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Tsinghua Science & Technology

Design and efficient hardware implementation schemes for non-Quasi-Cyclic LDPC codes

Baihong Lin, Yukui Pei, Liuguo Yin, Jianhua Lü

Published Jan 26, 2017• 5 citations
Publisher

Abstract

The design of a high-speed decoder using traditional partly parallel architecture for Non-Quasi-Cyclic (NQC) Low-Density Parity-Check (LDPC) codes is a challenging problem due to its high memory-block cost and low hardware utilization efficiency. In this paper, we present efficient hardware implementation schemes for NQCLDPC codes. First, we propose an implementation-oriented construction scheme for NQC-LDPC codes to avoid memory-access conflict in the partly parallel decoder. Then, we propose a Modified Overlapped Message-Passing (MOMP) algorithm for the hardware implementation of NQC-LDPC codes. This algorithm doubles the hardware utilization efficiency and supports a higher degree of parallelism than that used in the Overlapped Message Passing (OMP) technique proposed in previous works. We also present single-core and multi-core decoder architectures in the proposed MOMP algorithm to reduce memory cost and improve circuit efficiency. Moreover, we introduce a technique called the cycle bus to further reduce the number of block RAMs in multi-core decoders. Using numerical examples, we show that, for a rate-2/3, length-15360 NQC-LDPC code with 8.43-dB coding gain for Binary PhaseShift Keying (BPSK) in an Additive White Gaussian Noise (AWGN) channel, the decoder with the proposed scheme achieves a 23.8%-52.6% reduction in logic utilization per Mbps and a 29.0%-90.0% reduction in message-memory bits per Mbps.

