Subband TPMI Indication Using MAC-CE and DCI Bit Reduction
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Solution Overview
Problem
Existing wireless communication systems face challenges in efficiently indicating subband transmitted precoding matrix indicators (TPMI) due to excessive signaling overhead, particularly in uplink grants, which consume valuable resources.
Innovation Solution
Implementing a two-stage subband TPMI indication scheme where the UE transmits first TPMI information in a MAC-CE and more refined information in DCI, along with implicit TPMI indication using beamformed CSI-RS, to reduce signaling overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional subband TPMI indication is used in uplink grants, then precoding control precision is improved, but signaling overhead increases excessively
Solution Approach 1:
The frequency band is divided into multiple subbands, and TPMI indication is performed separately for each subband. This allows precise precoding control per subband while managing signaling overhead through structured segmentation of the indication process into two stages: MAC-CE for TPMI group selection and DCI for specific TPMI indication within the selected group.
Solution Approach 2:
The MAC-CE message is used to pre-indicate TPMI groups before the actual uplink transmission. By establishing the TPMI group in advance through MAC-CE, the subsequent DCI only needs to indicate the specific TPMI within the pre-selected group, significantly reducing the signaling overhead in time-critical uplink grants.
2Quantity of substance
If TPMI groups are indicated via MAC-CE and DCI, then signaling overhead is reduced, but system complexity increases
Solution Approach 1:
The TPMI indication process is segmented into two distinct stages: MAC-CE for indicating TPMI groups and DCI for indicating specific TPMIs. This segmentation allows each stage to have a simplified, focused function, reducing overall system complexity compared to a single-stage approach that would require handling all TPMI variations in one message.
Solution Approach 2:
The MAC-CE message acts as an intermediary between the network and the uplink transmission. It prepares the TPMI group information in advance, serving as a mediator that simplifies the subsequent DCI processing by limiting the search space to a pre-defined group, thereby reducing the complexity of real-time decision making.
3Quantity of substance
If beamformed CSI-RS is used for implicit TPMI indication, then signaling resources are conserved, but measurement precision requirements increase
Solution Approach 1:
Instead of directly signaling TPMI information, the system uses beamformed CSI-RS to create an implicit representation of the channel state. The UE measures the beamformed reference signals and derives TPMI information from the channel characteristics, effectively copying the essential precoding information from the physical channel rather than transmitting it explicitly through signaling.
Data Source
AI summary
Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may receive a configuration that indicates one or more transmitted precoding matrix indicator (TPMI) groups. The UE may receive a medium access control control element that indicates a TPMI group of the one or more TPMI groups. The UE may receive downlink control information (DCI) that indicates a TPMI within the TPMI group. Numerous other aspects are described.