KR20210109421A - Method and apparatus for data transmission based on channel state in d2d - Google Patents

Abstract

According to an exemplary embodiment of the present disclosure, a method for a first device to transmit data to a second device in device-to-device (D2D) communication includes the steps of: obtaining at least one measurement value corresponding to the relative speed of a first device and a second device; adjusting at least one transmission parameter based on the at least one measurement value; providing the at least one adjusted transmission parameter to the second device; and transmitting data to the second device based on the at least one adjusted transmission parameter.

Description

Method and apparatus for data transmission based on channel state in inter-terminal communication

The technical idea of the present disclosure relates to wireless communication, and more particularly, to a method and an apparatus for data transmission based on a channel state in communication between terminals.

Device-to-Device (D2D) communication may refer to communication between terminals through a sidelink, and the sidelink allows terminals to directly transmit voice or data without going through a base station. It may refer to a communication method of sending and receiving. As data traffic required for sidelink increases as well as uplink and downlink between a base station and a terminal, a method for achieving a high data rate in communication between terminals is required. .

The technical idea of the present disclosure provides a method and apparatus for communication between terminals having a high data transmission rate.

In order to achieve the above object, according to an aspect of the technical idea of the present disclosure, a method for a first device to transmit data to a second device in inter-terminal communication corresponds to the relative speed of the first device and the second device. obtaining at least one measurement value of and transmitting data to the second device based on the one transmission parameter.

According to an aspect of the present disclosure, there is provided a method for a second device to receive data from a first device in inter-terminal communication, at least one transmission parameter adjusted based on relative speeds of the first device and the second device. receiving from the first device, and receiving data from the first device based on the adjusted at least one transmission parameter.

According to an aspect of the technical spirit of the present disclosure, a first device configured to perform communication between a second device and a terminal processes a first signal received from the second device through at least one transceiver and at least one transceiver, and , at least one processor configured to generate a second signal to be transmitted to a second device via the at least one transceiver, wherein the at least one processor comprises at least one processor corresponding to the relative speed of the first device and the second device. obtain one measurement value, adjust the 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, and at least one adjusted The second signal may be generated based on the transmission parameter of .

According to an aspect of the technical concept of the present disclosure, a second device configured to perform communication between a first device and a terminal generates a first signal to be transmitted to the first device through at least one transceiver and at least one transceiver, and , at least one processor configured to process a second signal received from the first device via the at least one transceiver, wherein the at least one processor adjusts based on the relative speeds of the first device and the second device and receive the at least one transmission parameter from the first device, and process the second signal based on the adjusted at least one transmission parameter.

According to the method and apparatus according to an exemplary embodiment of the present disclosure, channel estimation may be performed in inter-terminal communication, and transmission parameters for inter-terminal communication may be appropriately determined based on the estimated channel state.

In addition, according to the method and apparatus according to an exemplary embodiment of the present disclosure, a channel state between terminals can be accurately estimated in consideration of various factors, and thus an optimal data transmission speed can be achieved in communication between terminals. .

In addition, according to the method and apparatus according to an exemplary embodiment of the present disclosure, a channel state between terminals can be efficiently estimated, and accordingly, an overhead for estimating a channel state in communication between terminals can be reduced.

Effects that can be obtained in the exemplary embodiments of the present disclosure are not limited to the above-mentioned effects, and other effects not mentioned are common knowledge in the art to which exemplary embodiments of the present disclosure pertain from the following description. It can be clearly derived and understood by those who have That is, unintended effects of carrying out the exemplary embodiments of the present disclosure may also be derived by those of ordinary skill in the art from the exemplary embodiments of the present disclosure.

1 is a diagram illustrating a wireless communication system according to an exemplary embodiment of the present disclosure.
2 is a diagram illustrating a slot structure of a radio frame according to an exemplary embodiment of the present disclosure.
3 is a diagram illustrating a resource unit for communication between terminals according to an exemplary embodiment of the present disclosure.
4A and 4B are diagrams illustrating examples of inter-terminal communication according to exemplary embodiments of the present disclosure.
5 is a diagram illustrating frequency hopping according to an exemplary embodiment of the present disclosure.
6 is a diagram illustrating an operation of estimating a wideband channel from partial SRS transmission according to an exemplary embodiment of the present disclosure.
7 is a diagram illustrating an SRS bandwidth configuration table according to an exemplary embodiment of the present disclosure.
8A and 8B are diagrams illustrating examples of antenna switching in reference signal transmission according to an exemplary embodiment of the present disclosure.
9 is a diagram illustrating a guard interval table according to an exemplary embodiment of the present disclosure.
10 is a diagram illustrating an example of channel estimation based on interference measurement according to an exemplary embodiment of the present disclosure.
11A and 11B show examples of a table referenced for determining a transmission parameter according to exemplary embodiments of the present disclosure.
12 shows examples of a table referenced for determining a transmission parameter according to an exemplary embodiment of the present disclosure.
13A and 13B are diagrams illustrating examples of terminals communicating with each other according to exemplary embodiments of the present disclosure.
14 is a flowchart illustrating a method for communication between terminals according to an exemplary embodiment of the present disclosure.
15A and 15B are flowcharts illustrating examples of a method for communication between terminals according to exemplary embodiments of the present disclosure.
16A, 16B, and 17 are diagrams illustrating examples of tables referenced when reporting CSI according to exemplary embodiments of the present disclosure.
18A to 18E are diagrams illustrating examples of tables referenced when reporting CSI according to exemplary embodiments of the present disclosure.
19 is a diagram illustrating an example of CSI feedback according to an exemplary embodiment of the present disclosure.
20A and 20B are flowcharts illustrating examples of a method for communication between terminals according to exemplary embodiments of the present disclosure.
21 shows an example of terminals performing inter-terminal communication according to an exemplary embodiment of the present disclosure.
22 is a block diagram illustrating a signal processing operation for transmission according to an exemplary embodiment of the present disclosure.

1 is a diagram illustrating a wireless communication system 10 according to an exemplary embodiment of the present disclosure. The wireless communication system 10 may also be referred to as a Radio Access Technology (RAT), and by way of non-limiting examples, Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), ), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), and the like, may be any wireless communication system based on multiple access schemes. For example, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) may employ OFDMA in downlink (DL), SC-FDMA in uplink (UL), and LTE-A ( Advanced) may correspond to an evolved version of 3GPP LTE. In addition, 5G (5th generation wireless) NR (New Radio) has been proposed following LTE-A for high performance, short delay, etc. f) All available spectrum resources such as bands can be utilized. Hereinafter, it is assumed that the communication system 10 is LTE-A and/or 5G NR, but it will be understood that exemplary embodiments of the present disclosure are not limited thereto.

A base station (BS) 15 may generally refer to a fixed station communicating with the terminal 11 or 12 and/or other base stations, and may refer to the terminal 11 or 12 and/or other base stations. By communicating with the base station, data and control information can be exchanged. For example, the base station 15 is a Node B, evolved-Node B (eNB), Next generation Node B (gNB), Sector, Site, Base Transceiver System (BTS), Access Pint (AP). , a relay node, a remote radio head (RRH), a radio unit (RU), a small cell, and the like. In this specification, the base station 15 or cell is a base station controller (BSC) in CDMA, Node-B in WCDMA, eNB in LTE, gNB in 5G NR or some area or function covered by a sector (site), etc. It can be interpreted as a comprehensive meaning representing a megacell, macrocell, microcell, picocell, femtocell and relay node, RRH, RU, and various coverage areas such as small cell communication range.

The terminal 11 or 12 may be fixed or mobile, and may refer to any devices capable of transmitting and receiving data and/or control information by communicating with the base station 15 . For example, the terminal is a user equipment (UE), terminal equipment (terminal equipment), MS (Mobile Station), MT (Mobile Terminal), UT (User Terminal), SS (Subscribe Station), wireless device (wireless) device), a handheld device, and the like. Referring to FIG. 1 , a first terminal 11 may communicate with a base station 15 through an uplink (UL) and a downlink (DL), and a second terminal 12 and a sidelink (SL) through a sidelink (SL). can communicate. For example, the first terminal 11 sends a signal (referred to as a sidelink signal) to the second terminal 12 using a specific resource unit in a resource pool corresponding to a set of a set of resources. can be transmitted), and the second terminal 12 may detect a signal transmitted by the first terminal 11 from a resource pool in which the first terminal 11 can transmit a signal. When the first terminal 11 is within the reachable range of the base station 15 , the base station 15 may inform the first terminal 11 of the resource pool, while the first terminal 11 is the base station 15 . If it is out of the reachable range of , the first terminal 11 may receive information about the resource pool from another terminal, or may set the resource pool as a set of predetermined resources. As will be described later with reference to FIG. 3 , the resource pool may include a plurality of resource units, and the first terminal 11 may transmit a signal to the second terminal 12 using at least one resource unit. have. In this specification, the first terminal 11 transmitting data may be referred to as a first apparatus, and the second terminal 12 receiving data may be referred to as a second apparatus.

Communication between the first terminal 11 and the second terminal 12 through the sidelink SL may be referred to as device-to-device (D2D) communication. As an example of inter-terminal communication, V2X (Vehicle-to-everything) may refer to a communication technology in which a vehicle exchanges information with another vehicle, a pedestrian, an infrastructure-built object, and the like through a side link (SL). In V2X, a terminal may refer to a terminal having high mobility and high power capability, such as a vehicle. For example, V2X is a Vehicle to Base station (V2B), Vehicle-to-Infrastructure (V2I), Vehicle-to-Pedestrian (V2P), Vehicle to Road side unit (V2R), Vehicle-to-Vehicle (V2V), It may include types such as Vehicle-to-Network (V2N) and the like (see document 1 "3GPP TS 38.885, NR; Study on Vehicle-to-Everything (Release 16)"). In some embodiments, when the network equipment such as the base station 15 transmits and receives signals according to the method of communication between terminals, the base station 15 may also be regarded as a terminal of communication between terminals. Exemplary embodiments of the present disclosure, when the first terminal 11 wants to transmit data to the second terminal 12 (or the second terminal 12 wants to receive data from the first terminal 11) case) will be mainly described, but it is noted that the second terminal 12 can be applied even when the second terminal 12 intends to receive data from the base station 15 or the RSU (Road Side Unit). In addition, it is noted that the exemplary embodiments of the present disclosure will be mainly described with reference to inter-terminal communication, but may also be applied to a communication scheme different from GERN (GSM Edge RAN) or inter-terminal communication.

