MU-MIMO BASED ON SDM FOR PUSCH

This disclosure provides systems, devices, apparatus, and methods, including computer programs encoded on storage media, for MU-MIMO communication based on SDM for a PUSCH. A UE may receive an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data. The number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2. The UE may transmit the PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data.

TECHNICAL FIELD

The present disclosure relates generally to communication systems, and more particularly, to multi-user multiple-input multiple-output (MU-MIMO) communication based on spatial division multiplexing (SDM) for a physical uplink shared channel (PUSCH).

INTRODUCTION

BRIEF SUMMARY

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may receive an indication of a plurality of demodulation reference signal (DMRS) ports for a physical uplink shared channel (PUSCH) transmission and a number of DMRS code division multiplexing (CDM) groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and transmit the PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data.

In another aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may transmit an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and receive the PUSCH transmission based on the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data.

DETAILED DESCRIPTION

A base station102, whether a small cell102′ or a large cell (e.g., macro base station), may include and/or be referred to as an eNB, gNodeB (gNB), or another type of base station. Some base stations, such as a gNB may operate in a traditional sub 6 GHZ spectrum, in millimeter wave frequencies, and/or near millimeter wave frequencies in communication with the UE104. When the gNB operates in millimeter wave or near millimeter wave frequencies, the gNB may be referred to as a millimeter wave base station. The millimeter wave base station180may utilize beamforming182with the UE104to compensate for the path loss and short range. The base station180and the UE104may each include a plurality of antennas, such as antenna elements, antenna panels, and/or antenna arrays to facilitate the beamforming.

The EPC160may include a Mobility Management Entity (MME)162, other MMEs164, a Serving Gateway166, a Multimedia Broadcast Multicast Service (MBMS) Gateway168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway172. The MME162may be in communication with a Home Subscriber Server (HSS)174. The MME162is the control node that processes the signaling between the UEs104and the EPC160. Generally, the MME162provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway166, which itself is connected to the PDN Gateway172. The PDN Gateway172provides UE IP address allocation as well as other functions. The PDN Gateway172and the BM-SC170are connected to the IP Services176. The IP Services176may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service, and/or other IP services. The BM-SC170may provide functions for MBMS user service provisioning and delivery. The BM-SC170may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN), and may be used to schedule MBMS transmissions. The MBMS Gateway168may be used to distribute MBMS traffic to the base stations102belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information. The core network190may include an Access and Mobility Management Function (AMF)192, other AMFs193, a Session Management Function (SMF)194, and a User Plane Function (UPF)195. The AMF192may be in communication with a Unified Data Management (UDM)196. The AMF192is the control node that processes the signaling between the UEs104and the core network190. Generally, the AMF192provides QoS flow and session management. All user Internet protocol (IP) packets are transferred through the UPF195. The UPF195provides UE IP address allocation as well as other functions. The UPF195is connected to the IP Services197. The IP Services197may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a Packet Switch (PS) Streaming (PSS) Service, and/or other IP services. The base station may include and/or be referred to as a gNB, Node B, eNB, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), a transmit reception point (TRP), or some other suitable terminology. The base station102provides an access point to the EPC160or core network190for a UE104. Examples of UEs104include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs104may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, heart monitor, etc.). The UE104may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. In some scenarios, the term UE may also apply to one or more companion devices such as in a device constellation arrangement. One or more of these devices may collectively access the network and/or individually access the network.

Referring again toFIG.1, in certain aspects, the UE104may include a spatial division multiplexing (SDM) component198configured to receive an indication of a plurality of demodulation reference signal (DMRS) ports for a physical uplink shared channel (PUSCH) transmission and a number of DMRS code division multiplexing (CDM) groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and transmit the PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. In certain aspects, the base station180may include a multi-user multiple-input multiple-output (MU-MIMO) component199configured to transmit an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and receive the PUSCH transmission based on the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. Although the following description may be focused on 5G NR, the concepts described herein may be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

At the UE350, each receiver354RX receives a signal through its respective antenna352. Each receiver354RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor356. The TX processor368and the RX processor356implement layer 1 functionality associated with various signal processing functions. The RX processor356may perform spatial processing on the information to recover any spatial streams destined for the UE350. If multiple spatial streams are destined for the UE350, they may be combined by the RX processor356into a single OFDM symbol stream. The RX processor356then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station310. These soft decisions may be based on channel estimates computed by the channel estimator358. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station310on the physical channel. The data and control signals are then provided to the controller/processor359, which implements layer 3 and layer 2 functionality. The controller/processor359can be associated with a memory360that stores program codes and data. The memory360may be referred to as a computer-readable medium. In the UL, the controller/processor359provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC160. The controller/processor359is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

At least one of the TX processor368, the RX processor356, and the controller/processor359may be configured to perform aspects in connection with the SDM component198ofFIG.1.

Wireless communication systems may be configured to share available system resources and provide various telecommunication services (e.g., telephony, video, data, messaging, broadcasts, etc.) based on multiple-access technologies such as CDMA systems, TDMA systems, FDMA systems, OFDMA systems, SC-FDMA systems, TD-SCDMA systems, etc. that support communication with multiple users. In many cases, common protocols that facilitate communications with wireless devices are adopted in various telecommunication standards. For example, communication methods associated with eMBB, mMTC, and ultra-reliable low latency communication (URLLC) may be incorporated in the 5G NR telecommunication standard, while other aspects may be incorporated in the 4G LTE standard. As mobile broadband technologies are part of a continuous evolution, further improvements in mobile broadband remain useful to continue the progression of such technologies.

FIG.4is a call flow diagram400illustrating communications between a base station404and a plurality of UEs (e.g., a first UE402and a second UE403). At406a-406b, the base station404may schedule an MU-MIMO communication based on an SDM scheme for at least one UE. For example, the base station404may schedule, at406a, the first UE402based on the SDM scheme and/or schedule, at406b, the second UE403based on the SDM scheme or a non-SDM scheme. The SDM scheme may be associated with a PUSCH that includes different sets of layers having different transmission parameters (e.g., different beams, different sets of power control parameters, different precoding, etc.).

