Application And Performance Analysis Of Ldpc Codes In Ofdm Systems

With the requirement of wireless data and multimedia business, the purpose of the Beyond 3G and 4G mobile communication system turns to be achieving omnipresent, high-caliber, and high-speed data transmission for mobile multimedia. The system requires support to the high-speed transmission in the high carrier and bandwidth, and with the rate in the range from 2Mbit/s to several megabits per second. And the question how to ensure the reliability of the data communication becomes very important, so we need overcome many difficult problems to achieve this goal. The problems mainly exhibit to be multi-path propagation in the wireless fading channel, signal fading caused by the scattering and Inter-Symbol Interference caused by the long multi-path time delay. The technique of Orthogonal Frequency Division Multiplexing divides the channel into many orthogonal sub-channels, so the data can be transmitted parallel in the sub-channel in order to achieve high-speed transmission. In order to prevent the transmission error, many techniques for correction error have applications in the OFDM system, such as convolutional code, Reed-Solomon code, Turbo code, and so on.The LDPC code proposed in the sixties of the last century is one of linear block code with sparse check matrix. And the research once more in the later period of nineties indicate that LDPC code has excellent performance close to Shannon limit when decoded with iterative algorithm, which can be operated parallel, and have upstanding application prospects in the reliable information transmission. Because all of these, LDPC code is paid high attentions by academic circles and Information Technology Industry. And it has turned to be one of the most attractive research hotspot in the resent area for channel codes.The key modulating technology for B3G and 4G mobile communication system willbe OFDM technology, and the LDPC-COFDM system constructed by LDPC code applied in OFDM proves to have a wide application prospect. In this paper, I established a simulating model for LDPC-COFDM communication system and did some research for LDPC-COFDM system in several aspects: 1)The influence to the system performance adapted with different code length. 2)The influence to the system performance adapted with different code rate. 3) The influence to the system performance adapted with different construction. 4)The influence to the system performance adapted with interweave technicque or without interweave technique.5)The influence to the system performance with different modulation method.And I get some conclusions from the simulation results: the BER performance of the LDPC-COFDM system will be excellent if we choose code length, code rate, code construction, modulation type and interweave technology reasonably, and it is specially suitable to extend to utilize in the future mobile communication system.