WO2020197610A1

WO2020197610A1 - Methods and apparatus for sidelink demodulation reference signals

Info

Publication number: WO2020197610A1
Application number: PCT/US2020/012512
Authority: WO
Inventors: Weimin Xiao; Majid GHANBARINEJAD; Philippe Sartori
Original assignee: Futurewei Technologies, Inc.
Priority date: 2019-03-28
Filing date: 2020-01-07
Publication date: 2020-10-01

Abstract

A method for performing sidelink (SL) communications includes obtaining, by the first SL UE, a configuration of a resource pool configured for SL communications, the configuration of the resource pool comprising one or more SL demodulation reference signals (SL-DMRS) configurations; selecting, by the first SL UE, a SL resource from the resource pool, the selected SL resource being associated with a SL-DMRS configuration; selecting, by the first SL UE, a SL-DMRS parameter in accordance with the SL-DMRS configuration; transmitting, by the first SL UE, a first SL control information (SCI) indicating the selected SL resource and the selected SL-DMRS parameter; and transmitting, by the first SL UE, to a second SL UE, a SL transmission in accordance with the selected SL resource and the selected SL-DMRS parameter.

Description

Methods and Apparatus for Sidelink Demodulation

Reference Signals

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Application No. 62/825,403, filed on March 28, 2019, entitled "System and Method for Sidelink Demodulation Reference Signal (SL-DMRS)," which application is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to methods and apparatus for digital communications, and, in particular embodiments, to methods and apparatus for sidelink demodulation reference signals (SL-DMRS).

BACKGROUND

It is expected that vehicle-to-eveiything (V2X) communications will play an essential role in the evolution of the automotive industry in the near future and revolutionize the field. Dedicated short-range communication (DSRC) by IEEE and the long-term evolution - vehicular (LTE-V) developed by 3GPP are two major vehicular communication technologies developed thus far.

The third generation partnership project (3GPP) has also approved a study item for the fifth generation (5G) new radio access technology (NR) V2X wireless communication with the goal of providing sG-compatible high-speed reliable connectivity for vehicular communications in the near future for applications such as safety systems and autonomous driving.

Device-to-device (D2D) mode of communication helps enable V2X. A major

improvement by NR V2X with respect to its counterpart LTE-V is that it is planned to support unicast communications, which will enable a vehicle to communicate with another specific vehicle, and groupcast communications, which will allow vehicles in a group of user equipments (UEs) to communicate. This is in contrast with LTE-V where vehicles only use a broadcast mode of communication that does not target any specific destination. Both LTE D2D and LTE-V allow UEs to communicate directly without network involvement in carrying the data. However, LTE D2D does not utilize channel state information (CSI) acquisition and link adaptation. Communications occur with a fixed modulation and coding scheme (MCS). While LTE-V supports only a broadcast mode of communication, not unicast or groupcast. LTE-V also does not support multiple layer (i.e., multiple input multiple output (MIMO)) transmission and hence has a rather simple demodulation reference signal (DMRS) design.

SUMMARY

According to a first aspect, a method for performing sidelink (SL) communications, the method implemented by a first SL user equipment (SL UE) is provided. The method comprising: obtaining, by the first SL UE, a configuration of a resource pool configured for SL communications, the configuration of the resource pool comprising one or more SL demodulation reference signals (SL-DMRS) configurations; selecting, by the first SL UE, a SL resource from the resource pool, the selected SL resource being associated with a SL-DMRS configuration; selecting, by the first SL UE, a SL-DMRS parameter in accordance with the SL-DMRS configuration; transmitting, by the first SL UE, a first SL control information (SCI) indicating the selected SL resource and the selected SL-DMRS parameter; and transmitting, by the first SL UE, to a second SL UE, a SL transmission in accordance with the selected SL resource and the selected SL-DMRS parameter.

In a first implementation form of the method according to the first aspect as such, the SL-DMRS parameter being an SL-DMRS antenna port index.

In a second implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the SL-DMRS parameter being an SL-DMRS pattern.

In a third implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the SL-DMRS configuration comprising a set of SL-DRMS ports.

In a fourth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, further comprising obtaining, by the first SL UE, the SL-DMRS configuration.

In a fifth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the SL transmission comprising a physical sidelink shared channel (PSSCH) transmission. In a sixth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the first SCI is transmitted to the second SL UE.

In a seventh implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the first SCI is broadcast to a plurality of SL UEs, including the second SL UE.

In an eighth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, further comprising broadcasting, by the first SL UE, a second SCI indicating the selected SL resource and the selected SL- DMRS parameter.

In a ninth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, obtaining the configuration of the resource pool comprising receiving a message including the configuration of the resource pool.

In a tenth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the message being a radio resource control (RRC) message.

In an eleventh implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, obtaining the configuration of the resource pool comprising receiving the configuration of the resource pool during an initial attachment procedure.

According to a second aspect, a method for performing SL communications is provided. The method implemented by a second SL UE. The method comprising; obtaining, by the second SL UE, a configuration of a resource pool configured for SL communications; receiving, by the second SL UE, from a first SL UE, a first SCI indicating a selected SL resource and a selected SL-DMRS parameter, the selected SL resource being a member of the resource pool configured for SL communications; and receiving, by the second SL UE, from the first SL UE, a SL transmission in accordance with the selected SL resource and a SL-DMRS configuration associated with the selected SL-DMRS parameter.

In a first implementation form of the method according to the second aspect as such, the SL-DMRS parameter being an SL-DMRS antenna port index. In a second implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the SL-DMRS parameter being an SL-DMRS pattern.

In a third implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the SL-DMRS configuration comprising a set of SL-DRMS ports.

In a fourth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the SL transmission comprising a PSSCH transmission.

In a fifth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the first SCI being addressed to the second SL UE.

In a sixth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, further comprising receiving, by the second SL UE, a second SCI indicating the selected SL resource and the selected SL-DMRS parameter.

In a seventh implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, obtaining the configuration of the resource pool comprising receiving a message including the configuration of the resource pool.

In an eighth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the message being a RRC message.

In a ninth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, obtaining the configuration of the resource pool comprising receiving the configuration of the resource pool during an initial attachment procedure.

According to a third aspect, a transmitting SL UE is provided. The transmitting SL UE comprising: a non-transitoiy memory storage comprising instructions; and one or more processors in communication with the memory storage, wherein the one or more processors execute the instructions to: obtain a configuration of a resource pool configured for SL communications, the configuration of the resource pool comprising one or more SL-DMRS configurations; select a SL resource from the resource pool, the selected SL resource being associated with a SL-DMRS configuration; select a SL-DMRS parameter in accordance with the SL-DMRS configuration; transmit a first SCI indicating the selected SL resource and the selected SL-DMRS parameter; and transmit, to a receiving SL UE, a SL transmission in accordance with the selected SL resource and the selected SL-DMRS parameter.

In a first implementation form of the transmitting SL UE according to the third aspect as such, the SL-DMRS parameter being an SL-DMRS antenna port index.

In a second implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the SL-DMRS configuration comprising a set of SL-DRMS ports

In a third implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the one or more processors further executing the instructions to obtain the SL-DMRS configuration.

In a fourth implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the SL transmission comprising a physical sidelink shared channel (PSSCH) transmission.

In a fifth implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the first SCI is transmitted to the receiving SL UE.

In a sixth implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the first SCI is broadcast to a plurality of SL UEs, including the receiving SL UE.

In a seventh implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the one or more processors further executing the instructions to broadcast a second SCI indicating the selected SL resource and the selected SL-DMRS parameter. In an eighth implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the one or more processors further executing the instructions to receive a message including the configuration of the resource pool.

In a ninth implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the message being a RRC message.

In a tenth implementation form of the transmitting SL UE according to the third aspect as such or any preceding implementation form of the third aspect, the one or more processors further executing the instructions to receive the configuration of the resource pool during an initial attachment procedure.

According to a fourth aspect, a receiving SL UE is provided. The receiving SL UE comprising: a non-transitoiy memory storage comprising instructions; and one or more processors in communication with the memory storage, wherein the one or more processors execute the instructions to: obtain a configuration of a resource pool configured for SL communications; receive, from a transmitting SL UE, a first SCI indicating a selected SL resource and a selected SL-DMRS parameter, the selected SL resource being a member of the resource pool configured for SL communications; and receive, from the transmitting SL UE, a SL transmission in accordance with the selected SL resource and a SL-DMRS configuration associated with the selected SL-DMRS parameter.

In a first implementation form of the receiving SL UE according to the fourth aspect as such, the SL-DMRS parameter being an SL-DMRS antenna port index.

In a second implementation form of the receiving SL UE according to the fourth aspect as such or any preceding implementation form of the fourth aspect, the SL-DMRS configuration comprising a set of SL-DRMS ports.

In a third implementation form of the receiving SL UE according to the fourth aspect as such or any preceding implementation form of the fourth aspect, the SL transmission comprising a PSSCH transmission. In a fourth implementation form of the receiving SL UE according to the fourth aspect as such or any preceding implementation form of the fourth aspect, the first SCI being addressed to the receiving SL UE.

In a fifth implementation form of the receiving SL UE according to the fourth aspect as such or any preceding implementation form of the fourth aspect, the one or more processors further executing the instructions to receive a second SCI indicating the selected SL resource and the selected SL-DMRS parameter.

In a sixth implementation form of the receiving SL UE according to the fourth aspect as such or any preceding implementation form of the fourth aspect, the one or more processors further executing the instructions to receive a message including the configuration of the resource pool.

In a seventh implementation form of the receiving SL UE according to the fourth aspect as such or any preceding implementation form of the fourth aspect, the one or more processors further executing the instructions to receive the configuration of the resource pool during an initial attachment procedure.

An advantage of a preferred embodiment is that demodulation reference signals (DMRSs) are configured, indicated, and signaled using robust, low communications overhead techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

Figure l illustrates an example communications system;

Figures 2A-2B illustrate diagrams of example Type-A front-loaded demodulation reference signals (DMRSs) with 2 additional DMRSs;

Figure 3 illustrates a diagram of example Type-B front-loaded DMRSs with 2 additional DMRSs;

Figures 4A-4B illustrate type-i and type-2 frequency DMRS patterns in New Radio (NR) Rel-15; Figure 5A illustrates a flow diagram of example operations occurring in an access node allocating and signaling sidelink DMRS (SL-DMRS) resources to sideline (SL) UEs according to example embodiments presented herein;

Figure 5B illustrates a flow diagram of example operations occurring in a transmitting UE as the transmitting UE receives an allocation of SL-DMRS resources and makes a SL transmission according to example embodiments presented herein;

Figure 5C illustrates a flow diagram of example operations occurring in a receiving UE as the receiving UE receives an allocation of SL-DMRS resources and receives a SL transmission according to example embodiments presented herein;

Figure 6A illustrates a flow diagram of example operations occurring in an access node allocating and signaling SL-DMRS resources to SL UEs, using mode 1 operation according to example embodiments presented herein;

Figure 6B illustrates a flow diagram of example operations occurring in a transmitting UE as the transmitting UE receives an allocation of SL-DMRS resources and makes a SL transmission, using mode 1 operation according to example embodiments presented herein;

Figure 6C illustrates a flow diagram of example operations occurring in a receiving UE as the receiving UE receives an allocation of SL-DMRS resources and receives a SL transmission, using mode 1 operation according to example embodiments presented herein;

Figure 7A illustrates a flow diagram of operations occurring in an access node participating in SL communications when the transmitting UEs select their own SL- DMRS ports from a resource pool (RP) of SL-DMRS ports according to example embodiments presented herein;

Figure 7B illustrates a flow diagram of operations occurring in a transmitting UE participating in SL communications when the transmitting UEs select their own SL- DMRS ports from a RP of SL-DMRS ports according to example embodiments presented herein;

Figure 7C illustrates a flow diagram of operations occurring in a receiving UE participating in SL communications when the transmitting UEs select their own SL- DMRS ports from a RP of SL-DMRS ports according to example embodiments presented herein; Figure 8A illustrates a flow diagram of example operations occurring in a transmitting UE participating in SL transmissions utilizing a RP of SL-DMRS resources according to example embodiments presented herein;

Figure 8B illustrates a flow diagram of example operations occurring in a receiving UE participating in SL transmissions utilizing a RP of SL-DMRS resources according to example embodiments presented herein;

Figure 9A illustrates a flow diagram of example operations occurring in a transmitting UE participating in SL transmissions utilizing a RP of SL-DMRS resources, with indication broadcasts according to example embodiments presented herein;

Figure 9B illustrates a flow diagram of example operations occurring in a receiving UE participating in SL transmissions utilizing a RP of SL-DMRS resources, with indication broadcasts according to example embodiments presented herein;

Figure to illustrates a diagram of an example slot including three PSSCHs according to example embodiments presented herein;

Figure 11 illustrates an example communication system according to example embodiments presented herein;

Figures 12A and 12B illustrate example devices that may implement the methods and teachings according to this disclosure;

Figure 13 is a block diagram of a computing system that may be used for implementing the devices and methods disclosed herein;

Figure 14 illustrates a block diagram of an embodiment processing system for performing methods described herein, which may be installed in a host device according to example embodiments presented herein; and

Figure 15 illustrates a block diagram of a transceiver adapted to transmit and receive signaling over a telecommunications network according to example embodiments presented herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The structure and use of disclosed embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific structure and use of embodiments, and do not limit the scope of the disclosure.

