Method and apparatus for transmitting data based on channel status in device-to-device communication

Abstract

A method and apparatus for transmitting data based on a channel state in device-to-device communication are provided. A method for performing device-to-device (D2D) communication by a first device includes: obtaining at least one measurement value corresponding to a relative speed between the first device and a second device; adjusting at least one transmission parameter based on the at least one measurement value; providing the adjusted at least one transmission parameter to the second device; and transmitting data to the second device based on the adjusted at least one transmission parameter.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 982,357, filed in the U.S. Patent and Trademark Office on February 27, 2020, and Korean Patent Application No. 10-2020-0107403, filed in the Korean Intellectual Property Office on August 25, 2020, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates to wireless communications, and more particularly to a method for transmitting data based on a channel state in device-to-device (D2D) communication.

[0004] equipment. Background Art

[0005] In D2D communication, terminals communicate with each other via sidelinks, a communication method in which terminals directly transmit and receive voice or data without using a base station. Due to the increase in data traffic required for sidelinks and uplinks and downlinks between base stations and terminals, a method for achieving high data rates in D2D communication is needed. Summary of the Invention

[0006] Example embodiments provide a method and apparatus for performing device-to-device (D2D) communication with a high data rate.

[0007] According to an aspect of an example embodiment, a method for performing device-to-device (D2D) communication by a first device is provided, the method comprising: obtaining at least one measurement value corresponding to a relative speed between the first device and a second device; adjusting at least one transmission parameter based on the at least one measurement value; providing the adjusted at least one transmission parameter to the second device; and sending data to the second device based on the adjusted at least one transmission parameter.

[0008] According to another aspect of an example embodiment, there is provided a method for performing device-to-device (D2D) communication by a second device, the method comprising: receiving, from a first device, at least one transmission parameter adjusted by the first device based on a relative speed between the first device and the second device; and receiving data from the first device based on the at least one transmission parameter received from the first device.

[0009] According to another aspect of an example embodiment, a first device is provided, which is configured to perform device-to-device (D2D) communication with a second device, the first device comprising: at least one transceiver; and at least one processor configured to process a first signal received from the second device through the at least one transceiver and generate a second signal to be sent to the second device through the at least one transceiver, wherein the at least one processor is further configured to: obtain at least one measurement value corresponding to a relative speed between the first device and the second device; adjust at least one transmission parameter based on the at least one measurement value; provide the adjusted at least one transmission parameter to the second device through the at least one transceiver; and generate the second signal based on the adjusted at least one transmission parameter.

[0010] According to another aspect of an example embodiment, a second device is provided, which is configured to perform device-to-device (D2D) communication with a first device, the second device including: at least one transceiver; and at least one processor configured to generate a first signal to be sent to the first device through the at least one transceiver, and to process a second signal received from the first device through the at least one transceiver, wherein the at least one processor is further configured to: receive, through the at least one transceiver, at least one transmission parameter adjusted by the first device based on a relative speed between the first device and the second device, and process the second signal based on the at least one transmission parameter received from the first device. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and other aspects will be more clearly understood from the following detailed description of example embodiments taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1 is a diagram illustrating a wireless communication system according to an example embodiment;

[0013] Figure 2 is a diagram illustrating a slot structure of a radio frame according to an example embodiment;

[0014] Figure 3 is a diagram illustrating a resource unit for device-to-device (D2D) communication according to an example embodiment;

[0015] Figure 4A and Figure 4B is a diagram illustrating an example of D2D communication according to an example embodiment;

[0016] Figure 5 is a diagram illustrating frequency hopping according to an example embodiment;

[0017] Figure 6is a diagram illustrating an operation of estimating a wideband channel based on partial sounding reference signal (SRS) transmission according to an example embodiment;

[0018] Figure 7 is a diagram illustrating an SRS bandwidth configuration table according to an example embodiment;

[0019] Figure 8A and Figure 8B is a diagram illustrating an example of antenna switching in reference signal transmission according to an example embodiment;

[0020] Figure 9 is a diagram illustrating a protection period table according to an example embodiment;

[0021] Figure 10 is a diagram illustrating an example of channel estimation based on interference measurement according to an example embodiment;

[0022] Figure 11A and Figure 11B shows an example of a table referenced for determining transmission parameters according to an example embodiment;

[0023] Figure 12 shows an example of a table referenced for determining transmission parameters according to an example embodiment;

[0024] Figure 13A and Figure 13B is a diagram illustrating an example of terminals communicating with each other according to an exemplary embodiment;

[0025] Figure 14 is a flowchart illustrating a method of performing D2D communication according to an example embodiment;

[0026] Figure 15A and Figure 15B is a flowchart illustrating an example of a method of performing D2D communication according to an example embodiment;

[0027] Figure 16A 、 Figure 16B and Figure 17 is a flow chart illustrating an example of a table referenced by reporting channel state information (CSI) according to an example embodiment;

[0028] 18A to 18E is a diagram illustrating an example of a table to which CSI is reported according to an example embodiment;

[0029] Figure 19 is a diagram illustrating an example of CSI feedback according to an example embodiment;

[0030] Figure 20A and Figure 20Bis a flowchart illustrating an example of a method of performing D2D communication according to an example embodiment;

[0031] Figure 21 is a diagram illustrating an example of a terminal performing D2D communication according to an exemplary embodiment; and

[0032] Figure 22 is a block diagram illustrating signal processing operations for transmission according to an example embodiment. DETAILED DESCRIPTION

[0033] Figure 1 is a diagram illustrating a wireless communication system 10 according to an example embodiment. The wireless communication system 10 may be referred to as a radio access technology (RAT) system, and in a non-limiting embodiment, the wireless communication system 10 may include any wireless communication system based on multiple access such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), or single carrier frequency division multiple access (SC-FDMA). For example, the third generation partnership project (3GPP) long term evolution (LTE) may use OFDMA in the downlink (DL) and SC-FDMA in the uplink (UL), and LTE-Advanced (LTE-A) may correspond to an advanced version of 3GPP LTE. In addition, LTE-A was followed by the fifth generation wireless (5G) new radio (NR) to achieve high performance and short latency, and 5G NR may use all available spectrum resources, such as low frequency bands less than 1 GHz, mid-frequency bands from 1 GHz to 10 GHz, and high frequency (millimeter wave) bands of 24 GHz or higher. Hereinafter, the wireless communication system 10 may be assumed to be LTE-A and / or 5G NR, but it may be understood that the embodiments are not limited thereto.

[0034] The base station 15 may represent a fixed station that communicates with the first terminal 11 or the second terminal 12 and / or another base station and may communicate with the first terminal 11 or the second terminal 12 and / or other base stations to exchange data and control information. For example, the base station 15 may be referred to as a node B, an evolved node B (eNB), a next-generation node B (gNB), a sector, a site, a base transceiver system (BTS), an access point (AP), a relay node, a remote radio head (RRH), or a radio unit (RU). Here, the base station 15 or cell may be understood as meaning any function or any meaning representing a portion of an area covered by a base station controller (BSC) in CDMA, a node B in WCDMA, an eNB in ​​LTE, and a sector (site) or gNB in ​​5G NR. The base station 15 or cell may cover various coverage areas, such as a macro cell, a macro cell, a micro cell, a pico cell, a femto cell, a relay node, an RRH, a RU, or a small cell communication range.

[0035] The first terminal 11 and the second terminal 12 may be fixed or mobile and may represent any device for communicating with the base station 15 to transmit and receive data and / or control information. For example, the terminal may be referred to as a user equipment (UE), a terminal device, a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscription station (SS), a wireless device, or a handheld device. Figure 1 , the first terminal 11 can communicate with the base station 15 through the uplink UP and the downlink DL, and can communicate with the second terminal 12 through the side link SL. For example, the first terminal 11 can send a signal (referred to as a side link signal) to the second terminal 12 by using a specific resource unit in a resource pool corresponding to a series of resources, and the second terminal 12 can detect the signal sent from the first terminal 11 from the resource pool of the signal that the first terminal 11 can send. When the first terminal 11 is within the accessible range of the base station 15, the base station 15 can notify the first terminal 11 of the resource pool, and when the first terminal 11 is out of the accessible range of the base station 15, the first terminal 11 can receive information about the resource pool from another terminal, or the resource pool can be set based on a set of predetermined resources. As described below with reference to Figure 3 As described above, the resource pool may include multiple resource units, and the first terminal 11 may use at least one resource unit to transmit a signal to the second terminal 12. Here, the first terminal 11 transmitting data may be referred to as a first device, and the second terminal 12 receiving data may be referred to as a second device.

[0036] The communication performed between the first terminal 11 and the second terminal 12 through the side link SL can be referred to as D2D communication. As an example of D2D communication, vehicle-to-everything (V2X) can refer to a communication technology in which a vehicle exchanges information with another vehicle, pedestrians, and things equipped with infrastructure through the side link SL. V2X can refer to a terminal with high mobility and high power performance like a vehicle. For example, V2X can include vehicle-to-base station (V2B), vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P), vehicle-to-roadside unit (V2R), vehicle-to-vehicle (V2V), and vehicle-to-network (V2N) (see "3GPP TS 38.885, NR; Study on Vehicle-to-Everything (Release 16)" (hereinafter referred to as "Document 1")). In some embodiments, when a network device such as base station 15 transmits and receives signals based on D2D communication, base station 15 can be considered a terminal for D2D communication. For example, the description will focus on a case where first terminal 11 wishes to transmit data to second terminal 12 (or a case where second terminal 12 wishes to receive data from first terminal 11), but the embodiments can also be applied to a case where second terminal 12 wishes to receive data from base station 15 or a roadside unit (RSU). Furthermore, the embodiments will be primarily described with reference to D2D communication, but the embodiments can also be applied to GSM Edge RAN (GERN) or other communications other than D2D communication.

[0037] Because D2D communication requires high data rates, first terminal 11 and second terminal 12 can communicate with each other based on transmission parameters determined based on channel conditions. For example, first terminal 11 can determine transmission parameters based on the estimated channel conditions and transmit the determined transmission parameters to second terminal 12, which can then transmit data to second terminal 12. Second terminal 12 can process the signal received from first terminal 11 based on the transmission parameters provided by first terminal 11, thereby obtaining the data transmitted by first terminal 11. Sidelinks (SLs) can have characteristics different from those of uplinks (ULs) and / or downlinks (DLs). Therefore, channel state-based data transmission in D2D communication may require new methods. As described below with reference to the accompanying drawings, according to example embodiments, efficient channel state estimation can be provided in D2D communication, thereby minimizing the overhead associated with channel state estimation. Furthermore, because various factors are considered, channel conditions can be accurately estimated, thereby enabling optimal transmission parameters to be determined in D2D communication and achieving an optimal data rate.

