Key Techniques Of Channel Coding In Broad-band Wireless Access System

The technology of Fixed Broad-band Wireless Access (FBWA) is one of the hot topics in research and development of wireless communication because of its special advantages, based on IEEE802.16 series standards whivh is the most popular standard. In wireless fading channel, channel code plays a key role in improving the performance of the communication system. This thesis shows our recent research work on channel coding, one of the key technigues in FBWA, and iterative mechanism used to improve the performance of the system, considering the whole base-band receiver of FBWA.Based on the wirelessMAN-OFDM PHY in IEEE802.16 standard, the research work begins with the channel model of FBWA. After the simulation of the SUI channel, the construction of the simulation platform for FBWA system based on OFDM technology is performed. Diversity technique is also applied to improve the performance effectively.Research on the channel coding and techniques is the main part of this thesis. After studying the general soft-input soft-output iterative decoding of Turbo codes based on MAP algorithm, this thesis gives a specialized iterative decoding algorithm for circular recursive systematic convolutional (CRSC) Turbo codes, so the performance is improved and the complexity is reduced. Research work also includes the study of LDPC. To reduce the high complexity in LDPC coding and solve the requirement of long codeword, this thesis presents a new construction method of LDPC, with simple coding algorithm and fits for short codeword. The BP algorithm is simplified on logarithm field to reducte the decoding complexity. Analysis and simulation results about LDPC can be applied to FBWA.Iterative idea is the common soul of Turbo codes and LDPC, and also presents a way to resolve problems in communication technology. In the thesis, joint LS channel estimation and decoding is presented to gain better performance than LS channel estimation and lower complexity than joint MMSE channel estimation and decoding. Joint channel estimation and soft-output demodulation proposed in this thesis is a good way to balance between the complexity and performance.