WO2013181825A1

WO2013181825A1 - Systems and methods for selection of wireless communication transmission modes

Info

Publication number: WO2013181825A1
Application number: PCT/CN2012/076589
Authority: WO
Inventors: Bo Chen; Neng Wang; Hao Xu; Jian Li; Zhifei Fan; Jilei Hou; Yongbin Wei
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2012-06-07
Filing date: 2012-06-07
Publication date: 2013-12-12
Anticipated expiration: 2014-12-07

Description

SYSTEMS AND METHODS FOR SELECTION OF WIRELESS COMMUNICATION

TRANSMISSION MODES

BACKGROUND

Field

[0001] Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to selection of transmission modes in LTE wireless communications. Background

[0002] Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC- FDMA) networks.

[0003] A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

[0004] A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink. [0005] As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

[0006] Long Term Evolution (LTE), for example, began at 3GPP in 2004 to provide a radio platform technology capable of achieving high peak throughput. Recently, LTE networks, implementing either a Frequency Division Duplex (FDD) or a Time Division Duplex (TDD) version of the technology, have begun to see wide deployment. In order to achieve the desired levels of throughput and spectral efficiency, such LTE networks implement Multiple Input Multiple Output (MIMO) systems, wherein MIMO refers to the use of multiple antennas at both the transmitter and receiver side. For the FDD LTE downlink, a 2x2 MIMO configuration (i.e., 2 transmit (TX) antennas at the Evolved Node B (eNB) and 2 receive (RX) antennas at the UE) is assumed as baseline configuration. Configurations with 4 antennas are also being supported in FDD LTE implementations (e.g., providing 4x2 and 4x4 MIMO configurations). For the TDD LTE downlink, in addition to the foregoing MIMO configurations, MIMO configurations with 8 transmit antennas and 2 receive antennas may be implemented due to 8 transmit antennas having been deployed at some eNBs of Time Division Synchronous Code Division Multiple Access (TD-SCDMA) commercial networks.

[0007] LTE releases 9 and greater provide support for multiple downlink transmission modes

(TMs). Specifically, 8 downlink transmission modes can be semi-statically configured by the eNB to transmit data in Physical Downlink Shared Channel (PDSCH). These modes include: Mode 1 providing downlink transmission using a single transmit antenna (i.e., port 0) at the eNB; Mode 2 providing transmit diversity (i.e., 2-TX antennas for Space-Frequency Block Coding (SFBC) implementations and 4-TX antennas for SFBC + Frequency-Shift Time Diversity (FSTD) implementations); Mode 3 providing open-loop spatial multiplexing using precoding with large delay Cyclic Delay Diversity (CDD) or transmit diversity, wherein selection of rank is based on UE feedback of Rank Indicator (RI); Mode 4 providing closed- loop spatial multiplexing based on UE feedback of RI and Precoding Matrix Indicator (PMI); Mode 5 providing multi-user MIMO having a single layer per user based on PMI feedback (i.e., having a maximum of 2 users for 2 transmit antennas and 4 users for 4 transmit antennas); Mode 6 providing closed- loop spatial multiplexing with rank=l precoding and single layer transmission based on PMI feedback; Mode 7 providing single-antenna port (i.e., port 5), single layer transmit beam forming with UE specific reference signal; and Mode 8 providing dual layer transmit beam forming (i.e., using port 7 and port 8) with UE specific reference signal. Mode 2, providing transmit diversity, is the fallback scheme for transmission modes 3-7 and SFBC is the default transmission mode (e.g., after cell acquisition, but before another transmission mode is signaled) for systems having antenna systems with 2 or more antennas.

SUMMARY

[0008] In one aspect of the disclosure, a method of selecting a transmission mode from a

plurality of transmission modes for wireless communication is provided. The method comprising updating transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information. The method also comprising choosing, using at least a portion of the updated transmission mode selection metrics, open-loop or closed-loop transmission and choosing, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize. The method further comprising selecting a particular transmission mode of the plurality of transmission modes having the chosen open-loop or closed-loop transmission and implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

[0009] In an additional aspect of the disclosure, a apparatus configured for selecting a transmission mode from a plurality of transmission modes for wireless communication is provided. The apparatus comprising means for updating transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information. The apparatus also comprising means for choosing, using at least a portion of the updated transmission mode selection metrics, open- loop or closed-loop transmission and means for choosing, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize. The apparatus further comprising means for selecting a particular transmission mode of the plurality of transmission modes having the chosen open-loop or closed-loop transmission and implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

In an additional aspect of the disclosure, a computer program product has a computer- readable medium having program code recorded thereon. This program code includes code for selecting a transmission mode from a plurality of transmission modes for wireless communications in a wireless network. The code comprising program code to update transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information. The code also comprising program code to choose, using at least a portion of the updated transmission mode selection metrics, open-loop or closed-loop transmission and program code to choose, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize. The code further comprising program code to select a particular transmission mode of the plurality of transmission modes having the chosen open- loop or closed-loop transmission and implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

In an additional aspect of the disclosure, an apparatus includes at least one processor and a memory coupled to the processor. The processor is configured to select a transmission mode from a plurality of transmission modes for wireless communication. Wherein at least one processor of the apparatus is configured to update transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information. The at least one processor of the apparatus also configured to choose, using at least a portion of the updated transmission mode selection metrics, open-loop or closed-loop transmission and to choose, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize. The at least one processor of the apparatus further configured to select a particular transmission mode of the plurality of transmission modes having the chosen open-loop or closed-loop transmission and implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

BRIEF DESCRIPTION OF THE DRAWING

[0010] FIG. 1 is a block diagram conceptually illustrating an example of a mobile communication system.

[0011] FIG. 2 is a block diagram conceptually illustrating an example of a downlink frame structure in a mobile communication system.

[0012] FIG. 3 is a block diagram conceptually illustrating an exemplary frame structure in uplink LTE/-A communications.

[0013] FIG. 4 is a block diagram conceptually illustrating time division multiplexed (TDM) partitioning in a heterogeneous network according to one aspect of the disclosure. [0014] FIG. 5 is a block diagram conceptually illustrating a design of a base station/eNB and a UE configured according to one aspect of the present disclosure.

[0015] FIG. 6 is a flow diagram conceptually illustrating operation to provide wireless communication transmission mode selection according to aspects of the disclosure.

[0016] FIG. 7 is a flow diagram conceptually illustrating transition between spatial layer selections according to one aspect of the disclosure.

[0017] FIGS. 8 A and 8B are transmit mode selection matrices conceptually illustrating selection of wireless communication transmission modes according to one aspect of the disclosure.

DETAILED DESCRIPTION

[0018] The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the inventive subject matter. It will be apparent to those skilled in the art that these specific details are not required in every case and that, in some instances, well-known structures and components are shown in block diagram form for clarity of presentation.

