宽带移动通信LDPC技术研究与应用
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摘要
近年来,第四代移动通信系统在国际上受到广泛关注。我国也启动了FuTURE计划以及Gbps重大项目对4G移动通信系统的关键技术进行研究。LDPC(Low Density Parity Check,低密度奇偶校验)码以其优异的性能、简洁的形式及良好的应用前景日益吸引了广大研究人员的注意。本文的主要任务就是完成高性能的LDPC译码器FPGA(Field Programmable Gate Array,现场可编程逻辑门阵列)实现设计。
本文的主要研究内容概括如下：
基于对BP(Belief Propagation,置信传播)算法和LLR BP(Log-Likelihood-Ratio Belief Propagation)算法的理论分析,研究了结构化LDPC码的UMP BP_based(Uniformly Most Powerful Belief-Propagation-Based)算法。该算法考虑Gbps系统实际工程应用,采用了分层消息传递机制,并简化了校验节点译码操作。仿真结果表明,该算法性能与BP算法相当,可降低运算复杂度及存储空间,是一种能较好兼顾性能与实现复杂度的译码算法。
接着提出一种高吞吐量、低复杂度、可扩展的LDPC准并行译码结构及其实现方案,针对不同码长的非正则结构化LDPC码可进行相应扩展。基于UMP BP-Based译码算法,通过优化常用的部分并行译码结构,同时对两个数据块进行操作,充分利用了硬件资源,并由此提高了译码器的吞吐量。利用Xilinx公司的Virtex-5 SX95t FPGA实现结果表明：该译码器在采用18次迭代情况下信息吞吐量可达344.9MbpS。
LDPC码技术具有广阔的应用前景。本文结合LDPC码和OFDM(Orthogonal Frequency Division Multiplexing,正交频分复用)系统进行了研究,希望可以对下一步的研究工作起到积极的作用。
Recently, the 4th generation (4G) of mobile communication system has received wide attention in the world. China also launched the "FuTURE" and "Gbps" program for the research on the key technologies of 4G Low-Density Parity-Check (LDPC) codes is a hot candidate channel code technology in 4G systems. LDPC has very attractive properties:error performance approaching Shannon limits, easy description and implementation, convenient theoretical analysis and research, easily decoded in complete parallel ways and suitable for hardware implementation. This thesis focuses on the LDPC decoder design in mobile communications system.
The research concerns in this thesis are as follows:
Based on theoretical analysis of Belief Propagation (BP) and Log-Likelihood-Ratio Belief Propagation (LLR BP) decoding algorithms, Uniformly Most powerful(UMP)BP_based decoding algorithm for structured LDPC codes is discussed with consideration of hardware implementation in 4G systems. UMP BP_based decoding algorithm can achieve performance which is very close to the BP algorithm's performance, while the computational complexity and memory requirement are greatly reduced. Besides, in UMP BP_based decoding algorithm the convergence property as layered BP decoding algorithm is remained. So UMP BP_based decoding algorithm is an advanced algorithm that can offer trade-offs between performance and complexity.
Then Low-density high-speed reconfigurable decoding architectures are proposed with the field programmable gate array (FPGA) implementation of irregular structured low density parity check (LDPC) codes. The enhanced semi-parallel decoding architectures are easily scalable and reconfigurable for different block sizes. Based on the UMP BP-Based (Uniformly Most Powerful Belief-Propagation-Based) algorithm, this thesis optimizes the common components of parallel decoder structure for two different code words at the same time. Thus, the throughout of the decoder is increased. The FPGA implementation results on Xilinx FPGA Virtex-5 SX95T show that the irregular LDPC encoder can achieve a maximum (source data) decoding throughput of 344.9 Mbps at 18 iterations.
LDPC has wide application foreground. This paper studies the LDPC decoder in OFDM system. Hopefully, it is beneficial to the further research work.
