LDPC Base Graph Selection for Reliable HARQ Retransmission Decoding
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Solution Overview
Problem
In wireless communication systems, particularly in LTE and NR, the selection of LDPC base graphs for initial and retransmission transmissions is challenging due to ambiguity in transport block size and code rate thresholds, leading to potential failure in decoding retransmissions when the initial transmission's base graph is unknown.
Innovation Solution
The method involves explicit signaling or identification of base graphs through high-layer signaling and configuration tables to ensure consistent base graph usage for both initial and retransmission transmissions, using either base graph 1 or base graph 2 based on transport block size and coding rate thresholds, and utilizing RRC configuration to simplify signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If base graph selection is based on transport block size and code rate thresholds, then coding performance is optimized, but ambiguity in threshold values leads to incorrect base graph selection for retransmissions
Solution Approach 1:
The patent applies preliminary action by pre-configuring base graph selection criteria through higher-layer signaling (RRC) before transmission occurs. The network configures threshold values for transport block size and code rate that determine base graph selection, ensuring both transmitter and receiver have identical selection criteria beforehand. This prevents ambiguity during retransmissions since the base graph can be determined in advance using the pre-configured thresholds rather than relying on potentially lost dynamic signaling.
2Measurement precision
If explicit signaling of base graph is implemented, then decoding accuracy is improved, but signaling overhead increases
Solution Approach 1:
The patent extracts the base graph indication from dynamic per-transmission signaling and moves it to higher-layer configuration. By separating base graph selection from immediate transmission control, the system eliminates the need for explicit base graph indication in downlink control information (DCI). The base graph is determined through pre-configured thresholds that are signaled once at configuration level rather than repeatedly with each transmission, significantly reducing signaling overhead while maintaining identification accuracy.
3Productivity
If base graph 2 is used for small transport block sizes, then coding efficiency is improved, but segmentation complexity increases
Solution Approach 1:
The patent applies parameter changes by using the configured transport block size threshold as a dynamic parameter that automatically determines base graph selection. When transport block size falls below the configured threshold, base graph 2 is selected to improve coding efficiency for small packets. The threshold parameter itself can be configured by the network to balance coding efficiency gains against segmentation complexity, allowing flexible optimization based on specific deployment scenarios and traffic patterns.
Data Source
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AI summary
Certain aspects of the present disclosure generally relate to wireless communication. In some aspects, a device may determine a nominal coding rate of a communication based at least in part on a modulation and coding scheme (MCS) of the communication; determine whether to use a first base graph or a second base graph for decoding or transmission of the communication, wherein the determination of whether to use the first base graph or the second base graph is based at least in part on the nominal coding rate and a transport block size (TBS) of the communication, and wherein the TBS is based at least in part on a nominal number of resources and the MCS of the communication; and perform the decoding or transmission based at least in part on the determination of whether to use the first base graph or the second base graph. Numerous other aspects are provided.