may reestablish the RBs, 2532, on the respective macro cell or small cell protocol stack. It may start synchronization, 2540 and 2542, with the target macro cell 2503 and target small cell 2505, respectively. The target macro cell 2503 may transmit and UL grant and a RAR message, 2544, with TA for WTRU 2502. The target small cell 2505 may transmit TA information, 2546, for WTRU 2502. The WTRU 2502 may transmit a RRCConnectionReconfigurationComplete message, 2548, to the target macro cell 2503.

[0263] The target macro cell 2503 may send a Path Switch request message, 2550, to MME/S-GW 2507, which may respond with a Path Switch request Ack, 2552, for path switching of macro cell and SC e-RABs. The target macro cell 2503 may transmit a WTRU Context Release message, 2554, to the source macro cell 2504. The source macro cell 2504 may transmit a WTRU Context Release message, 2556, to the source small cell 2506. At the end of the macro cell handover procedure 2500, the WTRU 2402 may perform packet data communication, 2558, with the target small cell 2505 and perform packet data communication, 2560, with the target macro cell 2503.

[0264] In order to support MSA, the RAN protocol architecture may need to be updated. The protocol architecture may vary based on the location of the anchor function in the network. Examples of protocol architectures are described below, where the location of the Anchor function may be at the macro cell eNB and at the S-GW.

[0265] The anchor function for a RAB may be defined for multi-site operation. The multi-site operation for a small cell using shared spectrum may assume umbrella macro cell coverage and may assume data radio bearers setup through the small cell. Control channels may be setup through the macro cell. In this case, the S-GW may act as the common anchor point for establishing DRBs. SRBs may be routed from the MME via the macro cell to the WTRU and DRBs may be routed from same or different S-GW via the small cell to the same WTRU. A transition may occur from a setup, where all SRBs and DRB are through the macro cell, to a setup where SRBs continue to route via the macro cell and the DRBs are routed via different small cells.

[0266] DRBs between the S-GW, the small cell and the WTRU may need to be moved from one S-GW to another S-GW, and/or from small cell to another small cell and/or from a small cell back to the macro cell. As SRBs and DRBs are separated and routed via different nodes, which may change frequently, the complexity of MSA operation may increase. In order to easily manage the splitting and moving of radio bearers, an anchor functionality may be used.

[0267] The anchor maybe a logical function and may perform any of the following features: maintain a mapping of RAB ID and Network Node ID for routing of bearers; from the CN perspective, DRB may always terminate at the anchor; and/or as the DRBs are added or moved, the anchor may be responsible for forwarding the DRB to the appropriate node.

[0268] The anchor function may be located at different network nodes, as in the following examples. For example, the Anchor function may reside in the macro cell eNB. From the CN perspective, SRBs and DRBs may go through the macro eNB for a particular WTRU. When a WTRU sets up DRB with a small cell, the macro cell eNB may forward or tunnel the DRB to the small cell. If the

WTRU changes the small cell and the DRB is relocated to a new small cell, then the macro cell eNB may be responsible for forwarding the DRB to the new small cell. If a WTRU changes the macro cell, then the anchor may need to be reassigned.

[0269] In another example, the S-GW may host the anchor function. The S-

GW may be responsible for forwarding the DRB to the small cell eNB. As the DRB is relocated, the S-GW may forward the DRB to the new small cell. In another example involving multi-RAT networks, including for example an interworking wireless LAN (IWLAN), the anchor function may reside on the Interworking Gateway (IW). In the following, it may be assumed that the anchor function is the S-GW, however the methods and procedures may apply to any other anchor point.

[0270] Figure 26 is an example protocol architecture 2600 for MSA with the macro cell 2604 as the anchor node. The anchor function maybe located at the macro cell 2604 eNB, and DRBs may be established and managed by the macro cell 2604. The Si control plane interface 2618 (e.g. Sl-MME) may be between the macro cell 2604 and the MME 2608. The Si user plane interface

2620 (e.g. Sl-U) may be between the macro cell 2604 and the S-GW 2610. The macro cell 2604 may forward the DRB traffic through the small cell 2606 to the

WTRU 2602. DRB path 2616, may exist between the WTRU 2602, small cell and macro cell 2604 acting as the anchor. Not all functionality in the WTRU 2602, macro cell 2604, small cell 2606, MME 2608 and S-GW 2610, is shown. The

WTRU 2602 may have split MAC and PHY layers (MAC/PHY 1, MACH/PHY 2) to handle the RABs with the macro cell 2604 and small cell 2606, respectively.