At408a-408b, the base station404may transmit, to the first UE402and/or the second UE403, an indication of DMRS ports for PUSCH transmission and a number of CDM groups without data. The indication of the DMRS ports for the PUSCH transmission and the number of CDM groups without data may be associated with the SDM scheme. The number of CDM groups without data may include the CDM groups of the indicated DMRS ports as well as additional CDM group(s). For example, in MU-MIMO communications, if another UE (e.g., the second UE403) is scheduled with DMRS ports in the additional CDM group(s), the number of CDM groups without data may also be indicative of the additional CDM group(s) that are not available for data REs. Configurations indicated, at408c, for the number of CDM groups without data may include that the number of CDM groups without data is: (1)≥ to 3 when DMRS ports {0, 2} is indicated; (2)> to 2 when DMRS ports {1, 3} is indicated; or (3)>2 when DMRS ports {0, 2} indicated and a number of front-loaded symbols=2.

At410, the first UE402may determine whether the SDM scheme is scheduled by the base station404based on the indication received, at406a, from the base station404of the DMRS ports for the PUSCH transmission and the number of CDM groups without data. For example, the configurations indicated, at408c, may indicate that the SDM scheme is scheduled for the first UE402. At412, the first UE402may determine an antenna ports table to reference based on the received indication, at408a, and whether the SDM scheme is determined, at410, to be scheduled. Based on the determined antenna ports table to reference, at412, the first UE402may transmit, at414a, a PUSCH to the base station404based on the SDM scheme (e.g., if the SDM scheme is determined, at412, to be scheduled). The base station404may also receive, at414b, a PUSCH from the second UE403, which may or may not be based on the SDM scheme.

FIGS.5A-5Billustrate diagrams500-550of DMRS port configurations. Different DMRS ports may be included within a same CDM group or different CDM groups. For example, DMRS ports {0,1} may be included within the same CDM group (e.g., CDM group 0502), whereas DMRS ports {0,2} may be included in different CDM groups. For example, DMRS port 0 may be included in CDM group 0502and DMRS port 2 may be included in CDM group 1504.

The DMRS port configurations may include DMRS configuration Type 1508and DMRS configuration Type 2510. DMRS configuration Type 1508may be associated with 2 CDM groups (e.g., CDM group 0502and CDM group 1504), whereas DMRS configuration Type 2510may be associated with 3 CDM groups (e.g., CDM group 0502, CDM group 1504, and CDM group 2506). DMRS configuration Type 1508may include up to 8 DMRS ports (e.g., DMRS ports 0-7) and may be associated with a comb of 2 and a cyclic shift of 2. The comb 2 may correspond to 2 CDM groups (e.g., CDM group 0502and CDM group 1504) for DMRS configuration Type 1508, whereas the cyclic shift of 2 may be within a particular CDM group.

The DMRS port configurations may also be based on a DMRS maximum symbol length of 1512a-512bor a DMRS maximum symbol length of 2514a-514b. For a DMRS maximum symbol length of 1 OFDM symbol (e.g., at512a), the comb 2 and the cyclic shift of 2 may be associated with up to 4 DMRS ports (e.g., DMRS ports 0-3) for DMRS configuration Type 1508. The 2 CDM groups of DMRS configuration Type 1508may include CDM group 0502and CDM group 1. CDM group 0502may correspond to DMRS ports {0,1} based on the DMRS maximum symbol length of 1512a. CDM group 1504may correspond to DMRS ports {2,3} based on the DMRS maximum symbol length of 1512a.

For a maximum symbol length of 2 OFDM symbols (e.g., at514a), the comb 2 and the cyclic shift of 2 may also be associated with a time division-orthogonal cover code (TD-OCC) and may support up to 8 DMRS ports (e.g., DMRS ports 0-7) for DMRS configuration Type 1508. The 2 CDM groups of DMRS configuration Type 1508may include CDM group 0502and CDM group 1. CDM group 0502may correspond to DMRS ports {0,1,4,5} based on the DMRS maximum symbol length of 2514a. CDM group 1504may correspond to DMRS ports {2,3,6,7} based on the DMRS maximum symbol length of 2514a. The DMRS ports of the different CDM groups may be combed to provide orthogonality in the frequency domain.

DMRS configuration Type 2510may include up to 12 DMRS ports (e.g., DMRS ports 0-11) for a DMRS maximum symbol length of 2514band may be associated with a frequency domain-orthogonal cover code (FD-OCC) having adjacent REs in the frequency domain. For a DMRS maximum symbol length of 1 OFDM symbol (e.g., at512b), 2 FD-OCCs may be utilized across adjacent REs in the frequency domain to support up to 6 DMRS ports (e.g., DMRS ports 0-5). DMRS configuration Type 2510may be associated with 3 CDM groups that include CDM group 0502, CDM group 1504, and CDM group 2506. CDM group 0502may correspond to DMRS ports {0,1} based on the DMRS maximum symbol length of 1512b, CDM group 1504may correspond to DMRS ports {2,3} based on the DMRS maximum symbol length of 1512b, and CDM group 2504may correspond to DMRS ports {4,5} based on the DMRS maximum symbol length of 1512b.

For a maximum symbol length of 2 OFDM symbols (e.g., at514b), the 2 FD-OCCs utilized across the adjacent REs in the frequency domain may also be associated with a TD-OCC to support up to 12 DMRS ports (e.g., DMRS ports 0-11) for DMRS configuration Type 2510. CDM group 0502may correspond to DMRS ports {0,1,6,7} based on the DMRS maximum symbol length of 2514b, CDM group 1504may correspond to DMRS ports {2,3,8,9} based on the DMRS maximum symbol length of 2514b, and CDM group 2504may correspond to DMRS ports {4,5, 10,11} based on the DMRS maximum symbol length of 2514b. The DMRS ports of the different CDM groups may be combed to provide orthogonality in the frequency domain. In examples, DMRS ports 0-11 may also be referred to as DMRS ports1000-1011.

FIGS.6-7illustrate antenna ports tables600-680and700-760indicative of DMRS ports. More specifically, the antenna ports tables600-680correspond to DMRS configuration Type 1 and the antenna ports tables700-760correspond to DMRS configuration Type2. For DMRS configuration Type 1, the antenna ports tables610-640are based on a DMRS maximum symbol length of 1 and the antenna ports tables650-680are based on a DMRS maximum symbol length of 2. The antenna ports table610corresponds to rank 1, the antenna ports table620corresponds to rank 2, the antenna ports table630corresponds to rank 3, and the antenna ports table640corresponds to rank 4. Similarly, the antenna ports table650corresponds to rank 1, the antenna ports table660corresponds to rank 2, the antenna ports table670corresponds to rank 3, and the antenna ports table680corresponds to rank 4.

