WO2017028000A1

WO2017028000A1 - Discovery signal transmission on unlicensed spectrum

Info

Publication number: WO2017028000A1
Application number: PCT/CN2015/086926
Authority: WO
Inventors: Zukang Shen
Original assignee: Lenovo Innovations Ltd Hong Kong
Current assignee: Lenovo Innovations Ltd Hong Kong
Priority date: 2015-08-14
Filing date: 2015-08-14
Publication date: 2017-02-23
Anticipated expiration: 2018-02-14

Abstract

Apparatuses, methods, and systems are disclosed for discovery signal transmission over unlicensed spectrum in a wireless communication system scheduling. One apparatus includes a processor and a memory that stores code executable by the processor. The code, in various embodiments, transmits a first CSI-RS on a first antenna port over a first CSI-RS resource. In a further embodiment, the code transmits a PSS on a PSS time-frequency resource. The code may also transmit a SSS on a SSS time-frequency resource. The code may further transmit a second CSI-RS on the first antenna port over a second CSI-RS resource. The first CSI-RS resource, the PSS, the SSS, and the second CSI-RS resource may be transmitted in consecutive ODFM symbols in time. The apparatus may include a transmitter that provides the uplink grant message to the user equipment.

Description

DISCOVERY SIGNAL TRANSMISSION ON UNLICENSED SPECTRUM

FIELD

The subject matter disclosed herein relates generally to wireless communications and more particularly relates to discovery signal transmission over unlicensed spectrum in a wireless communication system.

BACKGROUND

The following abbreviations are herewith defined， at least some of which are referred to within the following description.

3GPP： Third Generation Partnership Project

CA： Carrier Aggregation

CC： Component Carriers

CSI： Channel State Information

CSI-RS： Channel State Information Reference Signal

CRS： Common Reference Signal

DL： Downlink

DRS： Discovery Reference Signal

eNB： Evolved Node B

IEEE： Institute of Electrical and Electronics Engineers

LAA： License Assisted Access

LBT： Listen-Before-Talk

LTE： Long Term Evolution

OFDM： Orthogonal Frequency Division Multiplexing

PCell： Primary Cell

PCID： Physical-Layer Cell Identity

PSS： Primary Synchronization Signal

PRB： Physical Resource Block

RB： Resource Block

RE： Resource Element

RRC： Radio Resource Control

RSRP： Reference Signal Received Power

RSRQ： Reference Signal Received Quality

SC-FDMA： Single-Carrier Frequency-Division Multiple Access

SCell： Secondary Cell

SSS： Secondary Synchronization Signal

TB： Transport Block

UE： User Entity/Equipment (Mobile Terminal)

UL： Uplink

WiMAX： Worldwide Interoperability for Microwave Access

WLAN： Wireless Local Area Network

Mobile devices have exploded in popularity over the last several years. This leads to increased demand for high data rate. The demand for higher data rates encourages mobile communication operators to seek for additional spectrum. While licensed spectrum is of the first choice to operators due to the guaranteed quality of service (QoS) ， the large amount of available unlicensed spectrum is attractive to the operators.

One way to increase data rates is to supplement carriers on the licensed spectrum with carriers on the unlicensed spectrum. The licensed spectrum can provide services with all types of QoS services (e.g. delay sensitive service， guaranteed data rate service， etc. ) ， while the unlicensed spectrum is targeted for best effort type of services. Carrier (s) on the unlicensed spectrum is used in accompany to carrier (s) on the licensed spectrum.

The carrier (s) on the unlicensed spectrum and the licensed spectrum can be combined by a user equipment (UE) using the carrier aggregation (CA) technology developed by 3GPP， wherein a UE is configured with multiple serving cells at the same time. Therefore， a UE may receive data on multiple serving cells in the same subframe if CA is configured in the downlink (DL) ； and a UE may transmit data on multiple serving cells in the same subframe if CA is configured in the uplink (UL) . Among the configured serving cells， one and only one serving cell is the primary cell (PCell) ， while the other configured serving cells are the secondary cells (SCell) . A carrier or a cell on the unlicensed spectrum can only be used as a SCell for a UE. This combination of licensed carriers and unlicensed carriers is referred to as license assisted access (LAA) .

For a UE to successfully receive data on an unlicensed carrier， the UE needs to perform time and frequency synchronization， in order to obtain reasonably accurate receiving time window and carrier frequency of the unlicensed carrier. However， the receiving timing and carrier frequency derived for the licensed carrier cannot be directly used as the receiving timing and carrier frequency for the unlicensed carrier. This is because the transmitter local oscillator used to generate the transmission signal on the licensed and unlicensed carriers may be different. Additionally， the geographic location of the transmission point for the licensed and unlicensed carriers can be different， leading to different propagation delays and Doppler shifts on the licensed and unlicensed carriers. Therefore， it is necessary to transmit reference signals on the unlicensed carrier， to allow the UE to perform time and frequency synchronization to derive the receiving timing and cartier frequency. Time and frequency synchronization by the UE is also necessary to receive data on a licensed carrier.

Discovery signals are used on the licensed spectrum for an UE to detect nearby cells and to perform time/frequency synchronization. In LTE FDD systems， the discovery signal is sent during a discovery signal occasion. An LTE discovery signal consists of a Common Reference Signal (CRS) on antenna port 0 in every subframe of a discovery signal occasion， a Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) in the first subframe of the discovery occasion. The discovery signal occasion for a LTE FDD cell consists of a period with a duration of one to 5 consecutive subframes， the specific duration configured by higher layers. The details of PSS， SSS， and CRS for LTE systems can be found in 3GPP TS36.211 v 12.6.0.

In an LTE discovery signal， the PSS is a frequency-domain Zadoff-Chu sequence with length of 62. For LTE FDD， the PSS is transmitted in the center 62 resource elements (REs) in frequency and in the last OFDM symbol of the first slot in subframes zero and five of each radio frame. SSS is an interleaved concatenation of two 31-length binary sequences. The SSS is also transmitted in the center 62 REs in frequency， but in the second to last OFDM symbol of the first slot in subframes zero and five of each radio frame. The SSS transmitted in subframes zero and five differ from each other to allow the UE to obtain radio frame start timing. A physical-layer cell identity (PCID) is determined by the PSS sequence index and SSS index.

The UE can further improve its time and frequency synchronization accuracy by utilizing the CRS. For each CRS antenna port (LTE systems may have up to 4) ， the CRS is transmitted over all physical resource blocks (PRBs) in the system bandwidth and evenly spaced in frequency (e.g.， every other 6 REs) . Apart from the purpose of fine time and frequency synchronization， CRS can also be used to derive the channel state information (CSI) by the UE. UE feeds back the CSI to the eNB， allowing the eNB to perform fast link adaption and improve the spectral efficiency. In addition， CRS can be used by a UE to measure the Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) . In LTE systems， a CSI reference signal (CSI-RS) is optionally provided in the discovery signal which can also be used by a UE to measure the RSRP. CSI-RS is not transmitted on OFDM symbols containing CRS， in order to reduce the interference to CRS transmitted by a neighboring cell.

In LTE systems， the CSI-RS signal occupies two consecutive OFDM symbols and is evenly spaced in frequency by every other 12 REs. For each CSI-RS antenna port (3GPP TS36.211 defines up to 8 CSI-RS antenna ports) ， the CSI-RS is transmitted over all PRBs in the system bandwidth. The time-frequency location of each CSI-RS antenna ports is configured by higher layers. The periodicity of CSI-RS transmission as well as the subframe containing CSI-RS is also configured by higher layer among the values of {5， 10， 20， 40， 80} ms. A UE can measure the RSRP for each transmission point based on the non-zero power CSI-RS of the transmission point.

In LTE systems， the discovery signal occasion are periodic， with the periodicity configured by higher layers among the values of {40， 80， 160} ms. It is noted that since a discovery signal contains PSS/SSS， only subframe 0 can be the starting subframe of each discovery signal occasion. Therefore， within each discovery signal occasion， the time-frequency location of the CRS antenna port 0， PSS/SSS， and the possible non-zero power CSI-RS are fixed according to the relevant higher layer configurations. The non-zero power CSI-RS is unique to a transmission point and may be used in a geographic location having multiple transmission points of the same PCID (thus having the same PSS/SSS/CRS transmission) .

Since 3GPP Release 12， a cell can cease transmitting if there is no traffic to transmit， thus reducing power consumption and at the same time reducing the amount of inter-cell interference caused by CRS. However， the cell periodically transmits the discovery signal even ifit is in the off state， so that UEs are able to detect there is a cell around， even ifthe cell is in the off state. A UE can uniquely identify cells by their respective PSS， SSS， and CRS， since these three signals are dependent on the physical-layer cell identity (PCID) of a cell.

For LAA， in order for a UE to achieve time and frequency synchronization on an unlicensed carrier， some reference signals shall be transmitted on the unlicensed carrier. The unlicensed spectrum is shared by many different wireless communication systems (e.g. IEEE WLAN， Bluetooth， etc. ) . In order to provide fair access opportunities of different systems to the unlicensed spectrum， a listen-before-talk (LBT) mechanism is typically required for the systems operating on unlicensed spectrum. LBT requires a device to listen to the channel (i.e.， the unlicensed carrier) before performing a transmission. LBT mandates that a device shall not transmit if it senses that the channel is busy (i.e.， other devices are currently transmitting on the same unlicensed carrier) and shall attempt to sense whether the channel is busy in a later time.

Systems operating on unlicensed spectrum face further regulatory requirements， such as the transmitted signal occupying 80％ of the system bandwidth. Current LTE discovery signals do not meet requirements for operating on unlicensed spectrum.

BRIEF SUMMARY

Apparatus for discovery signal transmission over unlicensed spectrum in a wireless communication system are disclosed. Methods and systems also perform the functions of the apparatus. In one embodiment， the apparatus includes a network equipment having a radio transceiver configured to communicate with at least one user equipment over a mobile telecommunications network， a processor， and a memory that stores code executable by the processor. The code， in various embodiments， transmits at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n and n+1 in time. In a further embodiment， the code transmits a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is transmitted in at least one of two OFDM symbols n+2 and n+3.

The code may also transmit a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is transmitted in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is transmitted on each of OFDM symbols n+2 and n+3. The code may further transmit at least one second CSI-RS on the first antenna port over a second CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource， and wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.

In one embodiment， transmitting the PSS on at least one PSS time-frequency resource includes transmitting the PSS on j number of PSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth. In another embodiment， transmitting the PSS on at least one PSS time-frequency resource includes transmitting the PSS on Z number of REs within each PSS time-frequency resource， wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs， and wherein Z＜Y.

