Patent Description:
The following abbreviations and acronyms are herewith defined, at least some of which are referred to in the following description.

Third Generation Partnership Project ("3GPP"), Positive-Acknowledgment ("ACK"), Channel State Information ("CSI"), Control Channel ("CCH"), Device-to-Device ("D2D"), further enhancement Device-to-Device ("feD2D"), Downlink Control Information ("DCI"), Downlink ("DL"), Demodulation Reference Signal ("DMRS"), Evolved Node B ("eNB"), European Telecommunications Standards Institute ("ETSI"), Frequency Division Duplex ("FDD"), Frequency-Division Multiplexing ("FDM"), Frequency Division Multiple Access ("FDMA"), Long Term Evolution ("LTE"), LTE Advanced ("LTE-A"), Multiple Access ("MA"), Machine Type Communication ("MTC"), Narrowband ("NB"), Negative-Acknowledgment ("NACK") or ("NAK"), Orthogonal Frequency Division Multiplexing ("OFDM"), Physical Downlink Control Channel ("PDCCH"), Physical Downlink Shared Channel ("PDSCH"), Physical Sidelink Control Channel ("PSCCH"), Physical Sidelink Shared Channel ("PSSCH"), Physical Uplink Control Channel ("PUCCH"), Physical Uplink Shared Channel ("PUSCH"), Quality of Service ("QoS"), Radio Network Temporary ("RNTI"), Identity Radio Resource Control ("RRC"), Reference Signal Receiving Power ("RSRP"), Reference Signal Strength Indicator ("RSSI"), Receive ("RX"), Scheduling Assignment ("SA"), Scheduling Request ("SR"), Shared Channel ("SCH"), Sidelink Control Information ("SCI"), System Information Block ("SIB"), Sidelink ("SL"), Semi-Persistent Scheduling ("SPS"), Sounding Reference Signal ("SRS"), Transport Block ("TB"), Transport Block Size ("TBS"), Transmission Control Protocol ("TCP"), Time Division Duplex ("TDD"), Time-Division Multiplexing ("TDM"), Transmission Time Interval ("TTI"), Transmit ("TX"), Uplink Control Information ("UCI"), User Datagram Protocol ("UDP"), User Entity/Equipment (Mobile Terminal) ("UE"), Uplink ("UL"), Universal Mobile Telecommunications System ("UMTS"), Vehicle-to-Vehicle ("V2V") and Vehicle-to-Everything ("V2X"). As used herein, SL communication is also known as D2D communication.

In mobile communication networks, a remote UE may operate in an indirect communication mode where the remote UE accesses mobile network communication services via a relay UE. Both D2D and V2V communication are broadcast-based communication. However, broadcast-based communication does not meet the requirements for QoS, reliability, complexity and power consumption. Therefore, a new study on feD2D has been developed, that proposes to support unicast communication on sidelink.

<CIT> discloses a device-to-device (D2D) communication method in a wireless mobile communication system. A channel state measurement method for adaptive transmission of cellular network-based D2D communication, a data transmission/reception method of D2D communication, and a power control method for transmission power control of a D2D link in the D2D communication are provided. Specifically, cellular network-based D2D communication methods optimized for a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) system are provided. The above-described methods are also applicable to various cellular mobile communication systems as well as the 3GPP LTE system.

<CIT> discloses a User Equipment for a MulteFire wireless communication network. The User Equipment comprises processing circuitry and a transmitter, the User Equipment being adapted for utilizing the processing circuitry and the transmitter for performing a Listen-Before-Talk (LBT) procedure for one or more transmission bandwidths; transmitting Physical Uplink Shared CHannel (PUSCH) signalling in a PUSCH subframe on one or more interlaces within the one or more transmission bandwidths; and transmitting Sounding Reference Signalling on the one or more interlaces in the PUSCH subframe. Submission<NPL> concerns signalling between a relay UE and a remote UE in a D2D relay set up.

Claims <NUM> and <NUM> each define an apparatus. Claims <NUM> and <NUM> each define a method. In the following, any method and/or apparatus referred to as embodiments but nevertheless do not fall within the scope of the appended claims are to be understood as examples helpful in understanding the invention.

