An improved parallel weighted bit-flipping（PWBF） algorithm is presented. To accelerate the information exchanges between check nodes and variable nodes, the bit-flipping step and the check node updating step of the ...An improved parallel weighted bit-flipping（PWBF） algorithm is presented. To accelerate the information exchanges between check nodes and variable nodes, the bit-flipping step and the check node updating step of the original algorithm are parallelized. The simulation experiments demonstrate that the improved PWBF algorithm provides about 0. 1 to 0. 3 dB coding gain over the original PWBF algorithm. And the improved algorithm achieves a higher convergence rate. The choice of the threshold is also discussed, which is used to determine whether a bit should be flipped during each iteration. The appropriate threshold can ensure that most error bits be flipped, and keep the right ones untouched at the same time. The improvement is particularly effective for decoding quasi-cyclic low-density paritycheck（QC-LDPC） codes.展开更多
A new method of constructing regular low-density parity-check (LDPC) codes was proposed. And the novel class of LDPC codes was applied in a coded orthogonal frequency division multiplexing (OFDM) system. This method e...A new method of constructing regular low-density parity-check (LDPC) codes was proposed. And the novel class of LDPC codes was applied in a coded orthogonal frequency division multiplexing (OFDM) system. This method extended the class of LDPC codes which could be constructed from shifted identity matrices. The method could avoid short cycles in Tanner graphs with simple inequation in the construction of shifting identity matrices, which made the girth of Tanner graphs 8. Because of the quasicyclic structure and the inherent block configuration of parity-check matrices, the encoders and the decoders were practically feasible. They were linear-time encodable and decodable. The LDPC codes proposed had various code rates, ranging from low to high. They performed excellently with iterative decoding and demonstrate better performance than other regular LDPC codes in OFDM systems.展开更多
为了降低TCN(Train Communication Network)的数据误码率,需要采用一种高性能的差错控制方法。循环冗余校验(CRC)由于编码简单且高效,是一种最常见的信道编码方法。根据TCN协议,在TCNMVB总线中一个由7位CRC校验码和1位偶校验位构成的具...为了降低TCN(Train Communication Network)的数据误码率,需要采用一种高性能的差错控制方法。循环冗余校验(CRC)由于编码简单且高效,是一种最常见的信道编码方法。根据TCN协议,在TCNMVB总线中一个由7位CRC校验码和1位偶校验位构成的具有双重校验的8位校验序列。按照MVB总线中帧的格式不同,选择串行算法实现。最终得到校验序列编码器的正确仿真波形,并在FPGA硬件上实现。展开更多
A modified Benes network is proposed to be used as an optimal shuffle network in worldwide interoperability for microwave access （WiMAX） low density parity check （LDPC） decoders, When the size of the input is not ...A modified Benes network is proposed to be used as an optimal shuffle network in worldwide interoperability for microwave access （WiMAX） low density parity check （LDPC） decoders, When the size of the input is not a power of two, the modified Benes network can achieve the most optimal performance. This modified Benes network is non-blocking and can perform any sorts of permutations, so it can support 19 modes specified in the WiMAX system. Furthermore, an efficient algorithm to generate the control signals for all the 2 × 2 switches in this network is derived, which can reduce the hardware complexity and overall latency of the modified Benes network. Synthesis results show that the proposed control signal generator can save 25.4% chip area and the overall network latency can be reduced by 36. 2%.展开更多
Aim of the study: Several studies have shown the inferior performance of small prostheses in the narrowaortic root. However, modern low-profile mechanical prostheses have improved hemodynamic performance characteristi...Aim of the study: Several studies have shown the inferior performance of small prostheses in the narrowaortic root. However, modern low-profile mechanical prostheses have improved hemodynamic performance characteristics. By measuring the transprosthetic pressure gradient in vivo, we were able to characterize the hemodynamic features of two prostheses: the ATS Medical(ATS) and the Medtronic Hall(MH) valves. Methods: From October 1994 to April 2002, 113 patients received an aortic valve replacement(AVR) with either an ATS or a MH valve. The transprosthetic pressure gradients, calculated froma simplified Bernoulli equation during immediate postoperative Doppler echocardiographic examination, were compared for differently sized prostheses with respect to body surface area(BSA). Results: The mean pressure gradients and the mean BSAs were: 27.8±14.8 mm Hg and 1.50±0.10 m2 in ATS 19 mm(n=7), 20.4±8.5 mm Hg and 1.54±0.11 m2 in ATS 21 mm(n=22), 13.0±5.7 mm Hg, 1.70±0.13 m2 in ATS 23 mm(n=22), 10.9±3.5 mm Hg and 1.81±0.16 m2 in ATS 25 mm(n=19), 9.3±0.6 mm Hg and 1.72±0.17 m2 in ATS 27 mm(n=4), 13.5±6.5 mm Hg and 1.54±0.13 m2 in MH 20 mm(n=9), 10.9±4.7 mm Hg and 1.64±0.15 m2 in MH 22 mm(n=22), 9.3±3.1mmHg and 1.72±0.12 m2 in MH 24 mm(n=7). Conclusions: With the exception of the ATS 19mm valve, the variously sized prostheses have acceptable transprosthetic pressure gradient measurements. In addition, even-sized MH valves(20 and 22 mm) with a thinner sewing cuff showed better hemodynamic performances than similarly sized ATS valves.展开更多