In one embodiment， transmitting the SSS on at least one SSS time-frequency resource includes transmitting the SSS on j number of SSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth. In another embodiment， transmitting the SSS on at least one SSS time-frequency resource includes transmitting the SSS on Z’ number of REs within each SSS time-frequency resource， wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs， and wherein Z’＜Y.

In certain embodiments， the code transmits at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.

In some embodiments， the first CSI-RS， the PSS， the SSS， and the second CSI-RS comprise a discovery signal， and the code identifies a discovery signal transmission opportunity in a discovery signal transmission window， wherein the discovery signal transmission window occurs periodically with a periodicity of T subframes with T≥1 and each discovery signal transmission window comprises a set of S consecutive subframes with S≥1， wherein one or more discovery signal transmission opportunities are present in each discovery signal transmission window， and wherein each discovery signal transmission opportunity comprises a set of W consecutive OFDM symbols with W≥1. In certain embodiments， the code identifies a channel for transmitting the discovery signal， wherein the channel comprises a channel of unlicensed radio-frequency spectrum.

In one embodiment， the code transmits the discovery signal in the identified discover signal transmission opportunity， in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value Q. In a further embodiment， the code inhibits transmission of the discovery signal in the identified discover signal transmission opportunity in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value Q.

In certain embodiments， the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of： time and frequency. In one embodiment， the apparatus transmits a configuration message indicating the predetermined interleave pattern.

The method of a network equipment for discovery signal transmission over unlicensed spectrum in a wireless communication system includes transmitting at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n and n+1 in time. The method may also include transmitting a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is transmitted in at least one of two OFDM symbols n+2 and n+3. The method may further include transmitting a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is transmitted in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is transmitted on each of OFDM symbols n+2 and n+3. Additionally， the method may include transmitting at least one second CSI-RS on the first antenna port over a second CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource， and wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.

In some embodiments， the method further includes transmitting at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.

In some embodiments， the first CSI-RS， the PSS， the SSS， and the second CSI-RS comprise a discovery signal， and the method includes identifying a discovery signal transmission opportunity in a discovery signal transmission window， wherein the discovery signal transmission window occurs periodically with a periodicity of T subframes with T≥1 and each discovery signal transmission window comprises a set of S consecutive subframes with S≥1， wherein one or more discovery signal transmission opportunities are present in each discovery signal transmission window， and wherein each discovery signal transmission opportunity comprises a set of W consecutive OFDM symbols with W≥1. In certain embodiments， the method includes identifying a channel for transmitting the discovery signal， wherein the channel comprises a channel of unlicensed radio-frequency spectrum.

In one embodiment， the method includes transmitting the discovery signal in the identified discover signal transmission opportunity， in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value Q. In a further embodiment， the method includes inhibiting transmission of the discovery signal in the identified discover signal transmission opportunity in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value Q.

In certain embodiments， the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of： time and frequency. In one embodiment， the method includes transmitting a configuration message indicating the predetermined interleave pattern.

Also disclosed in an apparatus for receiving a discovery signal transmitted over unlicensed spectrum in a wireless communication system. This apparatus may include a user equipment having a radio transceiver configured to communicate with at least one network equipment over a mobile telecommunications network， a processor， and a memory that stores code executable by the processor. The code， in various embodiments， receives at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n and n+1 in time. In a further embodiment， the code receives a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is present in at least one of two OFDM symbols n+2 and n+3.

The code may also receive a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is present in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is present on each of OFDM symbols n+2 and n+3. The code may further receive at least one second CSI-RS on the first antenna port over a second CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource， and wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.

In one embodiment， receiving the PSS on at least one PSS time-frequency resource includes receiving the PSS on j number of PSS time-frequency resources， wherein j is the floor of M Y， wherein M is the total number of REs in the system bandwidth. In another embodiment， receiving the PSS on at least one PSS time-frequency resource includes receiving the PSS on Z number of REs within each PSS time-frequency resource， wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs， and wherein Z ＜Y.

In one embodiment， receiving the SSS on at least one SSS time-frequency resource includes receiving the SSS on j number of SSS time-frequency resources， whereinjis the floor of M/Y， wherein M is the total number of REs in the system bandwidth. In another embodiment， receiving the SSS on at least one SSS time-frequency resource includes receiving the SSS on Z’ number of REs within each SSS time-frequency resource， wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs， and wherein Z’ ＜Y.

In certain embodiments， the code receives at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.

In certain embodiments， the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of： time and frequency. In one embodiment， the apparatus receives a configuration message indicating the predetermined interleave pattern.

Also disclosed is a method of a user equipment for receiving a discovery signal transmitted over unlicensed spectrum in a wireless communication system. The method includes receiving at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n and n+1 in time. The method may also include receiving a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is present in at least one of two OFDM symbols n+2 and n+3. The method may further include receiving a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is present in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is present on each of OFDM symbols n+2 and n+3. Additionally， the method may include receiving at least one second CSI-RS on the first antenna port over a second CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource， and wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.

In some embodiments， the method further includes receiving at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.

In certain embodiments， the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of： time and frequency. In one embodiment， the method includes receiving a configuration message indicating the predetermined interleave pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the embodiments briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only some embodiments and are not therefore to be considered to be limiting of scope， the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings， in which：

Figure 1 is a schematic block diagram illustrating one embodiment of a wireless communication system for discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 2A is a schematic block diagram illustrating one embodiment of an radio frame structure that may be used for discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 2B is a schematic block diagram illustrating one embodiment of an downlink resource grid that may be used for discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 3 is a schematic block diagram illustrating one embodiment of a user equipment that may be used for receiving a discovery signal transmitted over unlicensed spectrum in a wireless communication system；

Figure 4 is a schematic block diagram illustrating one embodiment of a network equipment that may be used for discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 5 illustrates one embodiment of a discovery signal that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 6 illustrates another embodiment of a discovery signal that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 7 illustrates a third embodiment of a discovery signal that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 8 illustrates one embodiment of a discovery signal transmission schedule that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system；

Figure 9A is a schematic flow chart diagram illustrating one embodiment of a method for discovery signal transmission over unlicensed spectrum in a wireless communication system from a base unit； and

Figure 9B is a schematic flow chart diagram illustrating one embodiment of a method for a remote unit to receive a discovery signal transmitted over unlicensed spectrum in a wireless communication system from a base unit.

DETAILED DESCRIPTION

As will be appreciated by one skilled in the art， aspects of the embodiments may be embodied as a system， apparatus， method， or program product. Accordingly， embodiments may take the form of an entirely hardware embodiment， an entirely software embodiment (including firmware， resident software， micro-code， etc. ) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit， ” “module” or “system. ” Furthermore， embodiments may take the form of a program product embodied in one or more computer readable storage devices storing machine readable code， computer readable code， and/or program code， referred hereafter as code. The storage devices may be tangible， non-transitory， and/or non-transmission. The storage devices may not embody signals. In a certain embodiment， the storage devices only employ signals for accessing code.

Certain of the functional units described in this specification may be labeled as modules， in order to more particularly emphasize their implementation independence. For example， a module may be implemented as a hardware circuit comprising custom very-large-scale integration ( “VLSI” ) circuits or gate arrays， off-the-shelf semiconductors such as logic chips， transistors， or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays， programmable array logic， programmable logic devices or the like.

Any combination of one or more computer readable medium may be utilized. The computer readable medium may be a computer readable storage medium. The computer readable storage medium may be a storage device storing the code. The storage device may be， for example， but not limited to， an electronic， magnetic， optical， electromagnetic， infrared， holographic， micromechanical， or semiconductor system， apparatus， or device， or any suitable combination of the foregoing.

More specific examples (a non-exhaustive list) of the storage device would include the tollowing： an electrical connection having one or more wires， a portable computer diskette， a hard disk， a random access memory ( “RAM” ) ， a read-only memory ( “ROM” ) ， an erasable programmable read-only memory ( “EPROM” or Flash memory) ， a portable compact disc read-only memory ( “CD-ROM” ) ， an optical storage device， a magnetic storage device， or any suitable combination of the foregoing. In the context of this document， a computer readable storage medium may be any tangible medium that can contain， or store a program for use by or in connection with an instruction execution system， apparatus， or device.

Code for carrying out operations for embodiments may be any number of lines and may be written in any combination of one or more programming languages including an object oriented programming language such as Python， Ruby， Java， Smalltalk， C++， or the like， and conventional procedural programming languages， such as the ″C″ programming language， or the like， and/or machine languages such as assembly languages. The code may execute entirely on the user′s computer， partly on the user′s computer， as a stand-alone software package， partly on the user′s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario， the remote computer may be connected to the user′s computer through any type of network， including a local area network ( “LAN” ) or a wide area network ( “WAN” ) ， or the connection may be made to an external computer (for example， through the Internet using an Internet Service Provider) .

Reference throughout this specification to “one embodiment， ” “an embodiment， ” or similar language means that a particular feature， structure， or characteristic described in connection with the embodiment is included in at least one embodiment. Thus， appearances of the phrases “in one embodiment， ” “in an embodiment， ” and similar language throughout this specification may， but do not necessarily， all refer to the same embodiment， but mean “one or more but not all embodiments” unless expressly specified otherwise. The terms “including， ” “comprising， ” “having， ” and variations thereof mean “including but not limited to， ” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive， unless expressly specified otherwise. The terms “a， ” “an， ” and “the” also refer to “one or more” unless expressly specified otherwise.

Furthermore， the described features， structures， or characteristics of the embodiments may be combined in any suitable manner. In the following description， numerous specific details are provided， such as examples of programming， software modules， user selections， network transactions， database queries， database structures， hardware modules， hardware circuits， hardware chips， etc.， to provide a thorough understanding of embodiments. One skilled in the relevant art will recognize， however， that embodiments may be practiced without one or more of the specific details， or with other methods， components， materials， and so forth. In other instances， well-known structures， materials， or operations are not shown or described in detail to avoid obscuring aspects of an embodiment.

Aspects of the embodiments are described below with reference to schematic flowchart diagrams and/or schematic block diagrams of methods， apparatuses， systems， and program products according to embodiments. It will be understood that each block of the schematic flowchart diagrams and/or schematic block diagrams， and combinations of blocks in the schematic flowchart diagrams and/or schematic block diagrams， can be implemented by code. These code may be provided to a processor of a general purpose computer， special purpose computer， or other programmable data processing apparatus to produce a machine， such that the instructions， which execute via the processor of the computer or other programmable data processing apparatus， create means for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks.