For DMRS configuration Type 2, the antenna ports tables710-740are based on a DMRS maximum symbol length of 1 and the antenna ports tables750-760are based on a DMRS maximum symbol length of 2. The antenna ports table710corresponds to rank 1, the antenna ports table720corresponds to rank 2, the antenna ports table730corresponds to rank 3, and the antenna ports table740corresponds to rank 4. Similarly, the antenna ports table750corresponds to rank 1 and the antenna ports table760corresponds to rank 2. DMRS configuration Type 2 with a DMRS maximum symbol length of 2 may also be associated with a rank 3 antenna ports table and a rank 4 antenna ports table (not illustrated). Thus, 16 antenna ports tables may be defined in total to cover both DMRS configuration Type 1 and DMRS configuration Type 2 with DMRS maximum symbol lengths of 1 and 2.

An antenna ports field of a scheduling DCI (e.g., a DCI that schedules a PUSCH) may be used to indicate DMRS ports for a PUSCH transmission. For example, the indication of the DMRS ports may correspond to an entry of the antenna ports tables610-680and710-760, which may be RRC configured or indicted via DCI. A DMRS maximum symbol length (e.g., 1 symbol or 2 symbols) may also be RRC configured or indicated via DCI. In examples where the DMRS maximum symbol length is equal to 2, an actual DMRS symbol length may still be equal to 1.

Bits of the antenna ports field of the DCI may correspond to code points associated with the antenna ports tables610-680and710-760. For instance, if the antenna ports field includes 3 bits, the antenna ports field may be indicative of 8 code points/table rows associated with the antenna ports tables610-640. If the antenna ports field includes 4 bits, the antenna ports field may be indicative of 16 code points/table rows associated with the antenna ports tables650-680and710-740. If the antenna ports field includes 5 bits, the antenna ports field may be indicative of 32 code points/table rows associated with the antenna ports tables750-760as well as the rank 3 and rank 4 tables for DMRS configuration Type 2 with a DMRS maximum symbol length of 2. A rank/number of layers associated with a transmission may be indicated by other DCI fields, by an SRS resource indicator (SRI) field in cases of non-codebook based uplink transmission, and/or by a transmitted precoding matrix indicator (TPMI) field in cases of codebook-based uplink transmissions.

An antenna ports table indicated by the antenna ports field of the DCI may include one or more reserved rows. For example, the antenna ports table620may include 8 rows, where rows 0-3 include antenna port information and rows 4-7 are reserved rows. The reserved rows may be incorporated in the antenna ports tables610-680and710-760to provide a fixed size for the DCI, in cases where the antenna ports table610-680and710-760are not RRC configured. The antenna ports tables610-680and710-760may indicate DMRS port numbers as well as a number of CDM groups without data. If REs are used for DMRS, the REs may not be used for data/PUSCH. Hence, the number of CDM groups without data may include the CDM groups of the indicated DMRS ports as well as other CDM groups. For example, in MU-MIMO communications, if other UEs are scheduled with DMRS ports in the other CDM groups, the number of CDM groups without data column may also be indicative of the other CDM groups that are not available for data REs.

The antenna ports table650, for example, may include table rows for both DMRS port 0 and DMRS port 1 with a number of front-loaded symbols equal to 1. However, two options may be available for the number of CDM groups without data (e.g., 1 CDM group without data or 2 CDM groups without data). If there are 2 CDM groups without data and the DMRS port corresponds to DMRS port 0, the DMRS may be scheduled in a first CDM group (e.g., CDM group 0) and a second CDM group (e.g., CDM group 1) may also not be used for data, as the number of CDM groups without data corresponds to 2. DMRS configuration Type 2 may be associated with 3 CDM groups. Thus, the number of CDM groups without data may be 1, 2, or 3 CDM groups (e.g. CDM groups 0-2).

The antenna ports field of the DCI may be interpreted based on a corresponding row of an indicated antenna ports table. The number of CDM groups without data may include the CDM groups of the indicated/scheduled DMRS ports for the UE as well as additional CDM groups. For example, in MU-MIMO communication, the base station may schedule multiple UEs on the same resources (e.g., same PRBs), such that different DMRS ports may be indicated for different UEs. For a particular UE, if non-scheduled CDM groups are used for DMRS ports of one or more co-scheduled UEs, the non-scheduled CDM groups may be included in the number of CDM groups without data. The particular UE may not transmit data tones in REs that correspond to the CDM groups associated with the number of CDM groups without data. In addition to MU-MIMO scheduling across CDM groups, MU-MIMO scheduling may also be performed within a CDM group. For example, different ports of a same CDM group may be used for different co-scheduled UEs.

In an example associated with the antenna ports tables610and630, MU-MIMO communication may be performed via the same RBs for a first UE with a rank equal to 1 (e.g., based on DMRS port 3) and a second UE with a rank equal to 3 (e.g., based on DMRS ports 0-2). The number of CDM groups without data may be equal to 2, so that another CDM group may remain available for the MU-MIMO communication. In another example associated with the antenna ports table610, MU-MIMO communication may be performed within a same CDM group. For example, the first two rows of the antenna ports table610may be used for two different UEs, where the UEs may be scheduled on the same RBs. That is, both DMRS port 0 indicated in the first row of the antenna ports table610and DMRS port 1 indicated in the second row of the antenna ports table610may correspond to the same CDM group. In yet another example associated with the antenna ports table620, MU-MIMO communication may be performed across different CDM groups. For instance, DMRS ports {0, 1} may be used for a first UE and DMRS ports {2,3} may be used for a second UE, where each set of DMRS ports corresponds to a different CDM group.

FIG.8illustrates a diagram800associated with SDM for a PUSCH. For example, a first UE802amay transmit a PUSCH based on different sets of layers having different transmission parameters (e.g., different beams, different sets of power control parameters, different precoding, etc.). The different sets of layers may include a first set of layers directed toward a first TRP804aand a second set of layers directed toward a second TRP804b. Thus, in a given PUSCH, the different sets of layers may have different transmission parameters.