As a high data transmission rate is required in inter-terminal communication, the first terminal 11 and the second terminal 12 may communicate with each other based on the transmission parameters determined based on the channel state. For example, the first terminal 11 may determine transmission parameters based on the estimated channel state, and may transmit data after providing the determined transmission parameters to the second terminal 12 . The second terminal 12 may obtain data transmitted by the first terminal 11 by processing the signal received from the first terminal 11 based on the transmission parameters provided from the first terminal 11 . The sidelink (SL) may have different characteristics from the uplink (UL) and/or the downlink (DL), and accordingly, new schemes may be required for data transmission based on a channel state in inter-terminal communication. Hereinafter, as will be described below with reference to the drawings, exemplary embodiments of the present disclosure can provide efficient estimation of a channel state in inter-terminal communication, and thus the overhead for estimating the channel state can be minimized. . In addition, the channel state can be accurately estimated by taking various factors into consideration, so that optimal transmission parameters can be determined in inter-terminal communication, and an optimal data transmission speed can be achieved.

2 is a diagram illustrating a slot structure of a radio frame according to an exemplary embodiment of the present disclosure. In some embodiments, the slot structure of FIG. 2 may correspond to the slot structure of 5G NR.

Referring to FIG. 2 , a slot may include a plurality of symbols (eg, a plurality of OFDM symbols) on a time axis. For example, in a normal CP (Cyclic Prefix), one slot may include 14 symbols, while in an extended CP, one slot may include 12 symbols. Alternatively, one slot in the normal CP may include 7 symbols, while one slot in the extended CP may include 6 symbols.

A carrier may include a plurality of subcarriers (eg, up to 3300 subcarriers) in the frequency axis. A resource block (RB) may correspond to a plurality of consecutive subcarriers (eg, 12 subcarriers) in the frequency axis. A bandwidth part (BWP) may be defined as a plurality of contiguous resource blocks (or physical resource blocks (PRB)) in the frequency axis, and may be defined as one numerology, for example, Subcarrier Spacing (SCS). ), CP length, and the like. A carrier wave may include a maximum of N (eg, 5) BWPs, and data transmission may be performed through the activated BWP. One unit in the resource grid may be referred to as a resource element (RE), and one complex symbol may be mapped to one resource element.

In some embodiments, a BWP may be defined for a sidelink, and the same sidelink BWP may be used for transmission and reception. For example, the first terminal 11 of FIG. 1 may transmit a sidelink channel and/or a sidelink signal on a specific BWP, and the second terminal 12 may transmit a sidelink channel and/or a sidelink signal on the corresponding BWP. A sidelink signal can be received. In a licensed carrier, the sidelink BWP may be defined separately from the uplink/downlink BWP, that is, the Uu BWP, and the sidelink BWP may have separate configuration signaling from the Uu BWP. . For example, the first terminal 11 and/or the second terminal 12 may receive the configuration for the sidelink BWP from the base station 15 . The sidelink BWP may be preset for an out-of-coverage terminal and a terminal having an RRC_IDLE mode in the carrier, and at least one sidelink BWP for the terminal having the RRC_CONNECTED mode is activated in the carrier. can

3 is a diagram illustrating a resource unit for communication between terminals according to an exemplary embodiment of the present disclosure. Referring to FIG. 3 , the total frequency resources of the _{resource pool (RP) may be divided into N F} pieces, and the total time resources of the resource pool (RP) may be divided into _{N T pieces.} Accordingly, a total of N _F *N _T resource units may be defined in the resource pool (RP). 3 shows an example in which the resource pool _{is repeated in a period of N T subframes.}

In some embodiments, as shown in FIG. 3 , one resource unit (eg, Unit #0) may appear periodically and repeatedly. In some embodiments, in order to obtain a diversity effect on a time axis or a frequency axis, an index of a physical resource unit to which one logical resource unit is mapped may change in a predefined pattern according to time. In this way, the resource pool (RP) may correspond to a set of resource units that can be used by a terminal to transmit a sidelink signal. In some embodiments, the resource pool (RP) is, according to the content of the sidelink signal, a Physical Sidelink Control Channel (PSCCH), a Physical Sidelink Shared Channel (PSSCH), a Physical Sidelink Discovery Channel (PSBCH), a Physical Sidelink Discovery Channel (PSBCH). Sidelink Broadcast Channel), PSFCH (Physical Sidelink Feedback Channel), and the like may be classified.

4A and 4B are diagrams illustrating examples of inter-terminal communication according to exemplary embodiments of the present disclosure. Specifically, FIGS. 4A and 4B are examples of terminals and show examples in which vehicles perform inter-terminal communication based on a channel state.

Referring to FIG. 4A , a channel state between a first terminal 41a and a second terminal 42a may be estimated based on CSI feedback. For example, as shown in FIG. 4A , the first terminal 41a may transmit at least one reference signal to the second terminal 42a. For example, the first terminal 41a may transmit at least one reference signal for downlink to the second terminal 42a. The second terminal 42a may receive at least one reference signal from the first terminal 41a, and by estimating the channel state based on the received at least one reference signal, channel state information (CSI) can create For example, CSI includes 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 corresponding L1-RSRP (Reference). Signal Received Power), SRI (SRS Resource Indicator), and may include at least one of the corresponding L1-RSRP.

The second terminal 42a may transmit CSI to the first terminal 41a. For example, the second terminal 42a may transmit the CSI to the first terminal 41a on the PSFCH. When the second terminal 42a transmits CSI to the first terminal 41a, it may be referred to as CSI feedback, CSI reporting, or the like.

In some embodiments, the first terminal 41a may preselect a precoder to use when transmitting data, and a reference signal to which the selected precoder is applied, such as DRMS, precoded CSI-RS, precoder The coded SRS may be transmitted to the second terminal 42a. The second terminal 42a may assume an identity matrix as a precoder, and may calculate CSI, such as RI and/or CQI, based on this. Whether or not to use the precoded reference signal may be predefined, and may be previously provided to the first terminal 41a and/or the second terminal 42a through higher-layer signaling such as RRC (Radio Resource Control). It may be set or indicated. In addition, an indicator indicating whether to use the precoded reference signal may be included in (dynamic) control signaling through which aperiodic reference signal triggering is transmitted, and the first terminal 41a and/or the second terminal 42a is the corresponding indicator It is possible to identify whether the precoded reference signal is used or not.

In some embodiments, the first terminal 41a may transmit the precoded reference signal so that the precoded reference signal port becomes a candidate DMRS port in actual transmission, that is, to represent the data layer. The first terminal 41a may apply a precoder applied to each layer among the candidate precoders to a different precoded reference signal port, and the second terminal 42a (eg, one used for data transmission) At least one reference signal port index to which a preferred precoder is applied) may be selected, and the selected at least one reference signal port index may be reported to the first terminal 41a. The second terminal 42a may assume that the number of selected and reported reference signal port indexes matches the number of ranks, and the channel of each reference signal port is used for each layer transmission, and calculates the CQI, can report

In some embodiments, when DMRS is transmitted as at least one reference signal, CSI may be reported based on a precoded reference signal transmission similar to that described above. For example, when the second terminal 42a receives and measures the DMRS, the second terminal 42a may assume that the same precoder is applied in the frequency axis based on the PRG (Precoding RB Group) size, The channel state can be estimated. When the DMRS related to the PSBCH is received, the PSBCH may be received only in some bands of the entire bandwidth portion, and the second terminal 42a may assume that the channel through which the DMRS is received is the same for the entire PSSCH band, and wideband CSI can report

In some embodiments, the second terminal 42a may independently use the measurement result of the slot in which the reference signal is received to generate CSI, for example, inter-slot filtering such as average, interpolation, extrapolation, etc. may not apply. As described above with reference to FIG. 1, due to the high mobility of the terminal, the channel in V2X may change rapidly, and accordingly, the accuracy of the channel estimation may be reduced due to the channel state that rapidly fluctuates on a slot-by-slot basis. Inter-slot filtering can be excluded. For example, as a time-domain channel measurement restriction (restriction), regardless of the setting of the parameter "timeRestrictionForChannelMeasurements" that prevents inter-slot channel averaging in the time domain when activated, the estimation of the channel state in V2X is always "timeRestrictionForChannelMeasurements=Enable" " can be done as

In some embodiments, the second terminal 42a is a time-domain channel measurement restriction such as "timeRestrictionForChannelMeasurements" in a low-speed V2X situation is deactivated, in the time domain, inter-slot channel average can be allowed, and in each of the slots The accuracy of the measurement result may be improved by applying averaging, infinite impulse response (IIR) filtering, interpolation, or the like to the measured 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.

The first terminal 41a may receive CSI from the second terminal 42a, and may determine at least one transmission parameter based on the CSI. The transmission parameter is a parameter defining a method of 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 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 acquire data by processing the signal received from the first terminal 41a based on at least one transmission parameter received from the first terminal 41a.

Referring to FIG. 4B, the channel state between the first terminal 41b and the second terminal 42b may be estimated based on the reference signal provided by the second terminal 42b, and accordingly, the CSI feedback ( or CSI reporting) may be omitted. For example, as shown in FIG. 4B , 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 at least one reference signal from the second terminal 42b.

The first terminal 41b may estimate the channel state based on the received at least one reference signal. For example, the first terminal 41b may estimate a channel state corresponding to the transmission from the second terminal 42b to the first terminal 41b based on at least one reference signal, and A channel state corresponding to transmission from the first terminal 41b to the second terminal 42b may be estimated based on reciprocity. The first terminal 41b may determine at least one transmission parameter based on the finally estimated channel state. The first terminal 41b may transmit the determined at least one transmission parameter to the second terminal 42b, and may transmit data to the second terminal 42b based on the determined at least one transmission parameter. .

In some embodiments, at least one reference signal in FIGS. 4A and 4B may include a reference signal for uplink (UL) and/or downlink (DL). For example, the at least one reference signal may include a DM-RS (Demodulation Reference Signal) related to a V2X channel, such as PSFCH, PSBCH, PSCCH, PSSCH, etc., and PT- for PSSCH in Frequency Range 2 (FR2). It may include a Phase Tracking Reference Signal (RS). Also, the 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. In addition, the at least one reference signal may include a Sidelink Synchronization Signal (SLSS), such as a Primary Sidelink Synchronous Signal (P-SSS), and a Secondary Sidelink Synchronous Signal (S-SSS). Embodiments in which the first terminal 41a transmits the SRS as at least one reference signal to the second terminal 42a will be described below with reference to FIGS. 5 to 8B .

In this specification, the above-described inter-terminal communication with reference to FIG. 4A may be referred to as a channel state information (CSI) feedback method, and the above-described inter-terminal communication with reference to FIG. 4B is a channel reciprocity method. may be referred to as Hereinafter, embodiments of inter-terminal communication based on a CSI feedback scheme and/or a channel reciprocity scheme will be described with reference to FIGS. 4A and 4B .

5 is a diagram illustrating frequency hopping according to an exemplary embodiment of the present disclosure. In some embodiments, the second terminal 42b of FIG. 4B may transmit an SRS to the first terminal 41b as at least one reference signal, and FIG. 5 will be described below with reference to FIG. 4B .