本文的主要研究内容概括如下：
基于对BP(Belief Propagation,置信传播)算法和LLR BP(Log-Likelihood-Ratio Belief Propagation)算法的理论分析,研究了结构化LDPC码的UMP BP_based(Uniformly Most Powerful Belief-Propagation-Based)算法。该算法考虑Gbps系统实际工程应用,采用了分层消息传递机制,并简化了校验节点译码操作。仿真结果表明,该算法性能与BP算法相当,可降低运算复杂度及存储空间,是一种能较好兼顾性能与实现复杂度的译码算法。
接着提出一种高吞吐量、低复杂度、可扩展的LDPC准并行译码结构及其实现方案,针对不同码长的非正则结构化LDPC码可进行相应扩展。基于UMP BP-Based译码算法,通过优化常用的部分并行译码结构,同时对两个数据块进行操作,充分利用了硬件资源,并由此提高了译码器的吞吐量。利用Xilinx公司的Virtex-5 SX95t FPGA实现结果表明：该译码器在采用18次迭代情况下信息吞吐量可达344.9MbpS。
LDPC码技术具有广阔的应用前景。本文结合LDPC码和OFDM(Orthogonal Frequency Division Multiplexing,正交频分复用)系统进行了研究,希望可以对下一步的研究工作起到积极的作用。
Recently, the 4th generation (4G) of mobile communication system has received wide attention in the world. China also launched the "FuTURE" and "Gbps" program for the research on the key technologies of 4G Low-Density Parity-Check (LDPC) codes is a hot candidate channel code technology in 4G systems. LDPC has very attractive properties:error performance approaching Shannon limits, easy description and implementation, convenient theoretical analysis and research, easily decoded in complete parallel ways and suitable for hardware implementation. This thesis focuses on the LDPC decoder design in mobile communications system.
The research concerns in this thesis are as follows:
Based on theoretical analysis of Belief Propagation (BP) and Log-Likelihood-Ratio Belief Propagation (LLR BP) decoding algorithms, Uniformly Most powerful(UMP)BP_based decoding algorithm for structured LDPC codes is discussed with consideration of hardware implementation in 4G systems. UMP BP_based decoding algorithm can achieve performance which is very close to the BP algorithm's performance, while the computational complexity and memory requirement are greatly reduced. Besides, in UMP BP_based decoding algorithm the convergence property as layered BP decoding algorithm is remained. So UMP BP_based decoding algorithm is an advanced algorithm that can offer trade-offs between performance and complexity.
Then Low-density high-speed reconfigurable decoding architectures are proposed with the field programmable gate array (FPGA) implementation of irregular structured low density parity check (LDPC) codes. The enhanced semi-parallel decoding architectures are easily scalable and reconfigurable for different block sizes. Based on the UMP BP-Based (Uniformly Most Powerful Belief-Propagation-Based) algorithm, this thesis optimizes the common components of parallel decoder structure for two different code words at the same time. Thus, the throughout of the decoder is increased. The FPGA implementation results on Xilinx FPGA Virtex-5 SX95T show that the irregular LDPC encoder can achieve a maximum (source data) decoding throughput of 344.9 Mbps at 18 iterations.
LDPC has wide application foreground. This paper studies the LDPC decoder in OFDM system. Hopefully, it is beneficial to the further research work.
引文
[1]张平,许宁,王莹.后三代移动通信系统.中国科技论文在线.
[2]王锦山,赵建平,李树宏.多模移动终端芯片设计.中兴通讯技术.第五期.2005,5：37-40.
[3]John Wiley, Sons.4G Mobile Networks:Technologies for Mobile Communications of the Future,2005.
[4]R W hamming. Error Detecting and Error Correcting codes. Bell System Tech.J.,Vol.29,1950, pp.147-160.
[5]J Viterbi. Error Bounds of Convolutional Codes and an Asymptotically Optimum Decoding algorithm. IEEE transactions on Information Theory, Vol.13,1967, pp.260-269.
[6]袁东风,张海刚等.LDPC码理论与应用,人民邮电出版社,2008.2。
[7]Gallager R G. Low-density-parity-check codes [J].IRE Trans Inform Theory, 1962,1 (8):pp.21-28.