Both 3GPP Rel-<NUM>/Rel-<NUM> D2D communication and 3GPP Rel-<NUM> V2V communication are typical broadcast-based communications, wherein one of the main objectives is to enable as many receivers as possible to successfully decode the messages. Mechanisms such as blind (re)transmission without feedback are no longer suitable for unicast communication. Enhancements to SL should be studied to support unicast communication in order to meet the requirements for QoS, reliability, complexity and power consumption, and furthermore, to enable D2D-aided wearables and MTC applications.

Enhancements to enable reliable unicast SL communication require effective channel measurement for feD2D communication between a relay UE and a remote UE. But if the SL channel measurement is based on scheduled SL transmission (e.g., discovery, synchronization signal, SCI over PSCCH or data over PSSCH) or the DMRS within the SL transmission (e.g., DMRS occupies the resource of PSCCH/PSSCH), it is difficult to obtain an effective result to present a thorough overview for the SL channel. This impacts resource pool/resource selection for SL communication and reliable unicast PC5 link and decreases the performance of link adaptation in SL communication. There is thus a need to develop a new measurement and report/feedback mechanism in which link adaption SL transmission based on the result of SL channel measurement is supported at a relay/remote UE.

In feD2D, it might be beneficial for a relay/remote UE to perform SL communication using uplink resources of the relay UE. For this, the last symbol of each SL subframe is not necessary to be a guard gap so that it can be used as a SL SRS for SL channel measurement.

Additionally, the SL SRS can be used for other purposes, such as power control for relay/remote UEs, similar with UL SRS.

Methods and apparatus for SRS transmission on SL are disclosed. One method of a relay/remote UE comprises transmitting a SRS on a SL. The SRS is based on a SL SRS configuration which configures the location information of the SRS in time-frequency domain. The transmission of SRS can be either periodic or aperiodic. Further, the SRS is a single SRS or a set of SRS.

One method of a relay/remote UE comprises receiving a SRS on a SL. The SRS is based on a SL SRS configuration which configures location information of the SRS in time-frequency domain. Further, the SRS is a single SRS or a set of SRS.

Given that these drawings depict only some embodiments and are not therefore to be considered to limit scope, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:.

As will be appreciated by one skilled in the art, aspects of the embodiments may be embodied as a system, apparatus, method, or a program product. Accordingly, embodiments may take the form of an all-hardware embodiment, an all-software embodiment (including firmware, resident software, micro-code, etc.), or an embodiment combining software and hardware aspects.

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, collectively referred to hereafter as "code".

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 is not limited to being, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.

A non-exhaustive list of more specific examples of the storage device may include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, random-access memory ("RAM"), 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.

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. The terms "including", "comprising", "having", and variations thereof mean "including but not limited to", unless expressly specified otherwise. The terms "a", "an", and "the" also refer to "one or more" unless expressly specified otherwise.

This 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 - executed via the processor of the computer or other programmable data-processing apparatus - create a means for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagrams.

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.

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 executed on the computer or other programmable apparatus provides processes for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagram.

For example, two blocks shown in succession may, in fact, be substantially executed in concurrence, or the blocks may sometimes be executed in 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, from the illustrated Figures.

Enhancements to the SL communication in feD2D should be studied to enable effective channel measurement in order to meet the requirements for QoS, reliability, complexity and power consumption, and furthermore, to enable D2D-aided wearables and MTC applications. Disclosed herein are methods, apparatus, and systems that provide a mechanism of SL SRS transmission on a SL. As described herein, the SRS is based on a SL SRS configuration which configures location information of the SRS in the time-frequency domain. The SL SRS configuration is obtained by the remote/relay UE through receiving the SL SRS configuration from a network equipment such as eNB, pre-configuring the SL SRS configuration in the remote/relay UE, determining the SL SRS configuration according to a resource pool for SL communication, or receiving the SL SRS configuration from the relay/remote unit. The transmission/receiving of SRS from the relay/remote UE can be either periodic or aperiodic in which the transmission/receiving of SL SRS usually follows indication information indicating the SRS transmission/receiving.

Additionally, the SRS may be a single SRS which may occupy a portion of a whole SL bandwidth (also referred as a subband), or a set of SRS which includes one or more subband SRS and/or one wideband SRS.

The SL SRS is used for SL channel measurement hereinafter, but it should be understood that the SL SRS can be used for other purposes, such as power control for relay/remote UEs, similar with UL SRS.