The code may also be stored in a storage device that can direct a computer， other programmable data processing apparatus， or other devices to function in a particular manner， such that the instructions stored in the storage device produce an article of manufacture including instructions which implement the function/act specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks.

The code may also be loaded onto a computer， other programmable data processing apparatus， or other devices to cause a series of operational steps to be performed on the computer， other programmable apparatus or other devices to produce a computer implemented process such that the code which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The schematic flowchart diagrams and/or schematic block diagrams in the Figures illustrate the architecture， functionality， and operation of possible implementations of apparatuses， systems， methods and program products according to various embodiments. In this regard， each block in the schematic flowchart diagrams and/or schematic block diagrams may represent a module， segment， or portion of code， which includes one or more executable instructions of the code for implementing the specified logical function (s) .

It should also be noted that， in some alternative implementations， the functions noted in the block may occur out of the order noted in the Figures. For example， two blocks shown in succession may， in fact， be executed substantially concurrently， or the blocks may sometimes be executed in the reverse order， depending upon the functionality involved. Other steps and methods may be conceived that are equivalent in function， logic， or effect to one or more blocks， or portions thereof， of the illustrated Figures.

Although various arrow types and line types may be employed in the flowchart and/or block diagrams， they are understood not to limit the scope of the corresponding embodiments. Indeed， some arrows or other connectors may be used to indicate only the logical flow of the depicted embodiment. For instance， an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted embodiment. It will also be noted that each block of the block diagrams and/or flowchart diagrams， and combinations of blocks in the block diagrams and/or flowchart diagrams， can be implemented by special purpose hardware-based systems that perform the specified functions or acts， or combinations of special purpose hardware and code.

The description of elements in each Figure may refer to elements of proceeding Figures. Like numbers refer to like elements in all figures， including alternate embodiments of like elements.

Generally， the disclosed embodiments provide for a LAA discovery signal suitable for transmission over unlicensed spectrum. The suitability ofa LAA discovery signal on an unlicensed carrier may be determined based on 1) its compatibility with LBT operation， 2) its efficient usage of time-frequency resources， 3) the amount of bandwidth the LAA discovery signal occupies， 4) the time and frequency synchronization accuracy at the UE side， 5) its ability to uniquely identify the transmitting cell， and 6) its ability to provide channel state information (CSI) . The discovery signals disclosed herein take into consideration these aspects.

Due to the required LBT operation， the eNB may not always be able to gain access to the channel before each transmission of the LAA discovery signal. Therefore， even if the LAA discovery signal occasion is configured to occur periodically， there is no guarantee that the LAA discovery signal is transmitted periodically， as it depends on whether the eNB can gain access to the channel before the transmission of LAA discovery signal. Therefore， unlike the Rel-12 discovery signal that the time-frequency location for PSS/SSS/CRS/CSI-RS is fixed in each discovery signal occasion， it is preferable that there are multiple transmission opportunities in each LAA discovery signal occasion.

Further， when there are one or more vacant OFDM symbols between signals transmitted over the unlicensed spectrum 108， other devices on the unlicensed spectrum 108 may gain access to the channel and start transmission， thus create interference to the LAA discovery signal. The LAA eNB may transmit some reservation signals on these otherwise vacant OFDM symbol just to keep the channel， which however does not provide efficient usage of the time-frequency resource on the unlicensed carriers.

Beneficially， the disclosed discovery signals (as well as methods， systems and apparatus for transceiving the same) provide more opportunities for LAA discovery signal transmission， provide efficient usage of the time-frequency resource on the unlicensed carrier for LAA discovery signal transmission， are compliant with the regulatory requirement on the transmission signal bandwidth， provide good time and frequency synchronization accuracy， avoid PCID confusion among multiple operators， and utilize the LAA discovery signal for CSI measurement.

Figure 1 depicts an embodiment of a wireless communication system 100 for discovery signal transmission over unlicensed spectrum in a wireless communication system. In one embodiment， the wireless communication system 100 includes user equipments 102 and network equipments 104. The UEs 102 and network equipments 104 may communicate over licensed spectrum 106， unlicensed spectrum 108， or a combination of licensed spectrum 106 and unlicensed spectrum 108. In some embodiments， the network equipments 104 broadcast a LAA discovery signal 110 over the unlicensed spectrum 108. As used herein， an “LAA discovery signal” refers to a discovery signal communicated over the unlicensed spectrum 108. Also as used herein， an “LTE discovery signal” refers to a discovery signal 112 defined by the 3GPP LTE specification and communicated over the licensed spectrum 106.

Even though a specific number of UEs 102 and network equipments 104 are depicted in Figure 1， one of skill in the art will recognize that any number of UEs 102 and network equipments 104 may be included in the wireless communication system 100. Further， even though a UE 102 is depicted as communicating solely over the licensed spectrum 106 and a network equipment 104 is depicted as communicating solely over the unlicensed spectrum 108， one skilled in the art will recognize that a UE 102 may communicate over any combination of licensed spectrum 106 and unlicensed spectrum 108 and that a network equipment 104 may communicate over any combination of licensed spectrum 106 and unlicensed spectrum 108.

In one embodiment， the UEs 102 may include computing devices， such as desktop computers， laptop computers， personal digital assistants ( “PDAs” ) ， tablet computers， smart phones， smart televisions (e.g.， televisions connected to the Internet) ， set-top boxes， game consoles， security systems (including security cameras) ， vehicle on-board computers， network devices (e.g.， routers， switches， modems) ， or the like. In some embodiments， the UEs 102 include wearable devices， such as smart watches， fitness bands， optical head-mounted displays， or the like. Moreover， the UEs 102 may be referred to as subscriber units， mobiles， mobile stations， users， terminals， mobile terminals， fixed terminals， remote units， subscriber stations， user terminals， or by other terminology used in the art. The UEs 102 may communicate directly with one or more of the network equipments 104 via UL communication signals.

The network equipments 104 may be distributed over a geographic region. In certain embodiments， a network equipment 104 may also be referred to as an access point， an access terminal， a base， a base station， a base unit， a Node-B， an enhanced Node-B (eNB) ， a Home Node-B， a relay node， or by any other terminology used in the art. The network equipments 104 are generally part of a radio access network that includes one or more controllers communicably coupled to one or more corresponding network equipments 104. The radio access network is generally communicably coupled to one or more core networks， which may be coupled to other networks， like the Internet and public switched telephone networks， among other networks. These and other elements of radio access and core networks are not illustrated but are well known generally by those having ordinary skill in the art.

In one implementation， the wireless communication system 100 is compliant with the 3GPP LTE protocol， wherein the network equipment 104 transmits using an OFDM modulation scheme on the DL and the UEs 102 transmit on the UL using a SC-FDMA scheme. More generally， however， the wireless communication system 100 may implement some other open or proprietary communication protocol， for example， WiMAX， among other protocols. The present disclosure is not intended to be limited to the implementation of any particular wireless communication system architecture or protocol.

In one embodiment， the network equipments 104 may serve a number of UEs 102 within a serving area， for example， a cell or a cell sector via a wireless communication link. The network equipments 104 transmit DL communication signals to serve the UEs 102 in the time， frequency， and/or spatial domain. In some embodiments， the network equipments 104 serve the UEs 102 over licensed spectrum. In further embodiments， the network equipments 104 serve the UEs 102 over a combination of licensed spectrum 106 and unlicensed spectrum 108， for example using carrier aggregation (CA) in an LTE license assisted access (LAA) system.

In some embodiments， the wireless communication system 100 is configured with a specific frame structure and resource grid， such as those discussed below with reference to Figures 2A and 2B. In certain embodiments， the same frame structure is used on the unlicensed spectrum 108 as is used on the licensed spectrum 106. Similarly， the same resource grid may be used on the unlicensed spectrum 108 as is used on the licensed spectrum 106.

Figure 2A is a schematic block diagram illustrating one embodiment of a radio frame structure 200 that may be used for discovery signal transmission over unlicensed spectrum in a wireless communication system. The radio frame structure 200 includes a radio frame 202. In some embodiments， the radio frame 202 has a length of 10 ms. The radio frame 202 is composed of a plurality of subframes 204. In the depicted embodiment， the radio frame contains ten subframes， labeled “0” to “9. ” In certain embodiments， each subframe 204 has a length of 1ms. Each subframe 204 may be composed of two slots 206， each having a length of 0.5ms. Thus， the radio frame 202 may contain twenty slots 206. As depicted， the slots 206 may be labeled from “0” to “19. ”

In some embodiments， a slot 206 is a basic time resource in the wireless communication system 100. A discovery signal may be transmitted from a network equipment over the unlicensed spectrum 108 using one or more slots 206， as discussed below with reference to Figures 5-8. Within each slot 206， a plurality of OFDM symbols are transmitted， as discussed below with reference to Figure 2B.

Figure 2B is a schematic block diagram illustrating one embodiment of a downlink (DL) resource grid 250 that may be used for discovery signal transmission over unlicensed spectrum in a wireless communication system. The DL resource grid 250 may be used to transmit a discovery signal over the unlicensed spectrum 108. The DL resource grid 250 includes a transmission bandwidth 252 comprising a plurality of frequency subcarfiers. In some embodiments， the frequency subcarriers in the transmission bandwidth 252 are orthogonal subcarriers， to minimize inter-carrier interference. The DL resource grid 250 further includes a plurality of ODFM symbols 254， which may form one slot 206 in the radio frame structure 200. In the depicted embodiment， the DL resource grid 250 consists of 7 OFDM symbols 254， labeled from “0” to “6. ”

The DL resource grid 250 includes a plurality of physical resource block 256 (PRBs) . In some embodiments， a PRB 256 comprises 12 consecutive subcarriers in frequency and 7 consecutive OFDM symbols in time. One subcarrier in one OFDM symbol is defined as a resource element 258 (RE) ， which can be indexed by a pair of (k， l) ， wherein k is the RE index in frequency domain (in unit of subcarriers) and l is the RE index in time domain (in unit of OFDM symbols) .