[0019] The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network may implement a radio technology, such as Universal Terrestrial Radio Access (UTRA), Telecommunications Industry Association's (TIA's) CDMA2000®, and the like. The UTRA technology includes Wideband CDMA (WCDMA) and other variants of CDMA. The CDMA2000® technology includes the IS-2000, IS-95 and IS-856 standards from the Electronics Industry Alliance (EIA) and TIA. A TDMA network may implement a radio technology, such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, and the like. The UTRA and E-UTRA technologies are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE- Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization called the "3rd Generation Partnership Project" (3 GPP). CDMA2000® and UMB are described in documents from an organization called the "3rd Generation Partnership Project 2" (3GPP2). The techniques described herein may be used for the wireless networks and radio access technologies mentioned above, as well as other wireless networks and radio access technologies. For clarity, certain aspects of the techniques are described below for LTE or LTE-A (together referred to in the alternative as "LTE/- A") and use such LTE/-A terminology in much of the description below.

[0020] FIG. 1 shows wireless network 100 for communication, which may be an LTE-A network. Wireless network 100 includes a number of evolved node Bs (eNBs) 110 and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB 110 may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

[0021] An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown in FIG. 1, eNBs 110a, 110b and 110c are macro eNBs for macro cells 102a, 102b and 102c, respectively. eNB 11 Ox is a pico eNB for pico cell 102x. And, eNBs HOy and HOz are femto eNBs for femto cells 102y and 102z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

[0022] Wireless network 100 also includes relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB, a UE, or the like) and sends a transmission of the data and/or other information to a downstream station (e.g., another UE, another eNB, or the like). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in FIG. 1, relay station 11 Or may communicate with eNB 110a and UE 120r, in which relay station 11 Or acts as a relay between the two network elements (eNB 110a and UE 120r) in order to facilitate communication between them. A relay station may also be referred to as a relay eNB, a relay, and the like.

[0023] Wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

[0024] UEs 120 are dispersed throughout wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In FIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and an eNB.

[0025] LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC- FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 128, 256, 512, 1024 or 2048 for a corresponding system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands for a corresponding system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.

[0026] FIG. 2 shows a downlink frame structure used in LTE/-A. The transmission timeline for the downlink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each sub frame may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, e.g., 7 symbol periods for a normal cyclic prefix (as shown in FIG. 2) or 6 symbol periods for an extended cyclic prefix. The 2L symbol periods in each subframe may be assigned indices of 0 through 2L-1. The available time frequency resources may be partitioned into resource blocks. Each resource block may cover N subcarriers (e.g., 12 subcarriers) in one slot.

[0027] In LTE/-A, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The primary and secondary synchronization signals may be sent in symbol periods 6 and 5, respectively, in each of subframes 0 and 5 of each radio frame with the normal cyclic prefix, as shown in FIG. 2. The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carry certain system information.

[0028] The eNB may send a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe, as seen in FIG. 2. The PCFICH may convey the number of symbol periods (M) used for control channels, where M may be equal to 1 , 2 or 3 and may change from subframe to subframe. M may also be equal to 4 for a small system bandwidth, e.g., with less than 10 resource blocks. In the example shown in FIG. 2, M=3. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods of each subframe. The PDCCH and PHICH are also included in the first three symbol periods in the example shown in FIG. 2. The PHICH may carry information to support hybrid automatic retransmission (HARQ). The PDCCH may carry information on resource allocation for UEs and control information for downlink channels. The eNB may send a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink.

[0029] In addition to sending PHICH and PDCCH in the control section of each subframe, i.e., the first symbol period of each subframe, the LTE-A may also transmit these control- oriented channels in the data portions of each subframe as well. As shown in FIG. 2, these new control designs utilizing the data region, e.g., the Relay-Physical Downlink Control Channel (R-PDCCH) and Relay-Physical HARQ Indicator Channel (R-PHICH) are included in the later symbol periods of each subframe. The R-PDCCH is a new type of control channel utilizing the data region originally developed in the context of half-duplex relay operation. Different from legacy PDCCH and PHICH, which occupy the first several control symbols in one subframe, R-PDCCH and R-PHICH are mapped to resource elements (REs) originally designated as the data region. The new control channel may be in the form of Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), or a combination of FDM and TDM.

[0030] The eNB may send the PSS, SSS and PBCH in the center 1.08 MHz of the system bandwidth used by the eNB. The eNB may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The eNB may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The eNB may send the PDSCH to specific UEs in specific portions of the system bandwidth. The eNB may send the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs.

[0031] A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH.

[0032] A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNB may send the PDCCH to the UE in any of the combinations that the UE will search.

[0033] A UE may be within the coverage of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received power, path loss, Signal to Interference and Noise Ratio (SINR), etc.

[0034] FIG. 3 is a block diagram illustrating an exemplary frame structure 300 in uplink long term evolution (LTE/-A) communications. The available resource blocks (RBs) for the uplink may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The design in FIG. 3 results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section.

[0035] A UE may be assigned resource blocks in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks in the data section to transmit data to the eNode B. The UE may transmit control information in a Physical Uplink Control Channel (PUCCH) on assigned resource blocks 310a and 310b in the control section. The UE may transmit only data or both data and control information in a Physical Uplink Shared Channel (PUSCH) on assigned resource blocks 320a and 320b in the data section. An uplink transmission may span both slots of a subframe and may hop across frequency as shown in FIG. 3.

[0036] Referring back to FIG. 1, wireless network 100 uses a diverse set of eNBs (i.e., macro eNBs, pico eNBs, femto eNBs, and relays) to improve the spectral efficiency of the system per unit area. Because wireless network 100 uses such different eNBs for its spectral coverage, it may also be referred to as a heterogeneous network. Macro eNBs HOa-c are usually carefully planned and placed by the provider of wireless network 100. Macro eNBs 1 lOa-c generally transmit at high power levels (e.g., 5 W - 40 W). Pico eNB 1 lOx and relay station HOr, which generally transmit at substantially lower power levels (e.g., 100 mW - 2 W), may be deployed in a relatively unplanned manner to eliminate coverage holes in the coverage area provided by macro eNBs 1 lOa-c and improve capacity in the hot spots. Femto eNBs 110y-z, which are typically deployed independently from wireless network 100 may, nonetheless, be incorporated into the coverage area of wireless network 100 either as a potential access point to wireless network 100, if authorized by their administrator(s), or at least as an active and aware eNB that may communicate with other eNBs 110 of wireless network 100 to perform resource coordination and coordination of interference management. Femto eNBs 1 lOy-z typically also transmit at substantially lower power levels (e.g., 100 mW - 2 W) than macro eNBs 1 lOa-c.

[0037] In operation of a heterogeneous network, such as wireless network 100, each UE is usually served by the eNB with the better signal quality, while the unwanted signals received from the other eNBs are treated as interference. While such operational principals can lead to significantly sub-optimal performance, gains in network performance are realized in wireless network 100 by using intelligent resource coordination among eNBs 110, better server selection strategies, and more advanced techniques for efficient interference management. [0038] A pico eNB, such as pico eNB 1 lOx, is characterized by a substantially lower transmit power when compared with a macro eNB, such as macro eNBs 1 lOa-c. A pico eNB will also usually be placed around a network, such as wireless network 100, in an ad hoc manner. Because of this unplanned deployment, wireless networks with pico eNB placements, such as wireless network 100, can be expected to have large areas with low signal to interference conditions, which can make for a more challenging RF environment for control channel transmissions to UEs on the edge of a coverage area or cell (a "cell-edge" UE). Moreover, the potentially large disparity (e.g., approximately 20 dB) between the transmit power levels of macro eNBs 1 lOa-c and pico eNB 1 lOx implies that, in a mixed deployment, the downlink coverage area of pico eNB 1 lOx will be much smaller than that of macro eNBs 1 lOa-c.