<FIG> is a schematic diagram illustrating a case of unidirectional relay in unicast D2D communication. Both a relay UE and a remote UE are within the coverage of eNB. eNB communicates with the remote UE on DL, transmitting signaling/data to the remote UE bypass the relay UE, such as the SL SRS configuration as discussed below. The remote UE communicates with the relay UE over SL, thereby the signaling/data from the remote UE is transmitted to eNB through the relay UE, such as RSRP, RSSI or CSI as the result of SL channel measurement. Additionally, the result of eNB-remote UE DL channel measurement may also be reported to the eNB from the remote UE through the relay UE.

<FIG> is a schematic diagram illustrating a case of bidirectional relay in unicast D2D communication. Relay UE is in the coverage of eNB in <FIG>. eNB does not communicate with the remote UE in the bidirectional relay case, thereby the signaling/data to the remote UE is transmitted from eNB through the relay UE, such as SL SRS configuration as discussed below.

As described herein, the SL channel measurement is performed by a relay/remote UE based on a SRS which is also referred to as SL SRS herein. Two types of reference signals are supported on uplink between an eNB and a UE, which are DMRS and SRS. <FIG> is a schematic diagram illustrating SRS and DMRS in UL subframes for UL channel measurement. As shown in <FIG>, the DMRS is associated with transmissions of uplink data on PUSCH and/or signaling on the PUCCH, and is primarily used for channel estimation or coherent demodulation. Also, as shown in <FIG>, the SRS, also referred to as UL SRS, is associated with uplink data and/or signaling transmissions, and usually occupies the last symbol of the last UL subframe and the whole UL bandwidth of the UE, thereby the result of UL channel measurement based on UL SRS, such as UL CSI, RSSP, RSSI, etc., can reflect a thorough UL channel quality so that frequency-selective scheduling on the uplink is enabled. Additionally, the UL SRS can be used for other purposes, such as power control or power-up procedures for UEs not yet scheduled. The eNB selects the UL resources for UL transmission based on the measurement result, e.g. CSI. In LTE-TDD, due to channel reciprocal, the UL SRS based measurement can be further used for estimation of DL CSI.

Similar with the concept and usage of UL SRS, the reason that the SL channel measurement is based on SL SRS as described herein is that the measurement result in such a way can present a thorough SL channel quality. On the contrary, the result of SL channel measurement based on a scheduled SL transmission (e.g., discovery, synchronization signal, SCI on PSCCH or data on PSSCH) or the DMRS within the SL transmission (e.g., DMRS occupies the resource of PSCCH/PSSCH) only reflects the channel quality over a portion of a whole SL bandwidth, i.e. the scheduled transmission may not occupy the whole SL bandwidth. Additionally, if the SL channel measurement is based on one or more of the scheduled transmissions such as discovery, synchronization signal, SCI on PSCCH or data on PSSCH, the timing of SL channel measurement cannot be guaranteed due to uncertainty of these scheduled transmissions. There is thus a need to support SL channel measurement based on SL SRS. Further, the SL SRS can be used for other purposes in addition to the SL channel measurement, similar with UL SRS.

There are two types of UL SRS: periodic SRS (trigger type <NUM>) introduced in 3GPP Rel-<NUM> and aperiodic SRS (trigger type1) introduced in Rel-<NUM>. The eNB may either request an individual SRS transmission from a UE (trigger type <NUM>), or configure a UE to transmit SRS periodically until terminated (trigger type <NUM>). <NUM>-bit UE-specific signaling parameter of 'duration' in SoundingRS-UL-Config information element (3GPP TS36. <NUM>) indicates whether the requested SRS transmission is a one-time transmission or a periodic transmission. The types of SL SRS transmission as described herein are similar with those of UL SRS transmission, and can be indicated in a SL SRS configuration as described herein, which is similar with the known SoundingRS-UL-Config information element.

<FIG> describe periodic SL SRS transmission and aperiodic SL SRS transmission in both unidirectional relay scenario and bidirectional relay scenarios. It would be understood that the steps in <FIG> and <FIG> between the remote UE and relay UE can be exchanged with each other, e.g. as described below, the indication information for the SL SRS transmission can be transmitted from either the remote UE or the relay UE, and the SL SRS can also be transmitted from either the remote UE or relay UE, no matter whether it is the unidirectional relay scenario or the bidirectional relay scenario. The difference between the unidirectional relay scenario or bidirectional relay scenario is that the remote UE may receive the SL SRS configuration or trigger information for SL SRS transmission from the eNB in the unidirectional scenario, while the remote UE receives the above messages from the relay UE in the bidirectional scenario.

