Researches On Channel Model, Space-Time Codes And Key Techniques For Multiple-Input Multiple-Output Wireless Communications

Wireless communications is undergoing a key period.The major challenge in today's wireless communication is how to serve the explosively increasing demand of multimedia service within the limited bandwidth. Among those emerging technologies, multiple-input multiple-output (MIMO) communication architecture has showed its infinite potential to improve spectral efficiency dramatically. By deploying multiple antenna element at both transmitter and receiver, MIMO has been regarded as an inevitable promising approach to exploit maximum spatial resources among many emerging technologies.We firstly surveyed background and elements of MIMO techniques. Comparison is given between other techniques and MIMO wireless communications to demonstrate necessity and inevitability of research on MIMO. A variety of concentrated problems and fundamental questions are introduced.Research on MIMO channel model is beginning and principals' problem of the thesis. By focusing on the problem of modeling non-isotropic scattering around mobile user in MIMO channel model, we present a novel frequency-selective MIMO fading channel with von Mises probability density function, which is used to characterize non-uniform angle-of-arrival caused by non-isotropic scattering. Then we analyze partial cross correlation function of proposed model and proved the model theoretically. We also present a low-complexity general channel simulation model for both transmitter diversity case and downlink beamforming case. Numerical results are given to investigate statistical fading characteristics and its impact on capacity. With that, we reveal the essence of phenomenon of capacity degradation caused by non-uniform angle-of-arrivals.In Part II of this paper, we investigates the pairwise error probability of space- time-frequency block codes in MIMO orthogonal frequency-division multiplexing (OFDM) systems, which is now the focus of MIMO wireless communication research. Analysis shows that power delay profile of multipath channel seriously affects the upper bound of pairwise error probability of STC in OFDM systems. With simulation in ITU-R M.1225 vehicular channel A and vehicular channel B, we compare the performance of space time frequency code with different transmit antennas and verified the effect of power delay profile and fading rate on the performance of space-time-frequency block code. Finally some criterions of designing the space-time-frequency block code for fast fading channels are presented.In the complicated time-varying wireless propagation environment, it is very difficult to estimate channel information accurately, especially in multiple input multiple output wireless communication. So Part III presents a method of differential space-time-frequency code in quadrature-amplitude modulation (QAM) modulation, based on some existing research of differential STC. At the same time, this part analyzes the BER performance of unitary differential STC in OFDM system in various channel environments, and presents the design criterion and performance of differential STC in OFDM systems.In part IV, we propose a novel spatial spectrum estimation algorithm based on a special multiple-beam antenna in radio fading channel. Numerical simulation is performed under both single-user case and multiple-user case. Research results demonstrated robustness of the proposed algorithm. We also carry out quantitative and qualitative comparison with other methods. The low-complexity of the algorithm is verified and account for the feature of subspace smoothing within beamspace.Finally, we put forward some ideas about the future research on the key techniques of MIMO wireless communications.