When frequency hopping is activated, the first terminal 41b performs document 2 "3GPP TS 36.211, Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 15)" and/or document 3 "3GPP TS 38.211" , NR; Physical channels and modulation (Release 15)" can determine the SRS frequency position at a specific time (eg, specific slot, specific symbol) based on the frequency hopping pattern defined in ", and estimate the channel state at the determined position can do. In some embodiments, the first terminal 41b may estimate the wideband channel by collecting SRS subband measurement results after reception of the SRS in the entire BWP is completed for estimation of the wideband channel. For example, as shown in FIG. 5 , when the size of the subband is 4 and the size of the wideband is 16, the four subband SRSs SB1-1, SB2-1, SB1-2 according to the frequency hopping pattern. , SB2-2) may be sequentially received, and thus SRS reception may be completed in the entire broadband.

로부터 원하는 대역의 신호를 추출할 수 있고, 시간/주파수 보간/외삽(extrapolation) 또는 이와 유사한 방식들을 적용함으로써 추정된 채널

을 획득할 수 있다.The first terminal 41b may estimate a wideband channel by applying frequency interpolation such as Inverse Fast Fourier Transform (IFFT), Minimum Mean Square Error (MMSE), etc. to the SRS subband measurement results as a non-limiting example. can In addition, the first terminal 41b may calculate the average after adding the same or different weights to the subbands on the frequency axis, thereby reducing the contamination of the channel estimation due to the old measurement result. The first terminal 41b performs time/frequency filtering and results in a measurement

It is possible to extract a signal of a desired band from

can be obtained.

6 is a diagram illustrating an operation of estimating a wideband channel from partial SRS transmission according to an exemplary embodiment of the present disclosure, and FIG. 7 is a diagram illustrating an SRS bandwidth configuration table according to an exemplary embodiment of the present disclosure. As described above with reference to FIG. 5 , the second terminal 42b of FIG. 4B may transmit an SRS to the first terminal 41b as at least one reference signal, and frequency hopping may be activated. Hereinafter, FIGS. 6 and 7 will be described with reference to FIG. 4B , and content that overlaps with the description of FIG. 5 among the description of FIG. 6 will be omitted.

Due to the high mobility of the vehicle, the channel state in V2X can change rapidly. Accordingly, information measured from the initially received subband SRS may not be valid after the SRS is received in the entire wideband. Accordingly, instead of estimating the channel state based on the SRS received over the wideband, the first terminal 41b may estimate the wideband channel based on the recent N SRS receptions and interpolation/extrapolation (N is 1). greater integer). For example, instead of the four subband SRSs (SB1-1, SB2-1, SB1-2, SB2-2) sequentially received as described above with reference to FIG. 5, the first terminal 41b, As shown in FIG. 6 , a wideband channel can be estimated by applying interpolation and extrapolation to two recently received subband SRSs SB1-2 and SB2-2.

로 판정될 수도 있다.In some embodiments, the first terminal 41b may determine N based on the degree of change of the transmission period and/or the channel of the SRS. Referring to FIG. 7 , the SRS bandwidth configuration table of document 2 may define a frequency hopping pattern, where N may be greater than or equal to _{N b_hop+1 (N≥N b_hop+1} ). That is, when N=N _{b_hop+1} , the entire SRS band may be covered based on the smallest number of SRS subband transmissions, and thus extrapolation may be minimized. For example, in the table of FIG. 7, when b_hop=0, C _SRS =4, B _SRS =2 (ie, the SRS bandwidth is 16RB and the SRS subband size is 4RB), as shown in FIG. , the entire SRS bandwidth may be covered based on at least N _{2 =2 SRS subband transmissions.} In some embodiments, when uniform channel estimation of wideband SRS is expected, N is k = b _hop +1, b _hop +2...(B _SRS -1),

may be judged as

In some embodiments, N may be set in the first terminal 41b, and the base station may set N to instruct the first terminal 41b. Accordingly, the first terminal 41b can reduce the time consumed for estimating the channel state based on the SRS. Even when at least one reference signal includes SRS and frequency hopping is activated in the CSI feedback scheme of FIG. 4A , N may be configured similarly to the channel reciprocity scheme of FIG. 4B, and accordingly, the second terminal of FIG. 4A In step 42a, the time consumed for generating CSI based on SRS can be shortened, and the time (eg, period or offset in the case of periodic feedback) for feedback (or reporting) of CSI can be set more freely.

개 서브대역 SRS 송신들로서 전체 광대역의 채널 상태가 추정될 수 있고(

), 이 때 D는 데시메이션 인자(factor)일 수 있다. 일부 실시예들에서, D는 k = b_hop+1, b_hop+2...B_SRS일 때,

일 수 있고, D의 최대값은 k = b_hop+1일 때 발생할 수 있다.Similar to the above, a decimation of the reference signal may be defined. For example, if the number of subband SRS transmissions corresponding to the entire wideband is K,

As the subband SRS transmissions, the channel state of the entire wideband can be estimated (

), where D may be a decimation factor. In some embodiments, when D is k = b _hop +1, b _hop +2...B _SRS ,

, and the maximum value of D may occur when _{k = b hop +1.}

In some embodiments, the SRS may be transmitted aperiodically. V2X may have a relatively limited channel, and periodically transmitting SRS may cause high overhead. Accordingly, aperiodic (aperiodic) SRS may be employed in V2X. For example, the first terminal 41b of FIG. 4B may instruct the second terminal 42b to transmit SRS through a PSCCH or the like, and the first terminal 41a of FIG. 4A triggers an aperiodic CSI. CSI trigger), the measurement of the reference signal may be instructed by notifying the second terminal 42a of the transmission of the SRS.

In some embodiments, frequency hopping may occur within one slot and/or one subframe. For example, intra-slot/subframe SRS frequency hopping may be applied in V2X, and accordingly, transmission of SRS to which frequency hopping is applied in a relatively short time may be possible, and as a result, a wideband channel may be estimated more accurately and quickly can be

In some embodiments, SRS repetition may be employed, so that the channel state may be more accurately estimated. For example, in V2X, the same SRS may be transmitted in a plurality of OFDM symbols on the time axis, and the second terminal 42a of FIG. 4a and/or the first terminal 41b of FIG. 4b may repeatedly receive SRSs. By measuring, it is possible to more accurately estimate the channel state.

8A and 8B are diagrams illustrating an example of antenna switching in reference signal transmission according to an exemplary embodiment of the present disclosure, and FIG. 9 is a diagram illustrating a guard interval table according to an exemplary embodiment of the present disclosure. Specifically, FIGS. 8A and 8B show an example of antenna switching in SRS transmission, and FIG. 9 is a table showing a minimum guard period (GP) between two SRS resources among SRS resource sets for antenna switching ( Document 4 "3GPP TS 38.214, NR; Physical layer procedures for data (Release 16)"). In some embodiments, the second terminal 42b of FIG. 4B may transmit an SRS to the first terminal 41b based on antenna switching, hereinafter, FIGS. 8A, 8B, and 9 are FIG. 4B . reference will be made.

In some embodiments, antenna switching may be employed for transmission of the reference signal, so that the channel condition may be more accurately estimated. For example, in a Time Division Duplex (TDD) channel, the second terminal 42b may have a limited number of Transceiver Units (TXRUs), so that the second terminal 42b has more than TX antenna ports. A large number of RX antenna ports may be implemented. In this case, the state of the channel (eg, uplink channel) estimated based on the SRS transmission through the TX antenna ports of the second terminal 42b occurs in reception through the RX antenna ports of the second terminal 42b. The state of the channel (eg, downlink channel) may not be accurately reflected, and accordingly, the accuracy of estimating the channel state based on channel reciprocity may decrease.

The second terminal 42b may enable more accurate estimation of the channel state based on channel reciprocity by performing antenna switching so that the TX antenna ports can cover (eg, all) RX antenna ports during SRS transmission. . For example, as shown in FIG. 8A , the second terminal 42b may include a transceiver unit 80 , in which one TX antenna port and two RX antenna ports are implemented in the second terminal 42b. can be After SRS#1 is transmitted through antenna port TX#1, antenna switching may occur, and SRS#0 may be transmitted through antenna port TX#0. Accordingly, as shown in FIG. 8B , the first terminal 41b may sequentially receive SRS#0, SRS#1, and SPUCCH (Short Physical Uplink Control Channel) on the PUSCH, and SRS#0, SRS A guard period (GP) may be inserted between #1 and SPUCCH.

In some embodiments, antenna switching may be employed for transmission of other reference signals in addition to the SRS described above. For example, the second terminal 42b may transmit the CSI-RS as at least one reference signal to the first terminal 41b. The first terminal 41b may estimate the channel state by measuring the CSI-RS received from the second terminal 42b, and according to at least one transmission parameter determined based on the estimated channel state and channel reciprocity, 2 It is possible to transmit data to the terminal 42b. A smaller number of TX antenna ports than RX antenna ports may be implemented in the second terminal 42b, and accordingly, the second terminal 42b may apply antenna switching during CSI-RS transmission.

When antenna switching occurs from the first CSI-RS port group to the second CSI-RS port group during CSI-RS transmission, the first CSI-RS port group and the second CSI-RS port group may be defined in different symbols. can For example, when T TX antenna ports are implemented in the second terminal 42b and R RX antenna ports are implemented (T<R, T and R are integers greater than 1), the second terminal 42b may perform antenna switching based on the CSI-RS resource defined as follows.

1) One CSI-RS resource set in which R/T CSI-RS resources of T ports are arranged in different R/T symbols

2) One CSI-RS resource in which a frequency domain code division multiplexing (FD-CDM) group of length T is arranged in different R/T symbols

The second terminal 42b may measure an aggregated channel instead of deriving a CSI-RS Resource Index (CRI) for the CSI-RS resources included in the CSI-RS resource set of 1). have.

In some embodiments, the first terminal 41b may provide an indicator indicating antenna switching to the CSI-RS resource and/or the CSI-RS resource set to the second terminal 42b, and accordingly the CSI-RS resource set The RS resource and/or CSI-RS resource set may be distinguished from a CSI-RS resource set for beam management including multiple-resources or hybrid beamforming.

In some embodiments, when the second terminal 42b transmits the CSI-RS, a time gap for antenna switching may be inserted, and the second terminal 42b receives no information during the time gap, for example. Signals, reference signals, control and data information, etc. may not be transmitted. For example, in the case of 1), a time gap may be inserted between the two CSI-RS resources, and in the case of 2), a time gap may be inserted between the two CSI-RS CDM groups. In some embodiments, the time gap may be defined and set in units of symbols, and may be set according to subcarrier spacing. For example, the table of FIG. 9 defining the minimum guard interval between two SRS resources in document 4 may be employed to set the time gap.