<FIG> is a schematic diagram illustrating SL channel measurement in the unidirectional relay case according to one embodiment. As shown in <FIG>, eNB transmits SL SRS configuration to a remote UE over DL, and then the remote UE forwards the SL SRS configuration to a relay UE. The remote UE transmits SL SRS for one time, which is referred to as aperiodic transmission, or periodically. The relay UE performs the SL channel measurement based on the received SL SRS and transmits the measurement result such as RSRP or CSI to the eNB. Additionally, as shown in <FIG>, the remote UE may also performs DL channel measurement since the DL communication between the eNB and remote UE is allowed in the unidirectioal relay scenario, and transmits the corresponding measurement result to the relay UE which further forwards the result to the eNB.

As illustrated in <FIG>, the SL SRS configuration is received by the remote UE from the eNB and then forwarded from the remote UE to the relay UE, however, the SL SRS configuration may be pre-configured in both the remote UE and the relay UE. The SL SRS configuration may be similar with the known SoundingRS-UL-Config information element as mentioned above, and indicate location information of the SRS in time-frequency domain, e.g. the time/frequency offset between SL SA/data and SL SRS, the time/frequency offset between two SL SRS, or whether the transmission of SL SRS is periodic or aperiodic, e.g. indication by a signaling parameter of 'duration'.

The following is related to a claimed embodiment. <FIG> is a call flow illustrating that a remote UE aperiodically transmits a SL SRS to a relay UE following indication information from the remote UE in the unidirectional case according to one embodiment. As shown in <FIG>, the eNB transmits a SL SRS configuration to the remote UE on DL in step <NUM>, such as by higher layer signaling (RRC signaling). The remote UE forwards the SL SRS configuration to the relay UE in step <NUM>, such as by a higher layer signaling over PSSCH or by a discovery signaling over PSDCH. Step <NUM> and/or <NUM> are optional as illustrated with dash lines, e.g. the SL SRS configuration can be pre-configured in remote/relay UE, or the relay UE receives the SL SRS configuration from the eNB rather than the remote UE.

In step <NUM>, the eNB transmits trigger information for SL SRS transmission to the remote UE. The trigger information may be in a downlink control signaling such as DCI over PDCCH, or in a higher layer signaling such as a discovery response to the remote UE in the procedure of relay UE discovery, or over a piggyback in a higher layer signaling. The trigger information may indicate location information of the SL SRS to be transmitted in the frequency-time domain, such as an time/frequency offset between SL SA/data and SL SRS to be transmitted.

Alternatively, the eNB may transmit a SL SRS to the remote UE in step <NUM>, i.e. the eNB selects the SL SRS. The SL SRS selected by eNB may be a single SRS or a set of SRS, as described below.

In step <NUM>, the remote UE transmits indication information to the relay UE according to the received trigger in step <NUM>, wherein the indication information indicates the SRS transmission. The indication information may be in sidelink control signaling such as SCI over PSCCH, or in a higher layer signaling over PSSCH, or in a discovery signaling over PSDCH. Additionally, step <NUM> is optional as illustrated with dash lines, i.e. the remote UE determines the SL SRS transmission by itself. Alternatively, the indication information may be transmitted from the relay UE to the remote UE, which is described in step <NUM> in <FIG>.

In step <NUM>, the remote UE transmits a SL SRS that includes a single SRS or a set of SRS to the relay UE according to the indication information.

<FIG> are schematic diagrams illustrating a single SRS according to one embodiment. As illustrated in <FIG> respectively, the SL SRS may occupy the bandwidth of both SA and SL data, or may only occupy the bandwidth of SL data. Further, as illustrated in <FIG>, the indication information in SA can indicate the location of SL SRS to be transmitted in time-frequency domain, such as an offset between the SL SRS and the SL data, or indicate whether the SL SRS is transmitted or not, or indicate which SRS is transmitted.