The small cell 2606 may have a MAC and PHY layer to support DRBs.

[0271] The control plane 2612 may carry RRC, MACl and PHY1 communication between WTRU 2602 and the macro cell 2604 eNB. The control plane 2614 between the WTRU 2602 and the small cell 2606 may carry MAC2 and PHY2 communication. The control plane 2614 may be used by the WTRU

2602 for a non-contention RACH procedure to perform initial timing adjustment with small cell 2606 and to get resource assignment for bearer setup. MAC2 and

PHY2 may be configured by the RRC layer in the WTRU 2602, which may receive configuration information from the macro cell 2604. The RRC layer in the WTRU 2602 may also be responsible for transmitting measurements gathered from PHY2 to the macro cell 2604. The RLC layer at the macro cell 2604 may forward the DRB related traffic to the MAC layer in small cell 2606 over a bidirectional interface, such as an X2 interface.

[0272] Figure 27 is an example protocol architecture 2700 for MSA with the S-GW 2710 as the anchor node. The Si control plane interface 2718 (e.g. Sl- MME) may be between the macro cell 2704 and the MME 2708. The Si user plane interface 2720 (e.g. Sl-U) may be between the small cell 2706 and the S- GW 2710. The WTRU 2702 may have a split PHY and MAC layer (MACl/PHYl and MAC2/PHY2) for the macro cell 2704 and the small cell 2706, respectively. A single RRC, PDCP, and RLC entity in the WTRU 2702 may be used to communicate with the macro cell 2704 and the small cell 2706. The control Plane 2712 may carry RRC, MACl and PHY1 communication between the WTRU 2702 and the macro cell 2704 eNB. The control plane 2714, between the WTRU 2702 and the small cell 2706, may carry MAC2 and PHY2 communication. The control plane 2714 may be used by the WTRU 2702 for non- contention RACH procedures to perform initial timing adjustment with the small cell 2706 and to get resource assignment for bearer setup. MAC2 and PHY2 may be configured by the RRC layer in the WTRU 2702, which may receive configuration information from the macro cell 2704. The RRC in the WTRU 2702 may also be responsible for transmitting measurements gathered from PHY2 to the macro cell 2704. A user plane 2716 may exist between the WTRU 2702 and the small cell 2706, however, a user plane may also exist between the WTRU 2702 and the macro cell 2704 (not shown).

[0273] Figure 28 is an example of a protocol stack 2800 in a WTRU with a split MAC entity 2806. The protocol stack 2800 may include a PDCP entity

2802, an RLC entity 2804, and a split MAC entity 2806, with a MAC entity 2808

(MAC2) and MAC entity 2810 (MAC2). The PDCP entity 2802, which may receive radio bearers 2830 from higher layers, may include robust header compression (ROHC) 2812 and security 2814 functionality; the RLC entity may include segmentation and automatic repeat request (ARQ) 2816 functionality, and the MAC entities 2808 and 2810 may each include unicast scheduling and priority handling 2820, multiplexing 2822, and hybrid ARQ (HARQ) 2824 functionality and may communicate with the PHY layer via the downlink shared channel DL-SCH 2826.

[0274] In the UL, the RLC entity 2804 may create a PDU based on the

MAC entity 2808 or 2810 that requested data. The RLC entity 2804 may maintain a mapping of logical channels 2818 to the MAC entity 2806. When the RLC entity 2804 receives a request from the MAC entity 2808, it may know which logical channels 2818 should be polled for data. In the DL, the RLC entity 2804 may read data from the transport channels 2826 based on a logical channel 2818 to MAC entity 2806 mapping.

[0275] The S-GW may use a segregation algorithm to segregate RABs of a

WTRU according to the destination eNB. For example, the S-GW may use a Modify Bearer Request message to determine which RABs should stay mapped to the macro cell and to determine which RABs should be transferred to the small cell. Upon receiving traffic on these RABs, the S-GW may switch the traffic to the appropriate cell.