10 is a diagram illustrating an example of channel estimation based on interference measurement according to an exemplary embodiment of the present disclosure. Specifically, FIG. 10 shows an example of estimating a channel state based on SRS to which frequency hopping is applied. In some embodiments, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B determines the channel state based on interference as well as at least one reference signal received from the other party. can be measured accurately. Hereinafter, FIG. 10 will be described with reference to FIGS. 4A and 4B.

In order for the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B to measure interference, at least one reference signal received from the other party as well as at least one of the following resources is additionally configured and used can

- CSI-IM (CSI - Interference Measurement) (or blank-RE use scheme)

- NZP (Non-Zero Power) CSI-RS for interference measurement

- SRS for interference measurement

- AGC training signal

- P-SSS, S-SSS

For example, CSI-IM may be used for measurement of inter-cell interference and/or inter-terminal interference, and accordingly, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B may be used. Estimation of the channel state may have high accuracy.

In some embodiments, when CSI-IM or similar blank-RE scheme is employed, for more accurate measurement of interference, more resource elements than 4-port CSI-RS pattern of CSI-IM, such as one The entire symbol interval may be configured and used for interference measurement. To this end, CSI-IM may be configured through at least one CSI-IM symbol index. Unlike the base station, symbol-level rate matching at any location in the terminal may be limited, and accordingly, in inter-terminal communication, CSI-IM is a shared channel. It may be limited to the position of the first symbol and/or the last symbol of the region that can be set. Accordingly, the at least one CSI-IM symbol index may be simplified to indicate at least one of the first symbol and the last symbol.

In some embodiments, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B may regard a portion remaining except for at least one reference signal received from the counterpart as interference. For example, a separate resource for interference measurement may not be set in inter-terminal communication, and accordingly, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B estimate the channel state. In order to measure interference using an NZP signal (eg, CSI-RS, SRS) configured for A portion remaining after excluding at least one reference signal may be regarded as interference.

In some embodiments, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B may measure interference in radio resources in which at least one reference signal is not transmitted. For example, when SRS is used for estimating a channel state and received according to a frequency hopping pattern, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B receives the frequency at which the SRS is not transmitted. Interference can be measured in the area. As shown in FIG. 10, when a subband SRS (SB1-1) corresponding to the size of 4 resource elements (RE) is received in a wideband corresponding to the size of 16 resource elements (RE), The second terminal 42a and/or the first terminal 41b of FIG. 4B may measure interference on the remaining 12 resource elements (REs).

The second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B may estimate the channel state based on the channel and/or interference measurement. For example, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B may determine the RI and/or PMI based on the channel and/or interference measurement. Further, the second terminal 42a of FIG. 4A and/or the first terminal 41b of FIG. 4B may determine an optimal CQI based on the channel and/or interference measurement, for example, a result of the channel measurement and the interference measurement. CQI may be determined based on capacity based on these factors or a channel state indicator that can represent this well.

11A and 11B show examples of a table referenced for determining a transmission parameter according to exemplary embodiments of the present disclosure. Specifically, FIG. 11a shows a modulation, transmission block size (TBS) index and redundancy version table for LTE Physical Uplink Shared Channel (PUSCH), and FIG. 11b shows NR PDSCH (Physical Downlink Shared Channel) and PUSCH Indicates the MCS index table for In some embodiments, the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B refer to the table of FIG. 11A and/or the table of FIG. 11B to determine at least one transmission parameter. can Hereinafter, FIGS. 11A and 11B will be described with reference to FIGS. 4A and 4B .

A modulation coding scheme (MCS) may refer to information including a code rate and a modulation order used for data encoding and mapping. The first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B may determine the MCS index based on the table of FIG. 11A and the table of FIG. 11B . For example, the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B refers to the table of FIG. 11A and corresponds to the modulation order, TBS size, and redundancy version to be used for data transmission. It is possible to determine the MCS index. In addition, the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B refer to the table of FIG. 11B to determine the modulation order, code rate, and spectral efficiency to be used for data transmission. It is possible to determine the MCS index corresponding to . As described above with reference to FIGS. 4A and 4B , the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B uses the determined MCS index as a transmission parameter in FIG. 4A . It may be provided to the second terminal 42a and/or the second terminal 42b of FIG. 4B . In LTE, the table of FIG. 11a may be predefined (document 5 "3GPP TS 36.213, LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures"), and in NR the table of FIG. 11b may be predefined Yes (document 6 "3GPP TS 38.214, NR; Physical layer procedures for data").

12 shows examples of a table referenced for determining a transmission parameter according to an exemplary embodiment of the present disclosure. Specifically, the left side of FIG. 12 shows a 4-bit CQI table for NR, and the right side of FIG. 12 shows an MCS index table for NR PDSCH and PUSCH. In some embodiments, the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B may determine the at least one transmission parameter with reference to the tables of FIG. 12 . Hereinafter, FIG. 12 will be described with reference to FIGS. 4A and 4B , and a rank may refer to the number of layers to which transmitted data is mapped, and means the number of layers in LTE and NR. can do.

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

In some embodiments, the first terminal 41a may determine the final MCS index based on the CQI index and the MCS index pair corresponding to the same inefficiency and/or spectral efficiency. For example, the first terminal 41a may obtain the inefficiency and/or the spectral efficiency corresponding to the CQI index reported from the second terminal 42a from the CQI table shown on the left side of FIG. 12 , and obtain An MCS index corresponding to the specified code rate and/or spectral efficiency may be determined from the MCS table shown on the right side of FIG. 12 . Accordingly, as indicated by arrows in FIG. 12 , when the CQI indexes correspond to 2, 7, and 10, respectively, the first terminal 41a may determine the MCS indexes corresponding to 0, 11, and 18, respectively. In some embodiments, when the CQI index is 0 or 1, that is, when the channel condition is very poor, the first terminal 41a omits data scheduling for data transmission to the second terminal 42a until the channel condition improves. and may determine the MCS index to be 1. Although the tables of FIG. 12 are tables for NR, it will be understood that the MCS index may be determined similarly as described above in LTE. However, in LTE, a code rate and/or spectral efficiency calculated based on the TBS size and allocated time/frequency resources may be used.

In some embodiments, the first terminal 41a may determine the transmission parameter further based on the CSI provided from the second terminal 42a, as well as other factors affecting the channel state. For example, the first terminal 41a may determine the MCS index further based on an arbitrary outer-loop process result, that is, a result provided from the base station, and may determine the MCS index that occurs in data transmission as described below. The MCS index may be determined based on an error rate. 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 is the initial MCS index and the MCS offset. It can be calculated as the sum of (MCS index = initial MCS index + MCS offset).

In some embodiments, the first terminal 41a may determine the transmission parameter based on an error history of data transmission, for example, a frame error rate (FER), a block error rate (BLER), and the like. For example, the first terminal 41a may store a history of HARQ (Hybrid Automatic Repeat Request) ACK/NACK generated during data transmission, and an error rate (eg, FER) in the history of ACK/NACK in a certain period in the past. If the threshold is exceeded, it may be determined that the CQI provided from the second terminal 42a is incorrect or that the channel state has changed, and accordingly, an MCS offset for adjusting the initial MCS index may be determined. In some embodiments, the first terminal 41a may determine the MCS offset based on only the previous ACK or NACK instead of a predetermined period in order to reduce complexity and buffer size.

In some embodiments, the first FER, which is the FER of each transmission, may be used as a criterion, assuming that HARQ is not applied. For example, if the first FER exceeds 0.1 (first FER>0.1), the first terminal 41a may _{decrease the MCS offset by K offset_step_dec} , while if the first FER is 0.05 or less (first FER≤0.5) ), the first terminal 41a may increase the _{MCS offset by K offset_step_inc.} K _{offset_step_inc} and K _{offset_step_dec} may correspond to an increase amount and a decrease amount of the MCS offset, respectively, may be predefined (eg, K _{offset_step_inc} = K _{offset_step_dec} = 1), and through separate signaling such as RRC, the first terminal 41a and/or the second 2 may be set in the terminal 42a. In some embodiments, K _{offset_step_inc} and K _{offset_step_dec} may be different. For example, when high stability of data transmission is required, K _{offset_step_inc} is It may be less than _{K offset_step_dec (K offset_step_inc} < K _{offset_step_dec} ). In some embodiments, to reduce the complexity of the MCS decision, K _{offset_step_inc} is May match the _{offset_step_dec} K (K = K _{offset_step_inc offset_step_dec).}

The indicator may be predefined or may be set through separate signaling such as RRC. When an error rate E(i) such as BLER of time i is used as an index, the MCS offset can be determined as follows as described above.

1) MCS offset(0) = 0

2) if E(i) < e_inc

A. MCS offset(i+1) = MCS offset(i) + K _{offset_step_inc}

3) else if E(i) > e_dec

A. MCS offset(i+1) = MCS offset(i) - K _{offset_step_dec}

In the pseudo code, e_inc and e_dec are threshold values to be compared with an indicator, and may be predefined or set through separate signaling such as RRC.

In some embodiments, the first terminal 41a may use a weighted sum of the ACK/NACK result as an index, thereby reducing the complexity of storing and calculating the error history. For example, the error rate E(i) of the time point i may be determined as follows.

1) initial error history criteria E(0) = 0.1

2) if NACK

A. E(i+1) = E(i) * w

3) else if ACK

A. E(i+1) = E(i) * w + (1-w)

The first terminal 41a may perform the operation expressed by the pseudo code when ACK or NACK is received from the second terminal 42a. In pseudocode, the weight w can be a real number between 0 and 1. Similar to the above, the first terminal 41a may compare E(i) with threshold values, that is, e_inc and e_dec, and may increase or decrease the MCS offset according to the comparison result. For example, when E(i) is less than e_inc (eg, 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 decrease the _{MCS offset by K offset_step_dec.} Accordingly, a buffer size for storing the 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 is the speed, location, amount of data to be transmitted, resource pool setting, CSI, Channel Busy (CBR) of the first terminal 41a and/or the second terminal 42a. Ratio), the weight w may be determined.

In some embodiments, the MCS offset described above may be determined per rank. For example, the first terminal 41a may calculate an index in each of the ranks, and may calculate MCS offsets corresponding to each of the ranks based on the calculated index.

In some embodiments, the first terminal 41a may transmit a CSI-RS as at least one reference signal to the second terminal 42a, and the second terminal 42a may transmit a rank based on the CSI-RS. The CQI determined by assuming that is 1, that is, CQI_1, and the CQI determined by the assumption that the rank is 2, that is, CQI_2 may be fed back to the first terminal 41a. Based on the CQI_1 and CQI_2 reported from the second terminal 42a, the first terminal 41a may determine an appropriate MCS when transmitting in rank 1, that is, MCS_1 and an appropriate MCS when transmitting in rank 2, that is, MCS_2, respectively. Accordingly, MCS_1 may be determined based on CQI_1, and MCS_2 may be determined based on CQI_2.