Figure t illustrates an example communications system too. Communications system too includes an access node 105 serving user equipments (UEs), such as UEs 110, 112,

114, 116, and 118. In a first operating mode, communications to and from a UE passes through access node 105. In a second operating mode, communications to and from a UE do not pass through access node 105, however, access node 105 typically allocates resources used by the UE to communicate when specific conditions are met. Access nodes may also be commonly referred to as Node Bs, evolved Node Bs (eNBs), next generation (NG) Node Bs (gNBs), master eNBs (MeNBs), secondary eNBs (SeNBs), master gNBs (MgNBs), secondary gNBs (SgNBs), network controllers, control nodes, base stations, access points, transmission points (TPs), transmission -reception points (TRPs), cells, carriers, macro cells, femtocells, pico cells, and so on, while UEs may also be commonly referred to as mobile stations, mobiles, terminals, users, subscribers, stations, and the like. Access nodes may be fixed location devices or located in a moving vehicle, such as an automobile, plane, train, boat, etc. UEs may also be located in a moving vehicle, such as a device that is part of the moving vehicle or a device used by a user located in or on the moving vehicle.

Access nodes may provide wireless access in accordance with one or more wireless communication protocols, e.g., the Third Generation Partnership Project (3GPP) long term evolution (LTE), LTE advanced (LTE-A), 5G, 5G LTE, 5G NR, High Speed Packet Access (HSPA), the IEEE 802.11 family of standards, such as

802.na/b/g/n/ac/ad/ax/ay/be, etc. While it is understood that communications systems may employ multiple access nodes capable of communicating with a number of UEs, only one access node and five UEs are illustrated for simplicity.

In LTE, demodulation reference signals (DMRSs) are associated with physical sidelink shared channels (PSSCHs), physical sidelink control channels (PSCCH), physical sidelink downlink channels (PSDCH), and physical sidelink broadcast channels (PSBCH). The DMRSs are generated in a manner similar to that of LTE physical uplink shared channels (PUSCHs), but there are some exceptions, which include:

- Different tables are used for parameters such as group/sequence hopping, cyclic shifts, number of layers and antennas ports, etc.

- The set of physical resource blocks used in the mapping process should be identical to the corresponding PSSCH/PSCCH/PSDCH/PSBCH transmission.

- The interleaved single carrier frequency division multiple access (IFDMA) index in the mapping process should be identical to that for the corresponding

PSSCH/PSCCH/PSDCH/PSBCH transmission.

- For sidelink (SL) transmission modes 3 and 4 on the PSSCH and PSCCH, the mapping shall use the orthogonal frequency division multiplexed (OFDM) symbol indices l = 2 and 1 =5 for the first slot in the subframe and l = 1 and / = 4 for the second slot in the subframe.

- For SL transmission modes 3 and 4 on the PSBCH, the mapping shall use the OFDM symbol indices l = 4 and 1 = 6 for the first slot in the subframe and l = 2 for the second slot in the subframe.

- For SL transmission modes 1 and 2, the pseudo-random sequence generator shall be initialized at the start of each slot fulfilling «_s ^p _s ^SSCH = 0. For SL transmission modes 3 and 4 the pseudo-random sequence generator shall be initialized at the start of each slot fulfilling «^PSSCH mod2 = 0. Note that this parameter represents the number of the current slot in the subframe pool.

- For SL transmission modes 3 and 4 on the PSCCH, the cyclic shift to be applied for all DMRS in a subframe shall be chosen randomly from four different values.

- For SL transmission modes 1 and 2 and SL discovery, the quantity m takes the values m = 0,1 and for SL transmission modes 3 and 4, the quantity m takes the values m = 0,1, 2, 3 for PSSCH and m = 0,1,2 for PSBCH. The parameter m is defined in 3GPP TS 36.211, V14.3.0.

- For SL transmission modes 3 and 4, the quantity

equals the decimal representation of CRC on the PSCCH transmitted in the same subframe as the PSSCH according to

2 ¹ ' with p and L . The parameters are defined in 3GPP TS

36.211, V14.3.0.

Reference signals in NR including DMRS, channel state information reference signal (CSI-RS), and phase tracking reference signal (PTRS) in the downlink, and their counterparts in the uplink are used for various purposes such as demodulation, CSI acquisition, beam management, mobility management, time/frequency/phase tracking, and so on. NR does not support a common reference signal (CRS). Therefore, the Uu link transmission scheme(s) will only be based on the DMRS. The Uu link DMRS in NR Rel- 15 is UE-specifically configured.

For DMRS time (e.g., OFDM symbols) and frequency (e.g., subcarriers) patterns, 2 types (Type-i and Type-2) of DMRS configurations are introduced in NR Rel-15. Type-i DMRS supports up to 4 orthogonal DMRS ports when 1 symbol is configured for DMRS transmission and up to 8 orthogonal DMRS ports when 2 symbols are configured. Type-2 DMRS supports up to 6 orthogonal DMRS ports when t symbol is configured for DMRS transmission and up to 12 orthogonal DMRS ports when 2 symbols are configured. These orthogonal DMRS ports are multiplexed in the time domain, frequency domain, and code domain (orthogonal cover code (OCC)). Both types of DMRS configurations are configurable for downlink and for uplink and they can be configured such that the DMRS for downlink and uplink are orthogonal to each other.

Two 16-bit configurable DMRS scrambling identifiers (IDs) are supported. The configuration is by radio resource control (RRC) signaling, for example, and, in addition, the scrambling ID is dynamically selected and indicated by a downlink control information (DCI) message. Before RRC configuring the 16-bit DMRS scrambling IDs, the physical cell ID is used for DMRS scrambling.

When mapping to symbol locations of a physical downlink shared channel

(PDSCH)/PUSCH transmission within a slot, the DMRS can be configured to be only on front-loaded (FL) symbol(s), or on additional DMRS symbol(s) as well. The additional DMRS, when present, should be the exact copy of the front-loaded DMRS for the PDSCH/PUSCH transmission, i.e., the same number of symbols, antenna ports, sequence, etc.

With the front-loaded-only DMRS, channel estimation can only rely on t or 2 symbols in an early part of the data transmission duration in order to speed up demodulation and reduce overall latency. However, without additional DMRS symbols to enable time domain interpretation/filtering, the channel estimation, and hence, overall performance may degrade even for scenarios with only moderate mobility.

For PDSCH/PUSCH resource mapping Type-A, the front-loaded DMRS starts from the third or fourth symbols of each slot (or each hop if frequency hopping is supported). For PDSCH/PUSCH mapping Type-B, the front-loaded DMRS starts from the first symbol of the transmission duration. The number of additional DMRSs can be l, 2, or 3 per network configuration. The location of each additional DMRS depends on the transmission duration (i.e., number of OFDM symbols) of the PDSCH/PUSCH transmission and follows a set of general rules for better channel estimation

performance. These rules allow no more than 2 OFDM symbols for PDSCH after the last DMRS, allow 2 to 4 symbols between neighboring DMRSs, and DMRSs are almost evenly distributed in time. Figures 2A-2B illustrate diagrams of example Type-A front-loaded DMRSs with 2 additional DMRSs 200. As an example, a first Type-A front-loaded DMRS with 2 additional DMRS 210 includes a front-loaded DMRS 212 in slot #3 with 2 additional DMRSs 214 and 216 in slots #6 and #9, respectively. As another example, a second Type- A front-loaded DMRS with 2 additional DMRS 220 includes a front-loaded DMRS 222 in slot #3 with 2 additional DMRSs 224 and 226 in slots #7 and #11, respectively. As another example, a third Type-A front-loaded DMRS with 2 additional DMRS 230 includes a front-loaded DMRS 232 in slot #2 with 2 additional DMRSs 234 and 236 in slots #6 and #9, respectively. As another example, a fourth Type-A front-loaded DMRS with 2 additional DMRS 240 includes a front-loaded DMRS 242 in slot #2 with 2 additional DMRSs 244 and 246 in slots #7 and #11, respectively.

Figure 3 illustrates a diagram of example Type-B front-loaded DMRSs with 2 additional DMRSs 300. As an example, a first Type-B front-loaded DMRS with 2 additional DMRS 310 includes a front-loaded DMRS 312 in slot #0 with 2 additional DMRSs 314 and 316 in slots #3 and #6, respectively. As another example, a second Type-B front-loaded DMRS with 2 additional DMRS 320 includes a front-loaded DMRS 322 in slot #0 with 2 additional DMRSs 324 and 326 in slots #4 and #8, respectively.

The patterns and ports of additional DMRS are the same as those of front -loaded DMRS, with the number of additional DMRS and their positions being configured by RRC signaling. A maximum of 1 additional DMRS for a 2-symbol front-loaded DMRS, and a maximum of 3 additional DMRS for a l-symbol front-loaded DMRS are supported.

The positions of the additional DMRS are independent of that of front-loaded DMRS, and may be determined by the actual number of symbols of the front-loaded DMRS, PDSCH/PUSCH mapping type, maximum number of additional DMRS, and

PDSCH/PUSCH duration in symbols. For PDSCH/PUSCH mapping type A, a duration in symbols is defined as the duration between the 1st OFDM symbol of the slot and the last OFDM symbol of the scheduled PDSCH/PUSCH resources in the slot. For

PDSCH/PUSCH mapping type B, a duration in symbols is defined as the number of OFDM symbols of scheduled PDSCH/PUSCH resources as signaled.

NR supports 4 front-loaded DMRS patterns (2 types, each type with 1 or 2 symbols) for PDSCH/PUSCH data demodulation. The front-loaded DMRS pattern is configured by the RRC as follows:

- Configuration type 1 (supported for cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) and discrete Fourier transform spread OFDM (DFT-S- OFDM)): - l-symbol pattern is configured with Comb 2, i.e., every second resource element (RE) is used for the DMRS pattern, and a cyclic shift of 2 different values is supported. This option supports up to 4 ports.

- 2-symbol patter is configured with Comb 2, and a cyclic shift of 2 different values is supported. A time-domain OCC (TD-OCC) with two different values ({1 1} and {1 -1}) is also allowed over the two symbols, which increases the number of ports to up to 8 ports.

- Configuration type 2 (supported for CP-OFDM only):

- l-symbol pattern is configured with a 2-value frequency-division OCC (FD-OCC) across adjacent REs in the frequency domain, and supports up to 6 ports.

- 2-symbols pattern is also configured with a 2-value FD-OCC across adjacent REs in the frequency domain, and in addition, a 2-value TD-OCC ({1,1} and {1,- 1}) is also supported over the two symbols, increasing the number of ports to up to 12 ports.

In NR Rel-15, the access node should indicate the location and number of DMRS symbols to the UE for proper processing by the UE. This indication is performed at two stages by RRC signaling and DCI signaling. First, a maximum of 1 or 2 symbols for front-loaded DMRS is configured by RRC signaling for PUSCH or PDSCH. Then, the actual number for each instance is indicated by a DCI through an index to a table if a maximum of 2 symbols is configured for front-loaded DMRS.