<FIG> is a schematic diagram illustrating a set of SRS according to one embodiment. The set of SL SRS can include one or more subband SL SRS and/or one wideband SL SRS so that the set of SL SRS may occupy the whole SL bandwidth. Additionally, the time/frequency offset between two SL SRS in each set may be configured by the eNB, such as in the SL SRS configuration from eNB. Similar with the bandwidth occupation of a single SL SRS, the set of SL SRS may occupy the bandwidth of both SA and SL data, or may only occupy the bandwidth of SL data. Additionally, the subband SRS in a set of SL SRS is associated with a configured resource pool for SL transmission/reception.

An example of the set of SL SRS is described below. The set of SL SRS can be determined by the configured bandwidth for SL transmission/reception and the number of SL SRS in each set. For example, the bandwidth of SL transmission/reception is <NUM> and the number of SL SRS transmission is <NUM>. There are thus <NUM> subband SL SRS with the bandwidth of <NUM> for each subband SL SRS, and <NUM> wideband SL SRS with the bandwidth of <NUM>. Additionally, the frequency/time resource of subband SL SRS can follow legacy hopping rules.

Three examples of the indication information for the SL SRS transmission are described below. As an example, one bit field included in the indication information can be used to indicate whether the SL SRS is transmitted or not. For example, The location information of SL SRS is configured in the SL SRS configuration, the value of '<NUM>' of the indication information indicates that the SL SRS configured in the SL SRS configuration is to be transmitted, while the value of '<NUM>' indicates not.

As another example, at least one bits field included in the indication information is used to indicate which of SL SRS are transmitted. For example, the combinations of <NUM> bits represent one of <NUM> single SL SRS or <NUM> pre-configured sets of SL SRS which are determined according to the SL SRS configuration.

As yet another example, at least one bits field included in the indication information is used to indicate which of SL SRS are transmitted in a bitmap manner, e.g. whether the SL SRS represented in the corresponding bit of the bitmap is transmitted or not. For example, <NUM> bits of '<NUM>' represent that the SL SRS in subband #<NUM>, #<NUM> and the wideband SL SRS are to be transmitted, wherein the location information of the SL SRS in the time-frequency domain can be determined according to the SL SRS configuration.

Returning to <FIG>, in step <NUM>, the relay UE performs the SL channel measurement based on the received SL SRS, and then transmits the measurement result such as RSRP or CSI to the eNB. Future, the SL SRS can be used for other purposes in addition to the SL channel measurement, such as power control for relay/remote UEs.

<FIG> is a call flow illustrating that a remote UE aperiodically transmits a SL SRS to a relay UE following indication information from the relay UE in the unidirectional case according to one embodiment. The call flow in the <FIG> is similar with that in the <FIG>, except that the indication information is transmitted from the relay UE to the remote UE, and thereby the descriptions of the steps are omitted.

Another embodiment is that both the indication information and SL SRS are transmitted from the relay UE, and the remote UE performs the corresponding actions in the response to the SL SRS receiving, e.g., performs the SL channel measurement and transmits the measurement result to the relay UE (not shown). The indication information or the SL SRS can be transmitted from either the remote UE or relay UE, and correspondingly, the party which receives the SL SRS can perform the SL channel measurement based on the received SL SRS. That is, the indication information can be transmitted from either the relay UE or remote UE and indicates which of the relay UE and remote UE is transmitting the SL SRS. It should be noted that the format of the indication from the remote UE and from the relay UE may be different.

The following paragraphs describe embodiments, aspects and examples that are not specifically claimed but may be useful for understanding the invention. <FIG> is a call flow illustrating that a remote UE periodically transmits a SL SRS to a relay UE in the unidirectional case according to one embodiment. As shown in <FIG>, steps <NUM> and <NUM> are similar to steps <NUM> and <NUM> in <FIG>, and thereby the descriptions of these two steps are omitted. Similar with the option of step <NUM> and/or <NUM>, the step <NUM> and/or <NUM> are optional as illustrated by dash lines, e.g. the SL SRS configuration can be pre-configured in remote/relay UE.

In step <NUM>, the remote UE periodically transmits a SL SRS including a single SRS or a set of SRS to the relay UE. The single SL SRS has already been described above with reference to <FIG>, while the set of SL SRS has already been described above with reference to <FIG>. Additionally, the periodic transmission of SL SRS can be associated with SL SPS transmission/reception. For example, SL SRS may be on the last symbol of configured SPS transmission/reception subframes.