The first set of layers may be associated with a first SRS resource set and the second set of layers may be associated with a second SRS resource set. The SRS resource set may be used for indicating/enabling the different transmission parameters. Potential rank combinations for the PUSCH may include rank combinations 1+1, 1+2, 2+1, and 2+2. For instance, rank combination 1+1 may correspond to a PUSCH that includes 2 layers, where the first layer has a first set of transmission parameters and a second layer has a second set of transmission parameters. Similarly, rank combination 2+1 may correspond to a PUSCH that includes 3 layers, where the first 2 layers have the first set of transmission parameters and the third layer has the second set of transmission parameters.

DMRS ports that correspond to different CDM groups for the first set of layers and the second set of layers may provide improved channel estimations at a base station. For rank combination 1+1, DMRS ports {0,2} may be indicated, where DMRS port 0 may be included in the first CDM group (e.g., CDM group 0) and DMRS port 2 may be included in the second CDM group (e.g., CDM group 1). However, DMRS port 0 and DMRS port 1 may not both be indicated, given that DMRS port 0 and DMRS port 1 are included in the same CDM group (e.g., CDM group 0). For rank combination 2+1, DMRS ports {0, 1; 2} may be indicated, where DMRS port 0 and DMRS port 1 correspond to the first layer and may be included in the first CDM group (e.g., CDM group 0), and DMRS port 2 corresponds to the second layer and may be included in the second CDM group (e.g., CDM group 1).

Some antenna ports tables may not support SDM procedures of the first UE802aand/or MU-MIMO communication across different UEs (e.g., the first UE802aand a second UE802b). However, one or more co-scheduled UEs, such as the second UE802b, may be scheduled based on an SDM scheme. In the diagram800, if the first UE802ais scheduled based on the SDM scheme with rank combination 1+1 (e.g., the first UE802ais scheduled with 2 layers/DMRS ports), the first UE802amay be assigned DMRS ports {0,2}, such that the 2 layers/DMRS ports correspond to different CDM groups. DMRS port entry {1,3}, which may be absent from certain antenna ports tables, would have to be assigned to the second UE802b, if the second UE802bis also scheduled based on the SDM scheme with rank combination 1+1 in different CDM groups, or if the second UE802bis scheduled with 2 layers for a same beam (e.g., directed toward a same TRP) with 1 symbol for DMRS.

For DMRS configuration Type 1, the only available DMRS ports that may be assigned to the second UE802bmay be DMRS ports {1,3}. That is, if there are a total of 4 DMRS ports, and DMRS ports {0,2} are assigned to the first UE802a, DMRS ports {1,3} may be the only remaining available DMRS ports that can be assigned to the second UE802b. Alternatively, the second UE802bmay be scheduled with one layer/DMRS port (e.g., DMRS port 1). If DMRS port entry {1,3} is unavailable to the second UE802b, the second UE802bmay not be scheduled with rank 2. For DMRS configuration Type 2, a third CDM group may be used. However, DMRS port entry {0,2} having 3 CDM groups without data may be unavailable (e.g., absent from certain antenna ports tables) for the first UE802a. Utilizing a third CDM group may generate additional overhead, as 2 CDM groups would otherwise be sufficient if DMRS port entry {1,3} was an available DMRS port entry to be indicated. In examples, the SDM scheme may be implemented based on the number of CDM groups without data being equal to 3 or more when the DMRS ports are associated with a first orthogonal cover code (OCC) of {1,1} and being equal to 2 or more when the DMRS ports are associated with a second OCC of {1,−1}.

FIG.9illustrates rank tables910-930including DMRS port entries associated with SDM. The rank tables910are based on rank 2 and correspond to both DMRS configuration Type 1 and DMRS configuration Type 2 for DMRS maximum symbol lengths of 1 and 2. The rank tables920are based on rank 3 and correspond to both DMRS configuration Type 1 and DMRS configuration Type 2 for a DMRS maximum symbol length of 2. The rank tables930are based on rank 4 and correspond to both DMRS configuration Type 1 and DMRS configuration Type 2 for a DMRS maximum symbol length of 2.

One or more DMRS port entries for PUSCH scheduling at the UE (e.g., indicated via the rank tables910-930) may be added to the antenna ports tables620,660-680,720,760, and associated rank 3 and rank 4 tables (not illustrated inFIG.7) for DMRS configuration Type 2 with a DMRS maximum symbol length of 2. The one or more DMRS port entries may be added based on the reserved rows of the tables, so that no additional bits have to be added to the DCI. For example, the rank tables910indicate that DMRS port entry {1,3} may be added at a reserved row of the antenna ports tables620,660,720, and760for rank 2, which corresponds to cases of DMRS configuration Type 1 and DMRS configuration Type 2, as well as DMRS maximum symbol lengths of 1 and 2. The number of CDM groups without data may be 2 for the added table row that includes DMRS port entry {1,3}. Thus, two different UEs may be scheduled based on the additions of rank tables910, where a first UE may be scheduled based on DMRS ports {0,2} and a second UE may be scheduled based on DMRS ports {1,3}. Accordingly, the base station may schedule the 2 UEs with orthogonal DMRS ports (e.g., DMRS ports {0,2} and DMRS ports {1,3}) on the same PRBs. Both UEs may be scheduled based on the SDM scheme, or one of the UEs may be scheduled based on the SDM scheme and the other UE may communicate via 2 layers.

DMRS port entry {0,2} with a number of CDM groups without data being equal to 3 may also be added at a reserved row of the antenna ports table for rank 2, as indicated in the rank tables910. The DMRS port entry may be used for DMRS configuration Type 2, as DMRS configuration Type 1 may not include 3 CDM groups. DMRS port entry {0,2} may also be used when the number of CDM groups without data is equal to 2. However, the added DMRS port entry based on 3 CDM groups without data may allow the base station to schedule the SDM scheme for the UE with DMRS ports {0,2} and also schedule other UE(s) with DMRS ports from the third CDM group on the same PRBs. For example, the first UE may be scheduled with DMRS ports {0,2} and the second UE may be scheduled with DMRS ports {4,5}, which may correspond to the third CDM group. In further examples, a third UE may be scheduled with another DMRS port (e.g., DMRS port 1 based on 1 layer) and a fourth UE may be scheduled with yet another DMRS port (e.g., DMRS port 3). The first UE may receive an indication that the number of CDM groups without data is equal to 3, so that the other DMRS ports are not used by the first UE for data. A third DMRS port entry for DMRS ports {1,3} with the number of CDM groups without data being equal to 3 may also be added to the antenna ports tables720and760, as indicated in the rank tables910.