[0039] In the uplink case, however, the signal strength of the uplink signal is governed by the

UE, and, thus, will be similar when received by any type of eNBs 110. With the uplink coverage areas for eNBs 110 being roughly the same or similar, uplink handoff boundaries will be determined based on channel gains. This can lead to a mismatch between downlink handover boundaries and uplink handover boundaries. Without additional network accommodations, the mismatch would make the server selection or the association of UE to eNB more difficult in wireless network 100 than in a macro eNB-only homogeneous network, where the downlink and uplink handover boundaries are more closely matched.

[0040] If server selection is based predominantly on downlink received signal strength, the usefulness of mixed eNB deployment of heterogeneous networks, such as wireless network 100, will be greatly diminished. This is because the larger coverage area of the higher powered macro eNBs, such as macro eNBs HOa-c, limits the benefits of splitting the cell coverage with the pico eNBs, such as pico eNB 1 lOx, because, the higher downlink received signal strength of macro eNBs HOa-c will attract all of the available UEs, while pico eNB 1 lOx may not be serving any UE because of its much weaker downlink transmission power. Moreover, macro eNBs HOa-c will likely not have sufficient resources to efficiently serve those UEs. Therefore, wireless network 100 will attempt to actively balance the load between macro eNBs 1 lOa-c and pico eNB 11 Ox by expanding the coverage area of pico eNB 1 lOx. This concept is referred to as cell range extension (CRE).

[0041] Wireless network 100 achieves CRE by changing the manner in which server selection is determined. Instead of basing server selection on downlink received signal strength, selection is based more on the quality of the downlink signal. In one such quality- based determination, server selection may be based on determining the eNB that offers the minimum path loss to the UE. Additionally, wireless network 100 provides a fixed partitioning of resources between macro eNBs HOa-c and pico eNB 11 Ox. However, even with this active balancing of load, downlink interference from macro eNBs HOa-c should be mitigated for the UEs served by the pico eNBs, such as pico eNB 11 Ox. This can be accomplished by various methods, including interference cancellation at the UE, resource coordination among eNBs 110, or the like.

[0042] In a heterogeneous network with cell range extension, such as wireless network 100, in order for UEs to obtain service from the lower-powered eNBs, such as pico eNB 1 lOx, in the presence of the stronger downlink signals transmitted from the higher-powered eNBs, such as macro eNBs HOa-c, pico eNB 11 Ox engages in control channel and data channel interference coordination with the dominant interfering ones of macro eNBs HOa-c. Many different techniques for interference coordination may be employed to manage interference. For example, inter-cell interference coordination (ICIC) may be used to reduce interference from cells in co-channel deployment. One ICIC mechanism is adaptive resource partitioning. Adaptive resource partitioning assigns subframes to certain eNBs. In subframes assigned to a first eNB, neighbor eNBs do not transmit. Thus, interference experienced by a UE served by the first eNB is reduced. Subframe assignment may be performed on both the uplink and downlink channels.

[0043] For example, subframes may be allocated between three classes of subframes: protected subframes (U subframes), prohibited subframes (N subframes), and common subframes (C subframes). Protected subframes are assigned to a first eNB for use exclusively by the first eNB. Protected subframes may also be referred to as "clean" subframes based on the lack of interference from neighboring eNBs. Prohibited subframes are subframes assigned to a neighbor eNB, and the first eNB is prohibited from transmitting data during the prohibited subframes. For example, a prohibited subframe of the first eNB may correspond to a protected subframe of a second interfering eNB. Thus, the first eNB is the only eNB transmitting data during the first eNB's protected subframe. Common subframes may be used for data transmission by multiple eNBs. Common subframes may also be referred to as "unclean" subframes because of the possibility of interference from other eNBs.

[0044] At least one protected subframe is statically assigned per period. In some cases only one protected subframe is statically assigned. For example, if a period is 8 milliseconds, one protected subframe may be statically assigned to an eNB during every 8 milliseconds. Other subframes may be dynamically allocated.

[0045] Adaptive resource partitioning information (ARPI) allows the non-statically assigned subframes to be dynamically allocated. Any of protected, prohibited, or common subframes may be dynamically allocated (AU, AN, AC subframes, respectively). The dynamic assignments may change quickly, such as, for example, every one hundred milliseconds or less.

[0046] Heterogeneous networks may have eNBs of different power classes. For example, three power classes may be defined, in decreasing power class, as macro eNBs, pico eNBs, and femto eNBs. When macro eNBs, pico eNBs, and femto eNBs are in a co-channel deployment, the power spectral density (PSD) of the macro eNB (aggressor eNB) may be larger than the PSD of the pico eNB and the femto eNB (victim eNBs) creating large amounts of interference with the pico eNB and the femto eNB. Protected subframes may be used to reduce or minimize interference with the pico eNBs and femto eNBs. That is, a protected subframe may be scheduled for the victim eNB to correspond with a prohibited subframe on the aggressor eNB.

[0047] FIG. 4 is a block diagram illustrating time division multiplexed (TDM) partitioning in a heterogeneous network according to one aspect of the disclosure. A first row of blocks illustrate subframe assignments for a femto eNB, and a second row of blocks illustrate subframe assignments for a macro eNB. Each of the eNBs has a static protected subframe during which the other eNB has a static prohibited subframe. For example, the femto eNB has a protected subframe (U subframe) in subframe 0 corresponding to a prohibited subframe (N subframe) in subframe 0. Likewise, the macro eNB has a protected subframe (U subframe) in subframe 7 corresponding to a prohibited subframe (N subframe) in subframe 7. Subframes 1-6 are dynamically assigned as either protected subframes (AU), prohibited subframes (AN), and common subframes (AC). During the dynamically assigned common subframes (AC) in subframes 5 and 6, both the femto eNB and the macro eNB may transmit data.

[0048] Protected subframes (such as U/AU subframes) have reduced interference and a high channel quality because aggressor eNBs are prohibited from transmitting. Prohibited subframes (such as N/AN subframes) have no data transmission to allow victim eNBs to transmit data with low interference levels. Common subframes (such as C/AC subframes) have a channel quality dependent on the number of neighbor eNBs transmitting data. For example, if neighbor eNBs are transmitting data on the common subframes, the channel quality of the common subframes may be lower than the protected subframes. Channel quality on common subframes may also be lower for extended boundary area (EBA) UEs strongly affected by aggressor eNBs. An EBA UE may belong to a first eNB but also be located in the coverage area of a second eNB. For example, a UE communicating with a macro eNB that is near the range limit of a femto eNB coverage is an EBA UE.