[0276] Embodiments

[0277] 1. A method to enable multi-site aggregation (MSA) performed by a wireless transmit/receive unit (WTRU).

[0278] 2. The method of embodiment 1 further comprising receiving information from a macro cell.

[0279] 3. The method of any of the previous embodiments further comprising triggering a small cell evaluation procedure.

[0280] 4. The method of embodiment 3 wherein the triggering is based on the information from the macro cell.

[0281] 5. The method of any of the previous embodiments, wherein the information from the macro cell is updated system information including a list of available small cells within a coverage area of the macro cell.

[0282] 6. The method of any of the previous embodiments , wherein, the list of available small cells includes at least one of the following information: small cell identification (ID), public land mobile network (PLMN) ID, operator ID, TVWS band identifier, channel information, frequency information, discovery signal configuration, type of small cell, small cell geolocation and small cell coexistence schemes.

[0283] 7. The method of any of the previous embodiments, further comprising: on a condition that the list of available small cells is not empty, initiating the small cell evaluation procedure.

[0284] 8. The method of any of the previous embodiments, wherein the macro cell operates in licensed spectrum, and small cells operate in shared spectrum.

[0285] 9. The method of any of the previous embodiments, wherein the information from the macro cell includes a cell wide direct order indicating to all capable WTRUs to start the small cell evaluation procedure.

[0286] 10. The method of any of the previous embodiments, wherein the information from the macro cell is specific to the WTRU.

[0287] 11. The method of any of the previous embodiments wherein the information from the macro cell is sent as one of: a radio resource configuration (RRC) message, a medium access control (MAC) control element (CE) or physical (PHY) layer signaling.

[0288] 12. The method of any of the previous embodiments, wherein the triggering the small cell evaluation procedure is based on location information.

[0289] 13. The method of any of the previous embodiments, wherein the location information is derived from at least one of the following: global positioning system (GPS) information for the WTRU, GPS information for at least one small cell, and estimated small cell coverage range information.

[0290] 14. The method of any of the previous embodiments, wherein the location information includes macro cell markers that are pre-configured at the WTRU.

[0291] 15. The method of any of the previous embodiments, further comprising a method to enable multi-site aggregation (MSA) performed by a wireless transmit/receive unit (WTRU). [0292] 16. The method of any of the previous embodiments, further comprising receiving a discovery signal on a second frequency from a small cell.

[0293] 17. The method of any of the previous embodiments, wherein the second frequency is different from a small cell operating frequency.

[0294] 18. The method of any of the previous embodiments, wherein the discovery signal includes a cell information.

[0295] 19. The method of any of the previous embodiments, wherein the discovery signal includes the small cell cluster identification (ID) information.

[0296] 20. The method of any of the previous embodiments, wherein the cell information includes any of: a small cell indication, an indication of the small cell operating frequency, an indication of the small cell operator, a small cell identification, and an indication of the small cell type.

[0297] 21. The method of any of the previous embodiments , wherein the

WTRU is notified of the second frequency from system information provided by a macro cell.

[0298] 22. The method of any of the previous embodiments, wherein the second frequency is pre-configured at the WTRU.

[0299] 23. The method of any of the previous embodiments, further comprising performing inter-frequency measurements on the second frequency and performing a small cell ranking procedure.

[0300] 24. The method of any of the previous embodiments, wherein the ranking of the plurality of small cells is based on any of: a discovery quality and information contained in cell identification.

[0301] 25. The method of any of the previous embodiments, further comprising a method for transitioning from IDLE mode to Connected Mode with multi-site aggregation (MSA), performed by a wireless transmit/receive unit (WTRU).

[0302] 26. The method of any of the previous embodiments, further comprising powering on and attaching to a macro cell.

[0303] 27. The method of any of the previous embodiments, further comprising performing small cell discovery to discover at least one small cell. [0304] 28. The method of any of the previous embodiments, further comprising performing small cell evaluation to rank the discovered at least one small cell.

[0305] 29. The method of any of the previous embodiments, further comprising sending an indication and small cell information to a macro cell to move to transition to the Connected Mode with MSA enabled.