In some embodiments, the first terminal 41a may select one of rank 1 and rank 2 based on MCS_1 and MCS_2, and transmit data based on the selected rank and MCS. For example, when the inefficiency and modulation order corresponding to MCS_1 are code_rate_1 and Qm_1, respectively, the first terminal 41a calculates the data transmission rate rate_1 when using rank 1 as shown in [Equation 1] below. have.

In addition, when the inefficiency and modulation order corresponding to MCS_2 are code_rate_2 and Qm_2, respectively, the first terminal 41a calculates the data transmission rate rate_2 when using rank 2 as shown in [Equation 2] below.

The first terminal 41a may compare rate_1 of [Equation 1] and rate_2 of [Equation 2], and may select rank 1 and MCS_1 when rate_1 is greater than rate_2. On the other hand, if rate_2 is greater than rate_1, the rank 2 and MCS_2 can be selected. Accordingly, the first terminal 41a may compare the performances of the case of transmitting with one layer and the case of transmitting with two layers, and may select a more advantageous transmission parameter based on the comparison result.

13A and 13B are diagrams illustrating examples of terminals communicating with each other according to exemplary embodiments of the present disclosure. Specifically, FIG. 13A shows an example of communicating with the first terminal 131a through the rear panel of the second terminal 132a, and FIG. 13B shows the first terminal 131b through the side panel of the second terminal 132b. An example of communicating with Hereinafter, content overlapping with each other in the description of FIGS. 13A and 13B will be omitted.

The relative movement of the transmitting terminal and the receiving terminal in V2X, particularly V2V, can be simply modeled. For example, as shown in FIG. 13A , the first terminal 131a and the second terminal 132a may move on the same lane, and the relative speeds of the first terminal 131a and the second terminal 132a are It can be simplified as two cases of approaching each other or moving away from each other. Similarly, as shown in FIG. 13B , the first terminal 131b and the second terminal 132b may move on substantially the same movement path, and the first terminal 131b and the second terminal 132b are relative to each other. Velocity can be simplified as the two cases approaching each other or moving away from each other. A channel condition may be better when both terminals move closer to each other, while a channel condition may worsen when both terminals move away from each other. Accordingly, in inter-terminal communication, the relative speed of both terminals can be used to determine the transmission parameter. Hereinafter, examples of inter-terminal communication based on relative speed will be described with reference to FIGS. 14 to 20B .

14 is a flowchart illustrating a method for communication between terminals according to an exemplary embodiment of the present disclosure. Specifically, the flowchart of FIG. 14 shows a method for communication between terminals based on the relative speed between both terminals. As shown in FIG. 14 , the method for inter-terminal communication may include a plurality of steps ( S40 , S50 , S60 , S70 , and S80 ). In some embodiments, the method of FIG. 14 may be performed by the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B , hereinafter, FIG. 14 is a reference to FIGS. 4A and 4B . reference will be made.

In step S40, an operation of determining transmission parameters based on a channel state may be performed. For example, the first terminal 41a of FIG. 4A may estimate a channel state based on the CSI provided from the second terminal 42a, and may determine transmission parameters based on the estimated channel state. In addition, the first terminal 41b of FIG. 4B may estimate the channel state by measuring at least one reference signal received from the second terminal 42b, and may determine transmission parameters based on the estimated channel state. have.

In step S50, an operation of obtaining a measurement value corresponding to the relative speed may be performed. For example, the first terminal 41a of FIG. 4A may identify the relative speed from a measurement value provided from the second terminal 42a, and the relative speed based on the value provided from the second terminal 42a. can also be calculated. Also, the first terminal 41b of FIG. 4B may directly obtain a measurement value corresponding to the relative speed by measuring at least one reference signal received from the second terminal 42b.

In step S60, an operation of adjusting a transmission parameter may be performed. For example, the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B may set at least one transmission parameter among the transmission parameters determined in step S40 to the measured value obtained in step S50. can be adjusted based on When both terminals move closer to each other, i.e., when a negative relative speed is detected, at least one transmission parameter can be adjusted to correspond to a higher data transmission rate, while when both terminals move away from each other, i.e. when the positive relative speed is If detected, at least one transmission parameter may be adjusted to correspond to a lower data transmission rate. In this way, optimal transmission parameters can be determined by taking into account not only the estimated channel state but also the change in the channel state based on the relative speed, and thus efficient inter-terminal communication can be achieved.

In step S70, an operation of transmitting transmission parameters may be performed. For example, the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B may set parameters including the at least one transmission parameter adjusted in step S60 to the second terminal 42a of FIG. 4A . and/or to the second terminal 42b of FIG. 4B .

In step S80, an operation of transmitting data may be performed. For example, the first terminal 41a of FIG. 4A and/or the first terminal 41b of FIG. 4B transmits data according to the transmission parameters transmitted in step S70 to the second terminal 42a of FIG. 4A and/or Alternatively, it may transmit to the second terminal 42b of FIG. 4B .

15A and 15B are flowcharts illustrating examples of a method for communication between terminals according to exemplary embodiments of the present disclosure. Specifically, the flowcharts of FIGS. 15A and 15B show inter-terminal communication in consideration of the relative speed in the CSI feedback scheme. Hereinafter, content overlapping with each other in the description of FIGS. 15A and 15B will be omitted. 15A and 15B , a terminal is indicated as a user equipment (UE).

Referring to FIG. 15A , in step S10a , the first terminal 151a may transmit at least one reference signal to the second terminal 152a. In some embodiments, the first terminal 151a may transmit a reference signal for measurement of a Doppler shift as well as estimation of a channel state by the second terminal 152a to the second terminal 152a. have. For example, the first terminal 151a may transmit a synchronization signal, DL DMRS, DL CSI-RS, PT-RS, tracking reference signal (TRS), etc. to the second terminal 152a.

Step S20a may include steps S22a and S24a. In step S22a, the second terminal 152a may measure the Doppler shift from at least one reference signal. For example, the second terminal 152a may measure the Doppler shift based on a synchronization signal, TRS, PT-RS, DMRS, CSI-RS, or the like. In step S24a, the second terminal 152a may generate CSI. For example, the second terminal 152a may estimate the channel state by measuring at least one reference signal received from the first terminal 151a, and may generate CSI based on the estimated channel state. Also, the second terminal 152a may generate CSI including a measurement value corresponding to the Doppler shift measured in step S22a. Then, in step S30a, the second terminal 152a may transmit the CSI to the first terminal 151a.

In step S40a, the first terminal 151a may determine transmission parameters. For example, the first terminal 151a may determine the transmission parameters based on the CSI received from the second terminal 152a. In step S50a, the first terminal 151a may extract a measurement value from the CSI. Accordingly, the first terminal 151a can identify the Doppler shift measured by the second terminal 152a, and as a result, the relative speed of the first terminal 151a and the second terminal 152a can be detected. .

In step S60a, the first terminal 151a may adjust at least one transmission parameter based on the detected relative speed. For example, the first terminal 151a may calculate the MCS offset described above with reference to FIGS. 4A and 4B based on the detected relative velocity, and may change the hysteresis used to adjust the MCS. . In this specification, the measurement value, which corresponds to the detected relative velocity and is used to adjust the MCS index, may be referred to as a Channel Quality Offset Index (CQOI).

In some embodiments, the first terminal 151a may determine the MCS offset based on the CQOI as follows.

1) if E(i) < e_inc

A. MCS offset(i+1) = MCS offset(i) + K _{offset_step_inc} + α CQOI

2) else if E(i) > e_dec

A. MCS offset(i+1) = MCS offset(i) - K _{offset_step_dec} + β CQOI

α and β in the pseudo code may be the same or different.

In some embodiments, the first terminal 151a may adjust thresholds used for determining the MCS offset based on the CQOI. For example, the first terminal 151a may adjust the threshold values as follows, and e_inc' and e_dec' may be compared with the error rate E(i).

- e_inc' = e_inc + α' CQOI

- e_dec' = e_dec + β' CQOI

In the pseudo code, α′ and β′ may be the same or different.

In some embodiments, the first terminal 151a may adjust at least one transmission parameter based on at least one reference signal received from another terminal. For example, the first terminal 151a may measure the DMRS received from a different terminal than the second terminal 152a. The first terminal 151a transmits data to the second terminal 152a in a manner similar to LBT (Listen Before Talk), in order to determine whether another terminal occupies and uses the resource. DMRS can be observed. The first terminal 151a may measure signal strength, energy, etc. through the received DMRS, and may determine whether a resource (or channel) is occupied. Although the resource is occupied by another terminal or data transmission from another terminal occurs, the first terminal 151a may transmit data to the second terminal 152a, and at this time, the DMRS received from the other terminal It can be assumed that the measured result is interference. That is, the first terminal 151a may calculate a new SINR based on the interference, and may adjust at least one transmission parameter (eg, an MCS index) based on the calculated SINR.

In step S70a, the first terminal 151a may transmit transmission parameters including the adjusted at least one transmission parameter to the second terminal 152a, and in step S80a, the first terminal 151a transmits the data. 2 can be transmitted to the terminal 152a.

Referring to FIG. 15B , in step S10b , the first terminal 151b may transmit at least one reference signal to the second terminal 152b. For example, the first terminal 151b may transmit at least one reference signal for estimating the channel state by the second terminal 152b to the second terminal 152b.

Step S20b may include steps S22b and S24b. In step S22b, the second terminal 152b may acquire the speed of the second terminal 152b. For example, the second terminal 152b may include a speed sensor, a GPS sensor, and the like, and may obtain its own speed from at least one sensor. In step S24b, the second terminal 152b may generate CSI. For example, the second terminal 152b may generate CSI including a measurement value corresponding to the speed of the second terminal 152b obtained in step S22b as well as the estimated channel state by measuring at least one reference signal. can Then, the second terminal 152b may transmit the CSI to the first terminal 151b. In some embodiments, the second terminal 152b may provide a value corresponding to its own speed to the first terminal 151b separately from the CSI.

In step S40b, the first terminal 151b may determine the transmission parameters based on the CSI received from the second terminal 152b. In step S50b, the first terminal 151b may obtain a measurement value corresponding to the relative speed, and as shown in FIG. 15B , step S50b may include steps S52b, S54b, and S56b. In step S52b, the first terminal 151b may extract the speed of the second terminal 152b from the CSI. Also, in step S54b, the first terminal 151b may acquire the speed of the first terminal 151b. For example, the first terminal 151b may include a speed sensor, a GPS sensor, and the like, and may obtain its own speed from at least one sensor. In step S55b, the first terminal 151b may calculate a measurement value corresponding to the relative speed. For example, the first terminal 151b may calculate a measurement value corresponding to the relative speed based on the speed of the first terminal 151b and the speed of the second terminal 152b. In step S60b, the first terminal 151b may adjust at least one transmission parameter based on the detected relative speed. In step S70b, the first terminal 151b may transmit transmission parameters including the adjusted at least one transmission parameter to the second terminal 152b, and in step S80b, the first terminal 151b transmits the data. 2 can be transmitted to the terminal 152b.