[0038] Figure 2 is a diagram illustrating a time slot structure of a radio frame according to an example embodiment. In some embodiments, Figure 2 The time slot structure can correspond to the time slot structure of 5G NR.

[0039] Reference Figure 2 , a time slot may include multiple symbols (e.g., multiple orthogonal frequency division multiple access (OFDM) symbols) with respect to the time axis. For example, one time slot in a normal cyclic prefix (CP) may include fourteen symbols, and one time slot in an extended CP may include twelve symbols. As another example, one time slot in a normal CP may include seven symbols, and one time slot in an extended CP may include six symbols.

[0040] A carrier may include a plurality of subcarriers (e.g., a maximum of 3,300 subcarriers) relative to the frequency axis. A resource block RB may correspond to a plurality of consecutive subcarriers (e.g., twelve subcarriers) relative to the frequency axis. A bandwidth part (BWP) may be defined as a plurality of consecutive resource blocks (or a plurality of physical resource blocks (PRBs)) relative to the frequency axis and may correspond to a value such as a subcarrier spacing (SCS), a CP length, etc. A carrier may include a maximum of N (e.g., N is 5) BWPs, and data transmission may be performed based on the activated BWPs. One unit in a resource grid may be referred to as a resource element RE, and a complex symbol may be mapped to one resource element.

[0041] In some embodiments, a BWP may be defined relative to a sidelink, and the same sidelink BWP may be used for both transmission and reception. Figure 1 The first terminal 11 can transmit a sidelink channel and / or a sidelink signal via a specific BWP, and the second terminal 12 can receive the sidelink channel and / or the sidelink signal via a corresponding BWP. In a licensed carrier, the sidelink BWP can be defined independently of the uplink / downlink BWP (i.e., Uu BWP), and the sidelink BWP can have separate configuration signaling independent of the Uu BWP. For example, the first terminal 11 and / or the second terminal 12 can receive settings for the sidelink BWP from the base station 15. The sidelink BWP can be pre-set in the carrier for terminals out of coverage and terminals in RRC_IDLE mode, and in terminals in RRC_CONNECTED mode, at least one sidelink BWP can be activated in the carrier.

[0042] Figure 3 is a diagram illustrating resource units for D2D communication according to an example embodiment. Figure 3, the total frequency resources of the resource pool RP can be divided into N F units, and the total time resources of the resource pool RP can be divided into N T Therefore, a total of N units can be defined in the resource pool RP. F ×N T resource units. Figure 3 Shown with N T An example of a resource pool that repeats for a period corresponding to subframes.

[0043] In some embodiments, as Figure 3 As shown, a resource unit (e.g., unit #0) can be periodically repeated and provided. In some embodiments, on the time axis or frequency axis, in order to obtain a diversity effect, the index of the physical resource unit mapped to a logical resource unit can change based on a predetermined pattern relative to time. As described above, the resource pool RP can correspond to a set of resource units available to the terminal that wishes to send a side link signal. In some embodiments, the resource pool RP can be divided into a physical side link control channel (PSCCH), a physical side link shared channel (PSSCH), a physical side link discovery channel (PSDCH), a physical side link broadcast channel (PSBCH), and a physical side link feedback channel (PSFCH) based on the content of the side link signal.

[0044] Figure 4A and Figure 4B is a diagram illustrating an example of D2D communication according to an exemplary embodiment. In detail, Figure 4A and Figure 4B An example of a terminal is shown in which vehicles perform D2D communication based on a channel state.

[0045] Reference Figure 4A , the channel state between the first terminal 41a and the second terminal 42a can be estimated based on the CSI feedback. Figure 4A As shown, the first terminal 41a can send at least one reference signal to the second terminal 42a. For example, the first terminal 41a can send at least one reference signal for the downlink to the second terminal 42a. The second terminal 42a can receive at least one reference signal from the first terminal 41a and estimate the channel state based on the at least one received reference signal, thereby generating channel state information (CSI). For example, the CSI may include at least one of a channel quality indicator (CQI), a rank indicator (RI), a precoding matrix indicator (PMI), a layer indicator (LI), a CSI-RS resource indicator (CRI) and a reference signal received power (L1-RSRP) corresponding to the CRI, and an SRS resource indicator (SRI) and a L1-RSRP corresponding to the SRI.

[0046] The second terminal 42a may transmit CSI to the first terminal 41a. For example, the second terminal 42a may transmit CSI to the first terminal 41a via the PSFCH. Transmitting CSI from the second terminal 42a to the first terminal 41a may be referred to as CSI feedback or CSI reporting.

[0047] In some embodiments, the first terminal 41a can pre-select a precoder to be used in transmitting data, and can send a reference signal (e.g., DRMS, precoded CSI-RS, and precoded SRS) to which the selected precoder is applied to the second terminal 42a. The second terminal 42a can assume an identity matrix as a precoder, and can calculate CSI (e.g., RI and / or CQI) based on the identity matrix. Whether to use a precoded reference signal can be predefined and / or pre-set through high-layer signaling such as radio resource control (RRC), or the first terminal 41a and / or the second terminal 42a can be instructed whether to use a precoded reference signal. In addition, an indicator indicating whether a precoded reference signal is used can be included in (dynamic) control signaling, through which a non-periodic reference signal trigger is sent, and the first terminal 41a and / or the second terminal 42a can identify whether to use a precoded reference signal based on the corresponding indicator.

[0048] In some embodiments, the first terminal 41a may transmit a precoded reference signal such that the precoded reference signal port is a candidate DMRS port in actual transmission, i.e., represents a data layer. The first terminal 41a may apply a precoder applied to each layer from among the candidate precoders to different precoded reference signal ports, and the second terminal 42a may select at least one reference signal port index (e.g., an index applied by a precoder desired for data transmission), and may report the selected at least one reference signal port index to the first terminal 41a. The second terminal 42a may assume that the number of selected and reported reference signal port indices matches the number of ranks and that a channel of each reference signal port is used for each layer transmission, and the second terminal 42a may calculate and report a CQI.

[0049] In some embodiments, when DMRS is transmitted as at least one reference signal, similar to the above description, CSI can be reported based on the transmission of a precoded reference signal. For example, when the second terminal 42a receives and measures DMRS, the second terminal 42a can assume that the same precoder is applied to the frequency axis based on the size of the precoding RB group (PRG), and can estimate the channel state. When a DMRS associated with the PSBCH is received, the PSBCH can be received only through a portion of the frequency band of the entire BWP, and the second terminal 42a can assume that the channel for receiving the DMRS is constant throughout the PSSCH frequency band, and can report wideband CSI.

[0050] In some embodiments, the second terminal 42a may independently use the measurement results of the time slots in which the reference signal has been received when generating CSI, and may not apply inter-slot filtering such as averaging, interpolation, and extrapolation. Figure 1 As described above, due to the high mobility of terminals, channels can change rapidly in V2X. Therefore, inter-slot filtering can be excluded, as it may reduce the accuracy of channel estimation due to the rapidly changing channel state over time slot units. For example, with respect to time-domain channel measurement restrictions, regardless of the setting of the parameter "timeRestrictionForChannelMeasurements" for preventing inter-slot channel averaging in the time domain, channel state estimation in V2X can always be performed as if "timeRestrictionForChannelMeasurements = Enabled".

[0051] In some embodiments, when time-domain channel measurement restrictions such as "timeRestrictionForChannelMeasurements" are disabled in low-speed V2X scenarios, the second terminal 42a may allow inter-slot channel averaging in the time domain and may apply, for example, averaging, infinite impulse response (IIR) filtering, and interpolation to the results obtained across the measurement slots, thereby improving the accuracy of the measurement results. To this end, the first terminal 41a may not change the precoder applied to the reference signal, or may not apply the precoder to the reference signal.

[0052] The first terminal 41a may receive CSI from the second terminal 42a and may determine at least one transmission (TX) parameter based on the CSI. The transmission parameter may be a parameter used to define a method for transmitting data from the first terminal 41a to the second terminal 42a and may be referred to as a scheduling parameter. For example, the transmission parameter may include at least one of a modulation and coding scheme (MCS) index, a precoding index, and a rank index. The first terminal 41a may transmit the determined at least one transmission parameter to the second terminal 42a and may transmit data to the second terminal 42a based on the determined at least one transmission parameter. The second terminal 42a may process the signal received from the first terminal 41a based on the at least one transmission parameter received from the first terminal 41a to obtain data.

[0053] Reference Figure 4B , the channel state between the first terminal 41b and the second terminal 42b can be estimated based on the reference signal provided from the second terminal 42b, so, Figure 4A The CSI feedback (or CSI report) can be omitted. Figure 4B As shown, the second terminal 42b may transmit at least one reference signal to the first terminal 41b. In some embodiments, the second terminal 42b may transmit at least one reference signal for an uplink (UL) to the first terminal 41b. The first terminal 41b may receive the at least one reference signal from the second terminal 42b.

[0054] First terminal 41b may estimate the channel state based on the received at least one reference signal. For example, first terminal 41b may estimate the channel state corresponding to the transmission from second terminal 42b to first terminal 41b based on the at least one reference signal, and may estimate the channel state corresponding to the transmission from first terminal 41b to second terminal based on the estimated channel reciprocity. First terminal 41b may determine at least one transmission parameter based on the final estimated channel state. First terminal 41b may transmit the determined at least one transmission parameter to second terminal 42b, and may transmit data to second terminal 42b based on the determined at least one transmission parameter.

[0055] In some embodiments, Figure 4A and Figure 4BIn the embodiment of the present invention, at least one reference signal may include a reference signal for an uplink UL and / or a downlink DL. For example, at least one reference signal may include a demodulation reference signal (DMRS) associated with a V2X channel (e.g., PSFCH, PSBCH, PSCCH, and PSSCH), and may also include a phase tracking reference signal (PT-RS) for a PSSCH in frequency range 2 (FR2). Moreover, at least one reference signal may include a channel state information reference signal (CSI-RS), a sounding reference signal (SRS), and an automatic gain control (AGC) training signal. Moreover, at least one reference signal may include a side link synchronization signal (SLSS), such as a primary side link synchronization signal (P-SSS) and a secondary side link synchronization signal (S-SSS). The following will refer to Figures 5 to 8B An embodiment is described in which the first terminal 41 a transmits an SRS as at least one reference signal to the second terminal 42 a .

[0056] Here, the above reference Figure 4A The D2D communication described may be referred to as a CSI feedback scheme, and the above reference Figure 4B The D2D communication described can be referred to as a channel reciprocity scheme. Figure 4A and Figure 4B Embodiments of D2D communication based on a CSI feedback scheme and / or a channel reciprocity scheme are described.

[0057] Figure 5 is a diagram illustrating frequency hopping according to an example embodiment. In some embodiments, Figure 4B The second terminal 42b can send at least one reference signal as an SRS to the first terminal 41b. Figure 4B describe Figure 5 .

