| With the fast development of communication technology, especially the mobile communication technology, the power utilization ratio and frequency spectrum utilization ratio of communication system, and various kinds of interference and noise brought by mobile channels are the main problems to restrict the performance of communication system. Coded modulation technology, which combines the encode technology and modulation technology, obtains the coding gain and thereby improves the performance of system with no increase of power efficiency and frequency spectrum efficiency. However, it is optimal in AWGN channels but not optimal in fading channels. To solve this problem, BICM, which combines the bit interleaver and the coded modulation technology, is proposed. The results show that BICM can obtain more gain in Rayleigh channel. Then, with the development of turbo codes, people consider replacing the convolution codes in traditional BICM system with the turbo codes, and using iterative decoding in receiver. Thus, it not only has the high power efficiency of turbo codes, but also has the high bandwidth efficiency of coded modulation technology. The new technology can satisfy both the demand of high efficiency and high reliability in wireless communications, and possess wide application foreground.First, the coding and decoding structures of turbo codes are researched, and the basic principle of bit-interleaved coded modulation technology is also introduced. The thesis expounds the methods and process of coding, interleaving, modulation, demodulation and decoding in detail.Second, bit-interleaved coded modulation iterative decoding (BICM-ID) is researched. The simulation results indicate that the system with iterative decoding has better bit error performance.And then, bit-interleaved turbo coded modulation (BITCM), which combines turbo codes and BICM, is researched as an emphasis part. The thesis describes the basic principle of BITCM technology, builds the transmission model, researches several kinds of common decoding algorithms, and deduces MAP algorithm, Log-MAP algorithm and Max-Log-MAP algorithm in detail. The simulation proves that the performance of BITCM is better than that of traditional BICM-ID.To improve the performance of system further, and increase the diversity gain, two signal space diversity technologies named constellation rotation and Multi-QAM modulation are combined into BITCM system. The thesis gives the structure of this improved system, introduces the basic principle of constellation rotation and Multi-QAM modulation, analyses three corresponding demodulation algorithms named Vector Gaussian Approximation algorithm (VGA), Scalar Gaussian Approximation algorithm (SGA) and Multi-QAM demodulation algorithm.At last, do simulation and compare these algorithms. Results show that improved algorithm has good performance. And the more the iteration times are, or the more the dimensions of rotation matrix are, or the more the diversity channels are, or the fewer the modulation orders are, the better the performance is. |
