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US-20260128843-A1 - LOW OVERHEAD SUBBAND-BASED UPLINK PRECODING

US20260128843A1US 20260128843 A1US20260128843 A1US 20260128843A1US-20260128843-A1

Abstract

A wireless transmit/receive unit (WTRU) may receive a (RS) configuration. The RS may comprise an indication of a plurality of −RSs mapped in an irregular pattern in a channel over a plurality of subbands. The RS configuration may comprise information associated with the irregular pattern. The WTRU may estimate a channel information over the plurality of subbands that comprise no RSs. The estimation may be based on the one or more RSs mapped in the irregular pattern and the information associated with the irregular pattern. The WTRU may receive downlink control information (DCI). The DCI may comprise an indication of an uplink transmission and an indication of the subbands within the plurality of subbands available for the uplink transmission. The WTRU may determine, per each subband, uplink precoders for the scheduled uplink transmission based on the estimation. The WTRU may send the uplink transmission using the uplink precoders.

Inventors

  • Afshin Haghighat
  • Loic Canonne-Velasquez
  • Mohammad Irfan
  • Jonghyun Park
  • Roozbeh MOHAMMADIAN

Assignees

  • INTERDIGITAL PATENT HOLDINGS, INC.

Dates

Publication Date
20260507
Application Date
20241104

Claims (20)

  1. 1 . A wireless transmit/receive unit (WTRU) comprising: a processor configured to: receive a reference signal (RS) configuration, wherein the RS configuration comprises an indication of a plurality of RSs mapped in an irregular pattern in a channel over a plurality of subbands, wherein the RS configuration comprises information associated with the irregular pattern; estimate a channel information over the plurality of subbands that comprise no RSs, based on the one or more RSs mapped in the irregular pattern and the information associated with the irregular pattern; receive downlink control information (DCI), wherein the DCI comprises an indication of an uplink transmission and an indication of the subbands within the plurality of subbands available for the uplink transmission; determine, per each subband within the plurality of subbands, uplink precoders for the scheduled uplink transmission based on the estimation; and send the uplink transmission using the uplink precoders.
  2. 2 . The WTRU of claim 1 , wherein the irregular pattern comprises a plurality of RSs that are not uniformly distributed throughout the channel.
  3. 3 . The WTRU of claim 1 , wherein the irregular pattern comprises a plurality of RSs that are not evenly spaced throughout the channel.
  4. 4 . The WTRU of claim 1 , wherein the RS configuration comprises one or more of the configured bandwidth of the RSs, an indication of the mapping of the RSs in a frequency domain, or a rotation value of the irregular pattern.
  5. 5 . The WTRU of claim 4 , wherein the processor is further configured to: determine, by dividing the configured bandwidth of the RSs with a size of the subband on the channel for estimation, the number of subbands within the plurality of subbands on the channel for estimation.
  6. 6 . The WTRU of claim 4 , wherein the indication of the mapping of the RSs in a frequency domain comprises a bitmap, wherein the bitmap indicates the location of the RSs from a set of candidate locations.
  7. 7 . The WTRU of claim 4 , wherein the configured bandwidth of the RSs is wider than or equal to a bandwidth associated with the uplink transmission.
  8. 8 . The WTRU of claim 1 , wherein the information associated with the irregular pattern is a sparsity order.
  9. 9 . The WTRU of claim 1 , wherein the determination of the uplink precoders is based on a plurality of frequency locations within the plurality of subbands that comprise no RSs.
  10. 10 . The WTRU of claim 1 , wherein the processor is further configured to: receive configuration information, wherein the configuration information comprises one or more of a precoding resolution or an indication of a maximum number of multiple input multiple output (MIMO) layers.
  11. 11 . A method implemented by a wireless transmit/receive unit (WTRU), the method comprising: receiving a reference signal (RS) configuration, wherein the RS configuration comprises an indication of a plurality of RSs mapped in an irregular pattern in a channel over a plurality of subbands, wherein the RS configuration comprises information associated with the irregular pattern; estimating a channel information over the plurality of subbands that comprise no RSs, based on the one or more RSs mapped in the irregular pattern and the information associated with the irregular pattern; receiving downlink control information (DCI), wherein the DCI comprises an indication of an uplink transmission and an indication of the subbands within the plurality of subbands available for the uplink transmission; determining, per each subband within the plurality of subbands, uplink precoders for the scheduled uplink transmission based on the estimation; and sending the uplink transmission using the uplink precoders.
  12. 12 . The method of claim 11 , wherein the irregular pattern comprises a plurality of RSs that are not uniformly distributed throughout the channel.
  13. 13 . The method of claim 11 , wherein the irregular pattern comprises a plurality of −RSs that are not evenly spaced throughout the channel.
  14. 14 . The method of claim 11 , wherein the RS configuration comprises one or more of the configured bandwidth of the RSs, an indication of the mapping of the RSs in a frequency domain, or a rotation value of the irregular pattern.
  15. 15 . The method of claim 14 , further comprising: determining, by dividing the configured bandwidth of the RSs with a size of the subband on the channel for estimation, the number of subbands within the plurality of subbands on the channel for estimation.
  16. 16 . The method of claim 14 , wherein the indication of the mapping of the RSs in a frequency domain comprises a bitmap, wherein the bitmap indicates the location of the RSs from a set of candidate locations.
  17. 17 . The method of claim 14 , wherein the configured bandwidth of the RSs is wider than or equal to a bandwidth associated with the uplink transmission.
  18. 18 . The method of claim 11 , wherein the information associated with the irregular pattern is a sparsity order.
  19. 19 . The method of claim 11 , wherein the determination of the uplink precoders is based on a plurality of frequency locations within the plurality of subbands that comprise no RSs.
  20. 20 . The method of claim 11 , further comprising: receiving configuration information, wherein the configuration information comprises one or more of a precoding resolution or an indication of a maximum number of multiple input multiple output (MIMO) layers.