[0058] When frequency hopping is enabled, the first terminal 41b can determine the position of the SRS frequency at a specific time (e.g., a specific time slot or a specific symbol) based on the frequency hopping pattern defined in "3GPP TS 36.211, Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 15)" (hereinafter referred to as "Document 2") and / or "3GPP TS 38.211, NR; Physical channels and modulation (Release 15)" (hereinafter referred to as "Document 3"), and can estimate the channel state at the determined position. In some embodiments, the first terminal 41b can collect SRS subband measurement results after completing the reception of the SRS in the entire BWP, thereby estimating the wideband channel. For example, as Figure 5 As shown, when the subband size is 4 and the wideband size is 16, four subband SRSs SB1-1, SB2-1, SB1-2, and SB2-2 can be sequentially received based on the frequency hopping pattern, and thus, SRS reception can be completed in the entire wideband.

[0059] In a non-limiting embodiment, the first terminal 41b may apply frequency interpolation (such as inverse fast Fourier transform (IFFT) or minimum mean square error (MMSE)) to the SRS subband measurement results to estimate the wideband channel. In addition, the first terminal 41b may apply the same or different weight values ​​to the subbands with respect to the frequency axis and may calculate an average value. Moreover, the first terminal 41b may reduce contamination of the channel estimate based on undesirable previous measurement results. The first terminal 41b may perform time / frequency filtering to obtain the best channel estimate from the measurement results. The signal of the desired frequency band is extracted, and the estimated channel can be obtained by applying time / frequency interpolation / extrapolation or similar schemes.

[0060] Figure 6 is a diagram illustrating an operation of estimating a wideband channel according to partial SRS transmission according to an example embodiment, and Figure 7 : is a diagram showing an SRS bandwidth configuration table according to an exemplary embodiment. Figure 5 As stated, Figure 4B The second terminal 42b can send SRS as at least one reference signal to the first terminal 41b, and can enable frequency hopping. Figure 4B To describe Figure 6 and Figure 7 , and in the description Figure 6 When, with Figure 5 The descriptions that are the same or similar may be omitted.

[0061] Due to the high mobility of vehicles, the channel state in V2X can change rapidly. Therefore, the information measured from the initially received sub-band SRS may be invalid after the SRS is received in the entire broadband. Therefore, the first terminal 41b can estimate the wideband channel based on interpolation / extrapolation and the N most recent SRS receptions, rather than estimating the channel state based on the SRS received in the entire broadband. For example, the first terminal 41b can estimate the wideband channel based on interpolation / extrapolation and the N most recent SRS receptions. Figure 6 The two most recently received subbands SRSSB1-2 and SB2-2 are shown instead of the above referenced Figure 5 The four sequentially received sub-band SRSs SB1-1, SB2-1, SB1-2 and SB2-2 are used to estimate the wideband channel.

[0062] In some embodiments, the first terminal 41b may determine N based on the SRS transmission period and / or the degree of change in the channel. Figure 7 , the SRS bandwidth configuration table of document 2 may define a frequency hopping pattern, and in this case, N may be N b_hop+1 or greater (N≥N b_hop+1 ). That is, when N=N b_hop+1 When , the total SRS frequency band can be covered based on the minimum SRS subband transmission, so the extrapolation can be minimized. Figure 7 In the table, when b_hop=0, C SRS =4 and B SRS =2 (i.e., when the SRS bandwidth is 16 RB and the SRS subband is 4 RB), as Figure 6 As shown, the total SRS bandwidth can be covered based on at least 2 SRS subband transmissions (N2=2). In some embodiments, when uniform channel estimation of wideband SRS is desired, when k=b hop +1, b hop +2,…,(B SRS -1), N can be determined as

[0063] In some embodiments, N may be set in the first terminal 41b, or the base station may set N and instruct the first terminal 41b to set N. Therefore, the first terminal 41b can reduce the time taken to estimate the channel state based on the SRS. Figure 4A In the CSI feedback scheme of , when at least one reference signal includes SRS and frequency hopping is enabled, it can be similar to Figure 4BThe channel reciprocity scheme is used to set N, so Figure 4A The second terminal 42a can reduce the time it takes to generate CSI based on the SRS and can more freely set the time to feed back (or report) the CSI (for example, the period or offset in periodic feedback).

[0064] Similar to the above description, the decimation of the reference signal can be defined. For example, when the number of sub-band SRS transmissions corresponding to the total bandwidth is K, it can be determined by SRS is sent to estimate the channel state of the total bandwidth And in this case, D can be the decimation factor. In some embodiments, when k=b hop +1, b hop +2, ..., B SRS When D can be And when k=b hop When +1, the maximum value of D can appear.

[0065] In some embodiments, SRS can be transmitted aperiodically. V2X may have relatively limited channels, and periodic transmission of SRS may result in high overhead. Therefore, aperiodic SRS can be applied in V2X. For example, Figure 4B The first terminal 41b can instruct the second terminal 42b to send SRS through the PSCCH, and Figure 4A The first terminal 41a can notify the second terminal 42a of the transmission of the SRS and the aperiodic CSI triggering, so that Figure 4A The first terminal 41a may instruct the second terminal 42a to measure the reference signal.

[0066] In some embodiments, frequency hopping may occur within a time slot and / or a subframe. For example, intra-time slot / subframe SRS frequency hopping may be applied in V2X. Thus, an SRS with frequency hopping applied may be transmitted in a relatively short period of time, thereby enabling more accurate and rapid estimation of a wideband channel.

[0067] In some embodiments, SRS repetition can be used, so that the channel state can be estimated more accurately. For example, in V2X, the same SRS can be sent over multiple OFDM symbols with respect to the time axis, and Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b can measure the repeatedly received SRS, and thus can estimate the channel state more accurately.

[0068] Figure 8A and Figure 8B is a diagram illustrating an example of antenna switching in reference signal transmission according to an example embodiment, and Figure 9is a diagram illustrating a protection period table according to an example embodiment. In detail, Figure 8A and Figure 8B An example of antenna switching in SRS transmission is shown, and Figure 9 is a table showing the minimum guard period GP between two SRS resources of an SRS resource set for antenna switching ("3GPP TS 38.214, NR; Physical layer procedures for data (Release 16)" (3GPP TS 38.214, NR; Physical layer procedures for data (Release 16)) (hereinafter referred to as "Document 4"). In some embodiments, Figure 4B The second terminal 42b can send SRS to the first terminal 41b based on antenna switching. Figure 4B describe Figure 8A 、 Figure 8B and Figure 9 .

[0069] In some embodiments, antenna switching can be applied to the transmission of the reference signal, so that the channel state can be estimated more accurately. For example, in a time division duplex (TDD) channel, the second terminal 42b may include a limited number of transceiver units TXRU, and therefore, the second terminal 42b may include more RX antenna ports than the number of TX antenna ports. In this case, the state of the channel (e.g., uplink channel) estimated based on the SRS transmission performed through the TX antenna port of the second terminal 42b may not accurately reflect the state of the channel occurring in the reception performed through the RX antenna port of the second terminal 42b, and therefore, the accuracy of estimating the channel state based on channel reciprocity may be reduced.

[0070] The second terminal 42b can perform antenna switching so that the TX antenna port can cover the RX antenna port (e.g., all RX antenna ports) in SRS transmission, and thus can estimate the channel state more accurately based on channel reciprocity. Figure 8A As shown, the second terminal 42b may include the transceiver 200, and the second terminal 42b may include one TX antenna port and two RX antenna ports. SRS#1 may be transmitted through antenna port TX#1, and then antenna switching may be performed and SRS#0 may be transmitted through antenna port TX#0. Therefore, as Figure 8B As shown, the first terminal 41b may sequentially receive SRS#0, SRS#1, and a short physical uplink control channel (SPUCCH) through the PUSCH, and may insert a guard period GP between SRS#0, SRS#1, and the SPUCCH.

[0071] In some embodiments, antenna switching can be applied to the transmission of another reference signal as well as the aforementioned SRS. For example, the second terminal 42b can transmit a CSI-RS as at least one reference signal to the first terminal 41b. The first terminal 41b can measure the CSI-RS received from the second terminal 42b to estimate the channel state, and can transmit data to the second terminal 42b based on at least one transmission parameter determined based on the estimated channel state and channel reciprocity. In the second terminal 42b, the second terminal 42b can be implemented with fewer TX antenna ports than RX antenna ports, and therefore, the second terminal 42b can apply antenna switching when transmitting the CSI-RS.

[0072] When performing antenna switching from a first CSI-RS port group to a second CSI-RS port group when transmitting CSI-RS, the CSI-RS port group and the second CSI-RS port group may be defined using different symbols. For example, when the second terminal 42b is implemented with T TX antenna ports and R RX antenna ports (where T < R, and T and R are integers greater than 1), the second terminal 42b may perform antenna switching based on the CSI-RS resources defined as follows.

[0073] 1) A CSI-RS resource set, where R / T CSI-RS resources of T ports are provided in different R / T symbols;

[0074] 2) One CSI-RS resource in which a frequency-domain code division multiplexing (FD-CDM) group with a length of T is provided in different R / T symbols.

[0075] The second terminal 42b may measure the aggregate channel in association with the CSI-RS resources included in the CSI-RS resource set of item 1) instead of deriving a CSI-RS resource index (CRI).

[0076] In some embodiments, the first terminal 41b may provide an indicator to the second terminal 42b, which indicates antenna switching for CSI-RS resources and / or CSI-RS resource sets, so that the corresponding CSI-RS resources and / or CSI-RS resource sets can be distinguished from CSI-RS resource sets used for beam management or hybrid beamforming.

[0077] In some embodiments, when the second terminal 42b transmits CSI-RS, a time gap for antenna switching may be inserted, and the second terminal 42b may not transmit any information (e.g., signal, reference signal, control information, data information, etc.) during the time gap. For example, in item 1), a time gap may be inserted between two CSI-RS resources, and in item 2), a time gap may be inserted between two CSI-RS CDM groups. In some embodiments, the time gap may be defined and set by symbol units and may be set based on the subcarrier spacing. For example, in document 4, Figure 9 A table defining a minimum guard period between two SRS resources may be applied to the operation of setting a time gap.

[0078] Figure 10 is a diagram illustrating an example of channel estimation based on interference measurement according to an example embodiment. In detail, Figure 10 An example of estimating a channel state based on an SRS to which frequency hopping is applied is shown. In some embodiments, Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b can more accurately measure the channel state based on the interference and at least one reference signal received from the paired terminal. Figure 4A and Figure 4B describe Figure 10 .

[0079] In order to make Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b measures interference and may additionally set and use at least one of the following resources and at least one reference signal received from a third-party terminal.

