Optimization Of The Massive MIMO System

Massive MIMO systems have became wireless telecommunication key technologies through Increasing the antenna quantity can improve the system capacity. For a practical system, it is typical that multiple antennas have to be installed in a limited space area. Increasing the antenna quantity can degrade the system performance due to mutual coupling and spatial correlation, when the antenna space is fixed. There are relatively few reports on the spatial correlation and mutual coupling. This paper mainly investigates several optimization problems in the massive MIMO systems due to the spatial correlation and mutual coupling. The main innovation points are as follows.1. The optimal antenna layouts of the massive MIMO systems are investigated. When the number of the antenna elements is large, the mutual coupling and spatial correlation are complicated due to a variety of the shapes of the antenna layouts. Simulated annealing (SA) algorithm is used to search for the optimal antenna layouts for three antenna space constraint cases, which are sphere of fixed size, circle of fixed size and line of fixed length. The results show that the antenna elements of optimal antenna layouts for these three antenna space constraint cases are distributed on the surface of the sphere, on the edge of the circle and along the line, which are close to the uniform distributed antenna layouts for the three antenna space constraint cases.2. The optimization problems of the antenna element number are investigated and the optimal antenna number for some typical cases are simulated and showed. The optimization of the antenna element number in point-to-point MIMO system, multiuser MIMO uplink, multiuser MIMO downlink, is investigated in this paper. The results show that in the constraint of antenna space, when the antenna number is small,increasing antenna number will lead to the performance improvement.When the antenna number increases to an optimal value, increasing antenna number will aggravate the mutual coupling and spatial correlation and degrade the system performance. The optimal antenna number for some typical cases are simulated and showed. The optimal antenna number for some typical cases are simulated and showed.3. The antenna selection problems of massive IMIMO systems are investigated and the group switch-and-examine combining (GSEC)scheme is proposed. When mutual coupling exists, the selected channel matrix is not a subset of the full-MIMO channel matrix because input impedances of all the other antennas will change when any antenna is active or shut down. The channel examine overhead for conventional antenna selection system is too large to degrade the performance heavily.To solve this problem, the proposed group switch-and-examine combining (GSEC) scheme is proposed. The antennas of the massive MIMO system are divided into several groups; the antenna layout of every group can decrease the mutual coupling and spatial correlation. The groups work in the way of switch-and-examine combining system. The proposed group switch-and-examine combining (GSEC) scheme has a better capacity and lower operational complexity than the conventional antenna selection scheme in the presence of mutual coupling.