The Research On Capacity Of Massive-MIMO Wireless Communication Systems

Massive MIMO is a promising research field with high potential in the new generation of wireless com-munication technologies as it can offer great improvement in spectrum efficiency and energy efficiency of the system under the condition of limited frequency resources. In this thesis, we study the uplink capacity of multi cell multi-user MIMO systems.Firstly, we review the research background of massive MIMO. The advantages, achievements and prob-lems to be solved of different research branches of massive MIMO systems are introduced. In order to study the capacity of massive MIMO system, we establish the multi cell multi-user MIMO cellular system model and the channel model is build with fully consideration of the characteristics of wireless channels. Then we obtain the lower bound of the capacity for MMSE receivers with perfect CSI under this system model and give analysis on the system capacity while the number of antennas grows to infinite.As we know that pilot contamination is an unsolved problem of massive MIMO systems, system capacity with imperfect CSI is further investigated. We get the CSI by channel estimation in uplink, then build the equivalent model of the system and get the lower bound of the sum rate for MMSE receivers with pilot contamination. We establish an important relationship between the MIMO MMSE achievable sum rate and the ergodic MIMO mutual information with optimal receivers, by which three closed-form approximations of the lower bound are obtained with existing results on the ergodic mutual information for optimal receivers. We also get the upper bound of the capacity for MMSE receivers. The lower and upper bounds are also discussed in massive MIMO scenario when the number of antennas grows to infinite. Then all these results are analysed by simulation.After that, we build the system model of block fading channels, and further study the system performance while doing joint processing of pilots and data. Since the general mutual information expression is intractable, we rely on the lower bound of the spectral efficiency and discuss the value of joint processing on contrast with separate processing of pilots and data through simulation.