[0049] Another example interference management scheme that may be employed in LTE/-A is the slowly-adaptive interference management. Using this approach to interference management, resources are negotiated and allocated over time scales that are much larger than the scheduling intervals. The goal of the scheme is to find a combination of transmit powers for all of the transmitting eNBs and UEs over all of the time or frequency resources that maximizes the total utility of the network. "Utility" may be defined as a function of user data rates, delays of quality of service (QoS) flows, and fairness metrics. Such an algorithm can be computed by a central entity that has access to all of the information used for solving the optimization and has control over all of the transmitting entities. This central entity may not always be practical or even desirable. Therefore, in alternative aspects a distributed algorithm may be used that makes resource usage decisions based on the channel information from a certain set of nodes. Thus, the slowly-adaptive interference algorithm may be deployed either using a central entity or by distributing the algorithm over various sets of nodes/entities in the network.

[0050] In deployments of heterogeneous networks, such as wireless network 100, a UE may operate in a dominant interference scenario in which the UE may observe high interference from one or more interfering eNBs. A dominant interference scenario may occur due to restricted association. For example, in FIG. 1, UE 120y may be close to femto eNB 1 lOy and may have high received power for eNB 1 lOy. However, UE 120y may not be able to access femto eNB HOy due to restricted association and may then connect to macro eNB 110c (as shown in FIG. 1) or to femto eNB 1 lOz also with lower received power (not shown in FIG. 1). UE 120y may then observe high interference from femto eNB 1 lOy on the downlink and may also cause high interference to eNB HOy on the uplink. Using coordinated interference management, eNB 110c and femto eNB HOy may communicate over backhaul 134 to negotiate resources. In the negotiation, the femto eNB 1 lOy agrees to cease transmission on one of its channel resources, such that UE 120y will not experience as much interference from femto eNB 1 lOy as it communicates with eNB 110c over that same channel.

[0051] In addition to the discrepancies in signal power observed at the UEs in such a dominant interference scenario, timing delays of downlink signals may also be observed by the UEs, even in synchronous systems, because of the differing distances between the UEs and the multiple eNBs. The eNBs in a synchronous system are presumptively synchronized across the system. However, for example, considering a UE that is a distance of 5 km from the macro eNB, the propagation delay of any downlink signals received from that macro eNB would be delayed approximately 16.67 (5 km ÷ 3 x 10 , i.e., the speed of light, 'c'). Comparing that downlink signal from the macro eNB to the downlink signal from a much closer femto eNB, the timing difference could approach the level of a time-to-live (TTL) error.

[0052] Additionally, such timing difference may impact the interference cancellation at the

UE. Interference cancellation often uses cross correlation properties between a combination of multiple versions of the same signal. By combining multiple copies of the same signal, interference may be more easily identified because, while there will likely be interference on each copy of the signal, it will likely not be in the same location. Using the cross correlation of the combined signals, the actual signal portion may be determined and distinguished from the interference, thus, allowing the interference to be canceled.

[0053] FIG. 5 shows a block diagram of a design of a base station/eNB 110 and UE 120, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. For a restricted association scenario, eNB 110 may be macro eNB 110c in FIG. 1, and UE 120 may be UE 120y. eNB 110 may also be a base station of some other type. eNB 110 may be equipped with antennas 534a through 534t, and UE 120 may be equipped with antennas 552a through 552r.

[0054] At eNB 110, transmit processor 520 may receive data from data source 512 and control information from controller/processor 540. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. Transmit processor 520 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. Transmit processor 520 may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. Transmit (TX) multiple-input multiple-output (MIMO) processor 530 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to modulators (MODs) 532a through 532t. Each modulator 532 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 532 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators 532a through 532t may be transmitted via antennas 534a through 534t, respectively.

[0055] At UE 120, antennas 552a through 552r may receive the downlink signals from eNB

110 and may provide received signals to demodulators (DEMODs) 554a through 554r, respectively. Each demodulator 554 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 554 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. MIMO detector 556 may obtain received symbols from demodulators 554a through 554r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. Receive processor 558 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for UE 120 to data sink 560, and provide decoded control information to controller/processor 580.

[0056] On the uplink, at UE 120, transmit processor 564 may receive and process data (e.g., for the PUSCH) from data source 562 and control information (e.g., for the PUCCH) from controller/processor 580. Transmit processor 564 may also generate reference symbols for a reference signal. The symbols from transmit processor 564 may be precoded by TX MIMO processor 566 if applicable, further processed by demodulators 554a through 554r (e.g., for SC-FDM, etc.), and transmitted to eNB 110. At eNB 110, the uplink signals from UE 120 may be received by antennas 534, processed by modulators 532, detected by MIMO detector 536 if applicable, and further processed by receive processor 538 to obtain decoded data and control information sent by UE 120. Receive processor 538 may provide the decoded data to data sink 539 and the decoded control information to controller/processor 540.

[0057] Controllers/processors 540 and 580 may direct the operation at eNB 110 and UE 120, respectively. Controller/processor 540 and/or other processors and modules at eNB 110 may perform or direct the execution of the functional blocks illustrated in FIGS. 6 and 7, and/or other processes for the techniques described herein. Controllers/processor 580 and/or other processors and modules at UE 120 may also perform or direct the execution of various processes for the techniques described herein. Memories 542 and 582 may store data and program codes for eNB 110 and UE 120, respectively. Scheduler 544 may schedule UEs for data transmission on the downlink and/or uplink.

[0058] eNB 110 and UE 120 may cooperate to implement wireless communication modes adapted to provide throughput and spectral efficiency optimized for the communication conditions experienced. For example, any of transmit processor 520, receive processor 538, and controller/processor 540 of eNB 110 and/or receive processor 558, transmit processor 564, and controller/processor 580 of UE 120 may execute transmission mode selection logic to provide a transmission mode selection system operable to update, request, and control one or more wireless communication modes, such as the aforementioned downlink transmission modes, utilized by eNB 110 and UE 120. [0059] To aid in the understanding of the concepts herein, embodiments of the present disclosure will be described with reference to the 8 downlink transmission modes of LTE release 9 (i.e., single antenna port mode 1 (TM1), transmission diversity mode 2 (TM2), open loop spatial multiplexing mode 3 (TM3), closed loop spatial multiplexing mode 4 (TM4), multi-user MIMO mode 5 (TM5), closed loop spatial multiplexing with rank 1 mode 6 (TM6), single layer open loop beam forming mode 7 (TM7), and dual layer open loop beam forming mode 8 (TM8)). It should be appreciated, however, that the concepts described may be applied to additional or alternative transmission modes and/or to uplink transmission modes.

[0060] It should be appreciated that, although the LTE standards for release 9 and greater provide for 8 downlink transmission modes, criteria and algorithms for selection of any particular transmission mode from the 8 downlink transmission modes have not been specified. Embodiments of the disclosure herein, however, provide transmission mode selection systems operable in accordance with transmission mode selection logic to implement appropriate/optimized transmission modes of a plurality of transmission modes, such as the aforementioned 8 downlink transmission modes. For example, TM configure logic 502 (shown as operable within transmit processor 520), TM request logic 503 (shown as operable within receive processor 538), and TM control logic 504 (shown as operable within controller/processor 540) of embodiments (collectively referred to as transmission mode selection logic) operate to update, request, and control transmission modes according to the concepts herein.

