LDPC Encoding And Decoding Algorithm Research And Its Application

LDPC (Low Density Parity Check) code was first invented by Gallager [1] in 1962. Because of the limit of computer, the researches on this kind of code process slowly. People did not pay any attention on this kind of codes several decades, until Mackay and Neal [7] rediscovered it in 1998. The merit of this code was soon proved and LDPC code becomes people's research hotspot. After several years' development, researchers make great progress on every branches and LDPC techniques becomes mature and even has commercial applications.Current research branches on LDPC code are generally divided as follows:1) LDPC code structure analysis and optimization2) LDPC encoding methods research3) LDPC decoding algorithm performance analysis4) Hardware implementation of LDPC code5) The application of LDPC codeMy master dissertation mainly compared several important LDPC decoding algorithm and innovatively proposed a new decoding algorithm called CAMP (Cross Antenna Message Passing) which is special for the LDPC coded Space-time system. This algorithm has been published on CCNC2006 Demonstration proceedings. The discussion on CAMP algorithm is mainly in chapter 5. Following is the brief introduction of the background and basic contents of CAMP algorithm.Unlike Space-time block code, we transmit irrelevant information in each transmit antenna and only make use of the space time structure to increase the channel capacity. Without space diversity, LDPC is used to conquer the influence of fading.When the transmit antennas' number is more than 1, different antennas will interfere each others. The input of extrinsic information is the likelihood probability under AWGN channel with multiple-antenna interference. However, standard belief propagation was not designed special for space time structure and default extrinsic information is the likelihood probability under AWGN channel which is set fixed during whole recursive process. Obviously, it is not reasonable we use standard belief propagation algorithm in space time system. In order to solve the problem, this dissertation not only proposed a LDPC coded space time structure, but also proposed a belief propagation liked algorithm, CAMP algorithm. This algorithm updates extrinsic information by calculating other antennas' a posteriori probability and passing it to the current decoding antenna to cancel the interference introduced by symbols from other antennas.In order to filter multiple antenna interference, extrinsic information calculation nodes operate several computation together with decoders. In Tanner graph, besides variable nodes and parity check nodes, there are extrinsic information calculation nodes too.