The configurations described above are typically applied to 14 -symbol slots. Additionally, for 2/4/ 7-symbol non-slot based scheduling, type 1 and type 2 are both supported as follows: for 2/4-symbol transmissions, only l-symbol front-loaded DMRS is supported; and for 7-symbol, both 1- or 2-symbol front-loaded DMRS are supported.

Figures 4A-4B illustrate of type-i and type-2 frequency DMRS patterns in NR Rel-15. Diagram 400 of Figure 4A illustrates DMRS configuration type 1 single symbol front- loaded DMRS pattern 405 and double symbol front -loaded DMRS pattern 410. Diagram 450 of Figure 4B illustrates DMRS configuration type 2 single symbol front-loaded DMRS pattern 455 and double symbol front-loaded DMRS pattern 460.

On the maximum number of orthogonal DMRS ports, the following apply for UL/DL CP- OFDM. For single-user multiple-input multiple-output (SU-MIMO), a maximum of 8 orthogonal DMRS ports are supported for downlink and a maximum of 4 orthogonal DMRS ports are supported for uplink as follows:

- For the downlink with Type 1, 4 ports for l-symbol DMRS and 8 ports for 2- symbol DMRS are supported per UE. - For the downlink with Type 2, 6 ports for l-symbol DMRS and 8 ports for 2-symbol DMRS are supported per UE.

- For the uplink with Type t or Type 2, 4 ports for l-symbol or 2-symbol DMRS are supported per UE. For multiuser multiple-input multiple-output (MU-MIMO), a maximum of 12 orthogonal DMRS ports are supported for both downlink and uplink as follows:

- For Type 1, 2 ports for l-symbol or 2-symbol are supported.

- For Type 2, 4 ports for l-symbol or 2-symbol are supported.

For DFT-s-OFDM, only rank-i is supported from UE perspective. Table 1 summarizes the number of ports supported for different cases.

Table 1: Summary of ports supported.

In order to achieve high spectrum efficiency, MU-MIMO transmission and reception has to adapt dynamically to channel conditions, UE distribution, data traffic, and so on. Dynamic adaptation implies that the number of MIMO layers and the occupied DMRS ports for the paired UEs vary with time (from transmission to transmission, for example) and frequency (from resource block group (RBG) to RBG, for example). More transmission layers may provide higher throughput at the cost of increased DMRS overhead.

In NR Rel-15, in addition to the DMRS ports used for data transmission (PDSCH or PUSCH) of the intended UE, a DCI also indicates the number of DMRS code division multiplexing (CDM) group(s) that are without data mapped to their corresponding REs. These DMRS CDM groups include the CDM group(s) of the UE’s DMRS ports, and in addition, the DMRS CDM groups may include CDM group(s) that may be for other UEs’ DMRS ports. Therefore, this signal can be used to indicate MU-MIMO transmission and dynamically adjust the associated overhead. For the downlink (and in a sense, the uplink as well), this mode of operation falls between transparent MU-MIMO where the UE has no knowledge of the paired UE(s) in terms of their used DMRS ports, and the non transparent MU-MIMO where the UE knows exactly which DMRS ports are used for other UE(s).

As mentioned previously, when the access node is scheduling a data/shared channel for a UE in the downlink or uplink, the access node can indicate to the UE, through DCI signaling, information on a DMRS transmission. Multiple tables are defined by the specification 3GPP TS 38.212, V15.4.0, which is hereby incorporated herein by reference in its entirety, for indication of information such as the CDM groups, the number of ports, and the number of symbols for the front -loaded DMRS. If there are additional DMRSs, similar values for the parameters apply to the additional DMRS as well.

Details of the DCI indications are as follows: For the uplink or downlink DMRS port indication for CP-OFDM and DFT-s-OFDM, multiple tables are defined by the standard specification for DMRS configuration Type 1 and Type 2 with a maximum 1 or 2 symbols for the front -loaded DMRS. The scheduled DMRS ports are indicated in the DCI. The actual number of front-loaded DMRS symbols is indicated in the DCI when the maximum number of symbols for the front-loaded DMRS is configured as 2. NR supports rate-matching of DMRS by the parameter "number of CDM groups without data" indicated in the DCI; values of "1", "2", or "3" for this parameter correspond to CDM group o, {0,1}, or {0,1,2}, respectively.

A UE in the MU-MIMO mode should first be scheduled with ports within a specific CDM group, and then across CDM groups (for a single TRP). The ports within the same CDM group should be quasi-collocated (QCL’ed), meaning that they should be transmitted by antennas and pass through channels that show similar large-scale properties. In practice, that may mean that the QCL’ed ports are implemented on a same physical antenna.

NR Rel-15 does not support multiuser configurations between UEs with different DMRS configurations with respect to the actual number of front-loaded DMRS symbols, the number of additional DMRS symbols, DMRS symbol location(s), and the DMRS configuration type. That simplifies the design of the receiver as the receiver only combines measurements with tightly similar configurations of DMRS for the purpose of demodulating signals from multiple UEs.

As related to PUSCH transmission, DMRS port indication is further determined by the rank associated with the PUSCH. According to an example embodiment, apparatus and methods for SL demodulation reference signal (SL-DMRS) configuring, indicating, and signaling are provided.

Differences between the SL-DMRS and the DMRS for Uu links include:

- Antenna configurations for both transmitter (TX) and receiver (RX). Due to the form limitation of SL terminals (e.g., UEs), the number of antennas for transmission and reception will be relatively limited to, for example, 2 or 4. In addition, due to the mobility of the UEs and limited availability of CSI, the number of layers for PSSCH transmission will also likely to be limited to up to 2 layers, for example. However, this does not mean only 2 (or 4) ports SL-DMRS are used, especially considering that Uu link DMRS already supports up to 8 or 12 antenna ports for configuration Type 1 or Type 2, respectively. Having a relatively large total number of SL-DMRS ports for SL can be very helpful to support multiple pairs (or groups) of PSSCH transmissions within a proximity where pairs (or groups) of UEs use different orthogonal subsets of DMRS ports. A detailed discussion of example grouping and configuring/signaling is provided below.

- Resource pools (RPs) can be configured for transmission and reception. How PSSCH transmissions are scheduled and signaled can be performed in different ways or known at different modes. Depending on the modes, communication and coordination between the UEs in different RPs can be very limited. Therefore, the selection and signaling of the SL-DMRS parameters (for example, scrambling ID, number of symbols, occupied ports, additional symbols and locations) at the transmitter side should consider that the receiver may not have full knowledge of the configurations of the transmission RP. A detailed discussion of RPs, and the selection and signaling of SL-DRMS parameters is provided below.

- Furthermore, exact locations of DMRS symbols for Uu link depend on the PDSCH/PUSCH duration and resource mapping types (e.g., A versus B if defined for the SL). For PSSCH, time-domain (in term of OFDM symbols) resource mapping maybe different, for example, at least due to different multiplexing schemes for PSCCH. A detailed discussion of resource mapping, multiplexing schemes, etc., for the PSCCH is provided below.

According to an example embodiment, apparatus and methods for configuring and indicating SL-DMRS ports are provided. For discussion purposes, the following notation is used: Let

denote the maximum number of SL-DMRS ports allowed by the technical standard, possibly depending on a frame structure type, SL-DMRS

configuration type, and so on. The N^^ax SL-DMRS ports in a set p^max may be numbered _as p^max = [c, C + 1, ... , C + N™^ax— 1}, where C is a constant. For example, if Nj ^ax = 12, and the technical standard lets C = 1000, then p^max = {1000, 1001, ... , 1011}.

In an embodiment, a UE can be configured with a set of SL-DMRS ports P c p^max containing N_P £ N™^ax ports determined by the configuration. The configuration may be associated with a RP. For example, while the technical standard may allow up to N_P ^nax = 12 SL-DMRS ports, a particular configuration may allow up to N_P = 8 ports for a particular RP.

However, not all transmissions use the full set of the SL-DMRS ports in P. Indeed, in a practical scenario for NR V2X or generally SL, a low number of ports may be desired for a particular transmission, e.g., 1 or 2 ports, while a SL-DMRS design similar to that of NR Rel-15 may allow for a larger number of SL-DMRS ports, e.g., 8 or 12. In this case, configuration and indication can be performed in multiple stages. For example, a configuration can be signaled by an radio resource control (RRC) message where a maximum number of ports N_P is determined in the configuration; then, another message signaled using RRC, medium access control (MAC), or the physical layer (PHY) can allocate/indicate a subset of the N_P ports for a UE or a group of UEs, a transmission or group of transmissions, a period of time, and so on. A detailed discussion is provided below.

There are multiple different options for signaling the other parameters included in the configuration. A typical scenario should provide sufficient information by the configuration so that the number of ports and other key parameters such as the configuration type is already determined in the configuration. If more flexibility is desired, such parameters may be determined in multiple messages. For example, in a mode-i communication scenario, the full configurations may be determined by the network. However, in a mode-2 communication or a possibly hybrid type of

communication mode, some parameters may be determined by the network while other parameters are left to, for example, a master UE to determine. A master UE is the UE making the SL transmission to the receiving UE(s).

Once the set of ports P is determined by the configuration, it is possible to

allocate/indicate a subset P; c p to each UE, as well as, transmission, time period, and so on. As mentioned before, the allocation/indication can be performed by a signaling using RRC, MAC, PHY, or a combination thereof. Communications that are closely multiplexed or overlapped in resources can therefore be allocated different subsets of port numbers. In an embodiment, in order to reduce overhead, the subset of port numbers can be determined by indexing to the set P rather than indicating the actual port numbers, where the index can take values from {0, 1, ... , N_P - 1}. For example, let pm^ax ₌ iooo, 1001, ... , 1011} and P = {1002, 1003, 1006, 1007} for a particular configuration. Then, a subset P; = {1006, 1007} can be indicated by the index set {2, 3} to the set P in an indication message.

Consider the following example of configuration and indication. An access node or a master UE sends a configuration to a group of UEs in a vicinity with N_P = 8. The configured ports are therefore indexed by {0, 1, ... , 7}. Then, the access node or the master UE schedules three instances of a PSSCH on overlapping resources for UEt, UE2, and UE3. The PSSCH of UEt is allocated port indices o and 1, PSSCH of UE2 is allocated port index 3, and PSSCH of UE3 is allocated port indices 5 and 7. It is desired to allocate mutually exclusive subsets of the available ports in a group of ports in the configuration because each port is allocated, by design, a sequence and resources that are orthogonal to those of the other ports. But two SL-DMRS transmissions with the same port number may cause a large interference/collision on each other, hence degrading the

demodulation performance. Indeed, if two UEs in a close proximity happen to be allocated a same port number or overlapping subsets of port numbers, their signals may not be distinguishable by the receiver and, as a result, the whole transmissions by the two UEs may be discarded.

According to an example embodiment, apparatus and methods for allocating and indicating port number subsets are provided. A variety of techniques may be used to allocate and indicate the port number subsets. In an embodiment, another RRC message is sent indicating which subset of the port numbers is allocated to which UE. In a special case, this RRC message may be combined with the earlier RRC message. A combination of the two solutions is also possible, namely an RRC configuration can determine a set of port numbers or simply a value for N_P, and also indicate which port numbers from the set is available for the subject UE. In this case, the configuration sent to a group of UEs in a vicinity may be similar in terms of the set of the port numbers, but different in the subset of port numbers allocated to each of the UEs in the group. The option of a RRC message allocating port numbers by RRC signaling can be considered a persistent option as the UE should normally maintain the configuration for the duration that an RRC connection exists, for a certain duration determined by a timer, for the duration of a SL, and so on.

In an embodiment, lower-layer signaling, where the signaling does not necessarily associate the port number allocation to a particular transmission, is used. For example, a MAC message may be used to allocate a port number subset to a particular UE. The allocation may override any earlier indication indicated by an RRC configuration or an earlier MAC indication. This option may be considered a semi-persistent indication as it allows the UEs to maintain flexibility at the configuration level, but the UEs may be allocated different subsets of the ports available by the RRC configuration through a more dynamic signaling technique. Again, the UE behavior can be defined in a way to maintain the subset of the allocated port numbers for the duration of a connection, a time duration determined by a timer, or a combination thereof.