In some embodiments， the DL resource grid 250 includes

subcarriers and

OFDM symbols， wherein

is number of PRBs 256 in the DL (which is dependent on the transmission bandwidth of the cell) and

is the number of subcarriers in each PRB 256. Each subcarrier occupies a certain frequency of size Δf. In certain embodiments， the values of

Δf， and

depend on the cyclic prefix length used in the wireless communication system. For example， a system using a normal cyclic prefix may have a Δf of 15 kHz， a

of 12，and a

of 7. As another example， a system using an extended cyclic prefix may have a Δf of 15 kHz， a

of 12， and a

of 6. Alternatively， the system using an extended cyclic prefix may have a Δf of 7.5 kHz， a

of 24， and a

of 3. The disclosed embodiments are generally described using the normal cyclic prefix (e.g.， with the PRB 256 comprising 12 subcarriers in frequency and 7 OFDM symbols in time) . However， other embodiments may use the extended cyclic prefix.

The DL resource grid 250 may be transmitted over an antenna port. As used herein， as “antenna port” refers to a logical antenna port， i.e.， it does not necessarily refer to a physical antenna or antenna element. The mapping between an antenna port and the physical antenna element (s) is implementation specific. In other words， different devices may have a different mapping of physical antenna element (s) to the same antenna port. A receiving device can assume that the signals transmitted on the same antenna port go through the same channel. A receiving device cannot assume signals transmitted on different antenna ports go through the same channel. The DL resource grid 250 shown in Figure 2B is defined per antenna port.

Referring again to Figure 1， the wireless communication system 100 facilitates transmission of the LAA discovery signal 110 over the unlicensed spectrum 108， so that the UEs 102 may detect nearby cells， perform time/frequency synchronization， and obtain channel state information. In some embodiments， a network equipment 104 transmits a LAA discovery signal 110 on the unlicensed spectrum 108 during a discovery signal transmission window， as discussed in further detail below with reference to Figure 8.

Generally， the disclosed LAA discovery signal 110 includes multiple time-consecutive OFDM symbols， wherein each OFDM symbol carries a primary synchronization signal (PSS) ， a secondary synchronization signal (SSS) ， or a channel state information reference signal (CSI-RS) . The multiple time-consecutive OFDM symbols achieve efficient usage of the time-frequency resource on the unlicensed carrier， without requiring the network equipment 104 to transmit reservation signal on one or more otherwise vacant OFDM symbols within the LAA discovery signal 110. Beneficially， the required OFDM symbol for transmission of the LAA discovery signal 110 is reduced， in contrast to the LTE discovery signal 112 as defined by the 3GPP specification. Consequently， this also increases the number of LAA discovery signal transmission opportunities in a given time window， as discussed with reference to Figure 8.

In some embodiments， the LAA discovery signal 110 does not include a CRS， in contrast to an LTE discovery signal 112. Typically， a CRS is included in an LTE discovery signal 112 to allow a UE to perform fine time and frequency synchronization and also to measure RSRP. However， in some embodiments， the LAA discovery signal 110 is sufficiently dense in the frequency domain to allow the UE to perform fine time and frequency synchronization and RSRP measurement using the PSS， the SSS， and the CSI-RS. In further embodiments， the LAA discovery signal 110 includes sufficient CSI-RSs to allow a UE to derive the CSI without the CRS. Additionally， in LTE systems a CRS is transmitted in non-consecutive OFDM symbols. Therefore， the LAA discovery signal 110 may reduce its duration (e.g.， the number of OFDM symbols required to transmit the LAA discovery signal 110) by omitting a CRS. Beneficially， omitting CRS increases the number of LAA discovery signal transmission opportunities and more efficiently utilizes the time-frequency resources of the unlicensed spectrum 108.

In some embodiments， a LAA discovery signal 110 contains at least a first CSI-RS transmitted on a first CSI-RS resource and a second CSI reference signal transmitted on a second CSI-RS resource. In certain embodiments， the first CSI-RS resource and the second CSI-RS resource are transmitted over the same antenna port. Each CSI-RS resource consists of a set of REs in frequency and in a set of consecutive OFDM symbols. In certain embodiments， the REs in a CSI-RS are evenly spaced in frequency， thereby improving the fine frequency synchronization accuracy of a UE 102 receiving the LAA discovery signal 110. In one embodiment， the first CSI-RS resource comprises the same number of REs and the same number of OFDM symbols as the second CS I-RS resource.

In some embodiments， each CSI-RS resource occupies one RE and every 12 REs in frequency (e.g.， 2x＝12) ， similar to the LTE discovery signal 112. With a frequency decimation of 12， a single CSI-RS resource is not sufficient to provide fine time and frequency synchronization. However， the LAA discovery signal 110 containing at least two CSI-RS is sufficiently dense in frequency to provide fine time and frequency synchronization. In contrast， the CSI-RS of an LTE discovery signal 112 is insufficient for fine time and frequency synchronization thus requiring a CRS. In one embodiment， the first CSI-RS resource and the second CSI-RS resource are offset from each other. For example， the two CSI-RS resources may be offset by x resource elements in frequency， where the REs comprising the CSI-RS resource have an equal spacing of 2x within the transmission bandwidth. Thus， one of the first CSI-RS and the second CSI-RS may be transmitted every x frequency subcarriers in the transmission bandwidth.

In some embodiments， each CSI-RS resource occupies two consecutive OFDM symbols. In one embodiment， the first CSI-RS resource and the second CSI-RS resource may be transmitted on different sets of OFDM symbols. For example， the first CSI-RS resource may consist of two OFDM symbols starting at OFDM symbol n， and the second CSI-RS resource may consist of two OFDM symbols starting at OFDM symbol m， where m≥n+2. In a further embodiment， the OFDM symbols containing the first CSI-RS resource are not adjacent to the OFDM symbols containing the second CSI-RS resource. Placing at least two CSI-RS resources in nonadjacent OFDM symbols improves the fine time synchronization accuracy of a UE 102 receiving the LAA discovery signal 110. In certain embodiments， OFDM symbols containing PSS and/or SSS in the LAA discovery signal 110 do not contain CSI-RS.

In some embodiments， the LAA discovery signal 110 may include additional CSI-RS resources (e.g.， the network equipment 104 may transmit CSI-RS on three or more CSI-RS resources in the LAA discovery signal 110) . These additional CSI-RS resources may be used for CSI measurement purposes. In certain embodiments， CSI-RS of one or more antenna ports can be transmitted on a CSI-RS resource. Thus， the additional CSI-RS resources may be transmitted on different antenna ports than the first CSI-RS resource and the second CSI-RS resource， allowing for CSI measurements of additional channels. Beneficially， additional CSI-RS resources increase the ability of the UE 102 to obtain CSI measurements. In some embodiments， network equipment 104 may transmit a configuration message to the UE 102 configuring additional CSI resources to carry a needed amount of CSI-RS antenna ports for CSI measurement.

For example， in one embodiment the LAA discovery signal 110 may include a third CSI-RS over a third CSI-RS resource. The third CSI-RS may be transmitted on a different antenna port and the first CSI-RS resource and the second CSI-RS resource. The third CSI-RS resource may include a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols that are different than those OFDM symbols used for the first CSI-RS and the second CSI-RS.

In one embodiment， the LAA discovery signal 110 includes multiple PSS and/or multiple SSS transmitted in the OFDM symbols containing PSS and/or SSS. By the network equipment 104 transmitting multiple PSS and/or SSS， the LAA discovery signal 110 may occupy sufficient bandwidth in each OFDM symbol to meet regulatory requirements. Additionally， by the network equipment 104 transmitting additional PSS and/or SSS on other frequency resources， the LAA discovery signal 110 improves the PSS/SSS detection performance at the UE 102， and thus results in better time and frequency synchronization accuracy compared to the LTE discovery signal 112 (recall that the LTE discovery signal 112 only transmits one PSS/SSS on the center 62 REs of the transmission bandwidth) .

In some embodiments， the network equipment 104 transmits copies of the same PSS (and SSS) throughout the system bandwidth in the OFDM symbols containing PSS and/or SSS in the LAA discovery signal 110. In certain embodiments， the PSS and SSS may be interleaved in one or more of time and frequency based on a predetermined interleave pattern. For example， the LAA discovery signal 110 may include a plurality of PSS time-frequency resources， each PSS time-frequency resource carrying a PSS， and a plurality of SSS time-frequency resources each SSS time-frequency resource carrying an SSS. The PSS time- frequency resources and the SSS time-frequency resources forming the predetermined interleave pattern.

In one embodiment， the PSS time-frequency resource includes Y consecutive REs in frequency over one OFDM symbol in time. The number of PSS time-frequency resources j may be the floor of M/Y， wherein M is the total number of REs in the system bandwidth. Similarly， the SSS frequency resource may include Y consecutive REs in frequency over one OFDM symbol in time. The number of SSS time-frequency resources may also be j. In another embodiment， each PSS/SSS time-frequency may include one or more reserved REs. For example， the PSS may occupy Z number of REs within each PSS time-frequency resource， wherein Z＜Y. Similarly， the SSS may occupy Z’ number of REs within each SSS time-frequency resource， wherein Z’＜Y. In certain embodiments， Z＝Z’. In other embodiments， Z≠Z’.

In certain embodiments， the OFDM symbols containing PSS and SSS， the time-frequency resource for PSS and SSS transmission may be configured by higher layers within the wireless communication system 100. For example， the network equipment 104 may transmit a configuration message to the UE 102 indicating the predetermined interleave pattern. In another example， the interleave pattern may be predetermined according to a standard followed by the wireless communication system 100， such as the 3GPP LTE specification. As the unlicensed spectrum 108 is open to all， different wireless operators may configured different time-frequency resources for the transmission of PSS and SSS. Accordingly， in one embodiment， different wireless operators may configure the different time-frequency resources so as to uniquely identify the wireless operator within a particular radio coverage area， thereby avoiding PCID confusion. A UE 102 may differentiate between network equipments 104 belonging to different network operators based on the interleave pattern of PSS and SSS.

Figure 3 depicts one embodiment of an apparatus 300 that may be used for receiving a discovery signal transmitted over unlicensed spectrum in a wireless communication system. The apparatus 300 includes one embodiment of the UE 102. Furthermore， the UE 102 may include a processor 302， a memory 304， an input device 306， a display 308， and a transceiver 310. In some embodiments， the input device 306 and the display 308 are combined into a single device， such as a touchscreen.

The processor 302， in one embodiment， may include any known controller capable of executing computer-readable instructions and/or capable of performing logical operations. For example， the processor 302 may be a microcontroller， a microprocessor， a central processing unit ( “CPU” ) ， a graphics processing unit ( “GPU” ) ， an auxiliary processing unit， a field programmable gate array ( “FPGA” ) ， or similar programmable controller. In some embodiments， the processor 302 executes instructions stored in the memory 304 to perform the methods and routines described herein. The processor 302 is communicatively coupled to the memory 304， the input device 306， the display 308， and the transceiver 310.