Additionally, the periodic SL SRS transmission in step <NUM> can be further triggered by the indication information from the relay/remote UE and/or further by the trigger information from eNB (not shown). Further, the periodic SL SRS transmission can be terminated by the indication information from the relay/remote UE and/or further by the trigger information from eNB (not shown). The examples of the indication information is described above, which is omitted for the purpose of conciseness.

In step <NUM>, the relay UE performs the SL channel measurement based on the received SL SRS, and then transmits the measurement result such as RSRP or CSI to the eNB. Future, the SL SRS can be used for other purposes in addition to the SL channel measurement, such as power control for relay/remote UEs.

Alternatively, the SL SRS may be periodically transmitted from the relay UE to the remote UE, and correspondingly, the SL channel measurement can be performed by the remote UE, which is illustrated in steps <NUM> and <NUM> in <FIG>. Other steps in <FIG> are similar with that in <FIG>, thereby the corresponding descriptions are omitted for the purpose of conciseness.

That is, the SL SRS can be periodically transmitted from either the remote UE or relay UE, and correspondingly, the party which receives the SL SRS performs the corresponding actions in the response to the SL SRS receiving, e.g., performs the SL channel measurement based on the received SL SRS.

The following is related to a claimed embodiment. <FIG> is a schematic diagram illustrating SL channel measurement in the bidirectional relay case according to one embodiment. As shown in <FIG>, the eNB transmits SL SRS configuration to a relay UE over DL, and then the relay UE forwards the SL SRS configuration to the remote UE. The relay/remote UE transmits SL SRS for one time, which is referred to as aperiodic transmission, or periodically. The remote/relay UE performs the SL channel measurement based on the received SL SRS, and then the relay UE transmits the measurement result such as RSRP or CSI to the eNB. Additionally, as shown in <FIG>, there is not a direction link between eNB and a remote UE. The remote UE thus does not perform the DL channel measurement, comparing with <FIG>.

As illustrated in <FIG>, the SL SRS configuration is received from the eNB to the relay UE and then forwarded from the relay UE to the remote UE. However, the SL SRS configuration may be pre-configured in both the remote UE and the relay UE, or the SL SRS configuration may be selected from a resource pool for SL transmission/reception by the relay UE. The definition of the SL SRS configuration is the same as in the above description, which is omitted for the purpose of the conciseness.

The following paragraphs describe embodiments, aspects and examples that are not specifically claimed but may be useful for understanding the invention. <FIG> is a call flow illustrating that a remote UE aperiodically transmits a SL SRS to a relay UE following indication information from the relay UE in the bidirectional case according to one embodiment. As shown in <FIG>, the eNB transmits a SL SRS configuration to the relay UE on DL in step <NUM>, such as by higher layer signaling (RRC signaling). Alternatively, the relay UE selects the SL SRS configuration according to the resource pool for SL transmission/reception, as shown in step <NUM>'. The relay UE forwards the SL SRS configuration to the remote UE in step <NUM>, such as by a higher layer signaling over PSSCH or by a discovery signaling over PSDCH. Steps <NUM>, <NUM>' and/or <NUM> are optional as illustrated with dash lines, e.g. the SL SRS configuration can be pre-configured in remote/relay UE.

In step <NUM>, the eNB transmits trigger information for SL SRS transmission to the relay UE. The trigger information may be in a downlink control signaling such as DCI over PDCCH, or in a higher layer signaling such as a discovery response to the relay UE in the procedure of relay UE discovery, or over a piggyback in a higher layer signaling. The trigger information may indicate location information of the SL SRS to be transmitted in the frequency-time domain, such as a time/frequency offset between SL SA/data and SL SRS to be transmitted.

Alternatively, the eNB may transmit a SL SRS to the relay UE in step <NUM>, i.e. the eNB selects the SL SRS. The SL SRS selected by eNB may be a single SRS or a set of SRS, as described above.

