| With the development of3G and4G, people's requirements on the quality and reliability, channel capacity and spectrum utilization of the signal transmission of mobile communication get higher and higher. There are many methods to improve the reliable transmission of signal and to high channel capacity, it can make reliable signal transfer by channel coding, and compared with the Turbo codes, the performance of LDPC is the most, not only it has the advantages of describing simply, low complexity decoding, can parallel implementation and practical advantages of flexible, more lower BER platform, the most important is that it is the most close to the Shannon limit. MIMO communication system allocates multiple antennas in the transmitter and receiver at the same time, it can enhance the capacity and improve greatly the performance of the system in the case without increasing the bandwidth and transmission power, and MIMO system also has the advantages of using or mitigating multi-path fading, eliminating common channel interference, improving spectrum utilization and so on, it has became the one of the key technologies of mobile communication. This dissertation describes the following several main aspects:1. Describe characteristics of the wireless channel, transmission modes of the signal, channel fading and expansion, including frequency extension, time extension and angle extension. Describe some common channel models, the main are white Gaussian noise channel, Rayleigh fading channel, and Rician fading channel, analyse their probability distribution.2. Describe wireles MIMO communication system, consist mainly of the characteristics and the basic principles of MIMO communication system, the channel models of the system in non-frequency-selective channel and frequency selective fading channel. Describe the channel capacity of four communication systems of SISO, SIMO, MISO and MIMO, and comparison by Matlab simulation, highlight the advantages of MIMO system; Introduce the space-time coding technology for MIMO communication systems, including the principle of space-time coding, the key point is space-time block coding (STBC) technology.3. It introduced the matrix representation and Tanner representation of LDPC codes; Introduce the coding method based on Gaussian elimination, coding method based on approximate lower triangular matrix; the characteristics and coding methods of cyclic codes and quasi-cyclic code. It explained several construction methods of the parity-check matrix, primarily random construction method, including Gallger construction method, Mackey construction method, Davey construction method and so on. It introduced decoding algorithms of LDPC, themain is the belief propagation algorithm, and variety improved algorithms based on BP algorithm.4. It is a trend to use LDPC codes for MIMO communication system in the future mobile communication. So it will be introduced of the LDPC-MIMO communication system in this section, and simulate in the following several different cases, thereby it can compare the performance of the system more intuitive, thus the optimization schemes of the system can be proposed. Several cases are as follows:(1) The MIMO communication system with LDPC and did without LDPC codes;(2) Different lengths of LDPC codes;(3) Different channels;(4) Different modulation methods;(5) Different encoding methods;(6) Different decoding methods. |