The memory 304， in one embodiment， is a computer readable storage medium. In some embodiments， the memory 304 includes volatile computer storage media. For example， the memory 304 may include a RAM， including dynamic RAM ( “DRAM” ) ， synchronous dynamic RAM ( “SDRAM” ) ， and/or static RAM ( “SRAM” ) . In some embodiments， the memory 304 includes non-volatile computer storage media. For example， the memory 304 may include a hard disk drive， a flash memory， or any other suitable non-volatile computer storage device. In some embodiments， the memory 304 includes both volatile and non-volatile computer storage media. In some embodiments， the memory 304 stores data relating to frame periods. In some embodiments， the memory 304 also stores program code and related data， such as an operating system or other controller algorithms operating on the UE 102.

The input device 306， in one embodiment， may include any known computer input device including a touch panel， a button， a keyboard， a stylus， a microphone， or the like. In some embodiments， the input device 306 may be integrated with the display 308， for example， as a touchscreen or similar touch-sensitive display. In some embodiments， the input device 306 includes a touchscreen such that text may be input using a virtual keyboard displayed on the touchscreen and/or by handwriting on the touchscreen. In some embodiments， the input device 306 includes two or more different devices， such as a keyboard and a touch panel.

The display 308， in one embodiment， may include any known electronically controllable display or display device. The display 308 may be designed to output visual， audible， and/or haptic signals. In some embodiments， the display 308 includes an electronic display capable of outputting visual data to a user. For example， the display 308 may include， but is not limited to， an LCD display， an LED display， an OLED display， a projector， or similar display device capable of outputting images， text， or the like to a user. As another， non-limiting， example， the display 308 may include a wearable display such as a smart watch， smart glasses， a heads-up display， or the like. Further， the display 308 may be a component of a smart phone， a personal digital assistant， a television， a table computer， a notebook (laptop) computer， a personal computer， a vehicle dashboard， or the like.

In certain embodiments， the display 308 includes one or more speakers for producing sound. For example， the display 308 may produce an audible alert or notification (e.g.， a beep or chime) . In some embodiments， the display 308 includes one or more haptic devices for producing vibrations， motion， or other haptic feedback. In some embodiments， all or portions of the display 308 may be integrated with the input device 306. For example， the input device 306 and display 308 may form a touchscreen or similar touch-sensitive display. In other embodiments， the display 308 may be located near the input device 306.

The transceiver 310， in one embodiment， is configured to communicate wirelessly with the network equipment 104. In certain embodiments， the transceiver 310 comprises a transmitter 312 and a receiver 314. The transmitter 312 is used to transmit UL communication signals to the network equipment 104 and the receiver 314 is used to receive DL communication signals from the network equipment 104. For example， the receiver 314 may receive a discovery signal over unlicensed spectrum 108. Discovery signals transmitted over unlicensed spectrum 108 are described in further detail below， with reference to Figures 5-8. In another example， the transmitter 312 may transmit UL communication signals via the licensed spectrum 106 and/or unlicensed spectrum 108 and the receiver 314 may receiver DL communication signals from one or more network equipments 104 (via the licensed spectrum 106 and/or unlicensed spectrum 108) .

The transmitter 312 and the receiver 314 may be any suitable types of transmitters and receivers. Although only one transmitter 312 and one receiver 314 are illustrated， the transceiver 310 may have any suitable number of transmitters 312 and receivers 314. In some embodiments， the user equipment 102 includes a plurality of transmitter 312 and receiver 314 pairs for communicating on a plurality of wireless networks and/or radio frequency bands， each transmitter 312 and receiver 314 pair configured to communicate on a different wireless network and/or radio frequency band than the other transmitter 312 and receiver 314 pairs. For example， the transceiver 310 may include a first transmitter 312 configured to transmit on the licensed spectrum 106 and a second transmitter 312 configured to transmit on the unlicensed spectrum 108. As another example， the transceiver 310 may include a first receiver 314 configured to receive on the licensed spectrum 106 and a second receiver 314 configured to receive on the unlicensed spectrum 108.

Figure 4 depicts one embodiment of an apparatus 400 that may be used for discovery signal transmission over unlicensed spectrum in a wireless communication system. The apparatus 400 includes one embodiment of the network equipment 104. Furthermore， the network equipment 104 may include a processor 402， a memory 404， an input device 406， a display 408， and a transceiver 410. As may be appreciated， the processor 402， the memory 404， the input device 406， and the display 408 may be substantially similar to the processor 302， the memory 304， the input device 306， and the display 308 of the UE 102， respectively.

The transceiver 410， in one embodiment， is configured to communicate wirelessly with the user equipment 102. In certain embodiments， the transceiver 410 comprises a transmitter 412 and a receiver 414. The transmitter 412 is used to transmit DL communication signals to the user equipment 102 and the receiver 414 is used to receive UL communication signals from the user equipment 102. For example， the transmitter 412 may transmit a discovery signal over unlicensed spectrum 108. The discovery signals transmitted over unlicensed spectrum 108 are described in further detail below， with reference to Figures 5-8. In another example， the transmitter 412 may transmit DL communication signals via the licensed spectrum 106 and/or unlicensed spectrum 108 and the receiver 414 may receiver UL communication signals from one or more UEs 102 (via the licensed spectrum 106 and/or unlicensed spectrum 108) .

The transmitter 412 and the receiver 414 may be any suitable types of transmitters and receivers. Although only one transmitter 412 and one receiver 414 are illustrated， the transceiver 410 may have any suitable number of transmitters 412 and receivers 414. In some embodiments， the network equipment 104 includes a plurality of transmitter 412 and receiver 414 pairs for communicating on a plurality of wireless networks and/or radio frequency bands， each transmitter 412 and receiver 414 pair configured to communicate on a different wireless network and/or radio frequency band than the other transmitter 412 and receiver 414 pairs. For example， the transceiver 410 may include a first transmitter 412 configured to transmit on the licensed spectrum 106 and a second transmitter 412 configured to transmit on the unlicensed spectrum 108. As another example， the transceiver 410 may include a first receiver 414 configured to receive on the licensed spectrum 106 and a second receiver 414 configured to receive on the unlicensed spectrum 108.

Figure 5 illustrates one embodiment of a discovery signal 500 that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system. The depicted discovery signal 500 may be one embodiment of the LAA discovery signal 110， discussed above with reference to Figure 1. In some embodiments， the discovery signal 500 is transmitted over the unlicensed spectrum 108 by a network equipment 104 and is consequently received by a UE 102 on the unlicensed spectrum 108. The discovery signal 500 may be usable by the UE 102 to detect a cell provided by the network equipment 104， to obtain time and frequency synchronization with the network equipment 104 over the unlicensed spectrum 108， and/or to measure CSI on the unlicensed spectrum 108.

As depicted， the discovery signal 500 comprises a plurality of resource elements 525 over transmission bandwidth 505 and over a set of OFDM symbols 510. In one embodiment， the transmission bandwidth 505 may comprise 10 MHz of system bandwidth， wherein six hundred resource elements 525 are available in the frequency domain， each resource element 525 occupying 15 kHz in frequency. In a further embodiment， the set of OFDM symbols 510 may comprise six OFDM symbols.

The transmission bandwidth 505 of the discovery signal 500 may be divided into a plurality of frequency blocks 515， each frequency block 515 containing 72 consecutive resource elements 525 in frequency. The frequency blocks 515 may be divided into a plurality of resource blocks 520， each frequency block containing six resource blocks 520. In one embodiment， the transmission bandwidth 505 is arranged with eight frequency blocks 515 occupying the center of the transmission bandwidth 505 with one resource block 520 on either end of the transmission bandwidth 505.

The set of OFDM symbols 510 comprises six consecutive OFDM symbols， wherein a first CSI-RS 530 is present on the first and second OFDM symbols (e.g.， OFDM symbols n and n+1) ， a PSS 535 or an SSS 540 is present on the third and fourth OFDM symbols (e.g.， ODFM symbols n+2 and n+3) ， and a second CSI-RS 545 is present on the fifth and sixth OFDM symbols (e.g.， OFDM symbols n+4 and n+5) . The first CSI-RS 530 and the second CSI-RS 545 are transmitted on a first antenna port 550. in some embodiments， the first CSI-RS 530 and the second CSI-RS 545 are transmitted on the same antenna port as that of the PSS 535 and the SSS 540. In other embodiments， the first CSI-RS 530 and the second CSI-RS 545 may be transmitted on a different antenna port as that of the PSS 535 and the SSS 540. For convenience， the first CSI-RS 530， the second CSI-RS 545， the PSS 535， and the SSS 540 are shown in the same resource grid in Figure 5.

As depicted， the first CSI-RS 530 is transmitted on every tenth resource element 525 in frequency of the resource blocks 520 (e.g.， every twelve resource elements 525 in frequency) . Accordingly， a first CSI-RS resource is formed which consists of one resource element 525 every 2x in frequency (where 2x＝12) ， and over two consecutive OFDM symbols in time (e.g.， OFDM symbols n and n+1) . Thus， the first CSI-RS resource comprises a set of resource elements 525 with equal spacing of twelve resource elements 525 in frequency.

The second CSI-RS 545 is transmitted on every fourth resource element 525 of the resource blocks 520 (e.g.， every twelve resource elements 525 in frequency) . Accordingly， a second CSI-RS resource is formed consisting of one resource element 525 every 2x in frequency (where 2x＝12) ， and over two consecutive OFDM symbols in time (e.g.， OFDM symbols n+4 and n+5) . Thus， the second CSI-RS resource comprises a set of resource elements 525 with equal spacing of twelve resource elements 25 in frequency. The second CSI-RS resource is offset from the first CSI-RS resource by six resource elements 525 in frequency (e.g.， offset by x resource elements 525， where x＝6) . Accordingly， either the first CSI-RS 530 or the second CSI-RS 545 occurs once every six resource elements 525.

The PSS 535 is transmitted over a time-frequency resource comprising a set of seventy-two consecutive resource elements 525 in frequency (corresponding to one frequency block) and over one OFDM symbol in time. Similarly， the SSS 540 is transmitted over a time-frequency resource comprising a set of seventy-two consecutive resource elements 525 in frequency and over one OFDM symbol in the time. Figure 5 depicts one way to configure the PSS/SSS time-frequency resources， where the resource elements 525 are arranged into multiple frequency blocks 515 of seventy-two consecutive resource elements 525 each. As may be appreciated， other embodiments may comprise different arrangements of the resource elements 525.