DMRS port entry {0,2} with a number of front-loaded symbols equal to 2 may also be added to the antenna ports table660and760for rank 2, as indicated in the rank tables910. Some antenna ports tables may include DMRS port entry {0,2} with a number of front-loaded symbols equal to 1, but may not be based on the SDM scheme. For DMRS port entry {0,2} with the number of front-loaded symbols equal to 2, the number of CDM groups without data may be equal to 2 or 3. Three CDM groups without data may correspond to DMRS configuration Type 2.

The base station may schedule the SDM scheme for the UE based on DMRS ports {0,2} with 2 front-loaded DMRS symbols and may also schedule one or more UEs with other orthogonal DMRS ports on the same PRBs. For a large number of co-scheduled UEs, 2 front-loaded symbols may be used to double a number of available DMRS ports, e.g., where one of the UEs may be scheduled based on the SDM scheme via DMRS ports {0,2}. In an example for DMRS configuration Type 1 based on 8 total DMRS ports, where a DMRS maximum symbol length is equal to 2 and a number of front-loaded DMRS symbols is equal to 2, a first UE may be scheduled with DMRS ports {0,2} based on the SDM scheme. Further to the example, a second UE may be scheduled with DMRS ports {4,5}, a third UE3 may be scheduled with DMRS port 5, and a fourth UE may be scheduled with DMRS port 6. Still further to the example, a fifth UE could be scheduled with DMRS port 1 and a sixth UE could be scheduled with DMRS port 3. DMRS port numbers of 4 or larger may be associated with the second front-loaded DMRS symbol. For instance, if DMRS ports {0,2} are scheduled with 2 front-loaded symbols, the second UE may be scheduled with DMRS port {4,5}, etc.

The DMRS port entry {1,3} with the number of front-loaded DMRS symbols equal to 2 may also be utilized for the SDM scheme. Similarly, as indicated in the rank tables920, DMRS port entry {0,1,2} with rank 3 may be utilized for the SDM scheme, e.g., based on a rank combination of 2+1 layers. The DMRS port entry {0,1,2} may be scheduled based on the number of front-loaded symbols being equal to 2. That is, if the UE receives an indication of DMRS port entry {0,1,2} and is scheduled based on the SDM with the rank combination 2+1, the DMRS ports may be associated with 2 front-loaded DMRS symbols.

As indicated in the rank tables930, DMRS port entry {0,1,2,3} with rank 4 may likewise be scheduled based on the SDM scheme with a rank combination of 2+2 layers. DMRS ports {0,1} may correspond to the first set of layers and DMRS ports {2,3} may correspond to the second set of layers for a particular UE. In addition to the particular UE being scheduled based on the SDM scheme, other UEs may be scheduled with a further number of ports, such that the DMRS port entry may be associated with the number of front-loaded symbols being equal to 2. For example, DMRS entry {0,1,2,3} may be scheduled based on 2 front-loaded DMRS symbols.

If the UE is configured/scheduled with the SDM scheme for a PUSCH based on two sets of layers associated with two SRS resource sets having different transmission parameters, such as different beams parameters, precoding parameters, power control parameters, etc., the antenna ports field indicated via the DCI may correspond to an SDM antenna ports table. That is, rather than adding DMRS port entries to reserved rows of the antenna ports table, as indicated in the rank tables910-930, an SDM antenna ports table may be generated/configured based on DMRS port entries associated with the SDM scheme. The UE may determine whether to use the SDM antenna ports table or the non-SDM antenna ports table based on whether the UE is scheduled with the SDM scheme. If the UE is scheduled with the SDM scheme, the antenna ports field indicative via the DCI may be interpreted based on the SDM antenna ports table.

The SDM antenna ports table for a particular DMRS configuration Type, DMRS maximum symbol length, rank, etc., may include one or more non-SDM antenna port entries in addition to one or more SDM antenna port entries. Thus, rather than selecting between a non-SDM antenna ports table and an SDM antenna ports table, the SDM antenna port entries and the non-SDM antenna ports entries may be included in a single table from which the antenna ports field may indicate an entry via the DCI. The SDM scheme may be indicated based on the DCI or RRC signaling. The UE may determine a table to reference based on an RRC configuration and/or the indication in the DCI.

Some of the non-SDM antenna port entries may not be indicated in association with the SDM scheme. For example, non-SDM antenna port entries with one DMRS port or non-SDM antenna port entries with DMRS ports corresponding to one CDM group may not be used in association with the SDM scheme, which may be based on at least 2 layers. Removing antenna port entries associated with 1 DMRS port or one CDM group may reduce DCI overhead in cases where adding SDM antenna port entries to the tables increases a size of the antenna ports field.

For MU-MIMO communication, the base station may schedule a first UE with the SDM scheme based on indicating DMRS ports associated with the rank tables910-930. The first UE may be scheduled on same PRBs used for one or more UEs scheduled based on either the SDM antenna port entries or the non-SDM antenna ports entries. The DMRS port entry indicated to the UE may be based on rank combinations, such as 1+1, 1+2, 2+1, or 2+2, for the SDM scheme. The DMRS port entry indicated to the UE may also be based on whether the communication is an MU-MIMO communication, a number of co-scheduled UEs, a rank of the co-scheduled UEs, DMRS configuration type, and/or a DMRS maximum symbol length.

FIG.10is a flowchart1000of a method of wireless communication. The method may be performed by a first UE (e.g., the UE104,402,802a-802b; the apparatus1402; etc.), which may include the memory360and which may be the entire first UE104,402,802a-802bor a component of the first UE104,402,802a-802b, such as the TX processor368, the RX processor356, and/or the controller/processor359.

At1002, the first UE may receive an indication of a plurality of DMRS ports for an SDM PUSCH transmission and a number of DMRS CDM groups without data. For example, referring toFIG.4, the first UE402may receive, at408a, an indication from the base station404of DMRS ports for a PUSCH transmission and a number of CDM groups without data. The indicated number of CDM ports without data may be associated with an SDM scheme.

At1004, the first UE may transmit the SDM PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. For example, referring toFIGS.4and9, the first UE402may transmit, at414a, a PUSCH based on the SDM scheme associated with the indication received, at408a, of the DMRS ports for the PUSCH transmission and the number of CDM groups without data. The SDM scheme may correspond to one or more entries of the rank tables910-930.