Description

BACKGROUND In a multi-input multi-output (MIMO) system, there are two main modes of precoding: codebook-based precoding and non-codebook-based precoding. In a codebook-based uplink precoding, a wireless transmit/receive unit (WTRU) may receive an explicit indication as to which precoders may be used for a scheduled transmission. The indication may take the form of an index that points to a specific precoder from a codebook known to both WTRU and/or gNB, such as a transmitted precoding matrix indicator (TPMI) as used in new radio (NR). In a non-codebook-based uplink precoding, the scheduled uplink transmission may use and explicit indication of a precoder. Instead, the precoding determination may be based on channel reciprocity. In channel reciprocity, a WTRU may determines a best precoder for the uplink precoding based on the observed channel on a received downlink reference signal (RS), such as a channel state information (CSI) reference signal (RS). As wireless channels exhibit frequency selective behavior, it may be beneficial for a precoding-based MIMO system to support precoding on a subband-basis to better match channel frequency response. Due to concerns related to the required feedback overhead for precoder indication (e.g., in the case of codebook-based precoding) and/or downlink reference density (e.g., in the case of non-codebook-based precoding), uplink transmission may be based on wideband precoding. Therefore, design of an efficient procedure for subband-based precoding for uplink transmission remains an important issue. SUMMARY A wireless transmit/receive unit (WTRU) may receive a reference signal (RS) (e.g., a channel state information (CSI) reference signal (RS)) configuration. The RS may comprise an indication of a plurality of RSs mapped in an irregular pattern in a channel over a plurality of subbands. The RS configuration may comprise information associated with the irregular pattern. The WTRU may estimate a channel information over the plurality of subbands that comprise no RSs. The estimation may be based on the one or more RSs mapped in the irregular pattern and the information associated with the irregular pattern. The WTRU may receive downlink control information (DCI). The DCI may comprise an indication of an uplink transmission and an indication of the subbands within the plurality of subbands available for the uplink transmission. The WTRU may determine (e.g., per each subband within the plurality of subbands) uplink precoders for the scheduled uplink transmission based on the estimation. The WTRU may send the uplink transmission using the uplink precoders. The irregular pattern may comprise a plurality of RSs that are not uniformly distributed throughout the channel. The irregular pattern may comprise a plurality of RSs that are not evenly spaced throughout the channel. The RS configuration may comprise a configured bandwidth of the RSs, an indication of the mapping of the RSs in a frequency domain, or a rotation value of the irregular pattern. The WTRU may determine, by dividing the configured bandwidth of the RSs with a size of the subband on the channel for estimation, the number of subbands within the plurality of subbands on the channel for estimation. The indication of the mapping of the RSs in a frequency domain may comprise a bitmap, wherein the bitmap indicates the location of the RSs from a set of candidate locations. The configured bandwidth of the RSs may be wider than or equal to a bandwidth associated with the uplink transmission. The information associated with the irregular pattern may be a sparsity order. The determination of the uplink precoders is based on a plurality of frequency locations within the plurality of subbands that comprise no RSs. The WTRU may receive configuration information. The configuration information may comprise one or more of a precoding resolution or an indication of a maximum number of multiple input multiple output (MIMO) layers. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented. FIG. 1B is a system diagram illustrating an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A according to an embodiment. FIG. 1C is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communications system illustrated in FIG. 1A according to an embodiment. FIG. 1D is a system diagram illustrating a further example RAN and a further example CN that may be used within the communications system illustrated in FIG. 1A according to an embodiment. FIG. 2 depicts an example of reference signal (RS) optimization based on the determined channel sparsity. FIG. 3 depicts a process for sparse channel state information (CSI) reference signal (RS)-based TPMI determination by a wireless transmit/receive unit (W