[0306] 30. The method of any of the previous embodiments, wherein the indication and the small cell information are sent in at least one radio resource control (RRC) message, further comprising:

[0307] 31. The method of any of the previous embodiments, further comprising receiving an uplink grant allocation from the macro cell in response to the indication and the small cell information.

[0308] 32. The method of any of the previous embodiments, wherein the sending the indication and the small cell information to the macro cell is over the uplink grant allocation.

[0309] 33. The method of any of the previous embodiments, further comprising performing a random access channel (RACH) and radio bearer (RB) setup procedure with the discovered at least one small cell based on small cell configuration information received from the macro cell.

[0310] Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer- readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer- readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, WTRU, terminal, base station, RNC, or any host computer.

Claims

CLAIMS What is claimed:

1. A method to enable multi-site aggregation (MSA) performed by a wireless transmit/receive unit (WTRU), the method comprising:

receiving information from a macro cell;

triggering a small cell evaluation procedure based on the information from the macro cell.

2. The method of claim 1, wherein the information from the macro cell is updated system information including a list of available small cells within a coverage area of the macro cell.

3. The method of claim 2, wherein, the list of available small cells includes at least one of the following information: small cell identification (ID), public land mobile network (PLMN) ID, operator ID, TVWS band identifier, channel information, frequency information, discovery signal configuration, type of small cell, small cell geolocation and small cell coexistence schemes.

4. The method of claim 2, further comprising:

on a condition that the list of available small cells is not empty, initiating the small cell evaluation procedure.

5. The method of claim 1, wherein the macro cell operates in licensed spectrum, and small cells operate in shared spectrum.

6. The method of claim 1, wherein the information from the macro cell includes a cell wide direct order indicating to all capable WTRUs to start the small cell evaluation procedure,

7. The method of claim 1, wherein the information from the macro cell is specific to the WTRU and is sent as one of: a radio resource configuration (RRC) message, a medium access control (MAC) control element (CE) or physical (PHY) layer signaling.

8. The method of claim 1, wherein the triggering the small cell evaluation procedure is based on location information.

9. The method of claim 8, wherein the location information is derived from at least one of the following: global positioning system (GPS) information for the WTRU, GPS information for at least one small cell, and estimated small cell coverage range information.

10. The method of claim 8, wherein the location information includes macro cell markers that are pre-configured at the WTRU.

11. A method to enable multi-site aggregation (MSA) performed by a wireless transmit/receive unit (WTRU), the method comprising:

receiving a discovery signal on a second frequency from a small cell, wherein the second frequency is different from a small cell operating frequency and wherein the discovery signal includes a cell information.

12. The method of claim 11, wherein the discovery signal includes the small cell cluster identification (ID) information.

13. The method of claim 11, wherein the cell information includes any of: a small cell indication, an indication of the small cell operating frequency, an indication of the small cell operator, a small cell identification, and an indication of the small cell type.

14. The method of claim 11, wherein the WTRU is notified of the second frequency from system information provided by a macro cell.

15. The method of claim 11, wherein the second frequency is pre- configured at the WTRU.

16. The method of claim 11, further comprising:

performing inter-frequency measurements on the second frequency and performing a small cell ranking procedure.

17. The method of claim 11, wherein the ranking of the plurality of small cells is based on any of: a discovery quality and information contained in cell identification.

18. A method for transitioning from IDLE mode to Connected Mode with multi-site aggregation (MSA), performed by a wireless transmit/receive unit (WTRU), the method comprising:

powering on and attaching to a macro cell;

performing small cell discovery to discover at least one small cell;

performing small cell evaluation to rank the discovered at least one small cell; and

sending an indication and small cell information to a macro cell to move to transition to the Connected Mode with MSA enabled.

19. The method of claim 18, wherein the indication and the small cell information are sent in at least one radio resource control (RRC) message, further comprising:

receiving an uplink grant allocation from the macro cell in response to the indication and the small cell information, wherein the sending the indication and the small cell information to the macro cell is over the uplink grant allocation.

20. The method of claim 18, further comprising: performing a random access channel (RACH) and radio bearer (RB) setup procedure with the discovered at least one small cell based on small cell configuration information received from the macro cell.