에 기초하여 CSI를 도출할 수 있다. 이하에서 도 16a, 도 16b 및 도 17은 도 4a를 참조하여 설명될 것이다.16A, 16B and 17 are diagrams illustrating examples of tables referenced when reporting CSI according to exemplary embodiments of the present disclosure. Specifically, FIGS. 16A and 16B show tables referenced in NR, and FIG. 17 shows tables referenced in LTE. In some embodiments, the second terminal 42a of FIG. 4A may feed back CSI to the first terminal 41a with reference to the tables of FIGS. 16A, 16B and 17 , and the second terminal 42a may A channel estimated based on at least one reference signal received from the first terminal 41a

CSI can be derived based on 16A, 16B and 17 will be described below with reference to FIG. 4A.

In some embodiments, the first terminal 41a and the second terminal 42a may transmit/receive data based on an uplink data transmission method, and the second terminal 42a may refer to the uplink codebook for CSI can report For example, the first terminal 41a (or the base station) may set the codebook to be used for CSI feedback to the second terminal 42a as an uplink codebook through signaling such as RRC. In addition, in the case of an aperiodic CSI trigger, the first terminal 41a may set the codebook to be used for CSI feedback as an uplink codebook to the second terminal 42a through an indicator included in DCI (Downlink Control Information). have. Setting of the codebook may be performed by the first terminal 41a or the base station that transmits data to the second terminal 42a, and controls the transmission and reception of data between the first terminal 41a and the second terminal 42a It may be performed by a base station (eg, 15 in FIG. 1 ).

In some embodiments, the CQI and the RI as part of the CSI may be determined differently as follows according to whether the PMI is fed back.

- When the TX antenna port of the first terminal 41a is one

The second terminal 42a may calculate the RI and/or CQI by assuming the 1TX scheme, and may report it to the first terminal 41a. Also, the second terminal 42a may not report PMI and/or RI.

- If there are two or more TX antenna ports of the first terminal 41a and there is no PMI report

The second terminal 42a may calculate the CQI and/or RI based on what is defined in the PMI-free condition by the wireless communication system, and may report it to the first terminal 41a. For example, the second terminal 42a may assume “TM-related CSI assumption and without PMI reporting” in LTE and “non-PMI-port Selection scheme” in NR.

In some embodiments, when only the remaining CSI (eg, CQI or RI/CQI) except for PMI is fed back, the second terminal 42a may assume a TX diversity scheme, and may calculate RI and/or CQI have. Accordingly, the second terminal 42a may enable the first terminal 41a to transmit data more stably (robust) in spite of the rapid change of the V2X channel. For example, the second terminal 42a, the configuration of the first terminal 41a and the second terminal 42a, for example, the number of TX antenna ports, NR/LTE, transmission mode for LTE, transform precoding for NR A different transmission scheme and/or a diversity scheme using a precoder may be assumed according to on/off, and the like, and a CQI may be calculated based thereon. In this case, precoder cycling may transmit data using different precodings for each frequency/time of a unit (eg, PRG) predefined in the codebook. The precoder index may be selected based on the frequency/time unit index.

In some embodiments, as an assumption for the diversity scheme, the CQI may be calculated based on precoder cycling in which a codebook corresponding to the number of TX antenna ports of the first terminal 41a is used. For example, in the case of NR 2TX, the uplink codebooks of FIGS. 16A and 16B defined in document 3 may be used according to ranks. Accordingly, when the layer is 1 (layer=1), one of codebook indexes 0 to 5 may be differently selected for each frequency/time unit.

16A and 16B , some of the codebooks may not use a specific antenna port. Accordingly, for full-power transmission, precoder cycling may be performed only for a precoder having a size of 1 precoder. For example, in the table of FIG. 16B , when the rank is 1 (rank=1) and the TPMIs are 2 to 5, the precoder cycling can be performed only when the rank is 2 (rank=2) and the TPMIs are 1 and 2. have. Accordingly, due to an increase in the transmission power of the first terminal 41a, more accurate channel estimation and demodulation performance can be expected from the second terminal 42a. In addition, in LTE 2TX, CQI may be calculated based on precoder cycling using the uplink codebook of FIG. 17 defined in document 2.

In some embodiments, the second terminal 42a may report the CSI with reference to the downlink codebook. For example, in NR, the second terminal 42a may calculate a CQI based on a "single-panel codebook Type I DL codebook" in TX ports of 4TX or more as a downlink codebook, and due to a relatively small amount of calculation , may be advantageous for V2X requiring fast CSI reporting. In LTE, the second terminal 42a may assume one of the diversity schemes defined in LTE instead of precoding cycling. 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 may be determined by the transmission mode (TM) of the first terminal 41a (TM2 = transmit diversity (ie SFBC), TM3 = LD-CDD), and the first terminal 41a A diversity scheme may be designated to the second terminal 42a through signaling such as RRC.

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 the SFBC in the case of a two-port configuration, while in other cases, it may calculate and report the RI and/or CQI assuming a precoder cycling scheme.

In some embodiments, the first terminal 41a may preselect a precoder to use for data transmission (eg, a precoder cycling scheme), and a reference signal (eg, DMRS, precoded CSI-) to which the selected precoder is applied. RS/SRS, etc.) may be transmitted to the second terminal 42a. Accordingly, the degree of freedom in precoder selection in the first terminal 41a may increase, and the second terminal 42a may more easily generate CSI. For example, the second terminal 42a may assume an identity matrix as a precoder and may calculate RI and/or CQI.

In some embodiments, when the first terminal 41a transmits the precoded reference signal, the first terminal 41a assumes that the reference signal port represents a candidate DMRS port, ie, a data layer, when transmitting data. can Accordingly, the first terminal 41a may transmit a reference signal to the second terminal 42a by applying precoders applied to each layer among the candidate precoders to different RS ports, and the second terminal 42a can determine and report at least one reference signal port index to which the precoder most suitable for data transmission is applied to the first terminal 41a. In the second terminal 42a, the number of reference signal port indexes selected and reported by the second terminal 42a is equal to the number of ranks, and each reference signal (eg, CSI-RS/SRS) selected by the second terminal 42a ), it can be assumed that the channel of the port is used for each layer transmission, and can calculate and report the CQI.

In some embodiments, in the case of DMRS related to PSBCH, as described above with reference to FIG. 4A , the bandwidth of the DMRS may be smaller than the bandwidth of the PSSCH, and the second terminal 42a determines that the channel of the DMRS is the same for the PSSCH bandwidth. It can be assumed that this is the case, and the CQI can be calculated and reported.

In some embodiments, the second terminal 42a may report the 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 in the same manner as the above-described precoded reference signal, but measuring a rank higher than the transmission rank of DMRS is not recommended. It can be impossible. Accordingly, the second terminal 42a may report the rank offset indicator, and the rank offset indicator may request the first terminal 41a to increase or decrease the rank with respect to the currently received DMRS rank.

The second terminal 42a may calculate the SNR and/or SINR based on the above-mentioned precoding assumptions, such as SFBC, LD-CDD or precoding cycling, and the SNR and/or SINR and its corresponding capacity and/or CSI Based on the index, an optimal RI and/or CQI may be derived. In some embodiments, rank restrictions and/or codebook subset restrictions may be applied to the codebook described above. For example, only some RIs and/or PMIs designated as a higher-layer among the entire codebook may be used for CSI calculation and reporting.

- If there are two or more TX antenna ports of the first terminal 41a and there is a PMI report

The second terminal 42a is suitable for the configuration of the first terminal 41a and the second terminal 42a, for example, the number of TX antenna ports, NR/LTE, transmission mode for LTE, transform precoding for NR on/off, etc. Based on the codebook, an optimal RI, PMI and/or CQI may be derived and reported. For example, the second terminal 42a may calculate the SNR and/or SINR corresponding to each PR and PMI pair in the codebook, and based on the capacity and/or CSI index corresponding to the calculated SNR and/or SINR An optimal RI and PMI pair and a corresponding CQI may be calculated. In some embodiments, data transmission may be based on uplink transmission, and thus PMI may be determined based on the uplink codebook defined in document 2 and document 3 . Also, in some embodiments, rank restrictions and/or codebook subset restrictions may be applied to the codebook, eg, some RIs and/or PMIs of the entire codebook are not used for CSI calculation and reporting. it can't be

18A to 18E are diagrams illustrating examples of tables referenced when reporting CSI according to exemplary embodiments of the present disclosure. Specifically, FIGS. 18A to 18E show examples of a CQI table. In some embodiments, the second terminal 42a of FIG. 4A may feed back the CSI to the first terminal 41a with reference to the tables of FIGS. 16A, 16B, and 17 . 18A to 18E will be described below with reference to FIG. 4A.

In some embodiments, based on the SNR (or SINR) region to be used for data transmission and the associated modulation and code rate (eg, whether repetition is used) (eg, FIGS. 16A, 16B, and 17 ) Different CQI tables may be used (regardless of the presence or absence of the PMI report described above with reference). For example, when a modulation order and/or inefficiency above a certain level is not used in V2X, or an excessive data transmission rate is not used, the modulation order and/or inefficiency area used in V2X is converted to a higher resolution. A covering CQI table may be used. Accordingly, more accurate CQI calculation and reporting may be possible, and more efficient data transmission may be possible.

In some embodiments, when there is no separate setting in NR V2X (default), the CQI table of FIG. 18A may be used. When 256QAM is used in NR V2X, the CQI table of FIG. 18b may be used, and when a lower inefficiency is used, the CQI table of FIG. 18c may be used. When only QPSK and 16QAM are used in LTE, the CQI table of FIG. 18D may be used. In addition, when data transmission based on repetition is used in LTE, the CQI table of FIG. 18E may be used.

In some embodiments, the second terminal 42a is based on the difference between the reported CQI and the measurement result of the PSSCH DMRS received from the first terminal 41a, the mapping between the CQI index of the CQI table and the CSI index can be changed For example, based on the SNR and/or SINR measured in the PSSCH DMRS, the second terminal 42a may calculate the DMRS indicator in a manner similar to the CQI derivation method described above. When the calculated DMRS indicator corresponds to a lower throughput than the previously reported CQI, the second terminal 42a may adjust the CSI indicator and the CQI mapping so that a lower CQI is reported. In addition, when the calculated DMRS indicator corresponds to a transmission amount higher than the previously reported CQI, the second terminal 42a may adjust the CSI indicator and CQI mapping so that a higher CQI is reported.

