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An improved implementation of sum-product algorithm for LDPC decoder

Zhou Wang, Bin Wu, Tianchun Ye

Published Jan 1, 2019• 3 citations
Publisher

Abstract

An improved decoding algorithm for low-density parity-check (LDPC) codes is presented. By taking advantages of the first-term Taylor’s series multiple expansion to approximate the correction term of the Jacobian logarithm used in LLR-SPA (log-likelihood ratio sum-product algorithm), we propose an algorithm which significantly simplifies the check node update computation of the optimal LLR-SPA. Besides, the parameter δ is introduced to determine suitable expansion points. The simulation result shows that the proposed method with ten expansion points when δ is set to 0.01 has almost identical performance compared with ideal SPA algorithm and outperforms both the min-sum algorithm (MS), the offset min-sum algorithm (OMS) and the normalised min-sum algorithm (NMS). The architecture of proposed method is also presented for implementation, which has reduced computational complexity and is feasible for hardware implementation.

DOI
10.1587/elex.16.20180828

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An improved decoding algorithm for low-density parity-check (LDPC) codes is presented. By taking advantages of the first-term Taylor’s series multiple expansion to approximate the correction term of the Jacobian logarithm used in LLR-SPA (log-likelihood ratio sum-product algorithm), we propose an algorithm which significantly simplifies the check node update computation of the optimal LLR-SPA. Besides, the parameter δ is introduced to determine suitable expansion points. The simulation result shows that the proposed method with ten expansion points when δ is set to 0.01 has almost identical performance compared with ideal SPA algorithm and outperforms both the min-sum algorithm (MS), the offset min-sum algorithm (OMS) and the normalised min-sum algorithm (NMS). The architecture of proposed method is also presented for implementation, which has reduced computational complexity and is feasible for hardware implementation.
A simple,yet effective decoding algorithm for LDPC(low-density parity-check) codes over GF(q) is presented.By taking advantages of the first-term Taylor's series expansion to approximate the correction term of the Jacobian logarithm used in LLR-SPA(log-likelihood ratio sum-product algorithm),we propose an algorithm which significantly simplifies the check node update computation of the optimal LLR-SPA.Compared to the offset min-sum algorithm,the proposed algorithm achieves a gain of about 0.2dB at the BER of 10-4.Moreover,unlike the offset min-sum algorithm,parameters of this algorithm are independent of the order of the Galois Filed.
Low-Density Parity check (LDPC) codes offer high-performance error correction near the Shannon limit which employs large code lengths and some iterations in the decoding process. The conventional decoding algorithm of LDPC is the Log Likelihood Ratio based Belief Propagation (LLR BP) which is also known as the `Sum-Product algorithm' which gives the best decoding performance and requires the most computational complexity and implementations with increased hardware complexity. Another simpler variant of this algorithm is used which is known as `min-sum algorithm' which reduces computational complexity as well as hardware complexity but with reduced accuracy. This paper analyzes the reason min-sum algorithm is more prone to errors when compared to the sum-product algorithm, and puts forward two improved algorithms which improve the performance of the min-sum algorithm with comparable algorithmic complexity.
A novel effective decoding algorithm for LDPC codes is proposed, which significantly simplifies the check node update computation of the Sum-Product Algorithm (SPA). Through simplified Taylor Series algorithm, It made index operation for multiplication and addition operations in the check node update. Compared with the existing approximations, the proposed method is less computational complexity than SPA algorithm, simulation results show that the proposed algorithm can achieve an error performance better than the Min-sum (MS) algorithm with small increase computational complexity.
Many classes of high-performance Low-density parity check codes are based on parity check matrices composed of permutation sub matrices. The emulation-simulation framework further allows the algorithm and implementation to be iteratively redefined to improve the error floor performance of message passing decoder. Log-Like hood-Ratio (LLR) based Belief-Propagation (BP) algorithm is presented for Low Density Parity Check codes. Numerically accurate representation of check node update computation used in LLR-BP decoding is described. The implementation of Sum-Product algorithm (SPA) within Low Density Parity Check Code (LDPC) decoder is described in this paper and the correction term is used to improve the decoding performance of min-sum algorithm (MSA). Quantization and log-tanh function approximation in sum-product decoder strongly affect which absorbing set dominates in error floor region. For LDPC decoder, bit error rate (BER) decreases with increase in the signal to noise ratio.
This paper describes an efficient implementation of the Sum-Product Algorithm (SPA) within a Low Density Parity Check (LDPC) code decoder, where a horizontal process correction term is used to improve the decoding performance of the Min-Sum algorithms. The correction term is implemented as a look-up table. The algorithm uses the correction term redundancy by means of a coordinate transformation to reduce the hardware complexity. Simulations and hardware tests indicate that the decoding performance is very good with the appropriate look-up table.
In this paper, a non-uniform quantization scheme is proposed for the decoding of Low-Density Parity-Check (LDPC) codes with the Sum-Product Algorithm (SPA). With the proposed scheme, the quantization-range and quantization-interval for the soft Log-Likelihood-Ratio (LLR) values of the decoder input, the variable nodes, and the check nodes are set separately, and are also adjusted according to the evolution of the probability density distribution of the LLR values in the iterative decoding procedure to minimize the difference between the decoding values before quantization and that after quantization. Simulation results show that decoding with 3-bit non-uniform quantization of the proposed scheme may obtain a BER performance slightly better than that of decoding with 6-bits quantization of the traditional uniform quantization method.