[0080] -CSI-IM (CSI-Interference Measurement) (or Blank-RE scheme)

[0081] -NZP (non-zero power) CSI-RS for interference measurement

[0082] -SRS for interference measurement

[0083] -AGC training signal

[0084] -P-SSS, S-SSS

[0085] For example, CSI-IM can be used to measure inter-cell interference and / or inter-terminal interference. Figure 4A The second terminal 42a and / or Figure 4B The estimation of the channel state performed by the first terminal 41b can be more accurate.

[0086] In some embodiments, when CSI-IM or a blank-RE scheme similar thereto is applied, more resource elements (e.g., the entire symbol period) than the 4-port CSI-RS pattern of CSI-IM can be set and used to more accurately measure interference. To this end, CSI-IM can be set based on at least one CSI-IM symbol index. Unlike the base station, symbol-level rate matching at any position in the terminal can be limited. Therefore, CSI-IM in D2D communication can be limited to the position of the first symbol and / or the last symbol of the area where the shared channel is set. Therefore, at least one CSI-IM symbol index can be simplified to indicate at least one of the first symbol and the last symbol.

[0087] In some embodiments, Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b may regard the portion other than the at least one reference signal received from the paired terminal as interference. For example, a separate resource for interference measurement may not be set in D2D communication. Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b can be in addition to the paired terminal (ie, Figure 4A The first terminal 41a and / or Figure 4B The portion other than the at least one reference signal received by the second terminal 42b) is regarded as interference to measure the interference by using the NZP signal (for example, CSI-RS and SRS) set for estimating the channel state.

[0088] In some embodiments, Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b can measure the interference in the wireless resource that does not transmit at least one reference signal. For example, in the case where an SRS is received based on a frequency hopping pattern for estimating a channel state, Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b can measure the interference in the frequency domain where the SRS is not transmitted. Figure 10 As shown, when receiving the subband SRS SB1-1 corresponding to the size of four resource elements RE in the wideband corresponding to the size of sixteen resource elements RE, Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b may measure interference in the other twelve resource elements RE.

[0089] Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b may estimate the channel state based on channel and / or interference measurements. For example, Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b may determine the RI and / or PMI based on channel and / or interference measurements. Figure 4A The second terminal 42a and / or Figure 4B The first terminal 41b may determine the optimal CQI based on channel and / or interference measurements, and may determine the CQI based on, for example, capacity according to channel and interference measurements or a channel state criterion that is a good indicator of capacity.

[0090] Figure 11A and Figure 11B An example of a table referenced for determining transmission parameters according to an exemplary embodiment is shown. Figure 11A shows the modulation order, transport block size (TBS) and redundancy version table for the physical uplink shared channel (PUSCH), and Figure 11B A table showing the modulation and coding scheme (MCS) index for the NR physical downlink shared channel (PDSCH) (NR PDSCH) and PUSCH is shown. In some embodiments, Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b can refer to Figure 11A Table and / or Figure 11B In the following, reference will be made to Figure 4A and Figure 4B describe Figure 11A and Figure 11B .

[0091] The MCS may represent information including a coding rate and a modulation order used for data encoding and mapping. Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b can refer to Figure 11A Table and / or Figure 11B The table to determine the MCS index. For example, Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b can refer to Figure 11A The table determines the MCS index corresponding to the modulation order, TBS index and redundancy version used to transmit data. Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b can refer to Figure 11B The table determines the MCS index corresponding to the modulation order, coding rate and spectrum efficiency used to send data. Figure 4A and Figure 4B As stated, Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b can provide the determined MCS index as a transmission parameter to Figure 4A The second terminal 42a and / or Figure 4B The second terminal 42b can be predefined in LTE Figure 11A Table ("3GPP TS 36.213, LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (3GPP TS 36.213, LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures")) (hereinafter referred to as "Document 5") and may be predefined in NR Figure 11B Table (“3GPP TS 38.214, NR; Physical layer procedures for data (3GPP TS 38.214, NR; Physical layer procedures for data)” (hereinafter referred to as “Document 6”).

[0092] Figure 12 An example of a table referenced for determining transmission parameters according to an exemplary embodiment is shown. Figure 12 The left area shows the 4-bit CQI table for NR, and Figure 12 The right area of ​​​​shows the MCS index table for NR PDSCH and PUSCH. In some embodiments, Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b can refer to Figure 12 In the following, reference will be made to Figure 4A and Figure 4B describe Figure 12 , and the rank may indicate the number of layers onto which the transmitted data is mapped, or may indicate the number of layers in LTE and NR.

[0093] In the above reference Figure 4A In the described CSI feedback scheme, the first terminal 41a can determine the time / frequency resources and transmission parameters for data transmission based on the CSI reported from the second terminal 42a. For example, the first terminal 41a can trust the RI and / or PMI reported from the second terminal 42a and can determine the MCS corresponding to the CQI reported from the second terminal 42a.

[0094] In some embodiments, the first terminal 41a may determine the final MCS index based on a CQI index and MCS index pair corresponding to the same coding rate and / or spectrum efficiency. Figure 12 The coding rate and / or spectrum efficiency corresponding to the CQI index reported from the second terminal 42a can be obtained from the CQI table shown in the left area of ​​​​ Figure 12 The MCS index corresponding to the obtained coding rate and / or spectrum efficiency is determined in the MCS table shown in the right area of ​​. Figure 12 As shown by the arrows in , when the CQI index corresponds to each of 2, 7, and 10, the first terminal 41a may determine an MCS index corresponding to each of 0, 11, and 18. In some embodiments, when the CQI index is 0 or 1, that is, when the channel state is very bad, the first terminal 41a may omit data scheduling for data transmission to the second terminal 42a until the channel state is good, and may determine the MCS index to be 1. Although Figure 12 The table is a table for NR, but it can be understood that, similar to the above description, the MCS index is determined in LTE. However, in LTE, the coding rate and / or spectrum efficiency calculated based on the TBS index and the allocated time / frequency resources can be used.

[0095] In some embodiments, in addition to the CSI provided by the second terminal 42a, the first terminal 41a may also determine the transmission parameters based on other factors that affect the channel state. For example, the first terminal 41a may also determine the MCS index based on any outer loop processing results (i.e., the results provided by the base station), and may determine the MCS index based on the error rate that occurs in the data transmission as described below. In some embodiments, the first terminal 41a may determine the initial MCS index based on the CQI, and may determine the MCS offset based on other factors, and the final MCS index may be calculated as the sum of the initial MCS index and the MCS offset (MCS index = initial MCS index + MCS offset).

[0096] In some embodiments, the first terminal 41a may determine transmission parameters based on an error history such as a frame error rate (FER) and a block error rate (BLER) of data transmission. For example, the first terminal 41a may store a history of hybrid automatic repeat request (HARQ) ACK / NACKs, and when the error rate (e.g., FER) during a specific period in the past is greater than a threshold in the history of ACK / NACKs, the first terminal 41a may determine that the CQI provided from the second terminal 42a is incorrect or that the channel state has changed, and thus, the first terminal 41a may determine an MCS offset for adjusting the initial MCS index. In some embodiments, the first terminal 41a may determine the MCS offset based only on a single ACK or NACK to reduce complexity and buffer size.

[0097] In some embodiments, when it is assumed that HARQ is not applied, the first FER, which is the FER of each transmission, may be used as a criterion. For example, when the first FER is greater than 0.1 (first FER>0.1), the first terminal 41a may reduce the MCS offset by K.offset_step_dec , and when the first FER is 0.05 or less (first FER≤0.05), the first terminal 41a may increase the MCS offset by K offset_step_inc . K offset_step_inc and K offset_step_dec The MCS offset may correspond to an increment or decrement, or may be predefined (e.g., K offset_step_inc =K offset_step_dec =1), or may be set in the first terminal 41a and / or the second terminal 42a through separate signaling such as RRC. In some embodiments, K offset_step_inc and K offset_step_dec Can be different. For example, when high stability of data transmission is required, K offset_step_inc Can be smaller than K offset_step_dec (K offset_step_inc <K offset_step_dec In some embodiments, in order to reduce the complexity of MCS determination, K offset_step_inc Can be equal to K offset_step_dec (K offset_step_inc =K offset_step_dec ).

[0098] The criterion may be predefined or may be set through separate signaling such as RRC.When the error rate E(i) such as the BLER at time point i is used as a criterion, the MCS offset may be determined as follows.

[0099] 1) MCS offset (0) = 0

[0100] 2) If E(i) <e_inc

[0101] A.MCS offset (i+1) = MCS offset (i) + K offset_step_inc

[0102] 3) If E(i)>e_dec

[0103] A.MCS offset (i+1) = MCS offset (i) - K offset_step_dec

[0104] In pseudo code, e_inc and e_dec may be thresholds compared to a standard and may be predefined, or may be set through separate signaling such as RRC.

[0105] In some embodiments, the first terminal 41a may use a weighted sum of ACK / NACK results as a criterion, thereby reducing the complexity of storing and calculating error histories. For example, the error rate E(i) at time point i may be determined as follows.

[0106] 1) Initial error history standard E(0) = 0.1

[0107] 2) If NACK

[0108] AE(i+1)=E(i)×w

[0109] 3) If ACK

[0110] AE(i+1)=E(i)×w+(1-w)

[0111] When receiving an ACK or NACK from the second terminal 42a, the first terminal 41a may perform an operation represented as a pseudo code. In the pseudo code, the weight w may be a real number between 0 and 1. Similar to the above description, the first terminal 41a may compare the error rate E(i) with the thresholds (i.e., e_inc and e_dec) and may increase or decrease the MCS offset based on the comparison result. For example, when E(i) is less than e_inc (e.g., e_inc=0.05), the first terminal 41a may increase the MCS offset by K. offset_step_inc , and when E(i) is greater than e_dec (eg, e_dec=0.1), the first terminal 41a may reduce the MCS offset by K offset_step_dec Therefore, the buffer size for storing ACK / NACK history can be reduced, and excessive sensitivity of the MCS offset to ACK or NACK can be prevented. In some embodiments, the first terminal 41a can determine the weight w based on at least one of the following: the speed, location, amount of data to be transmitted, resource pool settings, CSI, and channel busy rate (CBR) of the first terminal 41a and / or the second terminal 42a.

[0112] In some embodiments, the MCS offset may be determined by rank units. For example, the first terminal 41a may calculate a criterion in each rank, and may calculate MCS offsets corresponding to the ranks based on the calculated criterion.

[0113] In some embodiments, the first terminal 41a may transmit a CSI-RS as at least one reference signal to the second terminal 42a. Based on the CSI-RS, the second terminal 42a may feed back to the first terminal 41a a CQI determined by assuming a rank of 1 (i.e., CQI_1) and a CQI determined by assuming a rank of 2 (i.e., CQI_2). The first terminal 41a may determine an MCS suitable for rank-1 transmission (i.e., MCS_1) and an MCS suitable for rank-2 transmission (i.e., MCS_2) based on the CQI_1 and CQI_2 reported from the second terminal 42a. Therefore, MCS_1 may be determined based on CQI_1, and MCS_2 may be determined based on CQI_2.