In some embodiments, the second terminal 42a may change the CSI indicator and CQI mapping based on the ACK/NACK result. For example, based on the ACK / NACK result of the PSSCH, the second terminal 42a may report a CQI higher than the derived CSI indicator when the BLER is good (eg, when the BLER is less than a threshold). If the BLER is not good (eg, if the BLER exceeds a threshold), a lower CQI than the derived CSI indicator may be reported.

In some embodiments, the second terminal 42a may report CQIs corresponding to each rank so that the first terminal 41a can more accurately determine the rank. In this case, the second terminal 42a may not perform a separate rank feedback. Also, in some embodiments, the second terminal 42a may calculate and report CSI for beam management. For example, CSI may include at least one CSI-RS Resource Index (CRI), L1-RSRP corresponding to CRI and at least one SRS Resource Index (SRI), and L1 corresponding to CRI. -RSRP and P-SSS / S-SSS may be included, and may include L1-RSRP corresponding to CRI. Also, in some embodiments, as described above with reference to FIGS. 15A and 15B , the second terminal 42a may report the CQOI to the first terminal 41a.

In some embodiments, the second terminal 42a may report the above-described CSI to the first terminal 41a on a PSSCH and/or a PSFCH. For example, the second terminal 42a may report CSI on PSSCH and/or PSFCH, and the first terminal 41a may provide control information for demodulation, for example, DCI, to the second terminal 42a. can An example in which CSI is reported on a channel different from the PSSCH and PSFCH will be described later with reference to FIG. 19 .

19 is a diagram illustrating an example of CSI feedback according to an exemplary embodiment of the present disclosure. Specifically, FIG. 19 shows an example in which CSI is reported to the base station 195 that controls sidelink data transmission.

Referring to FIG. 19 , the first terminal 191 may transmit at least one reference signal to the second terminal 192 , and the second terminal 192 generates CSI generated by measuring the at least one reference signal. It may report to the base station 195 . For example, the second terminal 192 may report CSI to the base station 195 on 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 provide a second transmission parameter based on the at least one transmission parameter. 2 It is possible to transmit data to the terminal 192 .

In the above-described CSI feedback scheme through PSSCH, PSFCH, PUCCH, PUSCH, etc., periodic CSI reporting and aperiodic CSI reporting may be possible. For example, when periodic CSI reporting is employed, link adaptation can be easily performed. In addition, when aperiodic CSI reporting is employed, the first terminal 41a of FIG. 4a and/or the base station 195 of FIG. 19 may, if necessary, send the CSI report to the second terminal of FIG. 4b through dynamic signaling such as DCI ( 42a) and/or the second terminal 192 of FIG. 19 may be instructed, and accordingly, CSI reporting may be triggered. CSI may be reported on a control channel and/or a shared channel, and the former uses predefined resources, while in the latter, the resource to be used may be specified by dynamic signaling such as DCI. have.

In some embodiments, when CSI is reported on a shared channel such as PSSCH or PUSCH, calculation and reporting of subband CSI may be performed in addition to wideband CSI, and on a non-shared channel such as PSFCH or PUCCH When CSI is reported as , only wideband CSI may be reported. The payload of the PSFCH may be smaller than that of the PSSCH, and free resource use may be possible in the PSSCH than that of the PSFCH. Accordingly, the subband CSI, in which the payload varies according to the CSI content (eg, the number of subbands) and a large payload is required, may be reported on the PSSCH. Such subband CSI report may be applied to a part of CSI (eg, CQI) or may be applied to the entire CSI.

In some embodiments, aperiodic CSI may be reported on the PSSCH and periodic CSI may be reported on the PSFCH. For example, aperiodic CSI reporting may be triggered in the second terminal 42a of FIG. 4A by the dynamic control information, and a PSSCH resource for reporting CSI may be allocated. In addition, in order to make the CSI reporting time of the second UE 42a of FIG. 4A more flexible, the first UE 41a of FIG. 4A sets the CSI reporting time of the second UE 42a dynamic control information such as DCI. It can also be specified through The second terminal 42a of FIG. 4A may identify a resource based on resource allocation and/or MCS included in control information that triggers aperiodic CSI reporting, and may report CSI using the identified resource. .

In some embodiments, when the payload size of CSI is small, such as when the CSI payload size is 1 codeword, subband CSI reporting is not included, or when not NR Type II CSI reporting, aperiodic CSI reporting may be transmitted on the PSFCH alone or multiplexed with HARQ ACK/NACN. The time/frequency resource of the PSFCH may be predefined, and accordingly, a separate resource allocation for aperiodic CSI reporting is omitted, so that simpler CSI feedback may be possible.

In some embodiments, aperiodic CSI reporting may be performed in conjunction with periodic CSI reporting. In addition, in some embodiments, when the transmission amount is relatively small in V2X, periodic CSI reporting may be omitted and only aperiodic CSI reporting may be performed, and inter-terminal communication may be performed based on the aperiodic CSI report. For example, when periodic link adaptation is not advantageous because the transmission time of data is not expected to be long, an aperiodic CSI trigger may be used.

In some embodiments, in consideration of a rapidly changing channel, fast CSI feedback for V2X may be employed. For example, CIS feedback may satisfy at least some of the following conditions, and the following conditions may be set as defaults in V2X without a separate setting.

- Limit the maximum number of ports (eg 4 ports)

- Maximum rank limit (eg 2)

- Only report broadband CSI

- Skip PMI reporting

- Use only single panel Type I codebook

- Use only a single resource for channel measurement

In some embodiments, although the existing CSI in NR is divided into part 1/2, only one part (eg, part 1) may be used in V2X. For example, there may be no change in the payload according to the CSI content, and thus simpler CSI decoding and aperiodic CSI reporting on the PSFCH may be possible.

A terminal performing data transmission and a terminal performing data reception in V2X may be interchanged. That is, the terminal transmitting the first data may be a terminal receiving the second data transmitted by the terminal receiving the first data. As described above, when data transmission occurs between both terminals in both directions, it may be inefficient to separately report a channel according to a data transmission direction. Accordingly, one of the terminals may calculate and report CSI, and the CSI may be used for data transmission in both directions. For example, in FIG. 19 , when the second terminal 192 among the first terminal 191 and the second terminal 192 reports CSI to the first terminal 191, the first terminal 191 sends the CSI to the first terminal 191. On the other hand, the second terminal 192 can transmit data to the second terminal 192 based on the channel state estimated by measuring at least one reference signal (eg, SRS) transmitted to the first terminal 191 . and a transmission parameter for transmitting data to the first terminal 191 based on the CSI corresponding thereto, for example, MCS, RI, PMI, etc. may be determined. Accordingly, the overhead for CSI reporting may be reduced compared to that of both the first terminal 191 and the second terminal 192 reporting CSI, and resources for transmission of a reference signal may be saved.

In some embodiments, the base station 195 may designate a terminal reporting CSI among the first terminal 191 and the second terminal 192 , for example, a “CSI-reference UE”. The terminal designated as "CSI-reference UE" by the base station 195 can calculate and report CSI, while the other terminal refers to the CSI and transmits data (without calculating and reporting CSI for its reception channel). for transmission parameters, such as MCS, rank, precoding, and the like. The base station 195 may directly (explicitly) designate a "CSI-reference UE", and provides a configuration for CSI reporting to one of both terminals and a signal configuration (eg, a reference signal) to the other terminal. By doing so, it is also possible to implicitly designate "CSI-reference UE". Such CSI report may be used not only when channel reciprocity is good, but also in other cases, for example, when a diversity scheme is used. For example, when one UE does not support CSI reporting in V2X, CSI may be commonly used for bi-directional channel estimation, and the UE determines whether CSI reporting is supported by UE capability signaling. Through this, the base station 195 may be notified. In some embodiments, a geometry-based UE group configured for reporting of HARQ ACK/NACN may be employed.

In some embodiments, the UE may report delta-CSI based on the MCS, rank and/or precoding assigned to it, and thus CSI feedback overhead may be reduced. For example, instead of a value that may represent the entire CQI, an index deviation for the characteristic CQI criterion may be reported. The UE can report only the index change amount based on the MCS, RI, and/or PMI assigned to it as a dynamic signal, and accordingly, CSI reporting efficiency by reducing the overhead in feedback using a channel with a small payload such as PSFCH This can be improved. In MCS and CQI, the CQI index serving as a reference may be a CQI index having the same code rate as the MCS specified by control information such as DCI for a reference resource, and delta-CQI may be calculated and reported. . In addition, in the aperiodic CSI, the CQI criterion may be a CQI index corresponding to the same code rate as the MCS designated by the DCI that triggered the aperiodic CSI report. This method may be advantageous when channel reciprocity is good, that is, when characteristics of uplink/downlink channels are similar.

20A and 20B are flowcharts illustrating examples of a method for communication between terminals according to exemplary embodiments of the present disclosure. Specifically, the flowcharts of FIGS. 20A and 20B show inter-terminal communication in consideration of the relative speed in the channel reciprocity scheme. As described above with reference to FIG. 4B , the first terminal 201a transmitting data may estimate the channel state without CSI feedback from the second terminal 202a. Hereinafter, content overlapping with each other in the description of FIGS. 20A and 20B will be omitted. 20A and 20B , the terminal is indicated as a user equipment (UE).

Referring to FIG. 20A , in step S10c , the second terminal 202a may transmit at least one reference signal to the first terminal 201a. For example, the second terminal 202a may transmit a CSI-RS and/or an SRS to the first terminal 201a. In some embodiments, the second terminal 202a may transmit at least one reference signal based on antenna switching, as described above with reference to FIGS. 8A, 8B and 9 . For example, the first terminal 201a may set an SRS resource set including a plurality of SRS resources to the second terminal 202a, and configure the second terminal 202a to perform antenna switching in the SRS resource set. can be set. Accordingly, the second terminal 202a may transmit the SRS to the first terminal 201a so that SRS resources can be transmitted in different antenna port groups, respectively, based on the configuration of the first terminal 201a. . In addition, the second terminal 202a may transmit the CSI-RS based on antenna switching, and based on the configuration of the first terminal 201a, so that symbols can be transmitted in different antenna groups, respectively, the first terminal SRS may be transmitted to 201a.

일 때, 데이터를 송신하는 채널

는 아래 [수학식 3]과 같이 나타낼 수 있다.In step S20c, the first terminal 201a may estimate the channel state based on at least one reference signal received from the second terminal 202a. A channel through which the first terminal 201a transmits data may be regarded as a Hermitian of a channel through which at least one reference signal is received. That is, the channel estimated by measuring at least one reference signal received from the second terminal 202a is

When , the channel through which data is transmitted

can be expressed as [Equation 3] below.