Quasi-cyclic low-density parity-check （QC-LDPC） codes can be constructed conveniently by cyclic lifting of protographs. For the purpose of eliminating short cycles in the Tanner graph to guarantee performance, first...Quasi-cyclic low-density parity-check （QC-LDPC） codes can be constructed conveniently by cyclic lifting of protographs. For the purpose of eliminating short cycles in the Tanner graph to guarantee performance, first an algorithm to enumerate the harmful short cycles in the protograph is designed, and then a greedy algorithm is proposed to assign proper permutation shifts to the circulant permutation submatrices in the parity check matrix after lifting. Compared with the existing deterministic edge swapping （DES） algorithms, the proposed greedy algorithm adds more constraints in the assignment of permutation shifts to improve performance. Simulation results verify that it outperforms DES in reducing short cycles. In addition, it is proved that the parity check matrices of the cyclic lifted QC-LDPC codes can be transformed into block lower triangular ones when the lifting factor is a power of 2. Utilizing this property, the QC- LDPC codes can be encoded by preprocessing the base matrices, which reduces the encoding complexity to a large extent.展开更多
Abstract： The layered decoding algorithm has been widely used in the implementation of Low Density Parity Check （LDPC） decoders, due to its high convergence speed. However, the pipeline operation of the layered dec...Abstract： The layered decoding algorithm has been widely used in the implementation of Low Density Parity Check （LDPC） decoders, due to its high convergence speed. However, the pipeline operation of the layered decoder may introduce memory access conflicts, which heavily deteriorates the decoder throughput. To essentially deal with the issue of memory access conflicts,展开更多
Due to the ubiquitous open air links and complex electromagnetic environment in the satellite communications,how to ensure the security and reliability of the information through the satellite communications is an urg...Due to the ubiquitous open air links and complex electromagnetic environment in the satellite communications,how to ensure the security and reliability of the information through the satellite communications is an urgent problem.This paper combines the AES(Advanced Encryption Standard) with LDPC(Low Density Parity Check Code) to design a secure and reliable error correction method — SEEC(Satellite Encryption and Error Correction).This method selects the LDPC codes,which is suitable for satellite communications,and uses the AES round key to control the encoding process,at the same time,proposes a new algorithm of round key generation.Based on a fairly good property in error correction in satellite communications,the method improves the security of the system,achieves a shorter key size,and then makes the key management easier.Eventually,the method shows a great error correction capability and encryption effect by the MATLAB simulation.展开更多
基金The National High Technology Research and Development Program of China (863Program) ( No2009AA01Z235,2006AA01Z263)the Research Fund of the National Mobile Communications Research Laboratory of Southeast University(No2008A10)
文摘An improved parallel weighted bit-flipping（PWBF） algorithm is presented. To accelerate the information exchanges between check nodes and variable nodes, the bit-flipping step and the check node updating step of the original algorithm are parallelized. The simulation experiments demonstrate that the improved PWBF algorithm provides about 0. 1 to 0. 3 dB coding gain over the original PWBF algorithm. And the improved algorithm achieves a higher convergence rate. The choice of the threshold is also discussed, which is used to determine whether a bit should be flipped during each iteration. The appropriate threshold can ensure that most error bits be flipped, and keep the right ones untouched at the same time. The improvement is particularly effective for decoding quasi-cyclic low-density paritycheck（QC-LDPC） codes.
文摘A new method of constructing regular low-density parity-check (LDPC) codes was proposed. And the novel class of LDPC codes was applied in a coded orthogonal frequency division multiplexing (OFDM) system. This method extended the class of LDPC codes which could be constructed from shifted identity matrices. The method could avoid short cycles in Tanner graphs with simple inequation in the construction of shifting identity matrices, which made the girth of Tanner graphs 8. Because of the quasicyclic structure and the inherent block configuration of parity-check matrices, the encoders and the decoders were practically feasible. They were linear-time encodable and decodable. The LDPC codes proposed had various code rates, ranging from low to high. They performed excellently with iterative decoding and demonstrate better performance than other regular LDPC codes in OFDM systems.