In step <NUM>, the relay UE transmits indication information to the remote UE according to the received trigger in step <NUM>, wherein the indication information indicates the SRS transmission and indicates that the SL SRS is to be transmitted by the remote UE. The indication information may be in sidelink control signaling such as SCI over PSCCH, or in a higher layer signaling over PSSCH, or in a discovery signaling over PSDCH. Additionally, step <NUM> is optional as illustrated with dash lines, i.e. the relay UE determines the SL SRS transmission by itself. The examples of the indication information is described above, which is omitted for the purpose of conciseness.

In step <NUM>, the remote UE transmits a SL SRS including a single SRS or a set of SRS, which are described above with reference to <FIG> and <FIG>, to the relay UE according to the indication information.

Alternatively, both the indication information and the SL SRS may be transmitted from the remote UE to the relay UE, and correspondingly, the SL channel measurement can be performed by the relay UE based on the received SL SRS, which is described in steps <NUM> and <NUM> in <FIG>. Other steps in <FIG> are similar with that in <FIG>, thereby the descriptions thereof are omitted for the purpose of conciseness.

Another embodiment is that both the indication information and SL SRS are transmitted from the relay UE, and the remote UE performs the corresponding actions in the response to the SL SRS receiving, e.g., performs the SL channel measurement and transmits the measurement result to the relay UE (not shown). That is, the indication information can be transmitted from either the relay UE or remote UE and indicates which of the relay UE or remote UE is transmitting the SL SRS. It should be noted that the format of the indication from the remote UE and from the relay UE may be different.

<FIG> is a call flow illustrating that a remote UE periodically transmits a SL SRS to a relay UE in the bidirectional case according to one embodiment. As shown in <FIG>, steps <NUM>/<NUM>' and <NUM> are similar with steps <NUM>/<NUM>' and <NUM> in <FIG>, thereby the descriptions of these two steps are omitted. Similar with the option of steps <NUM> and/or <NUM>, the step <NUM> and/or <NUM> are optional as illustrated in dash lines, e.g. the SL SRS configuration can be pre-configured in remote/relay UE.

Additionally, the periodic SL SRS transmission in step <NUM> can be further triggered by the indication information from the relay/remote UE and/or further by the trigger information from eNB (not shown). Further, the periodic SL SRS transmission can be terminated by the indication information from the relay/remote UE and/or further by the trigger information from eNB (not shown). The examples of the indication information is described above, which is omitted for the purpose of conciseness. In step <NUM>, the relay UE performs the SL channel measurement based on the received SL SRS, and then transmits the measurement result such as RSRP or CSI to the eNB. Future, the SL SRS can be used for other purposes in addition to the SL channel measurement, such as power control for relay/remote UEs.

Alternatively, the SL SRS may be periodically transmitted from the relay UE to the remote UE, and correspondingly, the SL channel measurement is performed by the remote UE, which is illustrated in steps <NUM> and <NUM> in <FIG>. Other steps in <FIG> are similar with that in <FIG>, thereby the corresponding descriptions are omitted for the purpose of conciseness.

The following is related to a claimed embodiment. <FIG> is a schematic block diagram illustrating components of a relay/remote UE according to one embodiment.

Relay/Remote UE1100 is an embodiment of Relay/Remote UE described from <FIG>. Furthermore, Relay/Remote UE <NUM> may include a processor <NUM>, a memory <NUM>, and a transceiver <NUM>. In some embodiments, Relay/Remote UE <NUM> may include an input device <NUM> and/or a display <NUM>. In certain embodiments, the input device <NUM> and the display <NUM> may be combined into a single device, such as a touch screen.

The processor <NUM> is communicatively coupled to the memory <NUM>, the input device <NUM>, the display <NUM>, and the transceiver <NUM>.

In some embodiments, the processor <NUM> controls the transceiver <NUM> to transmit UL signals to Network Equipment <NUM> and/or receive DL signals from Network Equipment <NUM>. For example, the processor <NUM> may control the transceiver <NUM> to transmit CSI/RSRP as a SL channel measurement result to a network equipment such as eNB in the case that UE <NUM> is a relay UE. In another example, the processor <NUM> may control the transceiver <NUM> to receive a higher layer signaling such as RRC signaling including a SL SRS configuration, or a download control signaling such as a DCI format over PDCCH including trigger information for SL SRS transmission in the case that UE <NUM> is a remote or relay UE, as described above. In certain embodiments, the processor <NUM> may monitor DL signals received via the transceiver <NUM> for specific messages. For example, the processor <NUM> may monitor the trigger information for SL SRS transmission from a network equipment such as eNB.

