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Acta Scientiarum Naturalium Universitatis Sunyatseni

Serial Update Scheduling Based on Weighted Average Message of Check Nodes for LDPC Codes

Xingcheng Liu

Published Jan 1, 2010• 0 citations
OpenAlex

Abstract

For short and middle length LDPC codes,the oscillation of LLR owing to cycles degrades the performance of BP algorithm.In order to minimize the oscillation of LLR during BP decoding process,an improved BP algorithm with serial update scheduling using weighted average message to update the message of check-to-variable node is proposed.Currently computed message of check-to-variable node and the message of old check-to-variable node are weighted and then added up to update the message of check-to-variable node.By higher weighted currently computed message of check-to-variable node than the message of old check-to-variable node,the improved algorithm effectively minimizes oscillation of LLR,at the same time,keeps normal BP message propagation and low compute complexity.Simulation results show that,for short and middle length LDPC codes,the improved algorithm achieves more noticeable error performance than CSBP algorithm at middle to high signal to noise ratio.

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For short and middle length LDPC codes,the oscillation of LLR owing to cycles degrades the performance of BP algorithm.In order to minimize the oscillation of LLR during BP decoding process,an improved BP algorithm with serial update scheduling using weighted average message to update the message of check-to-variable node is proposed.Currently computed message of check-to-variable node and the message of old check-to-variable node are weighted and then added up to update the message of check-to-variable node.By higher weighted currently computed message of check-to-variable node than the message of old check-to-variable node,the improved algorithm effectively minimizes oscillation of LLR,at the same time,keeps normal BP message propagation and low compute complexity.Simulation results show that,for short and middle length LDPC codes,the improved algorithm achieves more noticeable error performance than CSBP algorithm at middle to high signal to noise ratio.
To reduce the average number of decoding iterations in the region of low SNR(signal to noise ratio) and weaken the oscillation of the LLR(logarithm likelihood ratio),discovered the variation law of the check nodes'LLR and the checksum,in the error frame of the short and middle length LDPC codes.Based on the law,proposed an improved BP algorithm of LDPC decoding.In the algorithm,developed an early stopping criterion to reduce the average number of decoding iterations in the region of low SNR.And to improve the decoding performance by weakening the oscillation of the LLR,modified the update algorithm of check node.Simulation results show that,the algorithm reduces the number of iteration while the performance is not reduced in the region of low SNR,the decoding performance is improved while the number of iteration is not changed in the region of middle and high SNR.
Among the belief-propagation (BP) decoding algorithms of low-density parity-check (LDPC) codes, the algorithms based on dynamic scheduling strategy show excellent performance. In this letter, we propose a variable-node-based dynamic scheduling decoding algorithm. For the proposed algorithm, the reliability of variable nodes is evaluated based on the log-likelihood ratio (LLR) values and the parity-check equations; then, a more accurate dynamic selection strategy is presented. Simultaneously, the oscillating variable nodes are processed so that the influence of the spread of error messages caused by oscillation are suppressed. In addition, the proposed algorithm updates the same number of messages in one iteration as the original BP decoding algorithm does, which is different from some other dynamic decoding algorithms. Simulation results demonstrate that the proposed algorithm outperforms other algorithms.
Compared to classic channel coding,Low-density parity-check(LDPC) codes have proved to be very powerful channel coding schemes with a broad range of applications.However,as maximum-likelihood decoding is too complex to implement,suboptimal decoders have to be employed.One of the most popular decoding algorithms of LDPC codes is belief propagation(BP) decoding.Informed Dynamic Scheduling(IDS) can provide a better BER performance,but hard to implement due to high computational complexity increased.In order to improve the convergence,a simple low-complexity sequential check-node-based scheduling strategy is proposed.A new check-node-based reliability measure is defined,which represents the degree of reliability approximately.The reliability measure is used for ordering while the actual message updates still use the exact BP equations.During an iteration,the schedule strategy finds an update sequence,which is arranged by the new defined reliability measure in ascending order.Complexity is compared among those algorithms.Mechanism why the new strategy works effective is presented.Simulation shows that the new approach significantly improves the BER performance using short-length block LDPC codes and reduces iterations.
In order to reduce the performance loss of UMP BP-based decoding algorithm relative to LLR-BP decoding algorithm,an improved UMP BP-based decoding algorithm is proposed.When the check nodes process the message,the normalized BP-based decoding algorithm and offset BP-based decoding algorithm are integrated effectively by setting a correction factor and an offset factor reasonably.When the variable nodes process the message,an oscillation compensation algorithm based on LLR-BP decoding algorithm is introduced.Simulation results show that based on the irregular LDPC codes and under the condition of the same bit error rate within a certain range,the improved UMP BP-based decoding algorithm improves the decoding performance greatly compared with the three decoding algorithms which are based on UMP BP,normalized BP and offset BP decoding algorithms,respectively,and therefore quite efficiently approaches to the LLR-BP decoding algorithm which has excellent performance.
In iterations processing of LLR BP algorithm for LDPC decoding,the computational of check nodes renewal is high;The decoding performance will be reduced,while there are lots of loops in short LDPC codes.According to these problems,a new LLR BP decoding algorithm based on Hybrid Check-Variable offset processing is proposed in this paper.Decrease complexity by adjusting amplitudes of check nodes processing and relativity of variable nodes by adjusting their information.Simulation results show that this improved decoding algorithm,compared with LLR BP algorithm,is consideration to decoding performance of LDPC and computational complexity.
In iterations processing of LLR BP algorithm for LDPC decoding, the computational complexity of check nodes renewal is high; The decoding performance will be reduced, while there are lots of loops in short LDPC codes. According to these problems, a new LLR BP decoding algorithm based on Hybrid Check-Variable offset processing is proposed in this paper. Decrease complexity by adjusting amplitudes of check nodes processing and relativity of variable nodes by adjusting their information. Simulation results show that this improved decoding algorithm, compared with LLR BP algorithm, is consideration to decoding performance of LDPC and computational complexity.