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IEEE Transactions on Circuits and Systems I Regular Papers

A 3.0 Gb/s Throughput Hardware-Efficient Decoder for Cyclically-Coupled QC-LDPC Codes

Qing Hua Lu, Jianfeng Fan, Chiu‐Wing Sham, Wai M. Tam, Francis C. M. Lau

Published Jan 1, 2016• 34 citations
Publisher

Abstract

In this paper, we propose a new class of quasi-cyclic low-density parity-check (QC-LDPC) codes, namely cyclically-coupled QC-LDPC (CC-QC-LDPC) codes, and their RAM-based decoder architecture. CC-QC-LDPC codes have a simple structure and are constructed by cyclically-coupling a number of QC-LDPC subcodes. They can achieve throughput and error performance as excellent as LDPC convolutional codes, but with much lower hardware requirements. They are therefore promising candidates for future generations of communication systems such as long-haul optical communication systems. In particular, a rate-5/6 CC-QC-LDPC decoder has been implemented onto a field-programmable gate array (FPGA) and it achieves a throughput of 3.0 Gb/s at 100 MHz clock rate with 10-iteration decoding. No error floor is observed up to an$E_{b}/N_{0}$of 3.50 dB, where all$1.14\times 10^{16}$transmitted bits have been decoded correctly.

DOI
10.1109/tcsi.2015.2510619

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The performance of a high-throughput long-distance communication system such as an optical transmission system is limited by the Net Coding Gain (NCG) of the Forward Error Correction (FEC) system. Summarizing the previous research works, Low-Density Parity-Check (LDPC) codes form one of the most promising FEC schemes to be applied in high-throughput communication systems. Designing a practical channel coding scheme with high code rate, low complexity, high throughput and extremely low error floor has always been a very challenging problem. Quasi-cyclic low-density parity-check (QC-LDPC) codes have been promising candidates to fulfill the above requirements but the implementation issues remain. In this paper, we propose a layered QC-LDPC decoder architecture with high code rate, low complexity, high throughput and excellent error performance. The architecture has been implemented using FPGA and the error performance has been shown to be good.
Cyclically-coupled quasi-cyclic low-density parity-check (CC-QC-LDPC) codes are a new class of QC-LDPC codes which can achieve excellent error performance and relatively low hardware requirement. In this paper, we modify the CC-QC-LDPC code construction by using random permutation matrices instead of circulant permutation matrices, forming the “random-permutation-matrix-based CC-LDPC (RP-CC-LDPC) code”. The objective is to achieve a better error performance under the same code length. We simulate the bit error rate using FPGA simulations. We also compare the BER results and decoder complexity of the above codes with those of regular and irregular QC-LDPC codes under the same code length and code rate.
This paper studies low-complexity high-speed decoder architectures for quasi-cyclic low density parity check (QC-LDPC) codes. Algorithmic transformation and architectural level optimization are incorporated to reduce the critical path. Enhanced partially parallel decoding architectures are proposed to linearly increase the throughput of conventional partially parallel decoders through introducing a small percentage of extra hardware. Based on the proposed architectures, a (8176, 7154) Euclidian geometry-based QC-LDPC code decoder is implemented on Xilinx field programmable gate array (FPGA) Virtex-II 6000, where an efficient nonuniform quantization scheme is employed to reduce the size of memories storing soft messages. FPGA implementation results show that the proposed decoder can achieve a maximum (source data) decoding throughput of 172 Mb/s at 15 iterations
Low-density parity-check (LDPC) codes are one of the most effective error controlling methods, which now are widely used in multiple communication systems, for example, DVB-S2, 802.16e, etc. In these communication standards, the adopted LDPC codes are all quasi-cyclic low-density parity-check (QC-LDPC) codes. The parity-check matrices of QC-LDPC codes consist of arrays of circulants, in which each row is the cyclic shift of the row above it, and the first row is the cyclic shift of the last row. This character of QC-LDPC codes results in the linear encoding complexity and opens the door for the multi-mode LDPC decoders with enough flexibility of resource multiplexing. Based on the quasi-cyclic character of QC-LDPC codes, a design method for multi-mode QC-LDPC decoders is proposed in this paper. The node memory is skillfully organized and can be expediently addressed by a simple control unit to save memory consumption in hardware implementation. Then this design method is implemented and test on Field Programmable Gate Array (FPGA) platform. The test results show that the resource occupied by the multi-mode decoder is only a little more than that of maximal resource occupied by the single-mode decoder, and this multi-mode decoder can support at least 3 code rates with the throughput higher than 100 Mbps when the iteration number is fixed to 12 and the clock frequency is set to 200 MHZ.
Low-Density Parity-Check (LDPC) codes have traditionally performed better at longer code lengths. This research develops and rigorously evaluates a layered Quasi-Cyclic Low-Density Parity-Check (QC-LDPC) decoder architecture intended for Ultra-Reliable Low-Latency Communication (URLLC) applications in 5G and subsequent technologies. The paper investigates LDPC codes in short-length contexts through architectural optimization based on a layered decoding approach, which provides improved convergence speed and reduced latency compared with traditional flooding techniques. The short block-length QC-LDPC code (280,176) addresses the dual challenge of achieving ultra-low latency while maintaining high performance relative to existing work. For a target BLER of 10−2, the decoder outperforms the shorter reference codes (60,40) and (96,64), with an Eb/N0 gain of up to 0.9 dB, part of which is attributable to the longer block length rather than to the decoder alone. The FPGA implementation results demonstrate that the design is hardware-efficient: it operates at a maximum frequency of 218.62 MHz, resulting in a throughput of 155.77 Mbps, while maintaining a decoding latency of only 1.129 µs and a power consumption of 0.201 W.
In this paper, we present a new microarchitecture of low-density parity-check (LDPC) decoder compliant to the specifications of 5G new-radio (NR) wireless-communication standard. This work suggests a fully-parallel VLSI architecture for this decoder to achieve high throughput. The digital architecture of internal modules as well as system-level design of the LDPC decoder are presented here. The comprehensive bit-error-rate (BER) performance analyses of our LDPC decoder has been performed in additive-white Gaussian-noise (AWGN) channel environment for various number of decoding iterations and bit-quantization. It delivers a BER of 10-6at 1 dB of Eb/N0while decoding for 10 iterations with 7-bits quantization. In addition, FPGA implementation and post-route simulation of the proposed LDPC decoder are carried out that can decode an encoded LDPC code of 26112 code-length for 1/3 code-rate. Our decoder has achieved a throughput of 2.9 Gbps while operating at a clock frequency of 102 MHz. These implementation results are compared with the reported works where our design delivered 20× better throughput compared to the state-of-the-art LDPC decoders.