The Research On Capacity Of Massive-MIMO Wireless Communication Systems

With the rapid development of mobile communication technology, wireless transmission rate and com-munication service experience is facing higher and higher demands. In order to cope with the future explosive mobile data traffic, the fifth generation mobile communication technology emerged. Large-scale MIMO, as one of the core technologies in 5G MIMO, has been widely concerned and researched, cause it can signifi-cantly improve transmission rate and spectrum efficiency. However, pilot reusing between cells will cause pilot contamination, which has become the bottleneck of large-scale MIMO system. The spectrum efficien-cy of MIMO system has been a focus in academic areas, besides in large-scale MIMO system. One of the research topic in this paper is the large-scale MIMO's spectrum efficiency considering pilot contamination and the correlation between antennas. Another topic is the diversity-multiplexing tradeoff considering pilot contamination.The paper firstly introduces the research background, the development history of MIMO technology and topic related current research status.Wireless communication environment is the basis of studying communication problems. With full con-sideration of large-scale MIMO's channel characteristics, the system model of this paper is introduced. Un-der this system model, the system's capacity with perfect CSI and single-cell diversity-multiplexing tradeoff problem with perfect CSI are studied. Perfect CSI and single cell means there's no pilot contamination and inter-cell interference.Pilot contamination has become the bottle-neck in large-scale MIMO system. The pilot reusing strategy in this paper are as follows:a sequence of orthogonal pilot signals are used in one cell, and all the cell use the same pilot sequences. Thus will cause pilot contamination. Then MMSE estimator is used to obtain CSI and the equivalent system model is obtained. With this equivalent system model, the capacity of MRC receiver are obtained. Then the paper discusses the capacity's asymptotic and lower bound of correlated and uncorrelated channel system. Then, the theoretical results are verified by simulation. The simulation results show that the derivation results no matter the asymptotic result and the lower-bound are quite accurate.Finally, the diversity-multiplexing tradeoff problem is studied. The same pilot reusing strategy is used to cause pilot contamination. Then capacity with MMSE receiver is derived of the target user. Based on this, the diversity-multiplexing tradeoff is analyzed under high SNR and finite SNR respectively. Finally, the simulation analysis are presented. The conclusion shows that due to pilot contamination and inter-cell interference, the diversity-multiplexing tradeoff gain is zero in high SNR regime but not zero in finite SNR regime.