[0061] In order to make an appropriate and/or optimized selection of a transmission mode of the plurality of transmission modes, embodiments may take a number of factors into consideration. Factors taken into consideration for selection of a transmission mode according to embodiments herein may include the number of RX antennas at the UE, wherein one RX antenna suggests that TM1, TM2, TM5, TM6, and TM7 are appropriate transmission mode candidates while more than one RX antenna suggests that any of TM1-TM8 are appropriate transmission mode candidates. Duplex modes supported/implemented is another factor which may be taken into consideration for selecting a transmission mode, wherein FDD suggest that TM1, TM2, TM3, TM4, TM5, and TM6 are appropriate transmission mode candidates while TDD suggests that TM1, TM2, TM3, TM4, TM7, and TM8 are appropriate transmission mode candidates. Another factor which may be taken into consideration for selecting a transmission mode is UE category, wherein TM2 is an appropriate transmission mode for all UE categories, UE category 1 suggests that TM2, TM6, and TM7 are appropriate transmission modes, UE categories 2-4 suggest that TM3, TM4, TM5, TM6, TM7, and TM8 with up to 2 layer transmission are appropriate transmission modes, and UE category 5 suggests that TM3, TM4, TM5, and TM6 with up to 4 layer transmission are appropriate transmission modes. UE mobility/channel variation is still another factor which may be taken into consideration for selecting a transmission mode, wherein high mobility suggest that TM1, TM2, TM3, and possibly TM7 and TM8 are appropriate transmission modes while low mobility suggests that TM1, TM4, TM5, TM6, TM7, and TM8 are appropriate transmission modes. UE channel condition (e.g., long-term SINR, wideband channel quality information (CQI) feedback, etc., collectively referred to as channel geometry) is yet another factor which may be taken into consideration for selecting a transmission mode, wherein low channel geometry suggests that TM1, TM2, TM6, TM7, and TM8 are appropriate transmission modes and high channel geometry suggests that TM1, TM3, TM4, and TM5 are appropriate transmission modes. Still yet another factor which may be taken into consideration for selecting a transmission mode is unpredictable instant channel condition (e.g., feedback channel breakdown, switching to a new cell, etc.), wherein the presence of unpredictable instant channel conditions suggests that TM1 and TM2 are appropriate transmission modes. Semi-persistent scheduling is another factor which may be taken into consideration in selecting a transmission mode, wherein semi-persistent scheduling suggests that TM1, TM2, TM7, and TM8 are appropriate transmission modes.

[0062] Using one or more transmission mode selection factors, such as the foregoing factors, embodiments herein operate to make an appropriate and/or optimized selection of a transmission mode of the plurality of transmission modes. Selection of a transmission mode according to embodiments involves choosing open-loop or closed-loop transmission, a choice of a number of spatial layers (which preferably includes selection between spatial multiplexing/beamforming and transmit diversity), and identification of a transmission mode or modes which meets these choices. Where more than one transmission mode meets the choices, a particular transmission mode of those transmission modes may be selected based upon one or more selection factors (e.g., one or more of the foregoing factors). Having selected a transmission mode, a request may be made to implement the transmission mode and, assuming the transmission mode request is honored, the selected transmission mode may be configured (e.g., the appropriate modules of the eNB and UE configured for the transmission mode) and the selected transmission mode implemented.

[0063] The flow diagram of FIG. 6 shows operation of update, request, and configure phases of transmission mode selection logic operable to implement transmission modes according to embodiments. Specifically, in the illustrated embodiment of flow 600, transmission mode selection metrics are updated at block 610 (e.g., by operation of TM request logic 503), transmission mode requests are provided at block 620 (e.g., by operation of TM request logic 503), and transmission mode configuration is provided at block 630 (e.g., by operation of TM control logic 504 and TM configure logic 502), as will be described in further detail below.

[0064] Although not shown in the illustrated embodiment for simplicity, a determination may be made as to whether flow 600, and the transmission mode selection provided thereby, is to be implemented. For example, if the number of antenna ports at eNB 110 is 1 , TM control logic 504 may operate to configure all UEs in communication with the eNB to TM1 and suspend further processing according to flow 600. However, in the case that the number of antenna ports at eNB 1 10 is greater than one, TM control logic 504 may initiate further processing according to flow 600 to facilitate switching between the transmission modes.

[0065] It should be appreciated that operation of flow 600 of FIG. 6 may begin at block 630 when communication is established between UE 120 and eNB 110, such as to provide implementation of a default transmission mode for establishing communications when transmission mode selection metrics are not yet available/collected, where processing of transmit metrics and/or a transmission mode request have not yet completed, etc. For example, where eNB 110 has more than 1 antenna port available/operational, transmission mode 2 (i.e., transmission diversity) may be implemented as a default transmission mode until operation of blocks 610 and 620 provide for selection of a different transmission mode (e.g., a transmission mode optimized for the wireless communication conditions experienced). Where eNB 110 has only 1 antenna port available/operational, transmission mode 1 would be selected.

[0066] At block 610 of the illustrated embodiment, various transmission mode selection metrics are collected/generated for use as the aforementioned factors for updating transmission mode selection. For example, UE feedback of various information, such as channel quality information (CQI), RI, etc., may be collected at block 611 by TM request logic 503 of eNB 110 for use in updating transmission mode selection. Additionally or alternatively, TM request logic 503 of eNB 110 may measure and/or estimate various metrics, such as to estimate the UE's Doppler, measure the uplink and/or downlink SINR, etc., at block 611. This information may be used by TM request logic 503 of embodiments at blocks 612-619 as and/or to generate the various factors considered in transmission mode selection according to embodiments herein.

[0067] At block 612 of the illustrated embodiment, a choice is made, such as by TM request logic 503, as to whether open- loop or closed- loop transmission is to be used. In a closed-loop system (e.g., TM4, TM5, and TM6) the receiver reports the channel information to the transmitter. In an open-loop system (e.g., TM2 and TM3) such information is not reported to the transmitter.

[0068] It should be appreciated that the receiver may determine such channel information in certain scenarios. For example, in some open-loop systems (e.g., TM7 and TM8) having highly correlated uplink and downlink (e.g., TDD implementations) channel reciprocity may be utilized to determine channel information for one link (e.g., downlink) using measurements from another link (e.g., uplink). That is, since the uplink and downlink share a single frequency band, uplink channel estimation can be used to make reasonable assumptions regarding downlink channel characteristics. This channel reciprocity leads to no requirements for the feedback of downlink channel information from UE. Instead, the UE may send a channel-sounding signal to the eNB. The eNB may then estimate the uplink channel by examining the relative phase difference between the co-polarized antennas. Thus, while this estimation is done in the uplink, the eNB uses channel reciprocity to transmit in the downlink based on the estimation of the uplink.

[0069] Accordingly, in choosing open-loop or closed-loop transmission, embodiments may operate to consider the duplex modes available/implemented. For example, where TDD is implemented open-loop transmission may be preferred in order to take advantage of channel reciprocity and avoid feedback overhead while still providing for CQI. Where FDD is implemented either open-loop or closed-loop transmission may be preferred depending upon UE speed (e.g., as provided by Doppler estimation). For example, open-loop transmission would be more beneficial for medium-to-high mobility UEs; while closed-loop transmission improves performance for low mobility UEs.

