A Study Of Decoding Algorithm For LDPC Codes Based On High Order Modulation Over Inpulsive Noise Channels

In this paper, the decoding and performance of Low-density parity check (LDPC) codes is discussed for additive impulse noise channels. The main contents can be summarized as follows:This paper introduces the principles of LDPC codes, including the encoding scheme codes and decoding scheme.A linear calibration of BP decoding algorithm is put forward which can simplify calculation complexity and make hardware convenient without negative effect on the performance of algorithm process.Then the performance for regular LDPC codes on AWGN channel is simulated. The actual advantages of regular LDPC codes under the short and middle frames can be verified through comparison with turbo codes.BP decoding algorithm is discussed for additive impulse noise channels. When BP algorithm is used for additive impulse noise channels, the initial channel log-likely ratio(LLR) messages have no close expression, and moreover, computation of the initial channel LLR is very difficult. By reexamined the computation of the initial channel LLR messages for AWGN channels, Least Square(LS) metric is proposed to compute the initial LLR messages for impulse noise channels, and the decoding algorithm is simplified. Since the characteristics of impulse noise, BP algorithm with LS metric occurs error floor. In order to dissolve this problem, another robust metric, i.e., Huber metric is introduced to compute the initial LLR messages. Simulation result of BP algorithm based Huber metric achieves good performance.Finally, the high order soft demodulation algorithms based on additive impulse noise channels were introduced. Then the BP algorithms were presented based on high order soft demodulation, such as 4QAM,16QAM. Simulation result shows that the coded-modulation algorithms can work reliably in high speed digital communication.