[8]Robert J McEliece, David J C MacKay and Jung-Fu Cheng. Turbo Decoding as an Instance of Pearl's 'Belief Propagation' Algorithm. IEEE Journal on Selected Areas in Communications, Vol.16, No.2,1998, pp.140-152.
[9]M G Luby, M Mitzenacher, M A Shokrollahi, D A Spielman.Efficient. Improved low-density Parity-check Codes Using Irregular Graphs. IEEE Transactions on Information Theory, Vol.47, Feb.2001, pp.585-598.
[10]M G Luby, M Mitzenacher, M A Shokrollahi, D A Spielman. Analysis of low-density Parity-check Codes and Improved Designs Using Irregular Graphs. Proceedings of the 30th annual symposium on Theory of Computing,1998, pp.249-258.
[11]M G Luby, M Mitzenacher, M A Shokrollahi, and D A Spielman. Efficient Erasure Correcting Codes. IEEE Transactions on Information Theory, Vol.IT-47,Feb.2001, pp.569-584.
[12]T J Richardson, M A Shokrollahi, and R L Urbanke. Design of Capacity-approaching Irregular Low-density Parity-check Codes. IEEE Transactions on Information Theory, Vol.IT-47,Feb.2001.
[13]T J Richardson, R L Urbanke, The capacity low-density parity-check codes under message-passing decoding, IEEE Transactions on Information Theory, 47(2).
[14]T J Richardson, R L Urbanke, The renaissance of Gallager's low-density parity-check codes, IEEE Communications Magazine, Aug.2003, pp.126-131.
[15]R M Tanner. A Recursive Approach to Low complexity codes. IEEE Transactions on Information. Theory, Vol.27, Sep.1981, pp.533-547.
[16]ETST EN 302 307 V1.1.1(2004-06), European Standard (Telecommunications series),Digital Video Broadcasting(DVB);Second Generation Framing structure, channel coding and modulation systems for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications.
[17]The International Forum on Future Mobile Telecommunications & China-EU Post Conference on Beyond 3G, the High Technology Research and Development center of MOST(HTRDC) FuTURE coordination Committee of 863 Program(FuTURE), Conference proceedings, Nov.20-22,2002, Beijing, China.
[18]http://ieee802.org/16.
[19]J Chen, and M P C Fossorier. Near optimum universal belief propagation based decoding of low-density-parity-check codes. IEEE Transactions on Communicaions, Mar 2002, pp.406-404.
[20]Fossorier M and Mihaljevic M. Reduced complexity iterative decoding of low-density parity check codes based on belief propagation. IEEE Transactions On Communications,1999.pp.673-680.
[21]Zhang T. and Parhi K. K. Joint (3, k)-Regular LDPC Code and Decoder/Encoder Design, IEEE Transactions on Signal Processing,52(4), April.2004, pp.1065-1079.
[22]Chen Y. and Hocevar D. A FPGA and ASIC implementation of rate 1/2, 8088-bit irregular low density parity check decoder, IEEE GLOBECOM'03, Vol.1, Dec.2003, pp.113-117.
[23]Kai Zhang. High-Throughput Layered Decoder Implementation for Quasi-Cyclic LDPC codes. IEEE Journal on Selected Areas in Communications, Vol.27, Aug.2009, pp 985-994.
[24]田耘,徐文波,胡彬等.Xilinx ISE Design Suite 10.x FPGA开发指南,人民 邮电出版社,2008.11。
[25]Xilinx, ML507 User Guide, Xilinx,2007。
[26]李亚卓,王勇,张平.B3G/4G TDD试验平台及研究现状.移动通信,2006年10月。
[2]王锦山,赵建平,李树宏.多模移动终端芯片设计.中兴通讯技术.第五期.2005,5：37-40.
[3]John Wiley, Sons.4G Mobile Networks:Technologies for Mobile Communications of the Future,2005.
[4]R W hamming. Error Detecting and Error Correcting codes. Bell System Tech.J.,Vol.29,1950, pp.147-160.