[0070] Accordingly, where the duplex mode is TDD or the Doppler is greater than a threshold determined to be indicative of low mobility, processing by block 612 of the illustrated embodiment proceeds to block 613 to choose open- loop transmission. However, where the duplex mode is not TDD or the Doppler is not greater than a threshold determined to be indicative of low mobility, processing by block 612 of the illustrated embodiment proceeds to block 614 to choose closed- loop transmission.

[0071] It should be appreciated that selection between open-loop and closed-loop transmission is not limited to the duplex mode or Doppler of the illustrated embodiment. For example, antenna correlation may also impact determination of open-loop or closed-loop transmission. In particular, it has been discovered that, for largely-spaced antennas, TM3 outperforms TM4, while for closely-spaced antennas, TM4 outperforms TM3 under low spatial channel variation. Accordingly, embodiments may utilize antenna correlation in addition to or in the alternative to the duplex mode or Doppler shown with respect to the illustrated embodiment. However, for UEs with fast spatial channel variations, such embodiments may switch to TM3 due to its robustness to channel feedback errors.

[0072] Blocks 615-619 of the illustrated embodiment provide, such as by operation of TM request logic 503, a choice of the number of spatial layers. At block 615 of the illustrated embodiment a determination is made as to whether the UE is a category 1 UE, such as using information collected/generated at block 611. If it is determined that the UE is a category 1 UE (i.e., supports only 1 layer transmission), processing according to the illustrated embodiment proceeds to block 616 wherein 1 layer transmission is selected. However, if it is determined that the UE is a category greater than 1 (i.e., supports 2 or more layer transmission), processing according to the illustrated embodiment proceeds to block 617 for further analysis to choose the number of spatial layers.

[0073] The number of spatial layers to be used may be chosen at block 617 of embodiments based on a number of metrics/measurements, such as mobile feedback of rank, the rank of estimated downlink channels based on reciprocity in TDD, UE channel geometry (e.g., long- term SINR, wideband CQI feedback, etc.), UE speed (e.g., Doppler estimate), and/or combinations thereof. For example, where the RI provided by the UE is greater than 1 and the SINR is determined to be sufficiently high to support a plurality of spatial layers, processing according to the illustrated embodiment may proceed to block 618 to choose N layer transmission (e.g., where N = the number of layers in the RI or N < the number of layers in the RI and is a function of the SINR). However, where the RI provided by the UE is 1 or the SINR is determined to be insufficiently high to support a plurality of spatial layers, processing according to the illustrated embodiment may proceed to block 619 to choose 1 layer transmission.

[0074] It should be appreciated that operation of blocks 615-619 provides for transition between 1 layer and N layer transmission based upon observed metrics/measurements as the transmission mode selection metrics are updated at each iteration of the operation of flow 600. Transition between 1 layer and 2 layer transmission based on the rank and CQI of the above example is illustrated in FIG. 7, wherein as the RI or SINR drops 1 layer transmission is selected and as the RI and SINR improves 2 layer transmission is selected.

[0075] The selection criteria implemented at blocks 617-619 of embodiments herein not only apply to the choice of spatial layers, but also apply to selection between spatial multiplexing/beam forming and transmit diversity as well. Rank adaptation for closed-loop spatial multiplexing, and switching between open-loop spatial multiplexing and transmit diversity lead to robust performance and improve system throughput. For example, 1 layer transmission (e.g., TM6 or TM7) may be chosen for low channel geometry regions due to beam forming gain, while for high SINR regions spatial multiplexing gain is significant and thus N layer transmission is chosen (e.g., TM4/TM5 or TM8).

[0076] Having chosen between open-loop and closed-loop transmission and the number transmission layers, processing according to the illustrated embodiment proceeds to block 620.

[0077] At block 620 of embodiments a transmission mode request is made. For example,

TM request logic 503 may utilize the foregoing choices, perhaps in combination with additional transmission mode selection metrics (e.g., as updated at block 611) to select a particular transmission mode to request. In operation according to embodiments, based upon the duplex mode implemented, whether open-loop or closed-loop transmission is to be used, the mobility of the UE, and the channel geometry associated with the UE, a particular transmission mode of TM1-TM8 is selected. A transmission mode selection matrix for FDD LTE systems as may be implemented at block 620 by TM request logic 503 of embodiments using the foregoing selection criteria is shown in FIG. 8A. A transmission mode selection matrix for TDD LTE systems as may be implemented at block 620 by TM request logic 503 of embodiments using the foregoing selection criteria is shown in FIG. 8B.

[0078] Once a particular transmission mode is selected, a request for implementing that transmission mode may be made. For example, TM request logic 503 may communicate the transmission mode request to TM control logic 504 at block 620, thus proceeding to block 630 of flow 600.

[0079] At block 630 TM control logic 504 and TM configure logic 502 operate to implement the requested transmission mode as appropriate. TM control logic 504 of embodiments may operate to determine if the requested transmission mode is to be implemented. For example, where scheduler 544 announces resource limitations for the PDCCH, a requested transmission mode which is incompatable with the resource limitations may not be implemented by TM control logic 504 (e.g., TM2 or TM6 for FDD and TM2 or TM7 for TDD may be chosen if the scheduler announces resource limitations for the PDCCH, such that UEs with low filtered downlink SINR and a history of low selected rank will be reconfigured to TM2 or TM6 for FDD and TM2 or TM7 for TDD based on their estimated Doppler). As another example, TM control logic 504 may operate to control the frequency of transmission mode changes, such as by implementing a time hysteresis with respect to transmission mode selection transitions (e.g., for a given Cell Radio Network Temporary Identifier (C-RNTI), the time gap between consecutive transmission mode changes would not be smaller than a hysteresis threshold).

[0080] Where TM control logic 504 determines that the requested transmission mode is to be implemented, TM configure 502 operates to implement the requested TM mode. For example, TM control logic 504 may communicate the transmission mode selection to scheduler 544. Scheduler 544 may provide a Radio Resource Control (RRC) signal to signal the UE of a transmission mode transition. Receive processor 558 and controller 580 of UE 120 may the implement the transmission mode at the appropriate time. Correspondingly, TM configure 502 of eNB 110 may cause the transmission mode to be implemented at the eNB at the appropriate time.

[0081] Processing according to flow 600 may the return to block 610 to update the transmission mode selection metrics. Thereafter, subsequent iterations of the transmission mode selection process may be performed to implement transmission modes adapted to provide throughput and spectral efficiency optimized for the communication conditions experienced. It should be appreciated from the foregoing, however, that transmission mode selection according to embodiments is semi-static, such that transmission mode selection only occurs when there is a significant change in the UE's channel condition such as channel geometry, Doppler, etc.

[0082] The processes of flow 600 of embodiments herein may be performed with respect to each UE in communication with the eNB. Accordingly, the transmission control logic of embodiments operates to pass the transmission mode for different UEs in the system to the downlink scheduler for scheduling and PDSCH data transmission and thereby control the transmission modes for UEs based on the UE characteristics, such as UE category, Doppler and location, etc..

