Predictive HARQ Using LDPC Subcodewords for Early Retransmission
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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 reducing latency by triggering retransmissions or requesting additional redundancy earlier.
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 patent applies preliminary action by transmitting a subcodeword (first part of the codeword) before the complete codeword is ready. The receiver performs decodability estimation on this partial information in advance, allowing early detection of decoding failures before the full codeword arrives. This eliminates the need to wait for the complete round-trip time, as retransmission decisions can be made based on preliminary decodability assessment of the subcodeword alone.
2Reliability
If complete codeword transmission is used, then reliability is improved, but productivity decreases due to waiting for complete reception before decoding
Solution Approach 1:
The patent segments the complete codeword into a subcodeword (first part) and remaining parts (second part). The subcodeword is transmitted and received first, allowing the receiver to perform decodability estimation on this segment independently. This segmentation enables parallel processing where the receiver can assess the subcodeword while the transmitter is still sending the remaining parts, improving transmission efficiency without sacrificing decoding accuracy.
Solution Approach 2:
The receiver performs decodability estimation on the subcodeword in advance, before the complete codeword is received. This preliminary action allows the system to determine whether full decoding will be successful without waiting for the entire transmission, enabling faster retransmission decisions and improving overall productivity.
3Loss of time
If early decodability estimation is implemented using subcodeword, then loss of time is reduced, but device complexity increases due to predictive HARQ processing
Solution Approach 1:
The patent implements preliminary decodability estimation by processing only the subcodeword (first part of the codeword) rather than waiting for the complete codeword. This preliminary action reduces retransmission delay because the receiver can make early decisions based on partial information. The complexity increase is manageable because the estimation is performed on a reduced subset of the codeword (the subcodeword) rather than the full codeword, and the estimation uses the same LDPC decoding algorithms already present in the system.
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.