Research On Rateless Codes, Vector OFDM And The Joint Coded Modulation

Broadband wireless communication with high speed mobility is becoming an attractive trend in the coming wireless communication. Mobility is a significant attribute of the present and future wireless communication system, such as the vehicle network and high speed train network. A broader band together with a higher speed mobility makes signals go through a more complicated channel, with both time dispersion and frequency dispersion. Thus, it is of great importance to enhance the communication reliability and promote the spectrum usage. This dis-sertation is mainly focus on Rateless Codes and Vector OFDM technology. The contents of this work can be listed as follows.An Adaptive Vector OFDM (AVOFDM) transmission system is proposed with the doubly selective fading channel characterized based on the basis expansion model (BEM) and time-frequency domain transformation. Different from the traditional Vector OFDM system with fixed modulation and cyclic prefix (CP) size, both the modulation and CP size are adaptive with a given bit error threshold when the channel state information (CSI) is estimated. The proposed AVOFDM increases the number of bits that per-symbol can carry and the overhead cost by the 2-dimension CP is reduced. Both factors contribute to an increased data throughput. Since the diversity gain is influenced by the degree of channel freedom, vector length and rate, it is demon-strated that AVOFDM can achieve considerable joint Multipath-and-Doppler diversity gain over doubly selective fading channels. It is even more closer to the upper bound in comparison with that can be achieved by the traditional non-adaptive Vector OFDM.A novel belief propagation (BP) decoding algorithm based on signal space set partition jointly with degree is developed. Unlike the conventional coding mapping scheme, it is motivated by the set partition introduced by Underboeck. The Euclidean distance is gradually increased with the process of set partition, resulting different bits of the same symbol with different LLR expectations. The potential unequal error protection (UEP) makes it possible to iterate the LLR faster and more accurate through the Tanner Graph at the receiver without actual comparing operations. Further more, theoretical BER and symbol LLR from channels are derived with 16QAM and 64QAM, followed with detailed BP decoding schedule strategy. It is shown that the performance of the BP decoding is improved without the sacrifice of extra spectrum.Finally, a joint modulation and coding scheme is introduced based on Rateless Codes and Vector OFDM systems to combat fading over doubly selective fading channels. Specifically, the lower bound of the decoding complexity of the block universal Raptor Codes and the upper bound of the probability to decode successfully in Binary Erasure Channels are derived theo-retically. The proposed propositions reveal the impacts of the degree distribution on the system performance. Furthermore, according to the propositions and the joint Multipath-and-Doppler diversity theory, two kinds of practical CMS are developed. One is Uniform-Biased CMS and the other is Diversity-Biased CMS. The two schemes can achieve considerable joint Multipath-and-Doppler diversity gain and coded modulation gain to improve the reliability of the system. Finally, simulation results validate the propositions and the reliability of the system is improved.