[0114] In some embodiments, the first terminal 41a may select a rank from rank 1 and rank 2 based on MCS_1 and MCS_2, and may transmit data based on the selected rank and the determined MCS. For example, when the coding rate and modulation order both corresponding to MCS_1 are code_rate_1 and Qm_1, respectively, the first terminal 41a may calculate the data rate rate_1 when using rank 1, as shown in the following equation 1.

[0115] [Equation 1]

[0116] rate_1=1×code_rate_1×Qm_1

[0117] In addition, when the coding rate and the modulation order both corresponding to MCS_2 are code_rate_2 and Qm_2, respectively, the first terminal 41a can calculate the data rate rate_2 when rank 2 is used, as shown in the following Equation 2.

[0118] [Equation 2]

[0119] rate_2=2×code_rate_2×Qm_2

[0120] The first terminal 41a can compare rate_1 in Equation 1 with rate_2 in Equation 2. When rate_1 is greater than rate_2, the first terminal 41a can select rank 1 and MCS_1. Alternatively, when rate_2 is greater than rate_1, the first terminal 41a can select rank 2 and MCS_2. Thus, the first terminal 41a can compare the performance of transmission based on one layer with the performance of transmission based on two layers, and based on the comparison result, the first terminal 41a can select relatively better transmission parameters.

[0121] Figure 13A and Figure 13B is a diagram illustrating an example of terminals communicating with each other according to an exemplary embodiment. In detail, Figure 13A An example is shown in which the second terminal 132a communicates with the first terminal 131a through the rear panel of the second terminal 132a, and Figure 13B An example is shown in which the second terminal 132b communicates with the first terminal 131b via the side panel of the second terminal 132b. Figure 13A and Figure 13B The repeated descriptions in the description are omitted.

[0122] In V2X (especially V2V), the relative movement of each of the transmitting terminal and the receiving terminal can be simply modeled. Figure 13AAs shown, the first terminal 131a and the second terminal 132a can move on the same lane, and the relative speed between the first terminal 131a and the second terminal 132a can be simplified into two cases, a case where the first terminal 131a and the second terminal 132a are close to each other and a case where the first terminal 131a and the second terminal 132a are far away from each other. Figure 13B As shown, the first terminal 131b and the second terminal 132b can move on substantially the same moving path, and the relative speed between the first terminal 131b and the second terminal 132b can be simplified into two cases, a case where the first terminal 131b and the second terminal 132b are close to each other and a case where the first terminal 131b and the second terminal 132b are far away from each other. When the two terminals are close to each other, the channel state may be better, and when the two terminals are far away from each other, the channel state may be worse. Therefore, in D2D communication, the relative speed between the two terminals can be used to determine the transmission parameters. In the following, reference will be made to Figures 14 to 20B An example of D2D communication based on relative speed is described.

[0123] Figure 14 is a flow chart illustrating a method for performing D2D communication according to an example embodiment. In detail, Figure 14 The flowchart of FIG. 1 shows a method for performing D2D communication based on the relative speed between two terminals. Figure 14 As shown, the method for performing D2D communication may include operations S40, S50, S60, S70 and S80. In some embodiments, Figure 14 The method can be Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b executes. Figure 4A and Figure 4B describe Figure 14 .

[0124] In operation S40, an operation of determining transmission parameters based on the channel state may be performed. For example, Figure 4A The first terminal 41a can estimate the channel state based on the CSI provided from the second terminal 42a, and can determine the transmission parameter based on the estimated channel state. Figure 4B The first terminal 41b may measure at least one reference signal received from the second terminal 42b to estimate a channel state, and may determine a transmission parameter based on the estimated channel state.

[0125] In operation S50, an operation of obtaining a measurement value corresponding to the relative speed may be performed. For example, Figure 4A The first terminal 41a may identify the relative speed based on the measurement value provided from the second terminal 42a, or may calculate the relative speed based on the value provided from the second terminal 42a. Figure 4B The first terminal 41b may measure at least one reference signal received from the second terminal 42b to directly obtain a measurement value corresponding to the relative speed.

[0126] In operation S60, an operation of adjusting transmission parameters may be performed. For example, Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b may adjust at least one of the transmission parameters determined in operation S40 based on the measurement value obtained in operation S50. When the two terminals are close to each other, that is, when the relative speed between the first terminal and the second terminal is detected to be negative, the at least one transmission parameter may be adjusted to correspond to a relatively high data rate, and when the two terminals are farther away from each other, that is, when the relative speed between the first terminal and the second terminal is detected to be positive, the at least one transmission parameter may be adjusted to correspond to a relatively low data rate. As described above, by using the change in the channel state based on the relative speed and the estimated channel state, the optimal transmission parameter can be determined, thereby effectively performing D2D communication.

[0127] In operation S70, an operation of sending transmission parameters may be performed. For example, Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b may send parameters including at least one transmission parameter obtained through the adjustment in operation S60 to Figure 4A The second terminal 42a and / or Figure 4B The second terminal 42b.

[0128] In operation S80, an operation of sending data may be performed. For example, Figure 4A The first terminal 41a and / or Figure 4B The first terminal 41b may send data to the Figure 4A The second terminal 42a and / or Figure 4B The second terminal 42b.

[0129] Figure 15A and Figure 15B is a flowchart illustrating an example of a method for performing D2D communication according to an example embodiment. In detail, Figure 15A and Figure 15B The flowchart of FIG represents the relative speed-based D2D communication in the CSI feedback scheme. Figure 15A and Figure 15B Duplicate description in the description of . Figure 15A and Figure 15B In the present invention, the terminal may be referred to as a user equipment (UE).

[0130] Reference Figure 15AIn operation S10a, the first UE 151a may transmit at least one reference signal to the second UE 152a. In some embodiments, the first UE 151a may transmit a reference signal for measuring Doppler shift and estimating a channel state using the second UE 152a to the second UE 152a. For example, the first UE 151a may transmit a synchronization signal, a DL DMRS, a DL CSI-RS, a PT-RS, and a tracking reference signal (TRS) to the second UE 152a.

[0131] Operation S20a may include operation S22a and operation S24a. In operation S22a, the second UE 152a may measure Doppler shift based on at least one reference signal. For example, the second UE 152a may measure Doppler shift based on a synchronization signal, a TRS, a PT-RS, a DMRS, and a CSI-RS. In operation S24a, the second UE 152a may generate CSI. For example, the second UE 152a may measure at least one reference signal received from the first terminal 151a to estimate a channel state, and may generate CSI based on the estimated channel state. In addition, the second UE 152a may generate CSI including a measurement value corresponding to the Doppler shift measured in operation S22a. In subsequent operation S30a, the second UE 152a may send the CSI to the first UE 151a.

[0132] In operation S40a, the first UE 151a may determine the transmission parameters. For example, the first UE 151a may determine the transmission parameters based on the CSI received from the second UE 152a. In operation S50a, the first UE 151a may extract the measurement value from the CSI. Therefore, the first UE 151a may identify the Doppler shift measured in the second UE 152a and may therefore detect the relative speed between the first UE 151a and the second UE 152a.

[0133] In operation S60a, the first UE 151a may adjust at least one transmission parameter based on the detected relative speed. For example, the first UE 151a may calculate the above reference speed based on the detected relative speed. Figure 4A and Figure 4B The MCS index described is offset, and the hysteresis for adjusting the MCS may be changed. Here, the measurement value corresponding to the detected relative speed and used to adjust the MCS index may be referred to as a channel quality offset index (CQOI).

[0134] In some embodiments, the first UE 151a may determine the MCS offset based on the CQOI as follows.

[0135] 1) If E(i) <e_inc

[0136] A.MCS offset (i+1) = MCS offset (i) + K offset_step_inc +α·CQOI

[0137] 2) If E(i)>e_dec

[0138] A.MCS offset (i+1) = MCS offset (i) - K offset_step_dec +β·CQOI

[0139] In the pseudo code, α and β may be the same or may be different.

[0140] In some embodiments, the first UE 151a may adjust the thresholds used to determine the MCS offset based on the CQOI. For example, the first UE 151a may adjust the thresholds as follows and may compare e_inc' and e_dec' with the error rate E(i).

[0141] e_inc′=e_inc+α′·CQOI

[0142] e_dec'=e_dec+β'·CQOI

[0143] In the pseudo code, α' and β' may be the same or may be different.

[0144] In some embodiments, the first UE 151a may adjust at least one transmission parameter based on at least one reference signal received from another UE. For example, the first UE 151a may measure a DMRS received from a UE different from the second UE 152a. Before sending data to the second UE 152a, the first UE 151a may observe the DMRS transmitted by the other UE based on a scheme similar to listen before talk (LBT) to determine whether the other UE is occupying and using the resource. The first UE 151a may measure the strength and energy of the signal based on the received DMRS and may determine whether the resource (or channel) is occupied. Even though the resource is occupied by another UE or data transmission by another UE is being performed, the first UE 151a may transmit data to the second UE 152a, and the first UE 151a may assume that the result obtained by measuring the DMRS received from the other UE is interference. That is, the first UE 151a may calculate a new signal to interference plus noise ratio (SINR) based on the interference and may adjust at least one transmission parameter (e.g., MCS index) based on the calculated SINR.

[0145] In operation S70a, the first UE 151a may transmit transmission parameters including the adjusted at least one transmission parameter to the second UE 152a, and in operation S80a, the first UE 151a may transmit data to the second UE 152a.

[0146] Reference Figure 15B In operation S10b, the first UE 151b may transmit at least one reference signal to the second UE 152b. For example, the first UE 151b may transmit at least one reference signal to the second UE 152b for the second UE 152b to estimate a channel state.

[0147] Operation S20b may include operation S22b and operation S24b. In operation S22b, the second UE 152b may obtain the speed of the second UE 152b. For example, the second UE 152b may include a speed sensor, a global positioning system (GPS) sensor, etc., and the speed of the second UE 152b may be obtained from at least one sensor. In operation S24b, the second UE 152b may generate CSI. For example, the second UE 152b may generate CSI that includes a measurement value corresponding to the speed of the second UE 152b obtained in operation S22b and an estimated channel state estimated by measuring at least one reference signal. Subsequently, the second UE 152b may send the CSI to the first UE 151b. In some embodiments, the second UE 152b may provide the first UE 151b with a value corresponding to the speed of the second UE 152b independently of the CSI.