In some embodiments， the PSS time-frequency resource comprises one or more reserved resource elements 525， wherein the PSS 535 is not transmitted on the reserved resource elements 525 within the PSS time-frequency resource. Similarly， the SSS time-frequency resource may comprise one or more reserved resource elements 525， wherein the SSS 540 is not transmitted on the reserved resource elements 525 within the SSS time-frequency resource. As depicted， both the PSS 535 and the SSS 540 are transmitted on the center sixty-two resource elements 525 within a frequency block 515， thus leaving five reserved resource elements 525 on each end (in frequency) of the frequency by 515.

In some embodiments， the network equipment 104 may transmit the PSS 535 on j number of PSS time-frequency resources， wherein j is the floor of M/Y (e.g.， the largest integer not greater than M/Y) ， wherein M is the total number of REs in the system bandwidth. Similarly， the network equipment 104 may transmit the SSS 540 on j number of SSS time-frequency resources. Here， M＝600 and Y＝72， wherein the floor of M/Y＝8. As depicted in Figure 5， the PSS 535 and the SSS 540 are transmitted on eight PSS/SSS time-frequency resources (e.g.， on eight frequency blocks 515) . In some embodiments， copies of the same a PSS 535 may be repeated in every frequency block 515， while copies of the same the SSS 540 may be repeated in every frequency block 515. In some embodiments， neither PSS 535 not SSS 540 are transmitted in the two resource blocks 520 at the ends of the transmission bandwidth 505. While Figure 5 depicts a specific arrangement of the PSS time-frequency resource and the SSS time-frequency resource， other embodiments may include different arrangements of the PSS time-frequency resource and the SSS time-frequency resource.

Figure 6 illustrates one embodiment of a discovery signal 600 that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system. The depicted discovery signal 600 may be one embodiment of the LAA discovery signal 110， discussed above with reference to Figure 1. In some embodiments， the discovery signal 600 is transmitted over the unlicensed spectrum 108 by a network equipment 104 and is consequently received by a UE 102 on the unlicensed spectrum 108. The discovery signal 600 may be usable by the UE 102 to detect a cell provided by the network equipment 104， to obtain time and frequency synchronization with the network equipment 104 over the unlicensed spectrum 108， and/or to measure CSI on the unlicensed spectrum 108.

As depicted， the discovery signal 600 comprises a plurality of resource elements 525 over transmission bandwidth 505 and over a set of OFDM symbols 510. The transmission bandwidth 505 of the discovery signal 500 may be divided into a plurality of frequency blocks 515， and the frequency blocks 515 may be divided into a plurality of resource blocks 520. As may be appreciated， the resource elements 525， transmission bandwidth 505， set of OFDM symbols 510， frequency blocks 515， and resource blocks 520 may be substantially similar to those described above with reference to Figure 5.

The set of OFDM symbols 510 comprises six consecutive OFDM symbols， wherein a first CSI-RS 530 is present on the first and second OFDM symbols (e.g.， OFDM symbols n and n+1 ) ， a PSS 535 or an SSS 540 is present on the third and fourth OFDM symbols (e.g.， ODFM symbols n+2 and n+3) ， and a second CSI-RS 545 is present on the fifth and sixth OFDM symbols (e.g.， OFDM symbols n+4 and n+5) . The first CSI-RS 530 and the second CSI-RS 545 may be transmitted on a first antenna port 550. In some embodiments， the first CSI-RS 530 and the second CSI-RS 545 are transmitted on the same antenna port as that of the PSS 535 and the SSS 540. In other embodiments， the first CSI-RS 530 and the second CSI-RS 545 may be transmitted on a different antenna port as that of the PSS 535 and the SSS 540. For convenience， the first CSI-RS 530， the second CSI-RS 545， the PSS 535， and the SSS 540 are shown in the same resource grid in Figure 6. As may be appreciated， the first CSI-RS 430， the PSS 535， the SSS 540， and the second CSI-RS 545 may be substantially similar to those described above with reference to Figure 5.

The discovery signal 600 differs from the discovery signal 500 in that the third and fourth OFDM symbols (e.g.， ODFM symbols n+2 and n+3) each include a PSS 535 and an SSS 540. As depicted， the PSS 535 and the SSS 540 are transmitted on PSS time-frequency resources and SSS time-frequency resources， respectively， that form a PSS/SSS interleave pattern 650. In some embodiments， the network equipment 104 notifies the UE 102 by higher labor signaling about the time-frequency resources used for PSS 535 and SSS 540 transmission in the third and fourth OFDM symbols (e.g.， ODFM symbols n+2 and n+3) ， including the PSS/SSS interleave pattern 650. For example， the network equipment 104 may transmit a configuration message to the UE 102 indicating a predetermined PSS/SSS interleave pattern 650. As another example， the PSS/SSS interleave pattern 650 may be predetermined according to a communication standard used in the wireless communication system 100， for example the 3GPP LTE specification.

In the depicted embodiment， the PSS/SSS interleave pattern 650 ranges the PSS 535 and the SSS 540 such that each PSS 535 is adjacent in frequency to an SSS 540 and that a frequency block 515 transmitting a PSS 535 on the third OFDM symbol (e.g.， n+2) transmits a SSS 540 on the fourth OFDM symbol (e.g.， n+3) . The PSS/SSS interleave pattern 650 may be described in terms of time-frequency resources for PSS or SSS transmission (e.g.， PSS/SSS time-frequency resources) which are indexed by a pair of (m， n) ， wherein m denotes a frequency block index (e.g.， where m ranges from 1 to 8) and n denotes an OFDM symbol index (e.g.， wheren ranges from 1 to 6) in the discovery signal 600. Assuming the frequency blocks are indexed in the ascending order of frequency， the time-frequency resources indexed by (m， n) used for PSS transmission in the PSS/SSS interleave pattern 650 are (1， 3) ， (2， 4) ， (3， 3) ， (4， 4) ， (5， 3) ， (6， 4) ， (7， 3) ，(8， 4) ； the time-frequency resources indexed by (m， n) used for SSS transmission in the PSS/SSS interleave pattern 650 are (1， 4) ， (2， 3) ， (3， 4) ， (4， 3) ， (5， 4) ， (6， 3) ， (7， 4) ， (8， 3) .

The embodiment of Figure 6 depicts one way to configure the PSS/SSS interleave pattern 650. As may be appreciated， other embodiments may comprise different PSS/SSS interleave patterns 650， where the PSS 535 and the SSS 540 alternate in time and frequency. In some embodiments， the number of frequency blocks used for PSS transmission may be different from the number of frequency blocks used for SSS transmission. For example， the network equipment 104 may configure a UE 102 to receive PSS/SSS interleave patterns 650 specific to the network operator.

Figure 7 illustrates a third embodiment of a discovery signal that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system. The depicted discovery signal 700 may be one embodiment of the LAA discovery signal 110， discussed above with reference to Figure 1. In some embodiments， the discovery signal 700 is transmitted over the unlicensed spectrum 108 by a network equipment 104 and is consequently received by a UE 102 on the unlicensed spectrum 108. The discovery signal 700 may be usable by the UE 102 to detect a cell provided by the network equipment 104， to obtain time and frequency synchronization with the network equipment 104 over the unlicensed spectrum 108， and/or to measure CSI on the unlicensed spectrum 108.

As depicted， the discovery signal 700 comprises a plurality of resource elements 525 over transmission bandwidth 505 and over a set of OFDM symbols 710. The transmission bandwidth 505 of the discovery signal 500 may be divided into a plurality of frequency blocks 515， and the frequency blocks 515 may be divided into a plurality of resource blocks 520. As may be appreciated， the transmission bandwidth 505， frequency blocks 515， resource blocks 520， and resource elements 525 may be substantially similar to those described above with reference to Figure 5.

The set of OFDM symbols 710 comprises eight consecutive OFDM symbols， wherein a first CSI-RS 530 is present on the first and second OFDM symbols (e.g.， OFDM symbols n and n+1) ， a PSS 535 or an SSS 540 is present on the third and fourth OFDM symbols (e.g.， ODFM symbols n+2 and n+3) ， and a second CSI-RS 545 is present on the fifth and sixth OFDM symbols (e.g.， OFDM symbols n+4 and n+5) . As may be appreciated， the first CSI-RS 430， the PSS 535， the SSS 540， and the second CSI-RS 545 may be substantially similar to those described above with reference to Figure 5.

The set of OFDM symbols 710 further comprises a third CSI-RS 750 present on the seventh and eighth OFDM symbols (e.g.， OFDM symbols n+6 and n+7) . The first CSI-RS 530 and the second CSI-RS 545 are transmitted on a first antenna port 550， while the third CSI-RS is transmitted on a second antenna port 755. In some embodiments， the first CSI-RS 530 and the second CSI-RS 545 are transmitted on the same antenna port as that of the PSS 535 and the SSS 540. In certain embodiments， the third CSI-RS 750 is transmitted on the same antenna port as that of the PSS 535 and the SSS 540. In other embodiments， the first CSI-RS 530， the second CSI-RS 545， and the third CSI-RS 750 may be transmitted on a different antenna port as that of the PSS 535 and the SSS 540. For convenience， the first CSI-RS 530， the second CSI-RS 545， the third CSI-RS 750， the PSS 535， and the SSS 540 are shown in the same resource grid in Figure 7. As depicted， the third CSI-RS 750 may be transmitted on every sixth resource element 525 in frequency of the resource blocks 520 (e.g.， every twelve resource elements 525 in frequency) . Accordingly， a third CSI-RS resource is formed which consists of one resource element 525 every 2x in frequency (where 2x＝12) ， and over two consecutive OFDM symbols in time (e.g.， OFDM symbols n+6 and n+7) . Thus， the third CSI-RS resource comprises a set of resource elements 525 with equal spacing of twelve resource elements 525 in frequency.

The CSI-

RS antenna ports

550 and 750 transmitted on the first CSI-RS resource 530， the second CSI-RS resource 545， and/or the third CSI-RS resource 750 may be used by the UE 102 for CSI measurement. In some embodiments， the second antenna port 755， on which third CSI-RS 750 is transmitted， is a different antenna port then the first antenna port 550. In certain embodiments， the third CSI-RS 750 is offset from the first CSI-RS 530 and/or the second CSI-RS 545， where the offset is configured by higher layers via radio resource control (RRC) signaling. CSI-RS offset is useful for time and frequency synchronization， however in certain embodiments the first CSI-RS 530 and the second CSI RS 545 are sufficient for time and frequency synchronization， such that the UE 102 does not require the third CSI-RS 750 for time and frequency synchronization.