The memory <NUM>, in one embodiment, is a computer-readable storage medium. For example, the memory <NUM> may include RAM, including dynamic RAM ("DRAM"), synchronous dynamic RAM ("SDRAM"), and/or static RAM ("SRAM"). For example, the memory <NUM> may include a hard disk drive, flash memory, or any other suitable non-volatile computer storage device. In some embodiments, the memory <NUM> stores data relating to the SL SRS configuration received from the network equipment. In some embodiments, the memory <NUM> also stores program code and related data, such as an operating system or other controller algorithms operating on Relay/Remote UE <NUM>.

Relay/Remote UE <NUM> may optionally include an input device <NUM>. In some embodiments, the input device <NUM> may be integrated with the display <NUM>, for example, as a touch screen or similar touch-sensitive display. In some embodiments, the input device <NUM> includes a touch screen such that text may be inputted using a virtual keyboard displayed on the touch screen and/or by handwriting on the touch screen. In certain embodiments, the input device <NUM> may include one or more sensors for monitoring an environment of Relay/Remote UE <NUM>.

Relay/Remote UE <NUM> may optionally include a display <NUM>. For example, the display <NUM> may include, but is not limited to being, an LCD display, an LED display, an OLED display, a projector, or a similar display device capable of outputting images, text, or the like, to a user. As another non-limiting example, the display <NUM> may include a wearable display such as a smart watch, smart glasses, a heads-up display, or the like.

In certain embodiments, the display <NUM> may include one or more speakers for producing sound. For example, the input device <NUM> and display <NUM> may form a touch screen or similar touch-sensitive display.

The transceiver <NUM>, in one embodiment, is configured to communicate wirelessly with the network equipment such eNB. In certain embodiments, the transceiver <NUM> comprises a transmitter <NUM> and a receiver <NUM>. The transmitter <NUM> is used to transmit UL communication signals to the network equipment and the receiver <NUM> is used to receive DL communication signals from the network equipment. For example, the transmitter <NUM> may transmit CSI/RSRP as a SL channel measurement result to the network equipment. As another example, the receiver <NUM> may receive a SL SRS configuration from the network equipment, or a single or set of SL SRS from the remote/relay UE as a peer party thereof. The SL SRS configuration received from the network equipment may be similar with the known SoundingRS-UL-Config information element as mentioned in 3GPP TS36. <NUM>, and indicates location information of the SRS in the time-frequency domain, e.g. the time/frequency offset between SL SA/data and SL SRS, the time/frequency offset between two SL SRS, or whether the transmission of SL SRS is periodic or aperiodic, e.g. indication by a signaling parameter of 'duration'. Based on the SL SRS configuration, the transceiver <NUM> may transmit/receive the SRS for SL channel measurement with the remote/relay UE as a peer party thereof.

The transmitter <NUM> and the receiver <NUM> may be any suitable type of transmitter or receiver, respectively. Although only one transmitter <NUM> and one receiver <NUM> are illustrated, the transceiver <NUM> may have any suitable number of transmitters <NUM> and receivers <NUM>. For example, in some embodiments, Relay/Remote UE <NUM> includes a plurality of transmitter <NUM> and receiver <NUM> pairs for communicating on a plurality of wireless networks and/or radio frequency bands, each transmitter <NUM> and receiver <NUM> pair configured to communicate on a different wireless network and/or radio frequency band than the other transmitter <NUM> and receiver <NUM> pairs.

Claim 1:
An apparatus (<NUM>) comprising a first user equipment, the apparatus (<NUM>) further comprising:
a transceiver (<NUM>) configured to:
receive a sidelink sounding reference signal configuration corresponding to a sidelink sounding reference signal, SRS, from a network equipment or a sidelink, SL, apparatus comprising a second user equipment;
in response to receiving the sidelink sounding reference signal configuration from the network equipment:
transmit the sidelink sounding reference signal configuration to the sidelink apparatus comprising the second user equipment; and
transmit the sidelink sounding reference signal to the sidelink apparatus comprising the second user equipment; and
in response to receiving the sidelink sounding reference signal configuration from the sidelink apparatus, transmit the sidelink sounding reference signal to the sidelink apparatus comprising the second user equipment.