Similarly to RRC signaling, MAC signaling allows for a more reliable communication technique as it requires an acknowledgement (ACK) from the receiver. Hence, the system can ensure that the subsets allocated to the different UEs are mutually exclusive at all times. If an access node, a master UE, or any other such entity that assigns port number subsets intends to release certain port numbers currently assigned to a UEt through a MAC signaling and reassign those port numbers to a UE2, the entity may (the access node, the master UE, or any other such entity that assigns port number subsets) only do so if UEt acknowledges that it has received the MAC signaling. Otherwise, the entity may retransmit the MAC message.

In an embodiment, a subset of port numbers is allocated through DCI signaling. Because this option has lower reliability compared to the aforementioned RRC or MAC signaling, it may be more suitable as an aperiodic option that merely allocates port numbers to individual transmissions (e.g., a particular PSSCH) and not to UEs. For example, in a mode-i communication scenario, the access node can schedule PSSCHs for UEt and UE2, allocating the port indices {o, l} and {2, 3} to UEt and UE2 transmissions, respectively. Next, the access node may choose to schedule for UEt, UE2, and UE3 allocating {o}, {1, 2} and {3} to the UEs, respectively.

Independent of the technique used for allocating and indicating port number subsets, the receiving UE also is informed of the port number/index allocations in order to measure SL-DMRS with the right sequences and on the right resources in order to then demodulate the signals of interest. In an embodiment, the receiving UE is informed through using signaling similar to the technique used for indicating port number subsets. For example, the receiving UE may be informed of the SL-DMRS configuration for the UE group without requiring an indication of a particular subset of ports to a particular UE or a particular PSSCH. Then, a second signaling may be used to indicate what subset of the ports are allocated to which UE. An advantage of this option is that it is sufficient for the SL control information (SCI) that schedules a PSSCH to mention the number of ports, rather than a whole subset, hence reducing overhead. For example, consider the example that a group of UEs is configured with an 8-port SL-DMRS configuration. Then, if UEt, UE2, UE3, UE4 are allocated port indices {o, l}, {2, 3}, {4, 5}, {6, 7}, respectively, and the receiving UE is aware of the latter UE-specific allocation, it is sufficient to signal only the number of ports in the SCI (in this case, an indicator that is only 1 bit in size is sufficient) and not the whole subset. For example, it can be understood that a value of o by UE3 indicates a one-port transmission through port 4, while a value of 1 by UE3 indicates a two-port transmission through ports 4 and 5. Other value mappings may also be used.

In summary, the set of SL-DMRS ports P p^max _can be determined by the

configuration, possibly through explicit indication of port numbers from p^max. Then, an allocation message may allocate a subset of the ports P_; c p to a UEi, either by providing actual ports numbers or by providing indices to the set P. Then, provided that information, the transmitting UE (UEi) and receiving UE(s) are aware of the port allocation P a subset P_{i 7} c p_t can be indicated for a PSSCH transmission PSSCHj from UEi, either by providing actual port numbers or by providing indices to either P_; or P.

Figure 5A illustrates a flow diagram of example operations 500 occurring in an access node allocating and signaling SL-DMRS resources to SL UEs. Operations 500 may be indicative of operations occurring in an access node as the access node allocates and signals SL-DMRS resources to SL UEs.

Operations 500 begin with the access node sending a SL-DMRS configuration (block 505). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P Q p^max .

The access node sends an allocation (block 507). The allocation may be UE-specific or group specific. The allocation specifies a subset of ports P_; c p to for UEi. The allocation may be sent using RRC signal, MAC signaling, or PHY signaling. The access node sends an indication scheduling a SL transmission for UEi (block 509). The indication of the SL transmission indicates SL-DMRS port R_{ί ;·}, where R_{ί ;·} c p for example. The indication scheduling the SL transmission may be sent using DCI.

Figure 5B illustrates a flow diagram of example operations 515 occurring in a transmitting UE as the transmitting UE receives an allocation of SL-DMRS resources and makes a SL transmission. Operations 515 may be indicative of operations occurring in a transmitting UE as the transmitting UE receives an allocation of SL-DMRS resources and the transmitting UE makes a SL transmission including a SL-DMRS on some of the allocated SL-DMRS resources. Operations 515 begin with the transmitting UE receiving a SL-DMRS configuration (block 520). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P p^maX _' T g transmitting UE receives an allocation (block 522). The allocation may be UE-specific or group specific. The allocation specifies a subset of ports P_; c p for the transmitting UE. The transmitting UE receives an indication scheduling a SL

transmission (block 524). The indication scheduling the SL transmission may be received as DCI. The indication of the SL transmission also indicates SL-DMRS port R_{ί 7·}, where Pi_j c p for example. The SL-DMRS port R_{ί ;·} may be where the SL-DMRS of the SL transmission will be located. The transmitting UE transmits an indication scheduling a PSSCHj transmission (block 526). The indication also indicates the SL-DMRS port _{i 7} used to convey the SL-DMRS of the SL transmission. The indication scheduling the PSSCHj transmission may be transmitted as SCI. The indication may be transmitted to a receiving UE, the UE that is the target of the SL transmission. The transmitting UE makes the SL transmission (block 528). The SL transmission includes the SL-DMRS conveyed on SL-DMRS port R_{ί ;·}.

Figure 5C illustrates a flow diagram of example operations 535 occurring in a receiving UE as the receiving UE receives an allocation of SL-DMRS resources and receives a SL transmission. Operations 535 may be indicative of operations occurring in a receiving UE as the receiving UE receives an allocation of SL-DMRS resources and the receiving UE receives a SL transmission including a SL-DMRS on some of the allocated SL-DMRS resources.

Operations 535 begin with the receiving UE receiving a SL-DMRS configuration (block 540). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P c p^,na* .

The receiving UE receives an allocation (block 542). The allocation may be UE-specific or group specific. The allocation specifies a subset of ports _j c p for the transmitting UE, which will be making a SL transmission to the receiving UE. The receiving UE receives control information scheduling a SL transmission (block 544). The control information may be in the form of DCI or SCI. The control information includes an indication of the SL-DMRS port R_{ί 7·} used to convey the SL-DMRS of the SL transmission. The receiving UE receives the SL transmission (block 546). The SL transmission includes the SL-DMRS conveyed on SL-DMRS port P_i In the flow diagram of access node operations shown in Figure 5A (and in other flow diagrams of access node operations below), the operations may also be applicable to other network entities or scheduling entities (such as a master UE). Additionally, in the situation with configuration or preconfiguration by the network or the technical standard, the flow diagram of access node operations may not be applicable. In such situation, the transmitting UE and the receiving UE may obtain the configuration or preconfiguration by methods other than receiving messages over-the-air. As an example, the UEs may receive the configuration or preconfiguration upon attachment to the communications system, or the configuration or preconfiguration may be specified by the technical standard or operator of the communications system.

In the example embodiments illustrated in Figure 5A-5C, if the receiving UE is aware of a particular SL-DMRS configuration with N ports, but is unaware of the UE -specific allocation, then a total of 2 * log₂N bits are used in the SCI or DCI to indicate two ports. The techniques disclosed in the example embodiments are robust because the access node or the master UE that allocate the SL-DMRS ports do not need to inform a large number of potential receivers of the SL-DMRS port allocations. Instead, the DCI (used in mode 1) or the SCI (used in mode 2) that carries the PSSCH scheduling information will be self-contained, including the SL-DMRS port allocation.

Figure 6A illustrates a flow diagram of example operations 600 occurring in an access node allocating and signaling SL-DMRS resources to SL UEs, using mode 1 operation. Operations 600 may be indicative of operations occurring in an access node as the access node allocates and signals SL-DMRS resources to SL UEs using mode 1 operation.

Operations 600 begin with the access node sending a SL-DMRS configuration (block 605). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P c p^,na* .

The access node sends an allocation (block 607). The allocation may be UE-specific or group specific. The allocation specifies a subset of ports P_; c p to for UEi. The allocation may be sent using RRC signal, MAC signaling, or PHY signaling. The access node sends an indication scheduling a SL transmission for UEi (block 609). The indication of the SL transmission indicates SL-DMRS port R_{ί ;·}, where R_{ί ;·} c p for example. The indication scheduling the SL transmission may be sent using DCI.

Figure 6B illustrates a flow diagram of example operations 615 occurring in a transmitting UE as the transmitting UE receives an allocation of SL-DMRS resources and makes a SL transmission, using mode 1 operation. Operations 615 may be indicative of operations occurring in a transmitting UE as the transmitting UE receives an allocation of SL-DMRS resources and the transmitting UE makes a SL transmission including a SL- DMRS on some of the allocated SL-DMRS resources, using mode t operation.

Operations 615 begin with the transmitting UE receiving a SL-DMRS configuration (block 620). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports p pm^aX _' T g transmitting UE receives an allocation (block 622). The allocation may be UE-specific or group specific. The allocation specifies a subset of ports _; c p for the transmitting UE. The transmitting UE receives an indication scheduling a SL

transmission (block 624). The indication scheduling the SL transmission may be received as DCI. The indication of the SL transmission also indicates SL-DMRS port R_{ί 7·}, where Pi_j c p for example. The SL-DMRS port R_{ί ;·} may be where the SL-DMRS of the SL transmission will be located. The transmitting UE transmits an indication scheduling a PSSCHj transmission (block 626). The indication also indicates the SL-DMRS port _{i 7} used to convey the SL-DMRS of the SL transmission. The indication scheduling the PSSCHj transmission may be transmitted as SCI. The indication may be transmitted to a receiving UE, the UE that is the target of the SL transmission. The transmitting UE makes the SL transmission (block 628). The SL transmission includes the SL-DMRS conveyed on SL-DMRS port R_{ί ;·}.

Figure 6C illustrates a flow diagram of example operations 635 occurring in a receiving UE as the receiving UE receives an allocation of SL-DMRS resources and receives a SL transmission, using mode 1 operation. Operations 635 maybe indicative of operations occurring in a receiving UE as the receiving UE receives an allocation of SL-DMRS resources and the receiving UE receives a SL transmission including a SL-DMRS on some of the allocated SL-DMRS resources, using mode 1 operation.

Operations 635 begin with the receiving UE receiving a SL-DMRS configuration (block 640). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P c p^,na* .

The receiving UE receives control information scheduling a SL transmission (block 642). The control information may be in the form of DCI or SCI. The control information includes an indication of the SL-DMRS port R_{ί ;·} used to convey the SL-DMRS of the SL transmission. The receiving UE receives the SL transmission (block 644). The SL transmission includes the SL-DMRS conveyed on SL-DMRS port R_{ί ;·}. In an embodiment, a set of SL-DMRS ports is a pool of ports (i.e., a RP) from which a UE is able to select a subset of SL-DMRS ports. The UE may select a subset of SL-DMRS ports for each SL transmission. Alternatively, the UE may select a subset of SL-DMRS ports for multiple SL transmissions. A RP of SL-DMRS ports is particularly useful for mode 2 communications where involvement of a central entity (such as an access node or a master UE) is not desired. Instead, each transmitting UE is able to schedule a PSSCH transmission using a SCI is also able indicate, in the SCI, for example, which of the SL- DMRS ports in the RP of SL-DMRS ports is used for the transmission of the SL-DMRS. The receiving UE tunes to the indicated SL-DMRS ports and makes measurements for the demodulation of the PSSCH. The indication may also be helpful for any PSSCH transmission on overlapping resources because it allows unintended UEs to measure interference and use the interference measurements into account when demodulating their own desired signals.

Figure 7A illustrates a flow diagram of operations 700 occurring in an access node participating in SL communications when the transmitting UEs select their own SL- DMRS ports from a RP of SL-DMRS ports. Operations 700 maybe indicative of operations occurring in an access node as the access node participates in SL

communications when the transmitting UEs select their own SL-DMRS ports from a RP of SL-DMRS ports.

Operations 700 begin with the access node sending a SL-DMRS configuration (block 705). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P c p^,na* .

