Polar Code Decoding with Unreliable Bit Inversion Ordering
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Solution Overview
Problem
Current polar code decoding methods, particularly successive cancellation decoding, suffer from high error propagation due to their sequential nature, leading to suboptimal error rates and increased complexity, especially when using methods like list decoding or inversion decoding with high maximum inversions.
Innovation Solution
A novel inversion decoding method that prioritizes the first incorrect bit in a frame using a new metric that considers the reliability of each bit and preceding decisions, reducing the number of inversions required for error correction and improving decoding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If successive cancellation decoding is used, then decoding speed is improved, but error propagation increases leading to suboptimal error rates
Solution Approach 1:
The patent performs preliminary identification of unreliable bits using a metric based on log-likelihood ratios before the decoding process. This preliminary action allows the decoder to anticipate and correct potential errors before they propagate through the sequential decoding process, thereby maintaining high decoding speed while improving error rates.
Solution Approach 2:
The patent implements a feedback mechanism where the reliability metric of each bit is continuously updated based on previous decoding decisions. When an unreliable bit is detected, the decoder adjusts subsequent decoding operations based on this feedback, preventing error propagation while maintaining the sequential decoding speed advantage.
2Reliability
If list decoding or inversion decoding with high maximum inversions is used, then error rates are improved, but decoding complexity increases
Solution Approach 1:
Instead of applying complex decoding operations uniformly to all bits, the patent identifies specific unreliable bits using a reliability metric and applies inversion operations only to those local positions. This selective approach achieves effective error correction without the exponential complexity increase associated with full list decoding.
Solution Approach 2:
The patent changes the parameter being optimized from the number of inversions to a reliability-based metric. By using log-likelihood ratios and a customized metric to identify unreliable bits, the decoder achieves optimal error correction with a controlled and limited number of inversions, avoiding the complexity of high-inversion schemes.
3Reliability
If maximum number of inversions is increased, then frame error rate decreases, but decoding latency increases
Solution Approach 1:
The patent performs preliminary identification of the exact number and positions of unreliable bits using the reliability metric before executing inversion operations. This allows the decoder to perform the minimum necessary inversions to correct errors, avoiding unnecessary iterations and reducing decoding latency while achieving low frame error rates.
Solution Approach 2:
The patent replaces the mechanical iterative inversion process with a direct calculation based on the reliability metric. Instead of repeatedly inverting bits until convergence, the system calculates the optimal inversion set directly from the metric, significantly reducing the time required while maintaining low error rates.
Data Source
AI summary
A polar code decoding method in which a first decoding attempt by successive cancellation is performed and in the case where the decoded frame is erroneous, an ordered list of bit positions to be tested in the frame is generated, the order relation being given by a metric of first error, the value of this metric depending on the reliability of the decision about the bit as well as on the reliability of the decisions about the bits preceding it in the frame. For each of the positions of the list, an inversion of the bit and a decoding of the subsequent bits are undertaken, doing so as long as the list has not been exhausted or the frame has not been decoded without error. In case of failure, a new decoding attempt based on a double-inversion of bits can be envisaged.