Rateless Polar Code Retransmission for Decoding Reliability
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Solution Overview
Problem
Wireless communication systems using rateless polar codes face challenges in decoding information bits due to a gap between the channel capacity and the rate of the polar code, where the receiving device may fail to decode bits without defined feedback mechanisms, leading to increased latency and bandwidth usage.
Innovation Solution
The transmitting device identifies and retransmits a subset of information bits based on the likelihood of error associated with bit-channels used for encoding, using a different code or unencoded, to assist the receiving device in decoding, which combines soft information for successful decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the polar code rate is increased to approach channel capacity, then spectral efficiency is improved, but decoding reliability deteriorates due to the gap between channel capacity and code rate
Solution Approach 1:
The information bits are segmented into multiple subsets, where each subset is assigned to different bit-channels based on their error likelihood. This segmentation allows the receiver to selectively request retransmission of only those subsets that failed decoding, rather than retransmitting all information bits, thus improving spectral efficiency while maintaining decoding reliability.
Solution Approach 2:
The system dynamically changes the code rate by selectively transmitting different subsets of information bits based on decoding success. When decoding fails, the code rate is effectively reduced for the retransmitted subset, improving reliability. When decoding succeeds, the full code rate is utilized, maximizing spectral efficiency.
2Reliability
If all information bits are retransmitted upon decoding failure, then decoding reliability is improved, but bandwidth overhead and latency increase
Solution Approach 1:
The system extracts only the failed subset of information bits for retransmission, rather than retransmitting all information bits. The receiver identifies which specific subsets failed decoding and requests retransmission of only those subsets, reducing bandwidth overhead and latency while maintaining decoding reliability.
Solution Approach 2:
Instead of performing a complete retransmission of all information bits, the system performs a partial retransmission of only the failed subsets. This partial action is sufficient to achieve decoding reliability while minimizing bandwidth overhead and latency.
3Productivity
If feedback mechanisms are implemented to identify failed bits, then retransmission efficiency is improved, but system complexity increases
Solution Approach 1:
The receiver performs self-service by autonomously identifying which information bit subsets failed decoding and generating the necessary feedback requests. This self-service approach improves retransmission efficiency without requiring complex centralized control mechanisms, thus limiting the increase in system complexity.
4Productivity
If rateless polar codes are used to achieve flexible rate adaptation, then spectral efficiency is improved, but defined feedback mechanisms for retransmission are lacking
Solution Approach 1:
The system performs preliminary segmentation of information bits into subsets that can be independently encoded and retransmitted. This preliminary action establishes a framework for flexible feedback mechanisms in rateless polar codes, improving ease of operation by enabling selective retransmission while maintaining spectral efficiency.
Data Source
AI summary
Methods, systems, and devices for wireless communication are described. A first wireless device may transmit, to a second wireless device, a codeword corresponding to a set of information bits encoded using a polar code, and the second wireless device may obtain a first set of log likelihood ratios (LLRs) based on performing a first decoding operation on the codeword. In cases that the first wireless device identifies a failure of the second wireless device to decode one or more of the information bits, the first wireless device may retransmit a subset of the information bits to the second wireless device independently of the polar code. The second wireless device may then attempt to decode the codeword a second time using the polar code and based on a combination of a first set of LLRs and a second set of LLRs corresponding to the subset of the information bits.