Figure 7B illustrates a flow diagram of operations 710 occurring in a transmitting UE participating in SL communications when the transmitting UEs select their own SL- DMRS ports from a RP of SL-DMRS ports. Operations 710 may be indicative of operations occurring in a transmitting UE as the transmitting UE participates in SL communications when the transmitting UEs select their own SL-DMRS ports from a RP of SL-DMRS ports.

Operations 710 begin with the transmitting UE receiving a SL-DMRS configuration (block 715). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P p^maX _' T g transmitting UE selects the SL-DMRS port R_{ί ;·}, where R_{ί ;· Q} P_t (block 717). The transmitting UE transmits an indication scheduling a SL transmission (block 719). The indication may be in the form of a SCI. The indication also indicates the SL-DMRS port Pi_j. The indication may be transmitted to a receiving UE, the UE that is the target of the SL transmission. The transmitting UE makes the SL transmission (block 528). The SL transmission includes the SL-DMRS conveyed on SL-DMRS port R_{ί ;·}.

Figure 7C illustrates a flow diagram of operations 725 occurring in a receiving UE participating in SL communications when the transmitting UEs select their own SL- DMRS ports from a RP of SL-DMRS ports. Operations 725 may be indicative of operations occurring in a receiving UE as the receiving UE participates in SL

Operations 725 begin with the receiving UE receiving a SL-DMRS configuration (block 730). The SL-DMRS configuration may be sent using RRC signal, MAC signaling, or PHY signaling. The SL-DMRS configuration determines a set of SL-DMRS ports P c p^,na* . The receiving UE receives an indication scheduling a SL transmission (block 732). The control information may be in the form of SCI. The indication also indicates the SL- DMRS port Pi used to convey the SL-DMRS of the SL transmission. The receiving UE receives the SL transmission (block 734). The SL transmission includes the SL-DMRS conveyed on SL-DMRS port R_{ί ;·}.

In the example embodiment where the transmitting UE selects the SL-DMRS port from the RP of SL-DMRS ports, there is a non-zero probability of different transmitting UEs operating in the same general vicinity selecting the same SL-DMRS port. When such a situation occurs, interference that is destructive to the signal may occur. In this situation, the receiving UE may report to the transmitting UE that there was a SL-DMRS port selection collision, and that this collision is the reason that the signal could not be properly demodulated. The information provided in the report may be useful in link adaptation and for scheduling purposes. As an example, the transmitting UE may select a different subset of SL-DMRS ports and re-transmit over the different subset of SL-DMRS ports.

In general, interference arises when multiple SL-DMRS transmissions occur over the same SL-DMRS ports in the same general vicinity. Instead of eliminating the

interference, the different UEs in a group of UEs that are configured with the same set of SL-DMRS ports P Q p^max have the opportunity of transmitting SL-DMRSs that are orthogonal by design through the allocation of sequences and resources. Therefore, provided that the receivers of the SL transmissions are also aware of the full

configuration with the set of SL-DMRS ports P, the UE can measure not only the SL- DMRS in their transmission of interest, but also the SL-DMRS in the interfering transmissions, hence enabling the UE to be able to obtain the CSI required to demodulate and receive their transmission of interest, while taking into account the interference caused by the other overlapping transmissions in the vicinity. Furthermore, the interference detected by the receiver can be used to inform the transmitter(s) and/or the scheduler of a possibly large or prohibitive interference, which can be used for MCS adaptation, power control, scheduling, and so on. A detailed discussion of these options, and more, are provided below.

Because the pool of SL-DMRS ports (which, in current technical standards, is at a maximum of 8 or 12 ports, for example) may be too small compared to the total number of UEs operating in a same general vicinity, configurations may be associated to other parameters such as RPs and UE location in order to provide additional degrees of freedom. Indeed, when RPs are not overlapping, there is no risk of interference between SL-DMRSs, hence similar configurations can be used conveniently. A detailed discussion is presented below. An association with UE location is yet another degree of freedom because it allows for overlapping configurations in sufficiently distant areas, hence reducing the probability of large interference.

Any of the example embodiments of this disclosure may be applicable to parameters other than SL-DMRS ports or in addition to SL-DMRS ports. An example is code division multiplexing (CDM) groups associated with SL-DMRS ports. In some example embodiments, the method may be as follows. The technical standard provides a set p^max of options for SL-DMRS ports and/or CDM groups. Then, a configuration or

preconfiguration configures a subset P c p^max of the options/combinations, possibly assigning it to a RP, a UE or a group of UEs, a certain period of time, etc. Then, allocation and/or indication messages may select subsets P P_j, and/or P_{i ;·} for a UEi and/or transmission PSSCHj. In a special case that each CDM group is defined by the technical standard to be formed on a fixed subset of port numbers, then there may be no need to determine CDM groups in configurations or allocation/indication messages, and therefore the example techniques described earlier are applied on port numbers and port indices.

Additionally, rules may apply when SL-DMRS ports are associated with CDM groups. For example, when a subset of the SL-DMRS ports G are associated with a CDM group, other signals such as data signals in a channel should be punctured and/or rate-matched around the CDM group when G is indicated to be used in the channel. In addition, the same puncturing or rate-matching rule may apply if only a subset of G is indicated to be used in the channel. For example, if a CDM group o is associated with the SL-DMRS ports {Po, Pi, P6, P7} and a CDM group 1 is associated with the SL-DMRS ports {P2, P3, P8, P9}, then if a PSSCH is indicated to use SL-DMRS ports {Po, P3}, the PSSCH data should be punctured and rate-matched around all the REs associated with CDM group o and CDM group 1.

Because puncturing and rate-matching imposes overhead, it may be beneficial to select SL-DMRS ports from a same CDM group as much as possible. For example, a rule can be introduced that a UE must select SL-DMRS ports in a way that it minimizes the number of REs associated with their corresponding CDM groups.

In some example embodiments, the allocation/indication messages do not necessarily indicate SL-DMRS port numbers or indices, but CDM groups. For example, if CDM group o is associated with the SL-DMRS ports {Po, Pi}, then only the CDM group is indicated in an allocation/indication message. The advantage of this technique is that it reduces the indication overhead, and furthermore, CDM groups may work the best when used by one transmitting UE and not shared by multiple UEs that may not be fully synchronized or suffer from a large difference in mobility and Doppler.

The above extension from SL-DMRS ports to CDM groups can be further extended to other configuration parameters. Various configuration parameters such as group or sequence hopping for the DMRS sequence, cyclic shifts, frequency hopping and comb values for resource mapping, and so on, whether or not associated with SL-DMRS ports through design or configuration, may be helpful for allowing orthogonal SL-DMRSs across overlapping transmissions, or at least average/reduce the interference between SL-DMRS in order to improve the likelihood of successful demodulations. Therefore, all the disclosed techniques may fully or partially be applicable to any such configuration parameters.

In order to enable accurate measurements, when a UE transmits signals containing SL- DMRSs, it is beneficial that simultaneous transmissions by other UEs (operating in the same general vicinity) also puncture and/or rate-match around the SL-DMRS REs. For this purpose, control signaling can be introduced to inform other UEs and request that they do not interfere with SL-DMRS REs. The other UEs do not need to be informed of the specifics of the SL-DMRS configurations and transmissions, but it is sufficient to inform the other UEs of the REs that will contain SL-DMRS signals. Then, it is possible for the transmitting UEs to indicate the puncturing/ rate-matching information in their control signaling to their destination UE(s) for proper reception and processing of the signals. In some example embodiment, UEs may puncture and rate-match their signals around all the REs associated with the set of SL-DMRS ports P. This simplifies the signaling and avoids interference on SL-DMRS by any UE that has received the SL-DMRS

configuration indicating the set of SL-DMRS ports P. Yet in some other example embodiments, UEs may puncture and/or rate-match their signals around all the REs associated with p^max.

According to an example embodiment, the SL-DMRS ports are configured as RPs.

Similarly to LTE-V, NR V2X is expected to configure RPs for transmission and reception of signals. As an example, in a mode-t type of communication, a scheduler such as an access node or master UE schedules PSSCH from a RP for a UE that has data to transmit. The RP may be shared between all the UEs in a same general area or, instead, may be associated with attributes such as a location, a type of service, and so on. As another example, in a mode-2 communication, the UE may schedule a PSSCH for itself by selecting random resources from the RP. The PSSCH scheduling information should be communicated, normally prior to the PSSCH, by means of control signaling such as a SCI in a PSCCH.

The PSSCH may contain a SL-DMRS for proper demodulation of the signals by the receiver. However, the receiver may not have full knowledge of the SL-DMRS signals. Therefore, it is appropriate to signal any SL-DMRS information that may be

undetermined by the configuration through control signaling. The control message containing the information may be the same SCI that carries the PSSCH scheduling information, for example.

In general, it can be assumed that the receiving UE of a SL transmission possesses some prior knowledge of system configurations including SL-DMRS configurations. For example, when RPs are configured or preconfigured, the configuration or

preconfiguration can include SL-DMRS configurations associated with the RP. Indeed, as discussed in the previous subsections, a SL-DMRS configuration can provide a pool of SL-DMRS ports, typically more than is used by a single UE, and then the SL-DMRS ports can be allocated or selected for particular SL transmissions. If the SL-DMRS

configuration is associated with a RP, each transmission in the RP can use all or a subset of the SL-DMRS ports. Because the SL-DMRS signals associated with the different SL- DMRS ports are designed to be orthogonal through sequence design and/or resource mapping, if different transmissions use mutually exclusive subsets of the SL-DMRS ports from a single configuration, they allow the intended receivers to measure both the desired signal and interference and use the information for signal demodulation and possibly interference cancelation.

According to an example embodiment, UEs obtain a configuration or preconfiguration of RPs. The configuration or preconfiguration may be a configuration from the network such as an RRC configuration, a configuration from a mobile entity such as a master UE, a preconfiguration by the network or standard, etc. Along that, the UEs also receive a configuration or preconfiguration of SL-DMRS associated with the RP. One option may be the RP configuration comprises the SL-DMRS configuration. An alternative option may be the two configurations are associated through a parameter in either or both. For example, the RP configuration may contain a SL-DMRS configuration identifier (ID).

The SL-DMRS configuration may fully determine the parameters for SL-DMRS generation, resource mapping, and so on. Alternatively, especially for mode-2 type of communications, the SL-DMRS configuration may determine values for some of the parameters while leaving other parameters flexible or open for later indication. For example, as mentioned before, a SL-DMRS configuration may provide a large pool of SL- DMRS ports from which a subset can be selected for a particular transmission. Another example may be the SL-DMRS density changes in the time domain, allowing adaptation to match different UE speeds.

As an example, the parameter indication for SL-DMRS can be communicated by RRC signaling, MAC signaling, PHY layer signaling such as in an SCI, and so on. Accordingly, the indication may be persistent, semi-persistent, or aperiodic.

Figure 8A illustrates a flow diagram of example operations 8oo occurring in a transmitting UE participating in SL transmissions utilizing a RP of SL-DMRS resources. Operations 8oo may be indicative of operations occurring in a transmitting UE as the transmitting UE participates in SL transmissions utilizing a RP of SL-DMRS resources.

Operations 8oo begin with the transmitting UE obtaining the RP configuration (block 805). The RP configuration may be received from an access node or some other network entity. The RP configuration may be specified in a technical standard, and saved in the memory of the transmitting UE. The transmitting UE may then retrieve the RP configuration from the memory as needed. The RP configuration may be specified by an operator of the communications system, which may be provided to the transmitting UE when the transmitting UE attaches to the communications system. The transmitting UE obtains a SL-DMRS configuration associated with the RP (block 807). The SL-DMRS configuration may be a part of the RP configuration, for example. The SL-DMRS configuration may specify which SL-DMRS ports are associated with which resources of the RP, for example. The transmitting UE may receive the SL-DMRS configuration in a message (e.g., RRC, MAC, PHY, etc.). Alternatively, the transmitting UE may retrieve the SL-DMRS configuration from memory.

The transmitting UE selects resources from the RP (block 809). The transmitting UE selects one or more resources from the RP to make a PSSCH transmission, for example. The selection of the resources from the RP also results in the selection of SL-DMRS ports to convey the SL-DMRS for the PSCCH transmission. The transmitting UE selects SL- DMRS parameters in accordance with the SL-DMRS configuration (block 811). The SL- DMRS parameters may be selected in accordance with the SL-DMRS ports associated with the selected resources from the RP.