Figure 8 illustrates one embodiment of a discovery signal transmission schedule 800 that facilitates discovery signal transmission over unlicensed spectrum in a wireless communication system. The depicted discovery schedule 800 may include a plurality of discovery reference signal (DRS) transmission windows 805. Each DRS transmission window 805 has a predetermined duration， e.g.， S subframes in length， and includes one or more DRS transmission opportunities 810. An LAA discovery signal 110 may be transmitted during a DRS transmission opportunity 810. In some embodiments， the DRS transmission windows 805 repeats with a predetermined periodicity within the discovery signal transmission schedule 800. For example， each DRS transmission window 805 may repeat every T subframes， where T＞S. In certain embodiments， T may be much greater than S in order to save power at a network equipment 104 without traffic to transmit over the unlicensed spectrum 108 and to provide access opportunities for different systems on the unlicensed spectrum 108. However， too great a value for T may result in a UE 102 being unable to timely detect the network equipment 104 over the unlicensed spectrum 108.

In some embodiments， a DRS transmission opportunity 810 also has a predetermined duration. For example， each DRS transmission opportunity 810 may comprise W OFDM symbols， where W is based on the number of OFDM symbols in the LAA discovery signal 110. The DRS transmission opportunities 810 may repeat with a predetermined periodicity within the DRS transmission window 805. For example， the DRS transmission opportunities 810 may repeat every W’ OFDM symbols， where W’≥W. By repeating the DRS transmission opportunities 810 within a DRS transmission window 805 maximizes the probability of the network equipment 104 transmitting a LAA discovery signal 110 during the DRS transmission window 805. Additionally， a shorter LAA discovery signal 110 (e.g.， fewer OFDM symbols in the LAA discovery signal 110) may result in more DRS transmission opportunities 810 within the DRS transmission window 805. Thus， the discovery signal 700， which contains eight OFDM symbols， may result in fewer DRS transmission opportunities 810 than the discovery signal 500， which contains six OFDM symbols.

For example， a network equipment 104 may identify a DRS transmission opportunity 810 in a DRS transmission window 805， wherein the DRS transmission window occurs periodically with a periodicity of T subframes with T≥1 and each discovery signal transmission window comprises a set of S consecutive subframes with S≥1. In some embodiments， one or more DRS transmission opportunities 810 are present in each DRS transmission window 805， wherein each DRS transmission opportunity comprises a set of W consecutive OFDM symbols with W≥1. The network equipment 104 may further identify a channel for transmitting a LAA discovery signal 110， wherein the channel resides in the unlicensed spectrum 108.

In response to identifying a DRS transmission opportunity 810 and channel， but before transmitting a LAA discovery signal 110， the network equipment 104 may determine whether the channel is busy. In some embodiments， the network equipment 104 determines whether the channel is busy during a sensing period before the identified DRS transmission opportunity 810. In certain embodiments， the network equipment 104 determines that a channel is busy in response to the total energy received on the channel being above a threshold of value P， or in response to the energy of a certain sequence received on the channel being above a threshold value of Q. In one embodiment， the values of P and Q are predetermined， for example these values may be defined in a standard used in the wireless medication system 100. In another embodiment， the values of P and Q are based on operating conditions of the unlicensed spectrum 108. In yet another embodiment， the values of P and Q may be prescribed by regulation in the geographic location where the wireless communication system 100 resides.

The network equipment 104 transmits the LAA discovery signal 110 in the identified DRS transmission opportunity 801 in response to the channel not being busy (e.g.， the total energy being below P and/or the energy of the certain sequence being below Q) . Otherwise， in response to the channel being busy， the network equipment 104 inhibits transmission of the LAA discovery signal 110 in the identified DRS transmission opportunity 810. The network equipment 104 may then identity a next DRS transmission opportunity 810.

Figure 9A is a schematic flow chart diagram illustrating one embodiment of a method 900 for discovery signal transmission over unlicensed spectrum in a wireless communication system from a network equipment 104. In some embodiments， the method 900 is performed by an apparatus， such as the network equipment 104. In certain embodiments， the method 900 may be performed by a processor executing program code， for example， a microcontroller， a microprocessor， a CPU， a GPU， an auxiliary processing unit， a FPGA， or the like.

The method 900 may include transmitting 905 a first CSI-RS over a first CSI-RS resource. For example， the network equipment 104 may transmit 905 a LAA discovery signal 110 containing a first CSI-RS. In some embodiments， the first CSI-RS is transmitted 905 on a first antenna port. In certain embodiments， the first CSI-RS resource comprises a set of REs with equal spacing in frequency and over two consecutive OFDM symbols in time. The equal spacing may be 2x REs in frequency and the consecutive OFDM symbols may be denoted as n and n+1.

The method 900 may also include transmitting 910 a PSS on at least one PSS time-frequency resource. For example， the network equipment 104 may transmit 910 a LAA discovery signal 110 containing a PSS. In some embodiments， a PSS time-frequency resource includes a set of Y consecutive REs in frequency over one OFDM symbol in time. In certain embodiments， the PSS is transmitted in at least one of two OFDM symbols n+2 and n+3.

The method 900 may also include transmitting 915 a SSS on at least one SSS time-frequency resource. For example， the network equipment 104 may transmit 915 a LAA discovery signal 110 containing a SSS. In some embodiments， a SSS time-frequency resource includes a set of Y consecutive REs in frequency over one OFDM symbol in time. In certain embodiments， the SSS is transmitted in at least one of two OFDM symbols n+2 and n+3. In a further embodiment， at least one of a PSS and a SSS is transmitted on each of OFDM symbols n+2 and n+3.

The method 900 may provide transmitting 920 at least one second CSI-RS over a second CSI-RS resource. For example， the network equipment 104 may transmit 920 a LAA discovery signal 110 containing a second CSI-RS. In some embodiments， the second CSI-RS is transmitted 920 on the first antenna port. In certain embodiments， the second CSI-RS resource comprises a set of REs with equal spacing in frequency and over two consecutive OFDM symbols in time. The equal spacing may be 2x REs in frequency and the consecutive OFDM symbols may be denoted as n+4 and n+5， wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time. In a further embodiment， the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource. Then the method 900 may end.

In certain embodiments， transmitting 910 the PSS on at least one PSS time-frequency resource includes transmitting the PSS on j number of PSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth. For example， where the unlicensed spectrum 108 includes a system bandwidth of six hundred REs， and where each PSS time-frequency resource includes seventy-two REs， then the network equipment 104 may transmit 910 the PSS on eight PSS time-frequency resources. In a further embodiment， transmitting 910 the PSS at least one PSS time-frequency resource includes transmitting the PSS on Z number of REs within each PSS time-frequency resource， wherein Z＜Y and wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs. For example， the network equipment 104 may transmit 910 a 62-length Zadoff-Chu sequence on a center sixty-two REs of the PSS time-frequency resource， wherein the PSS time-frequency resource includes ten reserved REs.

In certain embodiments， transmitting 915 the SSS on at least one SSS time-frequency resource includes transmitting the SSS on j number of SSS time-frequency resources. For example， where the unlicensed spectrum 108 includes a system bandwidth of six hundred REs， and where each SSS time-frequency resource includes seventy-two REs， then the network equipment 104 may transmit the SSS on eight SSS time-frequency resources. In a further embodiment， transmitting 915 the SSS at least one SSS time-frequency resource includes transmitting the SSS on Z’ number of REs within each SSS time-frequency resource， wherein Z’＜Y and wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs. For example， the network equipment 104 may transmit 915 a 62-length sequence on a center sixty-two REs of the SSS time-frequency resource， wherein the SSS time-frequency resource includes ten reserved REs. In some embodiments， the SSS length differs from the PSS length.

In certain embodiments， transmitting 910 the PSS and transmitting 915 the SSS include transmitting based on a predetermined interleave pattern. For example， the at least one PSS time-frequency resource and at least one SSS time-frequency resource may form the predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and at least one SSS time-frequency resource in one or more of time and frequency.

Figure 9B is a schematic flow chart diagram illustrating one embodiment of a method 950 for a UE 102 to receive a discovery signal transmitted over unlicensed spectrum in a wireless communication system from a network equipment 104. In some embodiments， the method 950 is performed by an apparatus， such as the UE 102. In certain embodiments， the method 950 may be performed by a processor executing program code， for example， a microcontroller， a microprocessor， a CPU， a GPU， an auxiliary processing unit， a FPGA， or the like.

The method 950 may include receiving 955 a first CSI-RS over a first CSI-RS resource. For example， the UE 102 may receive 955 a LAA discovery signal 110 containing a first CSI-RS. In some embodiments， the first CSI-RS is receive 955 on a first antenna port. In certain embodiments， the first CSI-RS resource comprises a set of REs with equal spacing in frequency and over two consecutive OFDM symbols in time. The equal spacing may be 2x REs in frequency and the consecutive OFDM symbols may be denoted as n and n+1.

The method 950 may also include receiving 960 a PSS on at least one PSS time-frequency resource. For example， the UE 102 may receive 960 a LAA discovery signal 110 containing a PSS. In some embodiments， a PSS time-frequency resource includes a set of Y consecutive REs in frequency over one OFDM symbol in time. In certain embodiments， the PSS is present in at least one of two OFDM symbols n+2 and n+3.

The method 950 may also include receiving 965 a SSS on at least one SSS time-frequency resource. For example， the UE 102 may receive 965 a LAA discovery signal 110 containing a SSS. In some embodiments， a SSS time-frequency resource includes a set of Y consecutive REs in frequency over one OFDM symbol in time. In certain embodiments， the SSS is present in at least one of two OFDM symbols n+2 and n+3. Ina further embodiment， at least one of a PSS and a SSS are present on each of OFDM symbols n+2 and n+3.

The method 950 may provide receiving 970 at least one second CSI-RS over a second CSI-RS resource. For example， the UE 102 may receive 970 a LAA discovery signal 110 containing a second CSI-RS. In some embodiments， the second CSI-RS is receive 970 on the first antenna port. In certain embodiments， the second CSI-RS resource comprises a set of REs with equal spacing in frequency and over two consecutive OFDM symbols in time. The equal spacing may be 2x REs in frequency and the consecutive OFDM symbols may be denoted as n+4 and n+5， wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time. In a further embodiment， the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource. Then the method 950 may end.