文摘为了降低TCN(Train Communication Network)的数据误码率,需要采用一种高性能的差错控制方法。循环冗余校验(CRC)由于编码简单且高效,是一种最常见的信道编码方法。根据TCN协议,在TCNMVB总线中一个由7位CRC校验码和1位偶校验位构成的具有双重校验的8位校验序列。按照MVB总线中帧的格式不同,选择串行算法实现。最终得到校验序列编码器的正确仿真波形,并在FPGA硬件上实现。
基金The National Natural Science Foundation of China(No.60871079)
文摘A modified Benes network is proposed to be used as an optimal shuffle network in worldwide interoperability for microwave access （WiMAX） low density parity check （LDPC） decoders, When the size of the input is not a power of two, the modified Benes network can achieve the most optimal performance. This modified Benes network is non-blocking and can perform any sorts of permutations, so it can support 19 modes specified in the WiMAX system. Furthermore, an efficient algorithm to generate the control signals for all the 2 × 2 switches in this network is derived, which can reduce the hardware complexity and overall latency of the modified Benes network. Synthesis results show that the proposed control signal generator can save 25.4% chip area and the overall network latency can be reduced by 36. 2%.
文摘Aim of the study: Several studies have shown the inferior performance of small prostheses in the narrowaortic root. However, modern low-profile mechanical prostheses have improved hemodynamic performance characteristics. By measuring the transprosthetic pressure gradient in vivo, we were able to characterize the hemodynamic features of two prostheses: the ATS Medical(ATS) and the Medtronic Hall(MH) valves. Methods: From October 1994 to April 2002, 113 patients received an aortic valve replacement(AVR) with either an ATS or a MH valve. The transprosthetic pressure gradients, calculated froma simplified Bernoulli equation during immediate postoperative Doppler echocardiographic examination, were compared for differently sized prostheses with respect to body surface area(BSA). Results: The mean pressure gradients and the mean BSAs were: 27.8±14.8 mm Hg and 1.50±0.10 m2 in ATS 19 mm(n=7), 20.4±8.5 mm Hg and 1.54±0.11 m2 in ATS 21 mm(n=22), 13.0±5.7 mm Hg, 1.70±0.13 m2 in ATS 23 mm(n=22), 10.9±3.5 mm Hg and 1.81±0.16 m2 in ATS 25 mm(n=19), 9.3±0.6 mm Hg and 1.72±0.17 m2 in ATS 27 mm(n=4), 13.5±6.5 mm Hg and 1.54±0.13 m2 in MH 20 mm(n=9), 10.9±4.7 mm Hg and 1.64±0.15 m2 in MH 22 mm(n=22), 9.3±3.1mmHg and 1.72±0.12 m2 in MH 24 mm(n=7). Conclusions: With the exception of the ATS 19mm valve, the variously sized prostheses have acceptable transprosthetic pressure gradient measurements. In addition, even-sized MH valves(20 and 22 mm) with a thinner sewing cuff showed better hemodynamic performances than similarly sized ATS valves.
基金The National Key Technology R&D Program of China during the 12th Five-Year Plan Period(No.2012BAH15B00)
文摘Quasi-cyclic low-density parity-check （QC-LDPC） codes can be constructed conveniently by cyclic lifting of protographs. For the purpose of eliminating short cycles in the Tanner graph to guarantee performance, first an algorithm to enumerate the harmful short cycles in the protograph is designed, and then a greedy algorithm is proposed to assign proper permutation shifts to the circulant permutation submatrices in the parity check matrix after lifting. Compared with the existing deterministic edge swapping （DES） algorithms, the proposed greedy algorithm adds more constraints in the assignment of permutation shifts to improve performance. Simulation results verify that it outperforms DES in reducing short cycles. In addition, it is proved that the parity check matrices of the cyclic lifted QC-LDPC codes can be transformed into block lower triangular ones when the lifting factor is a power of 2. Utilizing this property, the QC- LDPC codes can be encoded by preprocessing the base matrices, which reduces the encoding complexity to a large extent.
基金the National Natural Science Foundation of China，the National Key Basic Research Program of China，The authors would like to thank all project partners for their valuable contributions and feedbacks
文摘Abstract： The layered decoding algorithm has been widely used in the implementation of Low Density Parity Check （LDPC） decoders, due to its high convergence speed. However, the pipeline operation of the layered decoder may introduce memory access conflicts, which heavily deteriorates the decoder throughput. To essentially deal with the issue of memory access conflicts,
基金supported by the National 863 Project of China under Grant No.2012AA01A509,No.2012AA120800
文摘Due to the ubiquitous open air links and complex electromagnetic environment in the satellite communications,how to ensure the security and reliability of the information through the satellite communications is an urgent problem.This paper combines the AES(Advanced Encryption Standard) with LDPC(Low Density Parity Check Code) to design a secure and reliable error correction method — SEEC(Satellite Encryption and Error Correction).This method selects the LDPC codes,which is suitable for satellite communications,and uses the AES round key to control the encoding process,at the same time,proposes a new algorithm of round key generation.Based on a fairly good property in error correction in satellite communications,the method improves the security of the system,achieves a shorter key size,and then makes the key management easier.Eventually,the method shows a great error correction capability and encryption effect by the MATLAB simulation.