The transmitting UE transmits one or more indications (block 813). The one or more indications indicate the selected RP resources and the SL-DMRS parameters. The one or more indications are transmitted in a single SCI, for example. As another example the one or more indications are transmitted in multiple SCIs. The transmitting UE transmits the PSSCH on the selected RP resources (block 815). The transmitted PSSCH includes data, as well as the SL-DMRS on the SL-DMRS resources associated with the selected RP resources.

Figure 8B illustrates a flow diagram of example operations 820 occurring in a receiving UE participating in SL transmissions utilizing a RP of SL-DMRS resources. Operations 820 may be indicative of operations occurring in a receiving UE as the receiving UE participates in SL transmissions utilizing a RP of SL-DMRS resources.

Operations 820 begin with the receiving UE obtaining the RP configuration (block 825). The RP configuration may be received from an access node or some other network entity. The RP configuration may be specified in a technical standard, and saved in the memory of the receiving UE. The receiving UE may then retrieve the RP configuration from the memory as needed. The RP configuration may be specified by an operator of the communications system, which may be provided to the receiving UE when the receiving UE attaches to the communications system. The receiving UE obtains a SL-DMRS configuration associated with the RP (block 807). The SL-DMRS configuration maybe a part of the RP configuration, for example. The SL-DMRS configuration may specify which SL-DMRS ports are associated with which resources of the RP, for example. The receiving UE may receive the SL-DMRS configuration in a message (e.g., RRC, MAC, PHY, etc.). Alternatively, the receiving UE may retrieve the SL-DMRS configuration from memory. The receiving UE receives one or more indications (block 829). The one or more indications indicate the selected RP resources and the SL-DMRS parameters. The one or more indications are received in a single SCI, for example. As another example the one or more indications are received in multiple SCIs. The receiving UE receives the PSSCH on the selected RP resources (block 815). The received PSSCH includes data, as well as the SL-DMRS on the SL-DMRS resources associated with the selected RP resources.

In a situation where the SL-DMRS parameter indication in the SCI includes parameters that are already set by the configuration, depending on what the technical standard determines, the parameters may be ignored by the receiving UE or the parameters may override the original parameter values specified by the configuration.

If resources are selected randomly from the resource pool and not by a central scheduler such as an access node, there is a nonzero probability that resources selected by multiple UEs for multiple PSSCH transmissions overlap. When more than one PSSCH is scheduled on certain resources, the pool of the parameters provided by a SL-DMRS configuration may or may not guarantee orthogonal SL-DMRSs by SCI indications.

When SL-DMRS orthogonality is guaranteed, the receiving UE should be able to measure the signal quality and interference and attempt to properly demodulate the signal.

However, when SL-DMRS orthogonality is not guaranteed, or when there is a nonzero probability of an overlap between SL-DMRS resources of one PSSCH and other signals of another PSSCH, the demodulation performance may be severely degraded, especially if the receiving UEs are not properly informed regarding the possibility of collision.

According to an example embodiment, a UE scheduling a PSSCH should transmit the SCI(s) containing scheduling and SL-DMRS information, not only to the destination UE(s), but also to other UEs operating in the same general vicinity, in a group, or associated with the RP. The transmission of the SCI(s) can be performed by broadcasting SCIs. Alternatively, the UE can transmit the SCI(s) to the intended UE(s), and in addition, broadcast replicas of the SCI(s) or a subset of their information to other UEs. This can allow all UEs in the same general vicinity, in the group, or associated with the RP to perform measurements on the SL-DMRS while taking into account the interference caused by other signals.

Figure 9A illustrates a flow diagram of example operations 900 occurring in a transmitting UE participating in SL transmissions utilizing a RP of SL-DMRS resources, with indication broadcasts. Operations 900 may be indicative of operations occurring in a transmitting UE as the transmitting UE participates in SL transmissions utilizing a RP of SL-DMRS resources, with indication broadcasts.

Operations 900 begin with the transmitting UE obtaining the RP configuration (block 905). The RP configuration may be received from an access node or some other network entity. The RP configuration may be specified in a technical standard, and saved in the memory of the transmitting UE. The transmitting UE may then retrieve the RP configuration from the memory as needed. The RP configuration may be specified by an operator of the communications system, which may be provided to the transmitting UE when the transmitting UE attaches to the communications system. The transmitting UE obtains a SL-DMRS configuration associated with the RP (block 907). The SL-DMRS configuration may be a part of the RP configuration, for example. The SL-DMRS configuration may specify which SL-DMRS ports are associated with which resources of the RP, for example. The transmitting UE may receive the SL-DMRS configuration in a message (e.g., RRC, MAC, PHY, etc.). Alternatively, the transmitting UE may retrieve the SL-DMRS configuration from memory.

The transmitting UE selects resources from the RP (block 909). The transmitting UE selects one or more resources from the RP to make a PSSCH transmission, for example. The selection of the resources from the RP also results in the selection of SL-DMRS ports to convey the SL-DMRS for the PSCCH transmission. The transmitting UE selects SL- DMRS parameters in accordance with the SL-DMRS configuration (block 911). The SL- DMRS parameters may be selected in accordance with the SL-DMRS ports associated with the selected resources from the RP.

The transmitting UE transmits to the receiving UE one or more indications (block 913). The one or more indications indicate the selected RP resources and the SL-DMRS parameters. The one or more indications are transmitted in a single SCI, for example. As another example the one or more indications are transmitted in multiple SCIs. The transmitting UE broadcasts the one or more indications (block 915). The one or more indications indicate the selected RP resources and the SL-DMRS parameters. The one or more indications may be replicas of the one or more indications transmitted in block 913. The one or more indications are transmitted in a single SCI, for example. As another example the one or more indications are transmitted in multiple SCIs. The single SCI or the multiple SCIs may be replicas of the SCIs transmitted in block 913. The transmitting UE transmits the PSSCH on the selected RP resources (block 917). The transmitted PSSCH includes data, as well as the SL-DMRS on the SL-DMRS resources associated with the selected RP resources. Figure 9B illustrates a flow diagram of example operations 925 occurring in a receiving UE participating in SL transmissions utilizing a RP of SL-DMRS resources, with indication broadcasts. Operations 925 may be indicative of operations occurring in a receiving UE as the receiving UE participates in SL transmissions utilizing a RP of SL- DMRS resources, with indication broadcasts.

Operations 925 begin with the receiving UE obtaining the RP configuration (block 930). The RP configuration may be received from an access node or some other network entity. The RP configuration may be specified in a technical standard, and saved in the memory of the receiving UE. The receiving UE may then retrieve the RP configuration from the memory as needed. The RP configuration may be specified by an operator of the communications system, which may be provided to the receiving UE when the receiving UE attaches to the communications system. The receiving UE obtains a SL-DMRS configuration associated with the RP (block 932). The SL-DMRS configuration maybe a part of the RP configuration, for example. The SL-DMRS configuration may specify which SL-DMRS ports are associated with which resources of the RP, for example. The receiving UE may receive the SL-DMRS configuration in a message (e.g., RRC, MAC, PHY, etc.). Alternatively, the receiving UE may retrieve the SL-DMRS configuration from memory.

The receiving UE receives one or more indications (block 934). The one or more indications are received from the transmitting UE and are specifically addressed to the receiving UE. The one or more indications indicate the selected RP resources and the SL- DMRS parameters. The one or more indications are received in a single SCI, for example. As another example the one or more indications are received in multiple SCIs. The receiving UE receives one or more indications (block 936). The one or more indications are received in broadcast message or messages from the transmitting UE. In an embodiment, the receiving UE also receives additional indications in broadcast messages from other UEs operating in the same general vicinity, members of the same group, or communicating with the same transmitting UE. The receiving UE receives the PSSCH on the selected RP resources (block 938). The received PSSCH includes data, as well as the SL-DMRS on the SL-DMRS resources associated with the selected RP resources.

Examples of the SL-DMRS parameters that a transmitting UE may select and their applications are as follows:

- SL-DMRS ports: As mentioned previously, selecting SL-DMRS ports from a pool of configured ports can allow for the transmission of orthogonal SL-DMRSs across multiple PSSCHs if they are synchronized. - Sequence/scrambling IDs: The IDs may be used for sequence generation, determining hopping patterns, and so on. While selecting different IDs may not guarantee orthogonal SL-DMRSs across PSSCHs, it still randomizes the SL-DMRSs and allows for the averaging of the interference that a particular SL-DMRS may cause on other SL-DMRS. By careful selection of the available IDs at the configuration or preconfiguration stage, the interference can be minimized if transmitting UEs select the IDs randomly and independently, and do not select identical IDs for simultaneous transmissions, by chance.

- Physical resources: Randomly selecting physical resources can help avoid or minimize interference. For example, if different group/sequence/frequency hopping patterns, different cyclic shift, or comb values are selected by different UEs, the interference may be avoided or minimized. Again, the resulting performance depends on the options provided at the configuration or preconfiguration stage.

- Additional SL-DMRS locations: Among the physical resources that can be selected by a UE is the density of resources in time and/ or frequency. Particularly, in the time domain, additional SL-DMRSs aim at providing up-to-date CSI to the demodulator at high mobility that causes sub-slot coherence times. The SL-DMRS configuration or preconfiguration may or may not allow selection of the number of additional SL-DMRSs by a UE. If the selection of the number of additional SL-DMRSs is allowed, then the additional SL-DMRSs may possibly be interfered with by non-SL-DMRS signals from simultaneously scheduled PSSCHs. The receiving UE should then take this knowledge into account when performing measurements on the additional SL-DMRSs.

According to an example embodiment, a SL-DMRS is extended beyond the resources allocated to the PSSCH. If the duration of a PSSCH is the entire slot, it may be guaranteed that there will be SL-DMRS symbols available during the PSSCH

transmission. However, it may be possible that a UE does not have sufficient data to transmit a PSSCH that is as long as an entire slot. Similarly, if a UE is willing to stretch the size of a PSSCH in the time domain instead of stretching the PSSCH in the frequency domain, then it is possible that the PSSCH will be too narrow in frequency, hence, providing an insufficient number of REs for the SL-DMRS.

Figure to illustrates a diagram of an example slot tooo including three PSSCHs. Slot 1000 includes PSSCHs, such as PSSCH 1 1005, PSSCH 2 1010, and PSSCH 3 1015. The PSSCHs include SL-DRMSs, which are scheduled for transmission on two possible SL- DMRS symbols 1020 and 1022. PSSCH 1 1005 spans a large time duration and uses both of the possible symbols for SL-DMRS transmission. Moreover, the SL-DMRS is extended beyond the PSSCH resources, hence occupying resources from PSSCH 2 1010 as well. PSSCH 2 loio is shorter in duration and, hence, uses only the first SL-DMRS symbol 1020. However, PSSCH 2 1010 uses resources from the whole available bandwidth including resources from PSSCH 1 1005 and unallocated resources of slot 1000. PSSCH 3 1015 uses both SL-DMRS symbols 1020 and 1022 and time-frequency resources from the whole bandwidth including resources from PSSCH 1 1005, PSSCH 2 1010, and unallocated resources of slot 1000.

In the situation when the SL-DMRS occupies resources of other channels, the other UEs may be informed for appropriate action. The UE behavior can be defined in a variety of ways to avoid or handle the interference that may be caused by this design choice.

As an example, a UE may have to monitor the control region and, upon receiving information that its data will collide with a SL-DMRS from another UE, puncture the REs colliding with the SL-DMRS and possibly rate-match around the punctured REs. Furthermore, the UE may have to select SL-DMRS parameters for its data transmission that avoid or reduce interference of its own SL-DMRS with the other UE’s SL-DMRS. Additionally, the UE may inform its destination UE of the actions that it is taking including puncturing, rate-matching, or selection or reselection of SL-DMRS parameters.