DOI
10.1109/tst.2017.7830899

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The design of a high-speed decoder using traditional partly parallel architecture for Non-Quasi-Cyclic (NQC) Low-Density Parity-Check (LDPC) codes is a challenging problem due to its high memory-block cost and low hardware utilization efficiency. In this paper, we present efficient hardware implementation schemes for NQCLDPC codes. First, we propose an implementation-oriented construction scheme for NQC-LDPC codes to avoid memory-access conflict in the partly parallel decoder. Then, we propose a Modified Overlapped Message-Passing (MOMP) algorithm for the hardware implementation of NQC-LDPC codes. This algorithm doubles the hardware utilization efficiency and supports a higher degree of parallelism than that used in the Overlapped Message Passing (OMP) technique proposed in previous works. We also present single-core and multi-core decoder architectures in the proposed MOMP algorithm to reduce memory cost and improve circuit efficiency. Moreover, we introduce a technique called the cycle bus to further reduce the number of block RAMs in multi-core decoders. Using numerical examples, we show that, for a rate-2/3, length-15360 NQC-LDPC code with 8.43-dB coding gain for Binary PhaseShift Keying (BPSK) in an Additive White Gaussian Noise (AWGN) channel, the decoder with the proposed scheme achieves a 23.8%-52.6% reduction in logic utilization per Mbps and a 29.0%-90.0% reduction in message-memory bits per Mbps.
The design of high speed decoders with traditional partly parallel architecture for non-quasi-cycle (NQC) LDPC codes is a challenging problem due to its high memory-block consumption and the low hardware utilization efficiency. In this paper, a general overlapped message passing (GOMP) decoding algorithm is proposed to improve the hardware utilization efficiency (HUE), which overcomes the limitation of overlapped message passing (OMP) decoders proposed before. On the basis of the given codes, this algorithm nearly doubles the throughput without sacrificing double memory or causing loss in performance compared to BP algorithm. Furthermore, we present a technique called cycle bus to reduce the number of block RAMs in the multi-core decoder. Moreover, an example of a rate-2/3, length-15360 irregular LDPC code with 8.43 dB coding gain for BPSK in AWGN channel is given, whose decoders features nearly double throughput, 22.22% increase in memory 8.35% reduction in logic registers cost and more reasonable distribution in block RAMs cost.
In this paper, the authors propose an efficient highly-parallel decoder architecture using partially overlapped decoding scheme for quasi-cyclic (QC) low-density parity-check (LDPC) codes, which leads to reduction in hardware complexity and power consumption. Generally, due to the regularly structured parity-check matrix H of QC LDPC codes, the message updating computations in the check node unit (CNU) and the variable node unit (VNU) can be efficiently overlapped, which increases the decoding throughput by maximizing the hardware utilization efficiency (HUE). However, the partially overlapped decoding scheme cannot be used to design a highly-parallel decoding architecture for high-throughput applications. For (3, 5)-regular QC LDPC codes, our proposed method could reduce the hardware complexity by approximately 33% for the CNU and 20% for the VNU in the highly-parallel decoder architecture without any performance degradation. In addition, the power consumption can be minimized by reducing the total number of memory accesses for updated messages.
Efficient hardware implementation of low-density parity-check (LDPC) codes is of great interest since LDPC codes are being considered for a wide range of applications. Recently, overlapped message passing (OMP) decoding has been proposed to improve the throughput and hardware utilization efficiency (HUE) of decoder architectures for LDPC codes. In this paper, we first study the scheduling for the OMP decoding of LDPC codes, and show that maximizing the throughput gain amounts to minimizing the intra- and inter-iteration waiting times. We then focus on the OMP decoding of quasi-cyclic (QC) LDPC codes. We propose a partly parallel OMP decoder architecture and implement it using FPGA. For any QC LDPC code, our OMP decoder achieves the maximum throughput gain and HUE due to overlapping, hence has higher throughput and HUE than previously proposed OMP decoders while maintaining the same hardware requirements. We also show that the maximum throughput gain and HUE achieved by our OMP decoder are ultimately determined by the given code. Thus, we propose a coset-based construction method, which results in QC LDPC codes that allow our optimal OMP decoder to achieve higher throughput and HUE.
Non-binary low-density parity-check (NB-LDPC) codes can achieve better error-correcting performance than binary LDPC codes when the code length is moderate. For the first time, this paper proposes a partial-parallel decoder architecture based on the Min-max algorithm for quasi-cyclic NB-LDPC codes. A novel boundary tracking based scheme and corresponding architecture are developed to implement the elementary step of the check node processing. In addition, layered decoding is applied, and the hardware units are optimized to reduce the latency and area. This paper also introduces an overlapped method for the check node processing among different layers to further speed up the decoding. From complexity analysis, the proposed decoder with 5 iterations for a (837,726) code over GF(25) can easily achieve 60 Mbps throughput on ASIC devices. It is 40% more efficient than prior designs.
Recently, non-binary low-density parity-check (NB-LDPC) codes starts to show their superiority in achieving significant coding gains when moderate codeword lengths are adopted. However, the overwhelming decoding complexity keeps NB-LDPC codes from being widely employed in modern communication devices. This paper proposes a hybrid message-passing decoding algorithm which consumes very low computational complexity. It achieves competitive error performance compared with conventional Min-max algorithm. Simulation result on a (255,174) cyclic code shows that this algorithm obtains at least 0.5dB coding gain over other state-of-the-art low-complexity NB-LDPC decoding algorithms. A partial-parallel NB-LDPC decoder architecture for cyclic NB-LDPC codes is also developed based on this algorithm. Optimization schemes are employed to cut off hard decision symbols in RAMs and also to store only part of the reliability messages. In addition, the variable node units are redesigned especially for the proposed algorithm. Synthesis results demonstrate that about 24.3% gates and 12% memories can be saved over previous works.
Non-binary low-density parity-check (NB-LDPC) codes can achieve better error-correcting performance than their binary counterparts at the cost of higher decoding complexity when the codeword length is moderate. The recently developed iterative reliability-based majority-logic NB-LDPC decoding has better performance-complexity tradeoffs than previous algorithms. This paper first proposes enhancement schemes to the iterative hard reliability-based majority-logic decoding (IHRB-MLGD). Compared to the IHRB algorithm, our enhanced (E-)IHRB algorithm can achieve significant coding gain with small hardware overhead. Then low-complexity partial-parallel NB-LDPC decoder architectures are developed based on these two algorithms. Many existing NB-LDPC code construction methods lead to quasi-cyclic or cyclic codes. Both types of codes are considered in our design. Moreover, novel schemes are developed to keep a small proportion of messages in order to reduce the memory requirement without causing noticeable performance loss. In addition, a shift-message structure is proposed by using memories concatenated with variable node units to enable efficient partial-parallel decoding for cyclic NB-LDPC codes. Compared to previous designs based on the Min-max decoding algorithm, our proposed decoders have at least tens of times lower complexity with moderate coding gain loss.