Research Of Key Techniques For Broadband Wireless Turbo MIMO Communication System

With the development of cellular wireless communication, Internet and multimedia services, the demand for capacity of worldwide wireless communication systems is growing at a very rapid pace. Dou to the severe limitation of available radio spectrum and the transmitter power provided by mobile or other portable terminal, seeking the more effective signal transmission techniques has become one of the most active research subjects in digital wireless communication system. In the progress of seeking effective techniques, the link reliability of wireless system is always one of the most attentive and active problems for researchers and electronic engineers who are working in the wireless communication systems.The research results in recent years have approved that the performance of the system with Turbo code and max likelihood decoding could approach to Shannon limit and the spectrum efficiency of wireless system could remarkably increase by using MIMO spatial multiplexing technology. To fully utilize these technology advantages and develop broadband wireless Turbo MIMO system with large capacity and high reliability, most research organizations throw all their energy into this work and have obtained some inspiring scientific achievements. There are, however, a lot of problems required for Turbo MIMO system, because of the difficulty of system itself and the complicacy of wireless channels.To expedite the course of developing feasible Turbo MIMO system with large capacity and high reliability, the four research projects, as follows, on Turbo MIMO system have been done based on recent research results in all over the world. There are some new results obtained from research.Firstly, for overcoming the disadvantage of original combined SMC (Sequential Monte Carlo) Turbo MIMO receiver that could not adapt random variety of wireless channels, two new combined SMC Turbo MIMO space-time decoding algorithms with dynamic boundary parameter d are proposed. They are called direct randomization dynamic combined SMC Turbo MIMO algorithm and system randomization SMC Turbo MIMO algorithm, respectively. In the direct randomization method, boundary parameter d is randomly modified, in order to improve the performance of system in sense of statistics. In the system randomization method, boundary parameter d is modified by utilizing indirectly the information from channels, to improve the ability that algorithm follows channel variety. The computer simulation results show that the space-time decoding performance could be enhanced by the two new algorithms without the burden of complexity related to the original combined scheme.Secondly, for the problem of the carrier phase recovery in Turbo MIMO system with low speed transmission over Rayleigh fading channels, a new carrier phase recovery scheme suited for Turbo systems in Rayleigh fading channels with AWGN is proposed. It is called joint carrier phase recovery and Turbo decoding based PSAM (Pilot Symbol Assisted Modulation) technology. This scheme involves the estimation with PSAM for Rayleigh fading channel and the joint phase recovery and turbo-decoder for AWGN. Simulation results show that the proposed method with small system expense can significantly improve the performance of carrier phase recovery for Turbo systems in Rayleigh fading channels with AWGN.Thirdly, for the disadvantage of original hierarchical transversal adaptive filtering algorithm with larger error in channel equalization because the filter operates at the state of prediction not at the state filtering, a modified hierarchical transversal adaptive filter is proposed, in witch each subfilter could operate at the state of filtering. Based on the new scheme, the modified hierarchical transversal adaptive filtering algorithms based LMS (Least Mean Square) and RLS (Recursive Least Square) are proposed, respectively. The results of simulation indicate that, under same conditions, the modified HLMS and HRLS algorithms can not only maintain the feature of speeding up convergence rate, but also obtain at least one order of magnitude improvement for the mean square error of channel equalization related to the original scheme.Lastly, to seek the application of V-BLAST (Vertical Bell Labs Layered Space-Time) MIMO system under macro-cell environments without rich-scattering, the performance of V-BLAST system with the nonuniform distribution of AOA (Angel of Arrival) of incident radio has been researched by the macro-cell MIMO channel model proposed by Ali Abdi. The research finds that BER for mobile station will increase with the angel diffusion decrease for AOA of incident radio, but the performance of base station is hardly affected by the beamwidth of incident radio. The results provide scientific basis for evaluating the performance of mobile station with the nonuniform distribution of AOA of incident radio, moreover, it could supply some references to the research of MIMO system under the macro-cell environments without rich-scattering and space-time correlative channels.