In an embodiment, a UE obtains a SL-DMRS configuration that allows it to transmit a SL-DMRS on a set of OFDM symbols. Each SL-DMRS symbol maybe associated, through design or by the configuration, to other parameters of SL-DMRS for sequence generation, resource mapping, and so on. The configuration may be in an RRC signaling and may further be further associated with the RP, a UE or a group of UEs, a time period, a location, a connection, and so on. Such associations may be directly determined by the configuration or indirectly determined by association to the RP that is, in turn, associated with the other parameters. For example, a SL-DMRS configuration may be associated with a RP that is associated with a location or a SL connection.

Once the UE obtains the SL-DMRS configuration, the UE may use all or a subset of the determined symbols for SL-DMRS transmission. Different variations are possible based on whether the communications are mode 1 or mode 2, whether the communications are scheduled in a type A configuration or a type B configuration, and so on.

As an example, in mode 1 communications, an access node can schedule a PSSCH and indicate in a DCI which SL-DMRS symbols are used. The DCI can be the same DCI that contains the scheduling information. Then, the transmitting UE can include this information in an SCI prior to transmitting signals on the scheduled PSSCH in order to make sure that the receiving UE obtains the information of SL-DMRS transmissions. As an example, in mode 2 communications, the transmitting UE schedules a PSSCH by transmitting the scheduling information in an SCI to receiving UE(s). Then, in the same or a separate SCI, the transmitting UE can indicate which SL-DMRS symbols are used.

According to an example embodiment, because there is a higher probability of interference between data transmissions in a SL, especially in mode 2 communications where UEs schedule transmissions rather than a central entity (such as an access node or a scheduler), it is beneficial to assign different SL-DMRS symbols to different UEs or group of UEs that may use the same RP. Then, if PSSCH transmissions from two UEs happen to overlap in time-frequency resources, their SL-DMRS may still suffer from interference, but the interference may be handled better than the situation when two (or more) SL-DMRS with the same sequence and resources collide.

In order to reduce overhead, it is possible to provide a same SL-DMRS configuration to different UEs, but assign different symbol locations to different UEs that may use overlapping resources. For example, the SL-DMRS locations assigned to a UE may be function of a UE ID, such as a radio network temporary identifier (RNTI), MAC address, etc. Alternatively, the SL-DMRS locations may be a function of SL ID or a like, which assigns different SL-DMRS locations to different UEs.

In order to enable accurate measurements, when a UE transmits signals containing a SL- DMRS, simultaneous transmissions by other UEs should puncture and/or rate-match around the SL-DMRS REs. For this purpose, UEs can puncturing/rate-match their signals around the SL-DMRS REs or symbols that are going to be transmitted simultaneously by other UEs.

Alternatively, the UEs may puncture and rate-match their signals around all the REs or symbols associated with the SL-DMRS configuration. This simplifies the signaling and avoids interference on the SL-DMRS by any UE that has received the SL-DMRS configuration. In yet another alternative, the UEs may puncture and/or rate-match their signals around all the REs or symbols that may possibly contain SL-DMRS.

Figure it illustrates an example communication system tioo. In general, the system tioo enables multiple wireless or wired users to transmit and receive data and other content. The system tioo may implement one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), or non-orthogonal multiple access (NOMA). In this example, the communication system tioo includes electronic devices (ED) litoa- litoc, radio access networks (RANs) ii2oa-ti2ob, a core network 1130, a public switched telephone network (PSTN) 1140, the Internet 1150, and other networks 1160. While certain numbers of these components or elements are shown in Figure 11, any number of these components or elements may be included in the system 1100.

The EDs moa-moc are configured to operate or communicate in the system 1100. For example, the EDs moa-moc are configured to transmit or receive via wireless or wired communication channels. Each ED moa-moc represents any suitable end user device and may include such devices (or may be referred to) as a user equipment or device (UE), wireless transmit or receive unit (WTRU), mobile station, fixed or mobile subscriber unit, cellular telephone, personal digital assistant (PDA), smartphone, laptop, computer, touchpad, wireless sensor, or consumer electronics device.

The RANs ii2oa-ti2ob here include base stations ii70a-ti70b, respectively. Each base station Ii70a-ti70b is configured to wirelessly interface with one or more of the EDs moa-moc to enable access to the core network 1130, the PSTN 1140, the Internet 1150, or the other networks 1160. For example, the base stations ii70a-ti70b may include (or be) one or more of several well-known devices, such as a base transceiver station (BTS), a Node-B (NodeB), an evolved NodeB (eNodeB), a Next Generation (NG) NodeB (gNB), a Home NodeB, a Home eNodeB, a site controller, an access point (AP), or a wireless router. The EDs moa-moc are configured to interface and communicate with the Internet 1150 and may access the core network 1130, the PSTN 1140, or the other networks 1160.

In the embodiment shown in Figure 11, the base station 1170a forms part of the RAN 1120a, which may include other base stations, elements, or devices. Also, the base station 1170b forms part of the RAN 1120b, which may include other base stations, elements, or devices. Each base station liyoa-nyob operates to transmit or receive wireless signals within a particular geographic region or area, sometimes referred to as a "cell." In some embodiments, multiple-input multiple-output (MIMO) technology maybe employed having multiple transceivers for each cell.

The base stations liyoa-nyob communicate with one or more of the EDs moa-moc over one or more air interfaces 1190 using wireless communication links. The air interfaces 1190 may utilize any suitable radio access technology.

It is contemplated that the system 1100 may use multiple channel access functionality, including such schemes as described above. In particular embodiments, the base stations and EDs implement 5G New Radio (NR), LTE, LTE-A, or LTE-B. Of course, other multiple access schemes and wireless protocols may be utilized.

The RANs Ii20a-ti20b are in communication with the core network 1130 to provide the EDs moa-moc with voice, data, application, Voice over Internet Protocol (VoIP), or other services. Understandably, the RANs ii2oa-ti2ob or the core network 1130 maybe in direct or indirect communication with one or more other RANs (not shown). The core network 1130 may also serve as a gateway access for other networks (such as the PSTN 1140, the Internet 1150, and the other networks 1160). In addition, some or all of the EDs moa-moc may include functionality for communicating with different wireless networks over different wireless links using different wireless technologies or protocols. Instead of wireless communication (or in addition thereto), the EDs may communicate via wired communication channels to a service provider or switch (not shown), and to the Internet 1150.

Although Figure 11 illustrates one example of a communication system, various changes may be made to Figure 11. For example, the communication system 1100 could include any number of EDs, base stations, networks, or other components in any suitable configuration.

Figures 12A and 12B illustrate example devices that may implement the methods and teachings according to this disclosure. In particular, Figure 12A illustrates an example ED 1210, and Figure 12B illustrates an example base station 1270. These components could be used in the system 1100 or in any other suitable system.

As shown in Figure 12A, the ED 1210 includes at least one processing unit 1200. The processing unit 1200 implements various processing operations of the ED 1210. For example, the processing unit 1200 could perform signal coding, data processing, power control, input/output processing, or any other functionality enabling the ED 1210 to operate in the system 1100. The processing unit 1200 also supports the methods and teachings described in more detail above. Each processing unit 1200 includes any suitable processing or computing device configured to perform one or more operations. Each processing unit 1200 could, for example, include a microprocessor, microcontroller, digital signal processor, field programmable gate array, or application specific integrated circuit.

The ED 1210 also includes at least one transceiver 1202. The transceiver 1202 is configured to modulate data or other content for transmission by at least one antenna or NIC (Network Interface Controller) 1204. The transceiver 1202 is also configured to demodulate data or other content received by the at least one antenna 1204. Each transceiver 1202 includes any suitable structure for generating signals for wireless or wired transmission or processing signals received wirelessly or by wire. Each antenna 1204 includes any suitable structure for transmitting or receiving wireless or wired signals. One or multiple transceivers 1202 could be used in the ED 1210, and one or multiple antennas 1204 could be used in the ED 1210. Although shown as a single functional unit, a transceiver 1202 could also be implemented using at least one transmitter and at least one separate receiver.

The ED 1210 further includes one or more input/output devices 1206 or interfaces (such as a wired interface to the Internet 1150). The input/output devices 1206 facilitate interaction with a user or other devices (network communications) in the network. Each input/output device 1206 includes any suitable structure for providing information to or receiving information from a user, such as a speaker, microphone, keypad, keyboard, display, or touch screen, including network interface communications.

In addition, the ED 1210 includes at least one memory 1208. The memory 1208 stores instructions and data used, generated, or collected by the ED 1210. For example, the memory 1208 could store software or firmware instructions executed by the processing unit(s) 1200 and data used to reduce or eliminate interference in incoming signals. Each memory 1208 includes any suitable volatile or non-volatile storage and retrieval device(s). Any suitable type of memory may be used, such as random access memory (RAM), read only memory (ROM), hard disk, optical disc, subscriber identity module (SIM) card, memory stick, secure digital (SD) memory card, and the like.

As shown in Figure 12B, the base station 1270 includes at least one processing unit 1250, at least one transceiver 1252, which includes functionality for a transmitter and a receiver, one or more antennas 1256, at least one memory 1258, and one or more input/output devices or interfaces 1266. A scheduler, which would be understood by one skilled in the art, is coupled to the processing unit 1250. The scheduler could be included within or operated separately from the base station 1270. The processing unit 1250 implements various processing operations of the base station 1270, such as signal coding, data processing, power control, input/output processing, or any other functionality. The processing unit 1250 can also support the methods and teachings described in more detail above. Each processing unit 1250 includes any suitable processing or computing device configured to perform one or more operations. Each processing unit 1250 could, for example, include a microprocessor, microcontroller, digital signal processor, field programmable gate array, or application specific integrated circuit. Each transceiver 1252 includes any suitable structure for generating signals for wireless or wired transmission to one or more EDs or other devices. Each transceiver 1252 further includes any suitable structure for processing signals received wirelessly or by wire from one or more EDs or other devices. Although shown combined as a transceiver 1252, a transmitter and a receiver could be separate components. Each antenna 1256 includes any suitable structure for transmitting or receiving wireless or wired signals. While a common antenna 1256 is shown here as being coupled to the transceiver 1252, one or more antennas 1256 could be coupled to the transceiver(s) 1252, allowing separate antennas 1256 to be coupled to the transmitter and the receiver if equipped as separate components. Each memory 1258 includes any suitable volatile or non-volatile storage and retrieval device(s). Each input/output device 1266 facilitates interaction with a user or other devices (network communications) in the network. Each input/output device 1266 includes any suitable structure for providing information to or receiving/providing information from a user, including network interface communications.

Figure 13 is a block diagram of a computing system 1300 that may be used for implementing the devices and methods disclosed herein. For example, the computing system can be any entity of UE, access network (AN), mobility management (MM), session management (SM), user plane gateway (UPGW), or access stratum (AS). Specific devices may utilize all of the components shown or only a subset of the components, and levels of integration may vary from device to device. Furthermore, a device may contain multiple instances of a component, such as multiple processing units, processors, memories, transmitters, receivers, etc. The computing system 1300 includes a processing unit 1302. The processing unit includes a central processing unit (CPU) 1314, memory 1308, and may further include a mass storage device 1304, a video adapter 1310, and an I/O interface 1312 connected to a bus 1320.

The bus 1320 may be one or more of any type of several bus architectures including a memory bus or memory controller, a peripheral bus, or a video bus. The CPU 1314 may comprise any type of electronic data processor. The memory 1308 may comprise any type of non-transitory system memory such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM), or a combination thereof. In an embodiment, the memory 1308 may include ROM for use at boot-up, and DRAM for program and data storage for use while executing programs.

The mass storage 1304 may comprise any type of non-transitory storage device configured to store data, programs, and other information and to make the data, programs, and other information accessible via the bus 1320. The mass storage 1304 may comprise, for example, one or more of a solid state drive, hard disk drive, a magnetic disk drive, or an optical disk drive.

The video adapter 1310 and the I/O interface 1312 provide interfaces to couple external input and output devices to the processing unit 1302. As illustrated, examples of input and output devices include a display 1318 coupled to the video adapter 1310 and a mouse, keyboard, or printer 1316 coupled to the I/O interface 1312. Other devices maybe coupled to the processing unit 1302, and additional or fewer interface cards may be utilized. For example, a serial interface such as Universal Serial Bus (USB) (not shown) may be used to provide an interface for an external device.

