GC-PDSCH Rate Matching With Explicit LBRM Selection
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Solution Overview
Problem
Existing multicast and broadcast services (MBS) face challenges in parameter alignment and rate matching due to unclear LBRM sizes and overhead values, leading to ambiguity in TBS determination across UEs in the same MBS group, especially when using different transmission schemes.
Innovation Solution
The method involves aligning parameters such as maximum MIMO layers, modulation order, and PRBs across UEs in an MBS group by configuring common information elements and overhead values specific to MBS, ensuring consistent TBS and LBRM calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different LBRM sizes are used for initial MBS transmission and subsequent retransmissions, then the chance of successful reception is increased, but ambiguity arises regarding which LBRM should be used
Solution Approach 1:
A new DCI field (3 bits) is introduced as an intermediary to explicitly indicate which LBRM size should be used for MBS retransmission. This field resolves the ambiguity by providing clear guidance to UEs about whether to use unicast LBRM or MBS LBRM size, while allowing the gNB to flexibly select the appropriate LBRM configuration to maximize reception success probability.
2Productivity
If MBS LBRM size is restricted based on least capable UE, then common frequency resource utilization is optimized, but transmission efficiency decreases compared to unicast LBRM
Solution Approach 1:
The LBRM size configuration is made dynamic through the new DCI field, allowing the gNB to adaptively select between unicast LBRM and MBS LBRM sizes based on current transmission conditions and UE capabilities. This dynamic selection enables optimal resource utilization for each specific transmission scenario, balancing efficiency and compatibility.
3Measurement precision
If separate xOverhead values are provided for MBS and unicast, then parameter precision is improved, but configuration complexity increases
Solution Approach 1:
The new DCI field serves multiple functions: it indicates LBRM size selection, implicitly selects the appropriate xOverhead value (MBS or unicast), and maintains backward compatibility with existing configurations. This multi-functionality approach provides precise parameter control without proportionally increasing configuration complexity.
Data Source
AI summary
Methods and apparatuses are provided for performing rate matching. A group common-physical downlink shared channel (GC-PDSCH) is received at a user equipment (UE) for communications in a common frequency resource (CFR). An information element that carries configurations for GC-PDSCH transmission in the CFR, is received at the UE. At least one parameter for determining a transport block size (TBS) for the GC-PDSCH transmission in the CFR is determined from at least one field of the information element. The TBS for the GC-PDSCH transmission in the CFR is determined based on the at least one parameter.