In certain embodiments， receiving 960 the PSS on at least one PSS time-frequency resource includes receiving the PSS on j number of PSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth. For example， where the unlicensed spectrum 108 includes a system bandwidth of six hundred REs， and where each PSS time-frequency resource includes seventy-two REs， then the UE 102 may receive 960 the PSS on eight PSS time-frequency resources. In a further embodiment， receiving 960 the PSS at least one PSS time-frequency resource includes receiving the PSS on Z number of REs within each PSS time-frequency resource， wherein Z＜Y and wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs. For example， the UE 102 may receive 960 a 62-length Zadoff-Chu sequence on a center sixty-two REs of the PSS time-frequency resource， wherein the PSS time-frequency resource includes ten reserved REs.

In certain embodiments， receiving 965 the SSS on at least one SSS time-frequency resource includes receiving the SSS on j number of SSS time-frequency resources. For example， where the unlicensed spectrum 108 includes a system bandwidth of six hundred REs， and where each SSS time-frequency resource includes seventy-two REs， then the UE 102 may receive 965 the SSS on eight SSS time-frequency resources. In a further embodiment， receiving 965 the SSS at least one SSS time-frequency resource includes receiving the SSS on Z’number of REs within each SSS time-frequency resource， wherein Z’＜Y and wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs. For example， the UE 102 may receive 965 a 62-length sequence on a center sixty-two REs of the SSS time-frequency resource， wherein the SSS time-frequency resource includes ten reserved REs. In some embodiments， the SSS length differs from the PSS length.

In certain embodiments， receiving 960 the PSS and receiving 965 the SSS include receiving based on a predetermined interleave pattern. For example， the at least one PSS time-frequency resource and at least one SSS time-frequency resource may form the predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and at least one SSS time-frequency resource in one or more of time and frequency.

Embodiments may be practiced in other specific forms. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is， therefore， indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

A method comprising：

transmitting at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n and n+1 in time；

transmitting a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is transmitted in at least one of two OFDM symbols n+2 and n+3；

transmitting a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is transmitted in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is transmitted on each of OFDM symbols n+2 and n+3；

transmitting at least one second CSI-RS on the first antenna port over a second CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource；

wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.
The method of claim 1， wherein transmitting the PSS on at least one PSS time-frequency resource comprises：

transmitting the PSS on j number of PSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth.
The method of claim 1， wherein transmitting the PSS on at least one PSS time-frequency resource comprises：

transmitting the PSS on Z number of REs within each PSS time-frequency resource， wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs， and wherein Z＜Y.
The method of claim 1， wherein transmitting the SSS on at least one SSS time-frequency resource comprises：

transmitting the SSS on j number of SSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth.
The method of claim 1， wherein transmitting the SSS on at least one SSS time-frequency resource comprises：

transmitting the SSS on Z′ number of REs within each SSS time-frequency resource， wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs， and wherein Z′＜Y.
The method of claim 1， further comprising：

transmitting at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.
The method of claim 1， wherein the first CSI-RS， the PSS， the SSS， and the second CSI-RS comprise a discovery signal， the method further comprising：

identifying a discovery signal transmission opportunity in a discovery signal transmission window， wherein the discovery signal transmission window occurs periodically with a periodicity of T subframes with T≥1 and each discovery signal transmission window comprises a set of S consecutive subframes with S≥1， wherein one or more discovery signal transmission opportunities are present in each discovery signal transmission window， and wherein each discovery signal transmission opportunity comprises a set of W consecutive OFDM symbols with W≥1；

identifying a channel for transmitting the discovery signal， wherein the channel comprises a channel of unlicensed radio-frequency spectrum； and

transmitting the discovery signal in the identified discover signal transmission opportunity in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value Q.
The method of claim 7， the method further comprising：

inhibiting transmission of the discovery signal in the identified discover signal transmission opportunity in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value Q.
The method of claim 1， wherein the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of： time and frequency.
The method of claim 9， further comprising：

transmitting a configuration message indicating the predetermined interleave pattern.
A network equipment comprising：

a radio transceiver configured to communicate with at least one user equipment over a mobile telecommunications network；

a processor； and

a memory that stores code executable by the processor， the code comprising：

code that transmits at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbolsn and n+l in time；

code that transmits a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is transmitted in at least one of two OFDM symbols n+2 and n+3；

code that transmits a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is transmitted in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is transmitted on each of OFDM symbols n+2 and n+3； and

code that transmits at least one second CSI-RS on the first antenna port over a second CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource，

wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.
The network equipment of claim 11， wherein transmitting the PSS on at least one PSS time-frequency resource comprises：

transmitting the PSS on j number of PSS time-frequency resources， wherein j is the floor of M T， wherein M is the total number of REs in the system bandwidth.
The network equipment of claim 11， wherein transmitting the PSS on at least one PSS time-frequency resource comprises：

transmitting the PSS on Z number of REs within each PSS time-frequency resource， wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs， and wherein Z＜Y.
The network equipment of claim 11， wherein transmitting the SSS on at least one SSS time-frequency resource comprises：

transmitting the SSS on j number of SSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth.
The network equipment of claim 11， wherein transmitting the SSS on at least one SSS time-frequency resource comprises：

transmitting the SSS on Z′ number of REs within each SSS time-frequency resource， wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs， and wherein Z′＜Y.
The method of claim 11， further comprising：

code that transmits at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.
The network equipment of claim 11， wherein the first CSI-RS， the PSS， the SSS， and the second CSI-RS comprise a discovery signal， the code further comprising：

code that identifies a discovery signal transmission opportunity in a discovery signal transmission window， wherein the discovery signal transmission window occurs periodically with a periodicity of T subframes with T≥1 and each discovery signal transmission window comprises a set of S consecutive subframes with S≥1， wherein one or more discovery signal transmission opportunities are present in each discovery signal transmission window， and wherein each discovery signal transmission opportunity comprises a set of W consecutive OFDM symbols with W≥1；

code that identifies a channel for transmitting the discovery signal， wherein the channel comprises a channel of unlicensed radio-frequency spectrum； and

code that transmits the discovery signal in the identified discover signal transmission opportunity， in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being below a threshold of value Q.
The network equipment of claim 17， the code further comprising：

code that inhibits transmission of the discovery signal in the identified discover signal transmission opportunity in response to the total energy received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value P or in response to the energy of a certain sequence received on the channel during a sensing period before the identified discovery signal transmission opportunity being above a threshold of value Q.
The network equipment of claim 11， wherein the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of： time and frequency.
The network equipment of claim 19， further comprising：

code that transmits a configuration message indicating the predetermined interleave pattern.
A method comprising：

receiving at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n and n+1 in time；

receiving a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is present in at least one of two OFDM symbols n+2 and n+3；

receiving a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is present in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is present on each of OFDM symbols n+2 and n+3；

receiving at least one second CSI-RS on a second antenna port over the first CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource；

wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.
The method of claim 21， wherein receiving the PSS on at least one PSS time-frequency resource comprises：

receiving the PSS on j number of PSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth.
The method of claim 21， wherein receiving the PSS on at least one PSS time-frequency resource comprises：

receiving the PSS on Z number of REs within each PSS time-frequency resource， wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs， and wherein Z＜Y.
The method of claim 21， receiving a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， further comprising：

receiving the SSS on j number of SSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth.
The method of claim 21， wherein receiving the SSS on at least one SSS time-frequency resource comprises：

receiving the SSS on Z′ number of REs within each SSS time-frequency resource， wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs， and wherein Z′＜Y.
The method of claim 21， further comprising：

receiving at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.
The method of claim 21， wherein the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of time and frequency.
The method of claim 25， further comprising receiving a configuration message indicating the predetermined interleave pattern.
A user equipment comprising：

a radio transceiver configured to communicate with at least one network equipment over a mobile telecommunications network；

a processor； and

a memory that stores code executable by the processor， the code comprising：

receiving at least one first channel state information reference signal (CSI-RS) on a first antenna port over a first CSI-RS resource， wherein the first CSI-RS resource comprises a set of resource elements (REs) with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n and n+1 in time；

receiving a primary synchronization signal (PSS) on at least one PSS time-frequency resource， wherein a PSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， and wherein the PSS is present in at least one of two OFDM symbols n+2 and n+3；

receiving a secondary synchronization signal (SSS) on at least one SSS time-frequency resource， wherein a SSS time-frequency resource comprises a set of Y consecutive REs in frequency over one OFDM symbol in time， wherein the SSS is present in at least one of two OFDM symbols n+2 and n+3， and wherein at least one of a PSS and a SSS is present on each of OFDM symbols n+2 and n+3；

receiving at least one second CSI-RS on a second antenna port over the first CSI-RS resource， wherein the second CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols n+4 and n+5 in time， and wherein the REs in the second CSI-RS resource are offset by x REs in frequency relative to the REs in the first CSI-RS resource；

wherein OFDM symbols n， n+1， n+2， n+3， n+4， n+5 are consecutive in time.
The user equipment of claim 29， wherein receiving the PSS on at least one PSS time-frequency resource comprises：

receiving the PSS on j number of PSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth.
The user equipment of claim 29， wherein receiving the PSS on at least one PSS time-frequency resource comprises：

receiving the PSS on Z number of REs within each PSS time-frequency resource， wherein the set of Y consecutive REs in each PSS time-frequency includes one or more reserved REs， and wherein Z＜Y.
The user equipment of claim 29， receiving the SSS on at least one SSS time-frequency resource comprises：

receiving the SSS on j number of SSS time-frequency resources， wherein j is the floor of M/Y， wherein M is the total number of REs in the system bandwidth.
The user equipment of claim 29， wherein receiving the SSS on at least one SSS time-frequency resource comprises：

receiving the SSS on Z′ number of REs within each SSS time-frequency resource， wherein the set of Y consecutive REs in each SSS time-frequency includes one or more reserved REs， and wherein Z′＜Y.
The user equipment of claim 29， further comprising：

receiving at least one third CSI-RS on a second antenna port over a third CSI-RS resource， wherein the third CSI-RS resource comprises a set of REs with equal spacing of 2x REs in frequency and over two consecutive OFDM symbols m and m+1 in time， wherein n-2≤m≤n+6.
The user equipment of claim 29， wherein the at least one PSS time-frequency resource and the at least one SSS time-frequency resource form a predetermined interleave pattern， the predetermined interleave pattern interleaving the at least one PSS time-frequency resource and the at least one SSS time-frequency resource in one or more of time and frequency.
The user equipment of claim 35， further comprising receiving a configuration message indicating the predetermined interleave pattern.