[5]J Viterbi. Error Bounds of Convolutional Codes and an Asymptotically Optimum Decoding algorithm. IEEE transactions on Information Theory, Vol.13,1967, pp.260-269.
[6]袁东风,张海刚等.LDPC码理论与应用,人民邮电出版社,2008.2。
[7]Gallager R G. Low-density-parity-check codes [J].IRE Trans Inform Theory, 1962,1 (8):pp.21-28.
[8]Robert J McEliece, David J C MacKay and Jung-Fu Cheng. Turbo Decoding as an Instance of Pearl's 'Belief Propagation' Algorithm. IEEE Journal on Selected Areas in Communications, Vol.16, No.2,1998, pp.140-152.
[9]M G Luby, M Mitzenacher, M A Shokrollahi, D A Spielman.Efficient. Improved low-density Parity-check Codes Using Irregular Graphs. IEEE Transactions on Information Theory, Vol.47, Feb.2001, pp.585-598.
[10]M G Luby, M Mitzenacher, M A Shokrollahi, D A Spielman. Analysis of low-density Parity-check Codes and Improved Designs Using Irregular Graphs. Proceedings of the 30th annual symposium on Theory of Computing,1998, pp.249-258.
[11]M G Luby, M Mitzenacher, M A Shokrollahi, and D A Spielman. Efficient Erasure Correcting Codes. IEEE Transactions on Information Theory, Vol.IT-47,Feb.2001, pp.569-584.
[12]T J Richardson, M A Shokrollahi, and R L Urbanke. Design of Capacity-approaching Irregular Low-density Parity-check Codes. IEEE Transactions on Information Theory, Vol.IT-47,Feb.2001.
[13]T J Richardson, R L Urbanke, The capacity low-density parity-check codes under message-passing decoding, IEEE Transactions on Information Theory, 47(2).
[14]T J Richardson, R L Urbanke, The renaissance of Gallager's low-density parity-check codes, IEEE Communications Magazine, Aug.2003, pp.126-131.
[15]R M Tanner. A Recursive Approach to Low complexity codes. IEEE Transactions on Information. Theory, Vol.27, Sep.1981, pp.533-547.
[16]ETST EN 302 307 V1.1.1(2004-06), European Standard (Telecommunications series),Digital Video Broadcasting(DVB);Second Generation Framing structure, channel coding and modulation systems for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications.
[17]The International Forum on Future Mobile Telecommunications & China-EU Post Conference on Beyond 3G, the High Technology Research and Development center of MOST(HTRDC) FuTURE coordination Committee of 863 Program(FuTURE), Conference proceedings, Nov.20-22,2002, Beijing, China.
[18]http://ieee802.org/16.
[19]J Chen, and M P C Fossorier. Near optimum universal belief propagation based decoding of low-density-parity-check codes. IEEE Transactions on Communicaions, Mar 2002, pp.406-404.
[20]Fossorier M and Mihaljevic M. Reduced complexity iterative decoding of low-density parity check codes based on belief propagation. IEEE Transactions On Communications,1999.pp.673-680.
[21]Zhang T. and Parhi K. K. Joint (3, k)-Regular LDPC Code and Decoder/Encoder Design, IEEE Transactions on Signal Processing,52(4), April.2004, pp.1065-1079.
[22]Chen Y. and Hocevar D. A FPGA and ASIC implementation of rate 1/2, 8088-bit irregular low density parity check decoder, IEEE GLOBECOM'03, Vol.1, Dec.2003, pp.113-117.
[23]Kai Zhang. High-Throughput Layered Decoder Implementation for Quasi-Cyclic LDPC codes. IEEE Journal on Selected Areas in Communications, Vol.27, Aug.2009, pp 985-994.
[24]田耘,徐文波,胡彬等.Xilinx ISE Design Suite 10.x FPGA开发指南,人民 邮电出版社,2008.11。
[25]Xilinx, ML507 User Guide, Xilinx,2007。
[26]李亚卓,王勇,张平.B3G/4G TDD试验平台及研究现状.移动通信,2006年10月。