The Technology Research On Channel Coding And Channel Estimation In MC-CDMA Systems

WPT-CDMA and CMFB-CDMA systems are two kinds of novel MC-CDMA systems. Compared with traditional OFDM-CDMA system using FFT/IFFT transformation, they not only can resolve the high side lode of OFDM modulation, but also decrease the SNR loss caused by using cyclic prefix. These two schemes enhance the transmission efficiency, and are more suitable for 4G application. Thus the researchs on key technologies in WPT-CDMA and CMFB-CDMA systems become important.Taking multiuser image transmission in the WPT-CDMA and CMFB-CDMA systems as the application background in this paper, we mainly research the blind channel estimation, robust adaptive beamforming and detection algorithm which combines LDPC codes with SD algorithm under multipath frequency selective Rayleigh fading channels.The blind channel estimation extracts the channel information based on the own feature of received signals, thus it saves the frequency resources owing to not using pilot signals. In this part of research, we propose a blind channel estimation algorithm based on noise subspace estimation algorithm with adaptive variable step-size in order to achieve a good trade-off between convergence speed and steady-state error. In the meantime, the application for ambiguous complex coefficient identification technique reduces the bias between estimated and actual channel impulse and make the accuracy of channel estimation improved.Another promising scheme for mitigating interferences in 4G techniques is the adaptive beamforming which can extract the signals of the desired user and suppress the signals from interference users in MIMO multiuser transmission environment. In this part of research, beacauses there are some shortages for constrain linear minimum square (CLMS) adaptive beamforming algorithm, e.g. the speed of convergence is slower, the output performance worsens and instability of systems appears owing to deviation from direction vector of received signal and limited samples. We propose a robust CLMS adaptive beamforming algorithm based on worst performance to address these problems. This algorithm improve the output SINR of beamformer and make weight vector closer to the optimal values.With union detection using LDPC codes and SD algorithm, we use LDPC codes with good error correction ability to deal with the influence of additive white noise to compressed images, and make use of SD algorithm to detect the multiuser image datas to resolve ISI caused by frequency selective Rayleigh fading channels. The proposed algorithm decreases the error rate of MC-CDMA systems.Connection the above proposed algorithms with novel WPT-CDMA and CMFB-CDMA systems not only is the prominent characteristics of this paper, but also is the important innovation spots.