The processing unit 1302 also includes one or more network interfaces 1306, which may comprise wired links, such as an Ethernet cable, or wireless links to access nodes or different networks. The network interfaces 1306 allow the processing unit 1302 to communicate with remote units via the networks. For example, the network interfaces 1306 may provide wireless communication via one or more transmitters/transmit antennas and one or more receivers/ receive antennas. In an embodiment, the processing unit 1302 is coupled to a local-area network 1322 or a wide-area network for data processing and communications with remote devices, such as other processing units, the Internet, or remote storage facilities.

Figure 14 illustrates a block diagram of an embodiment processing system 1400 for performing methods described herein, which may be installed in a host device. As shown, the processing system 1400 includes a processor 1404, a memory 606, and interfaces 1410-1414, which may (or may not) be arranged as shown in the figure. The processor 1404 may be any component or collection of components adapted to perform

computations and/or other processing related tasks, and the memory 1406 may be any component or collection of components adapted to store programming and/or instructions for execution by the processor 1404. In an embodiment, the memory 1406 includes a non-transitory computer readable medium. The interfaces 1410, 1412, 1414 may be any component or collection of components that allow the processing system 1400 to communicate with other devices/components and/or a user. For example, one or more of the interfaces 1410, 1412, 1414 may be adapted to communicate data, control, or management messages from the processor 1404 to applications installed on the host device and/or a remote device. As another example, one or more of the interfaces 1410, 1412, 1414 may be adapted to allow a user or user device (e.g., personal computer (PC), etc.) to interact/communicate with the processing system 1400. The processing system 1400 may include additional components not depicted in the figure, such as long term storage (e.g., non-volatile memory, etc.).

In some embodiments, the processing system 1400 is included in a network device that is accessing, or part otherwise of, a telecommunications network. In one example, the processing system 1400 is in a network-side device in a wireless or wireline

telecommunications network, such as a base station, a relay station, a scheduler, a controller, a gateway, a router, an applications server, or any other device in the telecommunications network. In other embodiments, the processing system 1400 is in a user-side device accessing a wireless or wireline telecommunications network, such as a mobile station, a UE, a personal computer (PC), a tablet, a wearable communications device (e.g., a smartwatch, etc.), or any other device adapted to access a

telecommunications network.

In some embodiments, one or more of the interfaces 1410, 1412, 1414 connects the processing system 1400 to a transceiver adapted to transmit and receive signaling over the telecommunications network. Figure 15 illustrates a block diagram of a transceiver 1500 adapted to transmit and receive signaling over a telecommunications network. The transceiver 1500 may be installed in a host device. As shown, the transceiver 1500 comprises a network-side interface 1502, a coupler 1504, a transmitter 1506, a receiver 1508, a signal processor 1510, and a device-side interface 1512. The network-side interface 1502 may include any component or collection of components adapted to transmit or receive signaling over a wireless or wireline telecommunications network.

The coupler 1504 may include any component or collection of components adapted to facilitate bi-directional communication over the network-side interface 1502. The transmitter 1506 may include any component or collection of components (e.g., up- converter, power amplifier, etc.) adapted to convert a baseband signal into a modulated carrier signal suitable for transmission over the network-side interface 1502. The receiver 1508 may include any component or collection of components (e.g., down -converter, low noise amplifier, etc.) adapted to convert a carrier signal received over the network-side interface 1502 into a baseband signal. The signal processor 1510 may include any component or collection of components adapted to convert a baseband signal into a data signal suitable for communication over the device-side interface(s) 1512, or vice-versa. The device-side interface(s) 1512 may include any component or collection of components adapted to communicate data-signals between the signal processor 1510 and components within the host device (e.g., the processing system 1400, local area network (LAN) ports, etc.). The transceiver 1500 may transmit and receive signaling over any type of

communications medium. In some embodiments, the transceiver 1500 transmits and receives signaling over a wireless medium. For example, the transceiver 1500 may be a wireless transceiver adapted to communicate in accordance with a wireless

telecommunications protocol, such as a cellular protocol (e.g., long-term evolution (LTE), etc.), a wireless local area network (WLAN) protocol (e.g., Wi-Fi, etc.), or any other type of wireless protocol (e.g., Bluetooth, near field communication (NFC), etc.). In such embodiments, the network-side interface 1502 comprises one or more

antenna/radiating elements. For example, the network-side interface 1502 may include a single antenna, multiple separate antennas, or a multi-antenna array configured for multi-layer communication, e.g., single input multiple output (SIMO), multiple input single output (MISO), MIMO, etc. In other embodiments, the transceiver 1500 transmits and receives signaling over a wireline medium, e.g., twisted-pair cable, coaxial cable, optical fiber, etc. Specific processing systems and/or transceivers may utilize all of the components shown, or only a subset of the components, and levels of integration may vary from device to device.

It should be appreciated that one or more steps of the embodiment methods provided herein may be performed by corresponding units or modules. For example, a signal may be transmitted by a transmitting unit or a transmitting module. A signal may be received by a receiving unit or a receiving module. A signal may be processed by a processing unit or a processing module. Other steps may be performed by an obtaining unit or module, or a selecting unit or module. The respective units or modules may be hardware, software, or a combination thereof. For instance, one or more of the units or modules may be an integrated circuit, such as field programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs).

Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the disclosure as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for performing sidelink (SL) communications, the method

implemented by a first SL user equipment (SL UE), the method comprising:

obtaining, by the first SL UE, a configuration of a resource pool configured for SL communications, the configuration of the resource pool comprising one or more SL demodulation reference signals (SL-DMRS) configurations;

selecting, by the first SL UE, a SL resource from the resource pool, the selected SL resource being associated with a SL-DMRS configuration;

selecting, by the first SL UE, a SL-DMRS parameter in accordance with the SL- DMRS configuration;

transmitting, by the first SL UE, a first SL control information (SCI) indicating the selected SL resource and the selected SL-DMRS parameter; and

transmitting, by the first SL UE, to a second SL UE, a SL transmission in accordance with the selected SL resource and the selected SL-DMRS parameter.

2. The method of claim l, the SL-DMRS parameter being an SL-DMRS antenna port index.

3. The method of claim l, the SL-DMRS parameter being an SL-DMRS pattern.

4. The method of any one of claims 1-3, the SL-DMRS configuration comprising a set of SL-DRMS ports.

5. The method of any one of claims 1-4, further comprising obtaining, by the first SL UE, the SL-DMRS configuration.

6. The method of any one of claims 1-2, the SL transmission comprising a physical sidelink shared channel (PSSCH) transmission.

7. The method of any one of claims 1-6, the first SCI is transmitted to the second SL UE.

8. The method of any one of claims 1-6, the first SCI is broadcast to a plurality of SL UEs, including the second SL UE.

9. The method of any one of claims 1-7, further comprising broadcasting, by the first SL UE, a second SCI indicating the selected SL resource and the selected SL-DMRS parameter.

10. The method of any one of claims 1-9, obtaining the configuration of the resource pool comprising receiving a message including the configuration of the resource pool.

11. The method of claim 10, the message being a radio resource control (RRC) message.

12. The method of any one of claims 1-9, obtaining the configuration of the resource pool comprising receiving the configuration of the resource pool during an initial attachment procedure.

13. A method for performing sidelink (SL) communications, the method

implemented by a second SL user equipment (SL UE), the method comprising;

obtaining, by the second SL UE, a configuration of a resource pool configured for SL communications;

receiving, by the second SL UE, from a first SL UE, a first SL control information (SCI) indicating a selected SL resource and a selected SL demodulation reference signal (SL-DMRS) parameter, the selected SL resource being a member of the resource pool configured for SL communications; and

receiving, by the second SL UE, from the first SL UE, a SL transmission in accordance with the selected SL resource and a SL-DMRS configuration associated with the selected SL-DMRS parameter.

14. The method of claim 13, the SL-DMRS parameter being an SL-DMRS antenna port index.

15. The method of claim 13, the SL-DMRS parameter being an SL-DMRS pattern.

16. The method of any one of claims 13-15, the SL-DMRS configuration comprising a set of SL-DRMS ports.

17. The method of any one of claims 13-16, the SL transmission comprising a physical sidelink shared channel (PSSCH) transmission.

18. The method of any one of claims 13-17, the first SCI being addressed to the second SL UE.

19. The method of any one of claims 13-18, further comprising receiving, by the second SL UE, a second SCI indicating the selected SL resource and the selected SL- DMRS parameter.

20. The method of any one of claims 13-19, obtaining the configuration of the resource pool comprising receiving a message including the configuration of the resource pool.

21. The method of claim 20, the message being a radio resource control (RRC) message.

22. The method of any one of claims 13-19, obtaining the configuration of the resource pool comprising receiving the configuration of the resource pool during an initial attachment procedure.

23. A transmitting sidelink (SL) user equipment (UE) comprising:

a non-transitory memory storage comprising instructions; and

one or more processors in communication with the memory storage, wherein the one or more processors execute the instructions to:

obtain a configuration of a resource pool configured for SL communications, the configuration of the resource pool comprising one or more SL demodulation reference signals (SL-DMRS) configurations;

select a SL resource from the resource pool, the selected SL resource being associated with a SL-DMRS configuration;

select a SL-DMRS parameter in accordance with the SL-DMRS configuration;

transmit a first SL control information (SCI) indicating the selected SL resource and the selected SL-DMRS parameter; and

transmit, to a receiving SL UE, a SL transmission in accordance with the selected SL resource and the selected SL-DMRS parameter.

24. The transmitting SL UE of claim 23, the SL-DMRS parameter being an SL-DMRS antenna port index.

25. The transmitting SL UE of any one of claims 23-24, the SL-DMRS configuration comprising a set of SL-DRMS ports

26. The transmitting SL UE of any one of claims 23-25, the one or more processors further executing the instructions to obtain the SL-DMRS configuration.

27. The transmitting SL UE of any one of claims 23-26, the SL transmission comprising a physical sidelink shared channel (PSSCH) transmission.

28. The transmitting SL UE of any one of claims 23-27, the first SCI is transmitted to the receiving SL UE.

29. The transmitting SL UE of any one of claims 23-27, the first SCI is broadcast to a plurality of SL UEs, including the receiving SL UE.

30. The transmitting SL UE of any one of claims 23-28, the one or more processors further executing the instructions to broadcast a second SCI indicating the selected SL resource and the selected SL-DMRS parameter.

31. The transmitting SL UE of any one of claims 23-30, the one or more processors further executing the instructions to receive a message including the configuration of the resource pool.

32. The transmitting SL UE of claim 31, the message being a radio resource control (RRC) message.

33. The transmitting SL UE of any one of claims 23-30, the one or more processors further executing the instructions to receive the configuration of the resource pool during an initial attachment procedure.

34. A receiving sidelink (SL) user equipment (UE) comprising:

a non-transitory memory storage comprising instructions; and

obtain a configuration of a resource pool configured for SL communications;

receive, from a transmitting SL UE, a first SL control information (SCI) indicating a selected SL resource and a selected SL demodulation reference signal (SL- DMRS) parameter, the selected SL resource being a member of the resource pool configured for SL communications; and

receive, from the transmitting SL UE, a SL transmission in accordance with the selected SL resource and a SL-DMRS configuration associated with the selected SL-DMRS parameter.

35. The receiving SL UE of claim 34, the SL-DMRS parameter being an SL-DMRS antenna port index.

36. The receiving SL UE of any one of claims 34-35, the SL-DMRS configuration comprising a set of SL-DRMS ports.

37. The receiving SL UE of any one of claims 34-36, the SL transmission comprising a physical sidelink shared channel (PSSCH) transmission.

38. The receiving SL UE of any one of claims 34-37, the first SCI being addressed to the receiving SL UE.

39. The receiving SL UE of any one of claims 34-38, the one or more processors further executing the instructions to receive a second SCI indicating the selected SL resource and the selected SL-DMRS parameter.

40. The receiving SL UE of any one of claims 34-39, the one or more processors further executing the instructions to receive a message including the configuration of the resource pool.

41. The receiving SL UE of any one of claims 34-39, the one or more processors further executing the instructions to receive the configuration of the resource pool during an initial attachment procedure.