Abstract
The successive cancellation list (SCL) decoding is used to achieve good error-correcting performance for practical finite-length polar codes. However, the metric sorting that is repeatedly performed in SCL decoding increases the overall decoding latency as the list size increases, making it difficult to apply the SCL decoding to the applications with limited processing time. To reduce the latency of the metric sorting, this paper proposes a new sorting method derived by analyzing path extension cases encountered in SCL decoding. The proposed method can avoid unnecessary sorting operations by adaptively determining the sorting size, and can be combined with other metric sorting methods. Simulation results show that the proposed method significantly reduces the decoding latency for various list sizes and code rates without degrading the error-correcting performance. The proposed method also becomes more effective as the code rate or the list size increases. Combined with the state-of-the-art sorting method, the proposed method reduces the average SCL decoding latency for a (1024, 512) polar code by 33.1% when the list size is 8.
Highlights
Polar codes are the first class of error-correcting codes that can probably achieve the channel capacity for any symmetric binary-input discrete memoryless channel (B-DMC), and have efficient encoding and decoding algorithms [1]
SIMULATION RESULTS All simulations have been performed with the binary phase-shift keying (BPSK) modulation and the additive white Gaussian noise (AWGN) channels
To determine which sorting method is applied, a threshold value is introduced; the incremental reliability values of all L paths are greater than the threshold value, the small sorting is used to reduce the overall latency without degrading the error-correcting performance noticeably
Summary
Polar codes are the first class of error-correcting codes that can probably achieve the channel capacity for any symmetric binary-input discrete memoryless channel (B-DMC), and have efficient encoding and decoding algorithms [1]. Successive cancellation (SC) decoding, the first polar-code decoding algorithm, can achieve the channel capacity when the code length goes to infinity. For a non-frozen bit, the SCL decoding extends L paths surviving in the previous decoding step to 2L path candidates It sorts the extended 2L path candidates to select L paths with the smallest metrics. When the SCL decoding reaches a non-frozen bit, every parent candidate is extended to a pair of child candidates corresponding to bit 0 and bit 1. It sorts the metrics of the extended 2L child candidates to select L paths with smallest metrics. The error-correcting performance of SCL decoding improves as the list size increases, the complexity of 2L-to-L metric sorting increases drastically, which in turn increases the overall decoding latency
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