[0148] In operation S40b, the first UE 151b may determine a transmission parameter based on the CSI received from the second UE 152b. In operation S50b, the first UE 151b may obtain a measurement value corresponding to the relative speed, and Figure 15BAs shown, operation S50b may include operations S52b, S54b, and S55b. In operation S52b, the first UE 151b may extract the speed of the second UE 152b from the CSI. In addition, in operation S54b, the first UE 151b may obtain the speed of the first UE 151b. For example, the first UE 151b may include a speed sensor, a GPS sensor, etc., and may obtain the speed of the first UE 151b from at least one sensor. In operation S55b, the first UE 151b may calculate a measurement value corresponding to the relative speed. For example, the first UE 151b may calculate the measurement value corresponding to the relative speed based on the speed of the first UE 151b and the speed of the second UE 152b. In operation S60b, the first UE 151b may adjust at least one transmission parameter based on the detected relative speed. In operation S70b, the first UE 151b may transmit transmission parameters including the adjusted at least one transmission parameter to the second UE 152b, and in operation S80b, the first UE 151b may transmit data to the second UE 152b.

[0149] Figure 16A 、 Figure 16B and Figure 17 is a flow chart illustrating an example of a table referenced by a reporting CSI according to an example embodiment. In detail, Figure 16A and Figure 16B shows the table referenced in NR, and Figure 17 A table referenced in LTE is shown. In some embodiments, Figure 4A The second terminal 42a can refer to Figure 16A 、 Figure 16B and Figure 17 The CSI is fed back to the first terminal 41a by the table, and the second terminal 42a can be based on the channel estimated according to at least one reference signal received from the first terminal 41a. To derive CSI. In the following, we will refer to Figure 4A describe Figure 16A 、 Figure 16B and Figure 17 .

[0150] In some embodiments, the first terminal 41a and the second terminal 42a can send and receive data between them based on an uplink data transmission scheme, and the second terminal 42a can report CSI with reference to the uplink codebook. For example, the first terminal 41a (or the base station) can set the codebook to be used for feedback CSI to the uplink codebook in the second terminal 42a through signaling such as RRC. In addition, in non-periodic CSI triggering, the first terminal 41a can set the codebook to be used for feedback CSI to the uplink codebook in the second terminal 42a by using an indicator included in the downlink control information (DCI). The operation of setting the codebook can be performed by the base station that sends data to the second terminal 42a or the first terminal 41a, or can be performed by the base station that controls data transmission / reception between the first terminal 41a and the second terminal 42a (for example, Figure 1 15)Execute.

[0151] In some embodiments, as described below, the CQI and RI, each corresponding to a portion of the CSI, may be determined differently based on feedback or non-feedback of the PMI.

[0152] When the number of TX antenna ports of the first terminal 41a is one, the second terminal 42a may calculate CQI and / or RI assuming a 1TX scheme and may report the calculated CQI and / or RI to the first terminal 41a. In addition, the second terminal 42a may not report PMI and / or RI.

[0153] When the number of TX antenna ports of the first terminal 41a is two or more and PMI is not reported, the second terminal 42a may calculate CQI and / or RI based on the definition of the wireless communication system without PMI, and may report the calculated CQI and / or RI to the first terminal 41a. For example, the second terminal 42a may assume "TM-related CSI assumption and no PMI reporting" in LTE, and may assume "non-PMI port selection scheme" in NR.

[0154] In some embodiments, when only CSI (e.g., CQI or RI / CQI) other than PMI is fed back, the second terminal 42a may adopt a TX diversity scheme and may calculate RI and / or CQI. Thus, despite the rapid changes in the V2X channel, the second terminal 42a may enable the first terminal 41a to transmit data more reliably. For example, the second terminal 42a may assume a diversity scheme that uses different transmission schemes and / or precoders based on the configuration of each of the first terminal 41a and the second terminal 42a (e.g., the number of TX antenna ports, NR / LTE, the transmission mode for LTE, and changing the precoding on / off for NR), and based on this, the second terminal 42a may calculate CQI. In this case, in a precoder cycle, data may be transmitted using different precoding for each frequency / time of a predefined unit (e.g., PRG) in the codebook. The precoder index may be selected based on the frequency / time unit index.

[0155] In some embodiments, under the assumption of a diversity scheme, the CQI may be calculated based on a precoder cycle that uses a codebook corresponding to the number of TX antenna ports of the first terminal 41a. For example, in NR 2TX, the rank definition based on Document 3 may be used. Figure 16A and Figure 16B Therefore, when the layer is 1 (layer=1), one of codebook indexes 0 to 5 may be selected differently for each frequency / time unit.

[0156] Reference Figure 16A and Figure 16B , a part of the codebook may not use a specific antenna port. Therefore, for full power transmission, the precoder cycle can be performed based only on the precoder size of 1. For example, if Figure 16B The rank in the table is 1 (rank = 1) and the TPMI is 2 to 5, only Figure 16B The precoder cycle can be performed only when the rank in the table is 2 (rank=2) and the TPMI is 1 and 2. Therefore, as the transmission power of the first terminal 41a increases, the second terminal 42a can estimate the channel more accurately, and the demodulation performance of the second terminal 42a can be enhanced. In addition, in LTE 2TX, the Figure 17 The CQI is calculated based on the uplink codebook of the precoder cycle.

[0157] In some embodiments, the second terminal 42a may report CSI with reference to a downlink codebook. For example, in NR, the second terminal 42a may calculate CQI based on a downlink codebook (e.g., a "single-panel codebook type I DL codebook" in 4TX or more TX ports), and since the number of calculations is relatively small, the downlink codebook may be suitable for V2X that requires fast CSI reporting. In LTE, the second terminal 42a may assume one of the diversity schemes defined in LTE instead of the precoding cycle. For example, LTE may define two diversity schemes, namely, space-frequency block coding (SFBC) and large-delay cyclic delay diversity (LD-CDD). The diversity scheme (TM2 = transmit diversity (i.e., SFBC), TM3 = LD-CDD) may be determined based on the transmission mode (TM) of the first terminal 41a, and the first terminal 41a may specify the diversity scheme to the second terminal 42a through signaling such as RRC.

[0158] In some embodiments, the TX diversity scheme may be determined based on the number of TX antenna ports of the first terminal 41a. For example, the second terminal 42a may determine SFBC in a 2-port configuration, but in other cases, the second terminal 42a may calculate and report RI and / or CQI based on the precoder cycle.

[0159] In some embodiments, the first terminal 41a can pre-select a precoder (e.g., a precoder cycling scheme) to be used for data transmission and can transmit a reference signal (e.g., DMRS, precoded CSI-RS, etc.) to which the selected precoder is applied to the second terminal 42a. Thus, the degree of freedom in selecting a precoder in the first terminal 41a can be increased, and the second terminal 42a can more easily generate CSI. For example, the second terminal 42a can assume an identity matrix as a precoder, and based on this, the second terminal 42a can calculate RI and / or CQI.

[0160] In some embodiments, when the first terminal 41a transmits a precoded reference signal, the first terminal 41a may assume that the reference signal port represents a candidate DMRS port (i.e., data layer) when transmitting data. Therefore, the first terminal 41a may apply the precoder applied to each layer among the candidate precoders to different RS ports, thereby transmitting the reference signal to the second terminal 42a, and the second terminal 42a may determine at least one reference signal port index to which the precoder most suitable for data transmission is applied, and the second terminal 42a may report the determined at least one reference signal port index to the first terminal 41a. The second terminal 42a may assume that the number of reference signal ports selected and reported by the second terminal 42a is the same as the number of ranks and that the channel of each reference signal (e.g., CSI-RS / SRS) port selected by the second terminal 42a is used in each layer transmission. The second terminal 42a may calculate and report the CQI.

[0161] In some embodiments, in the DMRS associated with the PSBCH, as described above with reference to Figure 4A As described above, the bandwidth of the DMRS may be smaller than the bandwidth of the PSSCH, and the second terminal 42a may assume that the channel of the DMRS corresponds to the bandwidth of the PSSCH and may calculate and report the CQI.

[0162] In some embodiments, the second terminal 42a may report a rank offset indicator to the first terminal 41a instead of the RI. When DMRS is used as at least one reference signal, the second terminal 42a may calculate and report CSI using the same scheme as the precoded reference signal described above, but may not be able to measure a rank higher than the transmission rank of the DMRS. Therefore, the second terminal 42a may report a rank offset indicator, and the rank offset indicator may request the first terminal 41a to increase or decrease the rank corresponding to the currently received DMRS rank.

[0163] The second terminal 42a can calculate the signal-to-noise ratio (SNR) and / or SINR based on the above-mentioned assumed precoding (e.g., SFBC, LD-CDD, or precoding cycle), and can derive the optimal RI and / or CQI based on the SNR and / or SINR and the capacity and / or CSI criteria corresponding thereto. In some embodiments, rank restrictions and / or codebook subset restrictions can be applied to the above-mentioned codebook. For example, some RIs and / or PMIs designated only as higher layers in the total codebook can be used to calculate and report CSI.

[0164] When the number of TX antenna ports of first terminal 41a is two or more and PMI is reported, second terminal 42a may derive and report the optimal RI, PMI, and / or CQI based on a codebook suitable for the configuration of first terminal 41a and second terminal 42a (e.g., the number of TX antenna ports, NR / LTE, LTE transmission mode, and precoding on / off for NR). For example, second terminal 42a may calculate the SNR and / or SINR corresponding to each PR and PMI pair in the codebook, and may calculate the optimal RI and PMI pair and the corresponding CQI based on the capacity and / or CSI criteria corresponding to each of the calculated SNR and / or SINR. In some embodiments, data transmission may be based on uplink transmission, and therefore, the PMI may be determined based on the uplink codebook defined in Document 2 and Document 3. In addition, in some embodiments, rank restriction and / or codebook subset restriction may be applied to the codebook, and, for example, some RIs and / or PMIs in the total codebook may not be used to calculate and report CSI.

[0165] 18A to 18E is a diagram illustrating an example of a table referenced by a reporting CSI according to an exemplary embodiment. In detail, 18A to 18E An example of a CQI table is shown. In some embodiments, Figure 4A The second terminal 42a can refer to Figure 16A 、 Figure 16B and Figure 17 The table feeds back the CSI to the first terminal 41a. Figure 4A describe 18A to 18E .

[0166] In some embodiments, different CQI tables (whether or not the above referenced tables are reported) may be used based on the SNR (or SINR) range to be used in data transmission and the associated modulation and coding rates (e.g., whether repetition is used). Figure 16A 、 Figure 16B and Figure 17 For example, when modulation orders and / or coding rates corresponding to a specific level or higher are not used in V2X, or when an excessively high data rate is not used, a CQI table can be used. In the CQI table, the modulation order and / or coding rate range used in V2X is covered with relatively high resolution. As a result, the CQI can be calculated and reported more accurately, and data transmission can be performed more efficiently.

