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Studies on the Performance of LDPC Codes at Low Signal to Noise Ratio

Author: ZhangJie
Tutor: ZhaoDanFeng
School: Harbin Engineering University
Course: Communication and Information System
Keywords: LDPC construction of parity check matrix CPM MSK
CLC: TN911.22
Type: Master's thesis
Year: 2009
Downloads: 66
Quote: 1
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Abstract


This thesis focuses on achieving the reliability and effectiveness of information transmission in narrow-band communication system at low signal to noise ratio. Based on the background, the thesis uses the method of combining LDPC code with continuous phase modulation (CPM). The narrow-band communication system requires that the LDPC codes have good error correction performance in the condition of low signal noise ratio. The thesis mainly researches on LDPC code encoding and decoding algorithms and the structure of parity-check matrix, as well as the performance of LDPC codes based on continuous phase modulation at low SNR.The main problem of LDPC implementation is the high complexity of its traditional encoding algorithm. In order to improve the encoding method, the thesis studies on three kinds of linear encoding algorithms. The advantages, disadvantages and implementation complexity of the various algorithms are analyzed. Then the thesis studies on the decoding algorithm of LDPC code. After studying on the BP decoding algorithm, the improved algorithms of BP decoding are researched. And the simulation performances of these algorithms are compared. Then the thesis studies on the structure of parity check matrix. The random algorithms of Gallager, Mackay, PEG and the algebraic algorithm that are based on the cyclic shift matrix, finite geometry, Optical Orthogonal Codes are researched.Minimum frequency shift keying (MSK) as a special kind of CPM is suitable for the transmission of narrow-band channels. The coding and modulation system model of LDPC and MSK are constructed. Then, the simulation performances of LDPC codes are analyzed at low SNR. And through the analysis of simulation results, the parity check matrix whose performance meets the requirements of the system is identified.At last, the thesis studies on the performance of LDPC codes based on the M-ary CPM at low signal to noise ratio. The serially concatenated continuous phase modulation system based on LDPC codes (LDPC-CPM) is researched. Through computer simulation results, the thesis analyses the compact of design parameters on LDPC-CPM system. The simulation results show that the system has a good error correction performance.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Communicate > Communication theory > Information Theory > Channel coding theory
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