FIG.11is a flowchart1100of a method of wireless communication. The method may be performed by a first UE (e.g., the UE104,402,802a-802b; the apparatus1402; etc.), which may include the memory360and which may be the entire first UE104,402,802a-802bor a component of the first UE104,402,802a-802b, such as the TX processor368, the RX processor356, and/or the controller/processor359.

At1102a, the first UE may receive an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data. For example, referring toFIG.4, the first UE402may receive, at408a, an indication from the base station404of DMRS ports for a PUSCH transmission and a number of CDM groups without data. The indicated number of CDM ports without data may be associated with an SDM scheme.

At1102b, the number of CDM groups without data is: (1) greater than or equal to 3 when the plurality of DMRS ports is {0, 2}; (2) greater than or equal to 2 when the plurality of DMRS ports is {1, 3}; or (3) greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2. For example, referring toFIGS.4-9, the number of CDM groups without data indicated, at408a, may correspond to configurations indicated, at408c, where the number of CDM groups without data is: (1)≥ to 3 when DMRS ports {0, 2} is indicated; (2)≥ to 2 when DMRS ports {1, 3} is indicated; or (3)≥2 when DMRS ports {0, 2} indicated and a number of front-loaded symbols=2. The configurations indicated, at408c, may correspond to one or more entries of the rank tables910-930.

At1104, the first UE may determine whether an SDM scheme is scheduled. For example, referring toFIGS.4and9, the first UE402may determine, at410, whether an SM scheme is scheduled (e.g., based on scheduling information received, at406a, from the base station404). The SDM scheme may correspond to one or more entries of the rank tables910-930.

At1106, the first UE may determine a table to reference based on the received indication and based on whether the SDM scheme is scheduled—the PUSCH transmission is based on the determined table. For example, referring toFIG.4, the first UE402may determine, at412, an antenna ports table to reference based on the received indication, at408a, from the base station404and whether the SDM scheme is determined, at412, to be scheduled by the base station404. The UE first402may transmit a PUSCH, at414a, to the base station404based on the antenna ports tabled determined, at412.

At1108, the first UE may transmit the PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. For example, referring toFIGS.4and9, the first UE402may transmit, at414a, a PUSCH based on the SDM scheme associated with the received indication, at408a, of the DMRS ports for the PUSCH transmission and the number of CDM groups without data. The SDM scheme may correspond to one or more entries of the rank tables910-930.

FIG.12is a flowchart1200of a method of wireless communication. The method may be performed by a base station (e.g., the base station102,404; TRP1804a; TRP2804b; the apparatus1502; etc.), which may include the memory376and which may be the entire base station102,404or a component of the base station102,404, such as the TX processor316, the RX processor370, and/or the controller/processor375.

At1202, the base station may transmit an indication of a plurality of DMRS ports for an SDM PUSCH communication and a number of DMRS CDM groups without data. For example, referring toFIG.4, the base station404may transmit, at408a-408b, an indication to the first UE402and/or the second UE403of the DMRS ports for the PUSCH transmission and the number of CDM groups without data. The indicated number of CDM ports without data may be associated with an SDM scheme.

At1204, the base station may receive the SDM PUSCH communication based on the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. For example, referring toFIGS.4and9, the base station404may receive, at414a-414b, one or more PUSCHs based on the SDM scheme associated with the transmitted indication, at408a-408b, of the DMRS ports for the PUSCH transmission and the number of CDM groups without data. The SDM scheme may correspond to one or more entries of the rank tables910-930.

FIG.13is a flowchart1300of a method of wireless communication. The method may be performed by a base station (e.g., the base station102,404; TRP1804a; TRP2804b; the apparatus1502; etc.), which may include the memory376and which may be the entire base station102,404or a component of the base station102,404, such as the TX processor316, the RX processor370, and/or the controller/processor375.

At1302, the base station may schedule a first UE and a second UE on a same PRB—the first UE is scheduled based on an SDM scheme associated with a plurality of DMRS ports and a number of DMRS CDM groups without data. For example, referring toFIG.4, the base station404may schedule, at406a-406b, an MU-MIMO communication based on an SDM scheme for at least one UE. That is, the base station404may schedule, at406a-406b, the first UE402and/or the second UE403based on the SDM scheme, which may correspond to the indication, at408a, of the DMRS ports for PUSCH transmission and the number of CDM groups without data.

At1304a, the base station may transmit an indication of the plurality of DMRS ports for a PUSCH communication and the number of DMRS CDM groups without data. For example, referring toFIG.4, the base station404may transmit, at408a-408b, an indication to the first UE402and/or the second UE403of the DMRS ports for the PUSCH transmission and the number of CDM groups without data. The indicated number of CDM ports without data may be associated with an SDM scheme.

At1304b, the number of CDM groups without data is: (1) greater than or equal to 3 when the plurality of DMRS ports is {0, 2}; (2) greater than or equal to 2 when the plurality of DMRS ports is {1, 3}; or (3) greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2. For example, referring toFIGS.4-9, the number of CDM groups without data indicated, at408a-408b, may correspond to configurations indicated, at408c, where the number of CDM groups without data is: (1)≥ to 3 when DMRS ports {0, 2} is indicated; (2)> to 2 when DMRS ports {1, 3} is indicated; or (3)≥2 when DMRS ports {0, 2} indicated and a number of front-loaded symbols=2. The configurations indicated, at408c, may correspond to one or more entries of the rank tables910-930.

At1306, the base station may receive the PUSCH communication based on the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. For example, referring toFIGS.4and9, the base station404may receive, at414a-414b, one or more PUSCHs based on the SDM scheme associated with the transmitted indication, at408a-408b, of the DMRS ports for the PUSCH transmission and the number of CDM groups without data. The SDM scheme may correspond to one or more entries of the rank tables910-930.