[0167] In some embodiments, when there is no separate setting in NR V2X (default), the Figure 18A In case of 256QAM in NR V2X, the CQI table can be used. Figure 18BCQI table, and in the case of using a relatively low coding rate, you can use Figure 18C In the case of using only QPSK and 16QAM in LTE, you can use Figure 18D In addition, in the case of using repetition-based data transmission in LTE, the CQI table can be used. Figure 18E CQI table.

[0168] In some embodiments, the second terminal 42a may change the mapping between the CQI index of the CQI table and the CSI standard based on the difference between the reported CQI and the measurement result of the PSSCH DMRS received from the first terminal 41a. For example, the second terminal 42a may calculate the DMRS standard based on the SNR and / or SINR both measured based on the PSSCH DMRS using a scheme similar to the above-mentioned CQI derivation scheme. When the calculated DMRS standard corresponds to a throughput lower than the previously reported CQI, the second terminal 42a may adjust the mapping between the CSI standard and the CQI to report a lower CQI. In addition, when the calculated DMRS standard corresponds to a throughput higher than the previously reported CQI, the second terminal 42a may adjust the mapping between the CSI standard and the CQI to report a higher CQI.

[0169] In some embodiments, the second terminal 42a may adjust the mapping between the CSI standard and the CQI based on the ACK / NACK result. For example, based on the ACK / NACK result of the PSSCH, when the BLER is good (e.g., when the BLER is less than a threshold), the second terminal 42a may report a CQI higher than the derived CSI standard, and when the BLER is not good (e.g., when the BLER is greater than the threshold), the second terminal 42a may report a CQI lower than the derived CSI standard.

[0170] In some embodiments, the second terminal 42a may report a CQI corresponding to each rank so that the first terminal 41a determines the rank more accurately. At this time, the second terminal 42a may not feed back the rank. Moreover, in some embodiments, the second terminal 42a may calculate and report CSI for beam management. For example, the CSI may include at least one CSI-RS resource index (CRI), may include at least one SRS resource index (SRI) and L1-RSRP corresponding to the CRI, may include P-SSS / S-SSS and L1-RSRP corresponding to the CRI, or may include L1-RSRP corresponding to the CRI. Moreover, in some embodiments, as described above with reference to Figure 15A and Figure 15B As described above, the second terminal 42a may report the CQOI to the first terminal 41a.

[0171] In some embodiments, the second terminal 42a may report the CSI to the first terminal 41a via the PSSCH and / or the PSFCH. For example, the second terminal 42a may report the CSI to the first terminal 41a via the PSSCH and / or the PSFCH, and the first terminal 41a may provide the second terminal 42a with control information (e.g., DCI) for demodulation. Figure 19 An example embodiment is described in which CSI is reported through a channel different from the PSSCH and the PSFCH.

[0172] Figure 19 is a diagram illustrating an example of CSI feedback according to an example embodiment. In detail, Figure 19 An example of reporting CSI to a base station 195 that controls sidelink data transmission is shown.

[0173] Reference Figure 19 , the first terminal 191 may transmit at least one reference signal to the second terminal 192, and the second terminal 192 may measure the at least one reference signal to generate CSI, and may report the generated CSI to the base station 195. For example, the second terminal 192 may report the CSI to the base station 195 through a physical uplink control channel (PUCCH) and / or a physical uplink shared channel (PUSCH). The base station 195 may provide at least one transmission parameter to the first terminal 191 and the second terminal 192 based on the CSI, and the first terminal 191 may transmit data to the second terminal 192 based on the at least one transmission parameter.

[0174] In the CSI feedback scheme based on the above-mentioned PSSCH, PSFCH, PUCCH and PUSCH, periodic CSI reporting and / or aperiodic CSI reporting can be performed. For example, when periodic CSI reporting is applied, link adaptation can be easily performed. In addition, when aperiodic CSI reporting is applied, Figure 4A The first terminal 41a and / or Figure 19 The base station 195 can optionally use dynamic signaling commands such as DCI Figure 4A The second terminal 42a and / or Figure 19 The second terminal 192 performs CSI reporting, so CSI reporting can be triggered. CSI can be reported through a control channel and / or a shared channel, and in this case, predefined resources can be used in the control channel, and resources to be used in the shared channel can be specified through dynamic signaling such as DCI.

[0175] In some embodiments, when CSI is reported through a shared channel such as PSSCH or PUSCH, subband CSI can be calculated and reported in addition to wideband CSI, and when CSI is reported through a channel such as PSFCH or PUCCH, only wideband CSI can be reported. The payload of PSFCH can be smaller than that of PSSCH, and resources can be used more freely in PSSCH than in PSFCH. Therefore, subband CSI can be reported through PSSCH, where the payload varies based on the CSI content (e.g., the number of subbands) and a large payload is required. The reporting of subband CSI can be applied to a portion of CSI (e.g., CQI) or can be applied to all CSI.

[0176] In some embodiments, aperiodic CSI may be reported via PSSCH and periodic CSI may be reported via PSFCH. Figure 4A The second terminal 42a triggers aperiodic CSI reporting and can allocate PSSCH resources for reporting CSI. Figure 4A The CSI reporting time point of the second terminal 42a, Figure 4A The first terminal 41a may specify a CSI reporting time point for the second terminal 42a based on dynamic control information such as DCI. Figure 4A The second terminal 42a may identify resources based on the MCS and / or resource allocation included in the control information for triggering the aperiodic CSI reporting, and may report the CSI by using the identified resources.

[0177] In some embodiments, when the CSI payload size is small (for example, when the CSI payload size is 1 codeword, subband CSI reporting is not provided, or the report is not an NR II type CSI report), the aperiodic CSI report can be sent alone via the PSFCH or multiplexed with the HARQ ACK / NACK. The time / frequency resources of the PSFCH can be predefined, so that the separate resource allocation for the aperiodic CSI report can be omitted, thereby enabling the CSI feedback to be further simplified.

[0178] In some embodiments, aperiodic CSI reporting can be performed together with periodic CSI reporting. Furthermore, in some embodiments, when V2X throughput is relatively low, periodic CSI reporting can be omitted and only aperiodic CSI reporting can be performed, and D2D communication can be performed based on the aperiodic CSI reporting. For example, in situations where periodic link adaptation is not useful because the expected data transmission time is short, aperiodic CSI triggering can be used.

[0179] In some embodiments, based on rapidly changing channels, fast CSI feedback for V2X can be applied. For example, CSI feedback can meet at least some of the following conditions, and the following conditions can be set as default values ​​in V2X without separate settings.

[0180] - Maximum number of ports (e.g., four ports)

[0181] - Maximum rank limit (e.g., 2)

[0182] - Report only wideband CSI

[0183] - Omit PMI report

[0184] -Using only a single-panel I-type codebook

[0185] - Use only a single resource for channel measurement

[0186] In some embodiments, although conventional CSI is divided into Part 1 and Part 2 in NR, only one part (e.g., Part 1) may be used in V2X. For example, the payload may not change based on the CSI content, so simple CSI decoding can be performed and aperiodic CSI reporting can be performed over the PSFCH.

[0187] In V2X, the terminal for performing data transmission and the terminal for performing data reception can be replaced between them. That is, the terminal that has sent the first data can be the terminal that receives the second data that has been sent by the terminal that has received the first data. In the case of performing data transmission in two directions between two terminals, reporting the channel separately in the data transmission direction may be inefficient. Therefore, one of the two terminals can calculate and report CSI, and the corresponding CSI can be used for bidirectional data transmission. For example, in Figure 19 In the case where second terminal 192 of first terminal 191 and second terminal 192 reports CSI to first terminal 191, first terminal 191 can transmit data to second terminal 192 based on the CSI, and second terminal 192 can determine transmission parameters (e.g., MCS, RI, and PMI) for transmitting data to first terminal 191 based on a channel state estimated by measuring at least one reference signal (e.g., SRS) transmitted by first terminal 191 and CSI corresponding thereto. Therefore, compared with a case where both first terminal 191 and second terminal 192 report CSI, overhead for CSI reporting can be further reduced, and resources for transmitting reference signals can be saved.

[0188] In some embodiments, base station 195 may designate a terminal (e.g., a "CSI reference UE") between first terminal 191 and second terminal 192 to report CSI. The terminal designated as the "CSI reference UE" by base station 195 may calculate and report CSI, and the other terminal may refer to the CSI (without calculating and reporting CSI corresponding to its receive channel) to determine transmission parameters (e.g., MCS, rank, and precoding) for data transmission. Base station 195 may explicitly designate the "CSI reference UE," or may implicitly designate the "CSI reference UE" by providing settings for CSI reporting to one of the two terminals and providing signal settings (e.g., reference signal) to the other terminal. Such CSI reporting can be used in situations with good channel reciprocity and in situations such as when using diversity schemes. For example, if a terminal does not support CSI reporting in V2X, the CSI can be used jointly for bidirectional channel estimation, and the terminal can notify base station 195 of support for CSI reporting through UE capability signaling. In some embodiments, a geometry-based UE group for HARQ ACK / NACN reporting settings can be used.

[0189] In some embodiments, the terminal may report delta-CSI based on the MCS, rank, and / or precoding specified by each, thereby reducing CSI feedback overhead. For example, instead of representing a value representing the total CQI, an index deviation corresponding to a specific CQI reference may be reported. The terminal may report only index changes based on MCS, RI, and / or PMI, all of which are specified as dynamic signals, thereby reducing feedback overhead for using channels with smaller payloads (such as PSFCH), thereby improving the efficiency of CSI reporting. In MCS and CQI, the CQI index corresponding to the reference may be a CQI index having the same coding rate as the coding rate of the MCS specified as control information associated with the reference resource (such as DCI), and delta-CQI may be calculated and reported. In addition, in aperiodic CSI, the CQI reference may be a CQI index corresponding to the same coding rate as the coding rate of the MCS specified in the DCI for triggering aperiodic CSI reporting. Such a method may be suitable for a case where channel reciprocity is good (ie, a case where the characteristics of the uplink channel are similar to those of the downlink channel).

[0190] Figure 20A and Figure 20B is a flowchart illustrating an example of a method for performing D2D communication according to an example embodiment. In detail, Figure 20A and Figure 20B The flowchart shows the D2D communication based on the relative speed in the channel reciprocity scheme. Figure 4BAs described above, in the absence of CSI feedback from the second UE 202a, the first UE 201a transmitting data can estimate the channel state. Figure 20A and Figure 20B Duplicate description in the description of . Figure 20A and Figure 20B In the present invention, the terminal can be referred to as UE.