[0083] Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0084] The functional blocks and modules in FIGS. 5-7 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof. [0085] Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0086] The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0087] The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

[0088] In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special- purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0089] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0090] WHAT IS CLAIMED IS:

Claims

1. A method of selecting a transmission mode from a plurality of transmission modes for wireless communication, comprising:

updating transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information;

choosing, using at least a portion of the updated transmission mode selection metrics, open-loop or closed-loop transmission;

choosing, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize; and

selecting a particular transmission mode of the plurality of transmission modes having the chosen open-loop or closed-loop transmission and implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

2. The method of claim 1, wherein the choosing open-loop or closed-loop transmission includes:

determining a duplex mode of the wireless communication from the updated transmission mode selection metrics;

if the duplex mode is a time division duplex mode, choosing open-loop transmission; and

if the duplex mode is a frequency division duplex mode, determining if the user equipment mobility information is greater than a threshold and choosing open-loop or closed- loop transmission as a function of the user equipment mobility information threshold determination, wherein the choosing open-loop or closed loop transmission for frequency division duplex mode includes:

if the user equipment mobility information is greater than the threshold, choosing open-loop transmission; and

if the user equipment mobility information is not greater than the threshold, choosing closed-loop transmission.

3. The method of claim 1, wherein the transmission mode selection metrics further include a rank indicator and channel quality information.

4. The method of claim 3, wherein the choosing the number of spatial layers includes:

determining a category of the user equipment from the updated transmission mode selection metrics;

if the category indicates an inability to implement a plurality of spatial layers, choosing 1 as the number of spatial layers to utilize; and

if the category indicates an ability to implement a plurality of spatial layers, determining a number of spatial layers to utilize as a function of the rank indicator and the channel quality information.

5. The method of claim 1, further comprising:

requesting the selected transmission mode;

determining if the requested transmission mode is to be implemented with respect to the wireless communication; and

if the requested transmission mode is to be implemented, scheduling the requested transmission mode for implementing with respect to the wireless communication.

6. The method of claim 5, wherein the determining if the requested transmission mode is to be implemented includes:

determining if channel restrictions with respect to the wireless communication are announced.

7. The method of claim 5, wherein the determining if the requested transmission mode is to be implemented includes:

determining if a time hysteresis with respect to transmission mode selection transitions is applicable.

8. The method of claim 1, further comprising:

implementing a default transmission mode prior to the selecting the transmission mode.

9. The method of claim 8, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9, and wherein the default transmission mode is TM2.

10. The method of claim 1, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a frequency division duplex mode is implemented with respect to the wireless communication, and wherein the selecting the transmission mode includes:

if the user equipment mobility is low and the user equipment channel geometry information is low, selecting TM6;

if the user equipment mobility is low and the user equipment channel geometry information is high, selecting TM4 if closed-loop transmission was chosen, otherwise selecting TM5;

if the user equipment mobility is high and the user equipment channel geometry information is low, selecting TM2; and

if the user equipment mobility is high and the user equipment channel geometry information is high, selecting TM3.

11. The method of claim 1, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a time division duplex mode is implemented with respect to the wireless communication, and wherein the selecting the transmission mode includes:

if the user equipment mobility is low and the user equipment channel geometry information is low, selecting TM7;

if the user equipment mobility is low and the user equipment channel geometry information is high, selecting TM4 if closed-loop transmission was chosen, otherwise selecting TM8;

12. An apparatus configured for selecting a transmission mode from a plurality of transmission modes for wireless communication, comprising:

means for updating transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information;

means for choosing, using at least a portion of the updated transmission mode selection metrics, open-loop or closed-loop transmission;

means for choosing, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize; and

means for selecting a particular transmission mode of the plurality of transmission modes having the chosen open-loop or closed-loop transmission and implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

13. The apparatus of claim 12, wherein the means for choosing open-loop or closed-loop transmission includes:

means for determining a duplex mode of the wireless communication from the updated transmission mode selection metrics;

means for choosing open-loop transmission if the duplex mode is a time division duplex mode; and

means for determining if the user equipment mobility information is greater than a threshold and choosing open-loop or closed-loop transmission as a function of the user equipment mobility information threshold determination if the duplex mode is a frequency division duplex mode, wherein the means for choosing open-loop or closed loop transmission for frequency division duplex mode includes:

means for choosing open-loop transmission if the user equipment mobility information is greater than the threshold; and

means for choosing closed-loop transmission if the user equipment mobility information is not greater than the threshold.

14. The apparatus of claim 12, wherein the transmission mode selection metrics further include a rank indicator and channel quality information.

15. The apparatus of claim 14, wherein the means for choosing the number of spatial layers includes:

means for determining a category of the user equipment from the updated

transmission mode selection metrics;

means for choosing 1 as the number of spatial layers to utilize if the category indicates an inability to implement a plurality of spatial layers; and

means for determining a number of spatial layers to utilize as a function of the rank indicator and the channel quality information if the category indicates an ability to implement a plurality of spatial layers.

16. The apparatus of claim 12, further comprising:

means for requesting the selected transmission mode;

means for determining if the requested transmission mode is to be implemented with respect to the wireless communication; and

means for scheduling the requested transmission mode for implementing with respect to the wireless communication if the requested transmission mode is to be implemented.

17. The apparatus of claim 16, wherein the means for determining if the requested transmission mode is to be implemented includes:

means for determining if channel restrictions with respect to the wireless

communication are announced.

18. The apparatus of claim 16, wherein the means for determining if the requested transmission mode is to be implemented includes:

means for determining if a time hysteresis with respect to transmission mode selection transitions is applicable.

19. The apparatus of claim 12, further comprising:

means for implementing a default transmission mode prior to the selecting the transmission mode.

20. The apparatus of claim 19, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9, and wherein the default

transmission mode is TM2.

21. The apparatus of claim 12, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a frequency division duplex mode is implemented with respect to the wireless communication, and wherein the means for selecting the transmission mode includes:

means for selecting TM6 if the user equipment mobility is low and the user equipment channel geometry information is low;

means for selecting TM4 if the user equipment mobility is low and the user equipment channel geometry information is high and if closed-loop transmission was chosen, and otherwise if the user equipment mobility is low and the user equipment channel geometry information is high selecting TM5;

means for selecting TM2 if the user equipment mobility is high and the user equipment channel geometry information is low; and

means for selecting TM3 if the user equipment mobility is high and the user equipment channel geometry information is high.

22. The apparatus of claim 12, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a time division duplex mode is implemented with respect to the wireless communication, and wherein the means for selecting the transmission mode includes:

means for selecting TM7 if the user equipment mobility is low and the user equipment channel geometry information is low;

means for selecting TM4 if the user equipment mobility is low and the user equipment channel geometry information is high and if closed-loop transmission was chosen, and otherwise if the user equipment mobility is low and the user equipment channel geometry information is high selecting TM8; means for selecting TM2 if the user equipment mobility is high and the user equipment channel geometry information is low; and

23. A computer program product for selecting a transmission mode from a plurality of transmission modes for wireless communications in a wireless network, comprising:

a non-transitory computer-readable medium having program code recorded thereon, the program code including:

program code to update transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information;

program code to choose, using at least a portion of the updated transmission mode selection metrics, open-loop or closed-loop transmission;

program code to choose, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize; and

program code to select a particular transmission mode of the plurality of transmission modes having the chosen open-loop or closed-loop transmission and

implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

24. The computer program product of claim 23, wherein the program code to choose open-loop or closed-loop transmission includes:

program code to determine a duplex mode of the wireless communication from the updated transmission mode selection metrics;

program code to choose open-loop transmission if the duplex mode is a time division duplex mode; and

program code to determine if the user equipment mobility information is greater than a threshold and choosing open-loop or closed-loop transmission as a function of the user equipment mobility information threshold determination if the duplex mode is a frequency division duplex mode, wherein the program code to choose open-loop or closed loop transmission for frequency division duplex mode includes:

program code to choose open-loop transmission if the user equipment mobility information is greater than the threshold; and program code to choose closed-loop transmission if the user equipment mobility information is not greater than the threshold.