FIG.14is a diagram1400illustrating an example of a hardware implementation for an apparatus1402. The apparatus1402may be a UE, a component of a UE, or may implement UE functionality. In some aspects, the apparatus1402may include a cellular baseband processor1404(also referred to as a modem) coupled to a cellular RF transceiver1422. In some aspects, the apparatus1402may further include one or more subscriber identity modules (SIM) cards1420, an application processor1406coupled to a secure digital (SD) card1408and a screen1410, a Bluetooth module1412, a wireless local area network (WLAN) module1414, a Global Positioning System (GPS) module1416, or a power supply1418. The cellular baseband processor1404communicates through the cellular RF transceiver1422with the UE104and/or BS102/180. The cellular baseband processor1404may include a computer-readable medium/memory. The computer-readable medium/memory may be non-transitory. The cellular baseband processor1404is responsible for general processing, including the execution of software stored on the computer-readable medium/memory. The software, when executed by the cellular baseband processor1404, causes the cellular baseband processor1404to perform the various functions described supra. The computer-readable medium/memory may also be used for storing data that is manipulated by the cellular baseband processor1404when executing software. The cellular baseband processor1404further includes a reception component1430, a communication manager1432, and a transmission component1434. The communication manager1432includes the one or more illustrated components. The components within the communication manager1432may be stored in the computer-readable medium/memory and/or configured as hardware within the cellular baseband processor1404. The cellular baseband processor1404may be a component of the UE350and may include the memory360and/or at least one of the TX processor368, the RX processor356, and the controller/processor359. In one configuration, the apparatus1402may be a modem chip and include just the baseband processor1404, and in another configuration, the apparatus1402may be the entire UE (e.g., see350ofFIG.3) and include the additional modules of the apparatus1402. The reception component1430is configured, e.g., as described in connection with1002and1102a, to receive an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data. The communication manager1432includes a determination component1440that is configured, e.g., as described in connection with1104and1106, to determine whether an SDM scheme is scheduled; and to determine a table to reference based on the received indication and based on whether the SDM scheme is scheduled—the PUSCH transmission is based on the determined table. The communication manager1432further includes a CDM component1442that is configured, e.g., as described in connection with1102b, to indicate that the number of CDM groups without data is: (1) greater than or equal to 3 when the plurality of DMRS ports is {0, 2}; (2) greater than or equal to 2 when the plurality of DMRS ports is {1, 3}; or (3) greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2. The transmission component1434is configured, e.g., as described in connection with1004and1108, to transmit the PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data.

As shown, the apparatus1402may include a variety of components configured for various functions. In one configuration, the apparatus1402, and in particular the cellular baseband processor1404, includes means for receiving an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and means for transmitting the PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. The apparatus1402further includes means for determining whether an SDM scheme is scheduled. The apparatus1402further includes means for determining a table to reference based on the received indication and based on whether the SDM scheme is scheduled, wherein the PUSCH transmission is based on the determined table.

The means may be one or more of the components of the apparatus1402configured to perform the functions recited by the means. As described supra, the apparatus1402may include the TX Processor368, the RX Processor356, and the controller/processor359. As such, in one configuration, the means may be the TX Processor368, the RX Processor356, and the controller/processor359configured to perform the functions recited by the means.

FIG.15is a diagram1500illustrating an example of a hardware implementation for an apparatus1502. The apparatus1502may be a base station, a component of a base station, or may implement base station functionality. In some aspects, the apparatus1502may include a baseband unit1504. The baseband unit1504may communicate through a cellular RF transceiver1522with the UE104. The baseband unit1504may include a computer-readable medium/memory. The baseband unit1504is responsible for general processing, including the execution of software stored on the computer-readable medium/memory. The software, when executed by the baseband unit1504, causes the baseband unit1504to perform the various functions described supra. The computer-readable medium/memory may also be used for storing data that is manipulated by the baseband unit1504when executing software. The baseband unit1504further includes a reception component1530, a communication manager1532, and a transmission component1534. The communication manager1532includes the one or more illustrated components. The components within the communication manager1532may be stored in the computer-readable medium/memory and/or configured as hardware within the baseband unit1504. The baseband unit1504may be a component of the base station310and may include the memory376and/or at least one of the TX processor316, the RX processor370, and the controller/processor375.

The reception component1530is configured, e.g., as described in connection with1204and1306, to receive the PUSCH communication based on the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data. The communication manager1532includes a scheduler component1540that is configured, e.g., as described in connection with1302, to schedule a first UE and a second UE on a same PRB—the first UE is scheduled based on an SDM scheme associated with a plurality of DMRS ports and a number of DMRS CDM groups without data. The communication manager1532further includes a CDM component1542that is configured, e.g., as described in connection with1304b, to indicate that the number of CDM groups without data is: (1) greater than or equal to 3 when the plurality of DMRS ports is {0, 2}; (2) greater than or equal to 2 when the plurality of DMRS ports is {1, 3}; or (3) greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2. The transmission component1534is configured, e.g., as described in connection with1202and1304a, to transmit an indication of the plurality of DMRS ports for a PUSCH communication and the number of DMRS CDM groups without data.

As shown, the apparatus1502may include a variety of components configured for various functions. In one configuration, the apparatus1502, and in particular the baseband unit1504, includes means for transmitting an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and means for receiving the PUSCH transmission based on the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data.

The means may be one or more of the components of the apparatus1502configured to perform the functions recited by the means. As described supra, the apparatus1502may include the TX Processor316, the RX Processor370, and the controller/processor375. As such, in one configuration, the means may be the TX Processor316, the RX Processor370, and the controller/processor375configured to perform the functions recited by the means. The apparatus1502further includes means for scheduling a first UE and a second UE on a same PRB, the first UE scheduled based on an SDM scheme associated with the plurality of DMRS ports and the number of DMRS CDM groups without data.

Aspect 1 is an apparatus for wireless communication at a UE including at least one processor coupled to a memory and configured to: receive an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and transmit the PUSCH transmission based on the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data.

Aspect 2 may be combined with aspect 1 and includes that the plurality of DMRS ports includes a first DMRS port associated with a first DMRS CDM group and a second DMRS port associated with a second DMRS CDM group, the received indication indicates the first DMRS port associated with the first DMRS CDM group and the second DMRS port associated with the second DMRS CDM group.

Aspect 3 may be combined with any of aspects 1-2 and includes that the first DMRS port is of a first plurality of DMRS ports associated with the first DMRS CDM group and the second DMRS port is of a second plurality of DMRS ports associated with the second DMRS CDM group.

Aspect 4 may be combined with any of aspects 1-3 and includes that the first plurality of DMRS ports includes DMRS ports {0,1}, the second plurality of DMRS ports includes DMRS ports {2,3}, the first DMRS port is DMRS port 0, the second DMRS port is DMRS port 2, and the received indication indicates DMRS ports {0,2} with at least 3 DMRS CDM groups without data.

Aspect 5 may be combined with any of aspects 1-3 and includes that the first plurality of DMRS ports includes DMRS ports {0,1}, the second plurality of DMRS ports includes DMRS ports {2,3}, the first DMRS port is DMRS port 1, the second DMRS port is DMRS port 3, and the received indication indicates DMRS ports {1,3} with at least 2 DMRS CDM groups without data.