[0191] Reference Figure 20A In operation S10c, the second UE 202a may transmit at least one reference signal to the first UE 201a. For example, the second UE 202a may transmit a CSI-RS and / or an SRS to the first UE 201a. In some embodiments, as described above with reference to Figure 8A 、 Figure 8B and Figure 9 As described above, the second UE 202a can transmit at least one reference signal based on antenna switching. For example, the first UE 201a can set an SRS resource set including multiple SRS resources in the second UE 202a, and can set the second UE 202a so that antenna switching is performed in the SRS resource set. Therefore, the second UE 202a can send an SRS to the first UE 201a based on the settings of the first UE 201a, thereby transmitting SRS resources in different antenna port groups. In addition, the second UE 202a can transmit a CSI-RS based on antenna switching, and can transmit an SRS to the first UE 201a based on the settings of the first UE 201a, thereby transmitting symbols in different antenna port groups.

[0192] In operation S20c, the first UE 201a may estimate the channel state based on at least one reference signal received from the second UE 202a. The channel through which the first UE 201a transmits data may be considered as the Hermitian of the channel through which the at least one reference signal is received. That is, when the channel estimated by measuring the at least one reference signal received from the second UE 202a is When the channel used to send data It can be expressed as the following equation 3.

[0193] [Equation 3]

[0194]

[0195] In some embodiments, when the number of RX antenna ports in the first UE 201a is equal to or greater than the number of TX antenna ports, the first UE 201a can use only the channel state corresponding to the portion to be used for actual data transmission (e.g., measurement results of the antenna ports corresponding to the TX antenna ports). In addition, in some embodiments, when the RX bandwidth of the first UE 201a is equal to or greater than the TX bandwidth of the first UE 201a, the first UE 201a can use only the channel state corresponding to the bandwidth corresponding to the portion to be used for actual data transmission. Therefore, the second UE 202a can more easily transmit a reference signal and can be simply implemented.

[0196] In operation S40c, the first UE 201a may determine transmission parameters. For example, the first UE 201a may determine the transmission parameters based on the channel state estimated in operation S20c. In operation S50c, the first UE 201a may measure Doppler shift. For example, the second UE 202a may send a reference signal for measuring Doppler shift and estimating channel state to the first UE 201a. For example, the second UE 202a may send an SRS, UL PT-RS, UL DMRS, etc. to the first UE 201a. The first UE 201a may measure Doppler shift based on at least one reference signal received from the second UE 202a, and thus, may detect the relative speed between the first UE 201a and the second UE 202a.

[0197] In operation S60c, the first UE 201a may adjust the transmission parameters based on the detected relative speed. Figure 15A As described, the first UE 201a may calculate an MCS offset based on the detected relative speed or may change the MCS hysteresis. In operation S70c, the first UE 201a may send transmission parameters including the adjusted at least one transmission parameter to the second UE 202a, and in operation S80c, the first UE 201a may send data to the second UE 202a.

[0198] Reference Figure 20B In operation S10d, the second UE 202b may transmit at least one reference signal to the first UE 201b. For example, the second UE 202b may transmit at least one reference signal to the first UE 201b for the first UE 201b to estimate the channel state. In operation S20d, the first UE 201b may measure the at least one reference signal to estimate the channel state, and may determine a transmission parameter based on the estimated channel state in operation S40d.

[0199] In operation S50d, the first UE 201b can measure the change of received power. For example, the first UE 201b can measure the signal (e.g., reference signal, NACK / ACK, and received power) received from the second UE 202b, and can detect the relative speed between the first UE 201b and the second UE 202b based on the change of received power. That is, when the received power increases, the first UE 201b can determine that the second UE 202b is close to it, and therefore, it can be determined that the channel state is improved. In addition, when the received power decreases, the first UE 201b can determine that the second UE 202b is far away from it, and therefore, it can be determined that the channel state is degraded.

[0200] In operation S60d, the first UE 201b may adjust at least one transmission parameter based on the detected relative speed. In operation S70d, the first UE 201b may send transmission parameters including the adjusted at least one transmission parameter to the second UE 202b, and in operation S80d, the first UE 201b may send data to the second UE 202b.

[0201] Figure 21 1 is a diagram illustrating an example of a terminal performing D2D communication according to an exemplary embodiment. Figure 21 As shown, the first UE 211 and the second UE 212 can send and receive wireless signals based on any RAT (e.g., LTE or NR). The first UE 211 can represent a terminal that sends data in D2D communication, and the second UE 212 can represent a terminal that receives data in D2D communication. In some embodiments, the first UE 211 and / or the second UE 212 may include any device that performs wireless communication, and may include, for example, a mobile phone, a home appliance, a vehicle, an autonomous driving vehicle, a cross-reality (XR) device, a robot, and an artificial intelligence (AI) device. Here, the first UE 211 or the at least one processor 211_4 included in the first UE 211 may be referred to as the first device, and the second UE 212 or the at least one processor 212_4 included in the second UE 212 may be referred to as the second device.

[0202] The first UE 211 may include a transceiver 211_2, at least one processor 211_4, and at least one antenna 211_6. The at least one processor 211_4 may process a first signal SIG1 provided from the transceiver 211_2 and may provide a second signal SIG2 to the transceiver 211_2. The at least one processor 211_4 may be referred to as a baseband processor, a modem, or a communication processor, and the first signal SIG1 and the second signal SIG2 may be baseband signals. The at least one processor 211_4 may perform at least some of the operations described above with reference to the accompanying drawings.

[0203] In some embodiments, at least one processor 211_4 may be implemented as a controller, a microcontroller, or a microprocessor. At least one processor 211_4 may be implemented as hardware, firmware, software, or a combination thereof. For example, at least one processor 211_4 may include an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), or a field programmable gate array (FPGA). At least some of the operations described above with reference to the accompanying drawings may be implemented by firmware or software, and the firmware or software may be stored in a memory device included in or accessed by at least one processor 211_4.

[0204] The transceiver 211_2 may process a radio frequency (RF) signal received via at least one antenna 211_6 to generate a first signal SIG1, and may process a second signal SIG2 to output an RF signal via at least one antenna 211_6. The transceiver 211_2 may include a mixer that converts an RF signal into a baseband signal and vice versa, and may also include an amplifier, a filter, and the like.

[0205] Like the first UE 211, the second UE 212 may include a transceiver 212_2, at least one processor 212_4, and at least one antenna 212_6.

[0206] Figure 22 is a block diagram illustrating signal processing operations for transmission according to an example embodiment. In some embodiments, Figure 22 The operations shown in can be performed by Figure 21 The at least one processor 211_4 included in the first UE 211 is executed. Figure 22 Two or more of the operations shown in the operation are not limited to Figure 22 instructions and can be combined and executed.

[0207] In a first operation 221, codewords may be scrambled. For example, coded bits in each codeword to be transmitted via a physical channel may be scrambled. In a second operation 222, the scrambled bits may be modulated. For example, the coded bits may be modulated to generate complex-valued modulation symbols. In a third operation 223, the modulation symbols may be mapped to transmission layers. For example, the complex-valued modulation symbols corresponding to the codewords to be transmitted may be mapped to one or more transmission layers. In a fourth operation 224, output y may be generated by precoding input x. For example, complex-valued modulation symbols corresponding to input x may be precoded in each transmission layer for transmission via an antenna port, thereby generating output y. In a fifth operation 225, the modulation symbols may be mapped to resource elements. For example, the complex-valued modulation symbols corresponding to the antenna ports may be mapped to resource elements. In a sixth operation 226, an OFDM signal may be generated. For example, a complex-valued time-domain OFDM signal may be generated on each antenna port.

[0208] While example embodiments have been particularly shown and described, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the appended claims.

Claims

1. A method for performing device-to-device communication by a first device, the method comprising: receiving at least one reference signal from a second device; estimating a channel state based on the at least one reference signal; determining a plurality of transmission parameters based on the estimated channel state; obtaining at least one measurement corresponding to a relative velocity between the first device and the second device; adjusting at least one transmission parameter included in the plurality of transmission parameters based on the at least one measurement value; providing the adjusted at least one transmission parameter to the second device; as well as Data is sent to the second device based on the adjusted at least one transmission parameter.

2. The method according to claim 1, wherein Obtaining the at least one measurement value includes measuring a Doppler shift based on the at least one reference signal.

3. The method according to claim 2, wherein: The at least one reference signal includes at least one of a sounding reference signal, a phase tracking reference signal, and a demodulation reference signal.

4. The method according to claim 1, further comprising: measuring a change in received power based on the at least one reference signal, The obtaining of the at least one measurement value includes determining the at least one measurement value based on a change in the received power.

5. The method according to claim 1, wherein Adjusting the at least one transmission parameter includes: adjusting the at least one transmission parameter to correspond to a first data rate based on the at least one measurement value corresponding to a negative relative speed between the first device and the second device; and adjusting the at least one transmission parameter to correspond to a second data rate based on the at least one measurement value corresponding to a positive relative speed between the first device and the second device, The first data rate is greater than the second data rate.

6. The method according to claim 5, wherein: Adjusting the at least one transmission parameter to correspond to the first data rate comprises increasing a modulation and coding scheme index, and Adjusting the at least one transmission parameter to correspond to the second data rate includes decreasing the modulation and coding scheme index.

7. The method according to claim 1, further comprising: receiving, from the second device, an acknowledgment corresponding to the sending of the data; as well as Based on the confirmed measurement error rate, When the error rate is less than a first threshold or greater than a second threshold, the at least one transmission parameter is adjusted.

8. The method according to claim 1, further comprising: receiving, from the second device, an acknowledgment corresponding to the sending of the data; as well as Measuring error rate based on said confirmation, The adjusting of the at least one transmission parameter includes: When the error rate is less than a first threshold, adjusting the at least one transmission parameter to correspond to a first data rate; When the error rate is greater than a second threshold, adjusting the at least one transmission parameter to correspond to a second data rate; and adjusting at least one of the first threshold and the second threshold based on the at least one measurement value, and The first data rate is greater than the second data rate.

9. A method for performing device-to-device communication by a second device, the method comprising: sending, to the first device, at least one reference signal based on which the first device estimates the channel state; receiving, from the first device, at least one transmission parameter adjusted by the first device based on a relative speed between the first device and the second device; as well as receiving data from the first device based on the at least one transmission parameter received from the first device, The at least one transmission parameter is included in a plurality of transmission parameters determined by the first device based on the estimated channel state.

10. A first device configured to perform device-to-device communication with a second device, the first device comprising: at least one transceiver; as well as at least one processor configured to process a first signal received from the second device through the at least one transceiver and generate a second signal to be sent to the second device through the at least one transceiver, Wherein, the at least one processor is further configured to: receiving at least one reference signal from the second device; estimating a channel state based on the at least one reference signal; determining a plurality of transmission parameters based on the estimated channel state; obtaining at least one measurement corresponding to a relative velocity between the first device and the second device, adjusting at least one transmission parameter included in the plurality of transmission parameters based on the at least one measurement value, providing the adjusted at least one transmission parameter to the second device via the at least one transceiver, and The second signal is generated based on the adjusted at least one transmission parameter.

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