LDPC Subcodeword Scheduling for Early HARQ Decodability Estimation
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Solution Overview
Problem
In communication networks, retransmissions due to noisy channels cause delays due to the additional round-trip time required for error correction, which is not efficiently addressed by conventional hybrid automatic repeat request (HARQ) mechanisms.
Innovation Solution
The implementation of a predictive HARQ process that uses low-density parity-check (LDPC) codes, where a subcodeword defined by selected variable nodes associated with check nodes of a bipartite graph is transmitted first, allowing the receiver to estimate decodability before receiving all variable nodes, enabling early detection of decoding failures and triggering retransmissions or additional redundancy requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional HARQ mechanisms are used for error correction in noisy channels, then reliability is improved, but loss of time increases due to additional round-trip time for retransmissions
Solution Approach 1:
The receiver performs preliminary decodability estimation using only a subset of received variable nodes before the complete codeword is received. This early estimation enables the receiver to predict whether full decoding will succeed, allowing proactive retransmission requests that eliminate waiting for the complete codeword and round-trip confirmation, thus reducing time loss while maintaining reliability
2Measurement precision
If all variable nodes of the codeword are received and evaluated before determining decodability, then measurement precision is improved, but loss of time increases due to waiting for complete reception
Solution Approach 1:
The receiver performs decodability estimation using only a partial set of variable nodes (a subset) rather than waiting for all variable nodes to be received. This partial action provides sufficiently accurate estimation to make informed retransmission decisions, eliminating the need to wait for complete codeword reception and significantly reducing time loss while maintaining acceptable estimation precision
3Loss of time
If a subcodeword is transmitted first for early decodability estimation, then loss of time is reduced, but device complexity increases due to selective variable node transmission
Solution Approach 1:
The codeword transmission is segmented into two phases: first transmitting a subset of variable nodes that form a subcodeword sufficient for decodability estimation, then transmitting the remaining variable nodes. This segmentation enables early estimation and proactive retransmission requests, reducing retransmission delay while the segmentation complexity is managed through systematic selection of variable nodes based on the bipartite graph structure
Data Source
AI summary
Data to be transmitted over a channel from a transmitter to a receiver is encoded to obtain a codeword. The codeword is defined by a plurality of variable nodes associated with a plurality of the check nodes of a bipartite graph representing the code. The codeword is transmitted over the channel such that certain variable nodes are transmitted prior to other variable nodes. The certain variable nodes are associated with a subset of the check nodes of the bipartite graph and define a subcodeword known at the receiver. At the receiver, a decodability of the transmitted codeword is estimated using the subcodeword prior to receiving all variable nodes of the codeword.