In some embodiments, when the number of RX antenna ports in the first terminal 201a is greater than or equal to the number of TX antenna ports, the first terminal 201a may have a channel state (eg, a TX antenna port) corresponding to a portion to be used for actual data transmission. Only the measurement result at the antenna port corresponding to ) can be used. In addition, in some embodiments, when the RX bandwidth of the first terminal 201a is equal to or greater than the TX bandwidth, the first terminal 201a may use the channel state only for a bandwidth corresponding to a portion to be used for actual transmission. Accordingly, The second terminal 202a may transmit a reference signal more simply, and the implementation of the second terminal 202a may be simplified.

In step S40c, the first terminal 201a may determine the transmission parameters. For example, the first terminal 201a may determine the transmission parameters based on the channel state estimated in step S20c. In step S50c, the first terminal 201a may measure the Doppler shift. For example, the second terminal 202a may transmit a reference signal for measurement of Doppler shift as well as estimation of a channel state to the first terminal 201a. For example, the second terminal 202a may transmit SRS, UL PT-RS, UL DMRS, etc. to the first terminal 201a. The first terminal 201a may measure the Doppler shift from at least one reference signal received from the second terminal 202a, and thus detect the relative velocities of the first terminal 201a and the second terminal 202a. can do.

In step S60c, the first terminal 201a may adjust the transmission parameter based on the detected relative speed. For example, based on the detected relative velocity, the first terminal 201a may calculate the MCS offset or change the MCS hysteresis, as described above with reference to FIG. 15A . In step S70c, the first terminal 201a may transmit transmission parameters including the adjusted at least one transmission parameter to the second terminal 202a, and in step S80c, the first terminal 201a transmits the data. 2 can be transmitted to the terminal 202a.

Referring to FIG. 20B , in step S10d, the second terminal 202b may transmit at least one reference signal to the first terminal 201b. For example, the second terminal 202b may transmit at least one reference signal for estimating the channel state by the first terminal 201b to the first terminal 201b. In step S20d, the first terminal 201b may estimate the channel state by measuring at least one reference signal, and may determine transmission parameters based on the channel state estimated in step S40d.

In step S50d, the first terminal 201b may measure a change in received power. For example, the first terminal 201b may measure the reception power of signals received from the second terminal 202b, for example, a reference signal, NACK/ACK, and the like, and based on the change in the reception powers, the first terminal 201b The relative speed of 201b and the second terminal 202b may be detected. That is, when the received power is increased, the first terminal 201b may determine that the second terminal 202b is approaching, and accordingly, the channel state may be determined to be good. On the other hand, when the received power is reduced, the first terminal 201b may determine that the second terminal 202b is moving away, and thus the channel state may be deteriorated.

In step S60d, the first terminal 201b may adjust at least one transmission parameter based on the detected relative speed. In step S70d, the first terminal 201b may transmit transmission parameters including the adjusted at least one transmission parameter to the second terminal 202b, and in step S80d, the first terminal 201b transmits the data. 2 can be transmitted to the terminal 202b.

21 shows an example of terminals performing inter-terminal communication according to an exemplary embodiment of the present disclosure. As shown in FIG. 21 , the first terminal 211 and the second terminal 212 may transmit and receive radio signals through any RAT, for example, LTE or NR. The first terminal 211 may refer to a terminal that transmits data in inter-terminal communication, and the second terminal 212 may refer to a terminal that receives data in inter-terminal communication. In some embodiments, the first terminal 211 and/or the second terminal 212 are any device that performs wireless communication, such as a mobile phone, home appliance, vehicle, autonomous vehicle, cross reality (XR) device. , a robot, an AI device, or the like. In this specification, the first terminal 211 or at least one processor 211_4 included in the first terminal 211 may be simply referred to as a first device, and the second terminal 212 or the second terminal ( At least one processor 212_4 included in 212 may be simply referred to as a second device.

The first terminal 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 the first signal SIG1 provided from the transceiver 211_2 and may provide the 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, a communication processor, or the like, 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 drawings.

In some embodiments, the at least one processor 211_4 may be implemented as a controller, a microcontroller, a microprocessor, or the like. At least one processor 211_4 may be implemented by hardware, firmware, software, or a combination thereof. For example, the 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). and the like. At least some of the operations described above with reference to the drawings may be implemented through firmware or software, and the firmware or software is included in the at least one processor 211_4 or a memory device accessed by the at least one processor 211_4 . can be stored in

The transceiver 211_2 may generate the first signal SIG1 by processing the RF signal received through the at least one antenna 211_6, and the at least one antenna 211_6 by processing the second signal SIG2. RF signal can be output through The transceiver 211_2 may include a mixer that converts an RF signal into a baseband and converts a baseband signal into an RF signal, and may further include an amplifier, a filter, and the like.

Similar to the first terminal 211 , the second terminal 212 may include a transceiver 212_2 , at least one processor 212_4 , and at least one antenna 212_6 .

22 is a block diagram illustrating a signal processing operation for transmission according to an exemplary embodiment of the present disclosure. In some embodiments, the operations illustrated in FIG. 22 may be performed by at least one processor 211_4 included in the first terminal 211 of FIG. 21 . Two or more of the operations illustrated in FIG. 22 may be integrated and performed despite the illustration of FIG. 22 .

In a first operation 221 , codewords may be scrambled. For example, coded bits may be scrambled in each of the codewords to be transmitted on the physical channel. In a second operation 222 , scrambled bits may be modulated. For example, modulation of the coded bits may be performed to generate complex-valued modulation symbols. In a third operation 223 , the modulated symbols may be mapped to a transmission layer. For example, the complex-valued modulation symbols for each of the codewords to be transmitted may be mapped to one or more transmission layers. In a fourth operation 224 , an output y may be generated by precoding the input x. For example, complex-valued modulation symbols on each transmit layer as input x may be precoded for transmission on antenna ports to produce output y. In a fifth operation 225 , the modulated symbols may be mapped to resource elements. For example, complex-value modulation symbols for each antenna port 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 for each antenna port.

Exemplary embodiments have been disclosed in the drawings and specification as described above. Although the embodiments have been described using specific terms in the present specification, these are used only for the purpose of explaining the technical spirit of the present disclosure and are not used to limit the meaning or the scope of the present disclosure described in the claims. . Therefore, it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the true technical protection scope of the present disclosure should be defined by the technical spirit of the appended claims.

Claims (20)

A method for a first device to transmit data to a second device in terminal-to-terminal communication, comprising:
obtaining at least one measurement value corresponding to the relative speed of the first device and the 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. The method according to claim 1,
transmitting at least one reference signal to the second device;
receiving channel state information from the second device; and
determining a plurality of transmission parameters based on the channel state information;
The adjusting of the at least one transmission parameter comprises adjusting the at least one transmission parameter of the plurality of transmission parameters. 3. The method according to claim 2,
The obtaining of the at least one measurement value comprises extracting the at least one measurement value from the channel state information. 4. The method according to claim 3,
The at least one measurement value comprises a value corresponding to a Doppler shift measured by the second device based on the at least one reference signal. 5. The method according to claim 4,
The at least one reference signal is at least one of a synchronization signal, a tracking reference signal (TRS), a phase tracking reference signal (PT-RS), a demodulation reference signal (DMRS), and a channel state information reference signal (CSI-RS). A method comprising one. 3. The method according to claim 2,
The step of obtaining the at least one measurement value comprises:
extracting, from the channel state information, the speed of the second device measured by the second device;
obtaining a speed of the first device; and
based on the speed of the first device and the speed of the second device, calculating the at least one measurement. The method according to claim 1,
receiving at least one reference signal from the second device;
estimating a channel state based on the at least one reference signal; and
determining a plurality of transmission parameters based on the estimated channel condition;
The adjusting of the at least one transmission parameter comprises adjusting the at least one transmission parameter of the plurality of transmission parameters. 8. The method of claim 7,
The obtaining of the at least one measurement value comprises measuring a Doppler shift based on the at least one reference signal. 9. The method of claim 8,
The at least one reference signal comprises at least one of a Sounding Reference Signal (SRS), a Phase Tracking Reference Signal (PT-RS), and a Demodulation Reference Signal (DMRS). 8. The method of claim 7,
The method further comprises measuring a received power change based on the at least one reference signal,
The obtaining of the at least one measurement value comprises calculating the at least one measurement value based on the received power change. The method according to claim 1,
Adjusting the at least one transmission parameter comprises:
adjusting the at least one transmission parameter to correspond to a higher data rate based on the at least one measurement corresponding to a negative relative speed; and
adjusting the at least one transmission parameter to correspond to a lower data transmission rate based on the at least one measurement corresponding to a positive relative rate. 12. The method of claim 11,
Adjusting the at least one transmission parameter to correspond to the higher data transmission rate includes increasing a Modulation and Coding Scheme (MCS) index,
and adjusting the at least one transmission parameter to correspond to the lower data transmission rate comprises decreasing the MCS index. The method according to claim 1,
receiving, from the second device, an acknowledgment corresponding to the transmission of the data; and
Further comprising the step of measuring an error rate (error rate) based on the acknowledgment,
and adjusting the at least one transmission parameter is performed when the error rate is below a first threshold or above a second threshold. The method according to claim 1,
receiving, from the second device, an acknowledgment corresponding to the transmission of the data; and
Further comprising the step of measuring an error rate (error rate) based on the acknowledgment,
Adjusting the at least one transmission parameter comprises:
if the error rate is less than a first threshold, adjusting the at least one transmission parameter to correspond to a higher data rate;
if the error rate is above a second threshold, adjusting the at least one transmission parameter to correspond to a lower data transmission rate; and
adjusting at least one of the first threshold value and the second threshold value based on the at least one measurement value. A method for a second device to receive data from a first device in terminal-to-terminal communication, the method comprising:
receiving from the first device at least one transmission parameter, adjusted based on the relative speeds of the first device and the second device; and
receiving data from the first device based on the adjusted at least one transmission parameter. 16. The method of claim 15,
receiving at least one reference signal from the first device;
generating channel state information based on the at least one reference signal; and
Further comprising the step of providing the channel state information to the first device,
The at least one transmission parameter is included in a plurality of transmission parameters determined by the first apparatus based on the channel state information. 17. The method of claim 16,
The generating of the channel state information comprises:
measuring a Doppler shift based on the at least one reference signal; and
and generating the channel state information including a value corresponding to the Doppler shift. 17. The method of claim 16,
The generating of the channel state information comprises:
obtaining a speed of the second device; and
and generating the channel state information including the speed of the second device. 16. The method of claim 15,
transmitting at least one reference signal to the first device;
The method of claim 1, wherein the at least one transmission parameter is included in a plurality of transmission parameters determined by the first apparatus based on the at least one reference signal. A first device configured to perform communication between a second device and a terminal, comprising:
at least one transceiver; and
at least one processor configured to process a first signal received from the second device via the at least one transceiver and to generate a second signal to be transmitted to the second device via the at least one transceiver;
the at least one processor,
obtaining at least one measurement value corresponding to the relative speed of the first device and the 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 generate the second signal based on the adjusted at least one transmission parameter.

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