Aspect 6 may be combined with any of aspects 1-3 or 5 and includes that the first plurality of DMRS ports includes DMRS ports {0,1}, the second plurality of DMRS ports includes DMRS ports {2,3}, the first DMRS port is DMRS port 1, the second DMRS port is DMRS port 3, the first DMRS port and the second DMRS port corresponding to at least one front-loaded DMRS symbol.

Aspect 7 may be combined with any of aspects 1-6 and includes that the first DMRS port associated with the first DMRS CDM group and the second DMRS port associated with the second DMRS CDM group correspond to two front-loaded DMRS symbols.

Aspect 8 may be combined with any of aspects 1-7 and includes that the first DMRS port associated with the first DMRS CDM group is included in a first set of one or more DMRS ports, the second DMRS port associated with the second DMRS CDM group is included in a second set of one or more DMRS ports, the received indication indicates the first set of one or more DMRS ports and the second set of one or more DMRS ports, at least one of the first set of one or more DMRS ports or the second set of one or more DMRS ports corresponding to two front-loaded DMRS symbols.

Aspect 9 may be combined with any of aspects 1-8 and includes that the at least one processor is further configured to: determine whether an SDM scheme is scheduled; and determine a table to reference based on the received indication and based on whether the SDM scheme is scheduled, wherein the PUSCH transmission is based on the determined table.

Aspect 10 may be combined with any of aspects 1-9 and includes that the received indication of the plurality of DMRS ports and the number of DMRS CDM groups without data is indicated based on at least one of DCI or RRC signaling.

Aspect 11 may be combined with any of aspects 1-10 and includes that the plurality of DMRS ports is associated with SDM based on different sets of one or more layers that correspond to different transmission parameters.

Aspect 12 is an apparatus for wireless communication at a base station including at least one processor coupled to a memory and configured to: transmit an indication of a plurality of DMRS ports for a PUSCH transmission and a number of DMRS CDM groups without data, wherein the number of DMRS CDM groups without data is: greater than or equal to 3 when the plurality of DMRS ports is {0, 2}, greater than or equal to 2 when the plurality of DMRS ports is {1, 3}, or greater than or equal to 2 when the plurality of DMRS ports is {0, 2} and a number of front-loaded symbols corresponding to the plurality of DMRS ports is 2; and receive the PUSCH transmission based on the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data.

Aspect 13 may be combined with aspect 12 and includes that the plurality of DMRS ports includes a first DMRS port associated with a first DMRS CDM group and a second DMRS port associated with a second DMRS CDM group, the transmitted indication indicates the first DMRS port associated with the first DMRS CDM group and the second DMRS port associated with the second DMRS CDM group.

Aspect 14 may be combined with any of aspects 12-13 and includes that the first DMRS port is of a first plurality of DMRS ports associated with the first DMRS CDM group and the second DMRS port is of a second plurality of DMRS ports associated with the second DMRS CDM group.

Aspect 15 may be combined with any of aspects 12-14 and includes that the first plurality of DMRS ports includes DMRS ports {0,1}, the second plurality of DMRS ports includes DMRS ports {2,3}, the first DMRS port is DMRS port 0, the second DMRS port is DMRS port 2, and the transmitted indication indicates DMRS ports {0,2} with at least 3 DMRS CDM groups without data.

Aspect 16 may be combined with any of aspects 12-14 and includes that the first plurality of DMRS ports includes DMRS ports {0,1}, the second plurality of DMRS ports includes DMRS ports {2,3}, the first DMRS port is DMRS port 1, the second DMRS port is DMRS port 3, and the transmitted indication indicates DMRS ports {1,3} with at least 2 DMRS CDM groups without data.

Aspect 17 may be combined with any of aspects 12-14 or 16 and includes that the first plurality of DMRS ports includes DMRS ports {0,1}, the second plurality of DMRS ports includes DMRS ports {2,3}, the first DMRS port is DMRS port 1, the second DMRS port is DMRS port 3, the first DMRS port and the second DMRS port corresponding to at least one front-loaded DMRS symbol.

Aspect 18 may be combined with any of aspects 12-17 and includes that the first DMRS port associated with the first DMRS CDM group and the second DMRS port associated with the second DMRS CDM group correspond to two front-loaded DMRS symbols.

Aspect 19 may be combined with any of aspects 12-18 and includes that the first DMRS port associated with the first DMRS CDM group is included in a first set of one or more DMRS ports, the second DMRS port associated with the second DMRS CDM group is included in a second set of one or more DMRS ports, the transmitted indication indicates the first set of one or more DMRS ports and the second set of one or more DMRS ports, at least one of the first set of one or more DMRS ports or the second set of one or more DMRS ports corresponding to two front-loaded DMRS symbols.

Aspect 20 may be combined with any of aspects 12-19 and includes that the transmitted indication indicates a table to reference based on whether an SDM scheme is scheduled, the PUSCH transmission based on the table.

Aspect 21 may be combined with any of aspects 12-20 and includes that the transmitted indication of the plurality of DMRS ports and the number of DMRS CDM groups without data is indicated based on at least one of DCI or RRC signaling.

Aspect 22 may be combined with any of aspects 12-21 and includes that the plurality of DMRS ports is associated with SDM based on different sets of one or more layers that correspond to different transmission parameters.

Aspect 23 may be combined with any of aspects 12-22 and includes that the at least one processor is further configured to schedule a first UE and a second UE on a same PRB, the first UE scheduled based on an SDM scheme associated with the plurality of DMRS ports and the number of DMRS CDM groups without data.

Aspect 24 may be combined with any of aspects 12-23 and includes that the scheduling of the first UE is based on at least one of a rank combination for the SDM scheme, an MU-MIMO communication, a number of co-scheduled UEs, a rank of the co-scheduled UEs, a DMRS configuration type, or a maximum length of DMRS symbols.

Aspect 25 may be combined with any of aspects 1-24 and further includes at least one of an antenna or a transceiver coupled to the at least one processor.

Aspect 26 is a method of wireless communication for implementing any of aspects 1-25.

Aspect 27 is an apparatus for wireless communication including means for implementing any of aspects 1-25.

Aspect 28 is a computer-readable medium storing computer executable code, the code when executed by at least one processor causes the at least one processor to implement any of aspects 1-25.