25. The computer program product of claim 23, wherein the transmission mode selection metrics further include a rank indicator and channel quality information.

26. The computer program product of claim 25, wherein the program code to choose the number of spatial layers includes:

program code to determine a category of the user equipment from the updated transmission mode selection metrics;

program code to choose 1 as the number of spatial layers to utilize if the category indicates an inability to implement a plurality of spatial layers; and

program code to determine a number of spatial layers to utilize as a function of the rank indicator and the channel quality information if the category indicates an ability to implement a plurality of spatial layers.

27. The computer program product of claim 23, further comprising:

program code to request the selected transmission mode;

program code to determine if the requested transmission mode is to be implemented with respect to the wireless communication; and

program code to schedule the requested transmission mode for implementing with respect to the wireless communication if the requested transmission mode is to be implemented.

28. The computer program product of claim 27, wherein the program code to determine if the requested transmission mode is to be implemented includes:

program code to determine if channel restrictions with respect to the wireless communication are announced.

29. The computer program product of claim 27, wherein the program code to determine if the requested transmission mode is to be implemented includes:

program code to determine if a time hysteresis with respect to transmission mode selection transitions is applicable.

30. The computer program product of claim 23, further comprising:

program code to implement a default transmission mode prior to the selecting the transmission mode.

31. The computer program product of claim 30, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9, and wherein the default transmission mode is TM2.

32. The computer program product of claim 23, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a frequency division duplex mode is implemented with respect to the wireless communication, and wherein the program code to select the transmission mode includes:

program code to select TM6 if the user equipment mobility is low and the user equipment channel geometry information is low;

program code to select TM4 if the user equipment mobility is low and the user equipment channel geometry information is high and if closed-loop transmission was chosen, otherwise if the user equipment mobility is low and the user equipment channel geometry information is high to select TM5;

program code to select TM2 if the user equipment mobility is high and the user equipment channel geometry information is low; and

program code to select TM3 if the user equipment mobility is high and the user equipment channel geometry information is high.

33. The computer program product of claim 23, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a time division duplex mode is implemented with respect to the wireless communication, and wherein the program code to select the transmission mode includes:

program code to select TM7 if the user equipment mobility is low and the user equipment channel geometry information is low;

program code to select TM4 if the user equipment mobility is low and the user equipment channel geometry information is high and if closed-loop transmission was chosen, otherwise if the user equipment mobility is low and the user equipment channel geometry information is high to select TM8;

34. An apparatus configured for selecting a transmission mode from a plurality of transmission modes for wireless communication, the apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor,

wherein the at least one processor is configured: to update transmission mode selection metrics, the transmission mode selection metrics including user equipment mobility information and user equipment channel geometry information;

choose, using at least a portion of the updated transmission mode selection metrics, open-loop or closed-loop transmission;

choose, using at least a portion of the updated transmission mode selection metrics, a number of spatial layers to utilize; and

select a particular transmission mode of the plurality of transmission modes having the chosen open-loop or closed-loop transmission and implementing the chosen number of spatial layers based at least in part upon the user equipment mobility information and user equipment channel geometry information.

35. The apparatus of claim 34, wherein the configuration to choose open-loop or closed-loop transmission includes the at least one processor configured to:

determine a duplex mode of the wireless communication from the updated

transmission mode selection metrics;

choose open-loop transmission if the duplex mode is a time division duplex mode; and

determine if the user equipment mobility information is greater than a threshold and choosing open-loop or closed-loop transmission as a function of the user equipment mobility information threshold determination if the duplex mode is a frequency division duplex mode, wherein the configuration to choose open-loop or closed loop transmission for frequency division duplex mode includes the at least one processor configured to:

choose open-loop transmission if the user equipment mobility information is greater than the threshold; and

choose closed-loop transmission if the user equipment mobility information is not greater than the threshold.

36. The apparatus of claim 34, wherein the transmission mode selection metrics further include a rank indicator and channel quality information.

37. The apparatus of claim 36, wherein the configuration to choose the number of spatial layers includes the at least one processor configured to:

determine a category of the user equipment from the updated transmission mode selection metrics;

choose 1 as the number of spatial layers to utilize if the category indicates an inability to implement a plurality of spatial layers; and determine a number of spatial layers to utilize as a function of the rank indicator and the channel quality information if the category indicates an ability to implement a plurality of spatial layers.

38. The apparatus of claim 34, wherein the at least one processor is further configured to:

request the selected transmission mode;

determine if the requested transmission mode is to be implemented with respect to the wireless communication; and

schedule the requested transmission mode for implementing with respect to the wireless communication if the requested transmission mode is to be implemented.

39. The apparatus of claim 38, wherein the configuration to determine if the requested transmission mode is to be implemented includes the at least one processor configured to:

determine if channel restrictions with respect to the wireless communication are announced.

40. The apparatus of claim 38, wherein the configuration to determine if the requested transmission mode is to be implemented includes the at least one processor configured to:

determine if a time hysteresis with respect to transmission mode selection transitions is applicable.

41. The apparatus of claim 34, wherein the at least one processor is further configured to:

implement a default transmission mode prior to the selecting the transmission mode.

42. The apparatus of claim 41, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9, and wherein the default transmission mode is TM2.

43. The apparatus of claim 34, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a frequency division duplex mode is implemented with respect to the wireless communication, and wherein the configuration to select the transmission mode includes the at least one processor configured to:

select TM6 if the user equipment mobility is low and the user equipment channel geometry information is low;

select TM4 if the user equipment mobility is low and the user equipment channel geometry information is high and if closed-loop transmission was chosen, otherwise to select TM5 if the user equipment mobility is low and the user equipment channel geometry information is high;

select TM2 if the user equipment mobility is high and the user equipment channel geometry information is low; and

select TM3 if the user equipment mobility is high and the user equipment channel geometry information is high.

44. The apparatus of claim 34, wherein the plurality of transmission modes include transmission modes TM1-TM8 of LTE release 9 and a time division duplex mode is implemented with respect to the wireless communication, and wherein the configuration to select the transmission mode includes the at least one processor configured to:

select TM7 if the user equipment mobility is low and the user equipment channel geometry information is low;

select TM4 if the user equipment mobility is low and the user equipment channel geometry information is high, and if closed-loop transmission was chosen, otherwise to select TM8 if the user equipment mobility is low and the user equipment channel geometry information is high;