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Journal of Chongqing University of Posts and Telecommunications

Design and implementation of a memory efficient QC-LDPC code decoder

Lei Wen

Published Jan 1, 2010• 0 citations
OpenAlex

Abstract

This paper studied the QC-LDPC(quasi-cyclic low density parity check) codes and min-sum decoding algorithm,and designed a proper ununiform decoding scheme for quantization.According to the structure of parity check matrix of QC-LDPC code,a decoder architecture was designed,with its components and function discussed in detail.According the decoding algorithm and quantization scheme,simulated error correcting performance was made.A QC-LDPC decoder was implemented in Xilinx XC3S2000 FPGA(field programmable gate array),whose codeword length is 9 216 and code rate 1/2.FPGA implementation results show that 30% memory can be reduced compared to the traditional designs,achieving better tradeoff between performance and complexity.

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Information•Nov 1, 2024•1 citation
This paper studied the QC-LDPC(quasi-cyclic low density parity check) codes and min-sum decoding algorithm,and designed a proper ununiform decoding scheme for quantization.According to the structure of parity check matrix of QC-LDPC code,a decoder architecture was designed,with its components and function discussed in detail.According the decoding algorithm and quantization scheme,simulated error correcting performance was made.A QC-LDPC decoder was implemented in Xilinx XC3S2000 FPGA(field programmable gate array),whose codeword length is 9 216 and code rate 1/2.FPGA implementation results show that 30% memory can be reduced compared to the traditional designs,achieving better tradeoff between performance and complexity.
Low-density parity-check (LDPC) have been shown to have good error correcting performance approaching Shannon’s limit. Good error correcting performance enables efficient and reliable communication. However, a LDPC code decoding algorithm needs to be executed efficiently to meet cost , time, power and bandwidth requirements of target applications. Quasi-cyclic low-density parity-check (QC-LDPC) codes are an important subclass of LDPC codes that are known as one of the most effective error controlling methods. Quasi cyclic codes are known to possess some degree of regularity. Many important communication standards such as DVB-S2 and 802.16e use these codes. The proposed Optimized Min-Sum decoding algorithm performs very close to the Sum-Product decoding while preserving the main features of the Min-Sum decoding, that is low complexity and independence with respect to noise variance estimation errors.Proposed decoder is well matched for VLSI implementation and will be implemented on Xilinx FPGA family
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.
In this paper, we construct the cyclic block-type low-density parity-check (CB-LDPC) codes for low complexity hardware implementation. The CB-LDPC code, which is a special class of quasi-cyclic LDPC (QC-LDPC), has an efficient encoding algorithm due to the simple structure of their parity-check matrices. A distribution of irregular parity-check matrix for the CB-LDPC is developed so that we can obtain an area-efficient decoder design, good error correction performance, and low complexity architecture implementation. The CB-LDPC code decoding uses the iterative min-sum algorithm (MSA) and the block parallel connection design to improve the hardware architecture complexity and area.
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.
We propose two decoding algorithms for quasi-cyclic LDPC codes (QC-LDPC) and implement the more efficient one in this paper. These algorithms depend on the split row for the layered decoding method applied to the Min-Sum (MS) algorithm. We designate the first algorithm “Split-Row Layered Min-Sum” (SRLMS), and the second algorithm “Split-Row Threshold Layered Min-Sum” (SRTLMS). A threshold message passes from one partition to another in SRTLMS, minimizing the gap from the MS and achieving a binary error rate of 3 × 10−5 with Imax = 4 as the maximum number of iterations, resulting in a decrease of 0.25 dB. The simulation’s findings indicate that the SRTLMS is the most efficient variant decoding algorithm for LDPC codes, thanks to its compromise between performance and complexity. This paper presents the two invented algorithms and a comprehensive study of the co-design and implementation of the SRTLMS algorithm. We executed the implementation on a Xilinx Kintex-7 XC7K160 FPGA, achieving a maximum operating frequency of 101 MHz and a throughput of 606 Mbps.