Evaluation of Massive MIMO Considering Real Propagation Characteristics in the 20-GHz Band

This paper presents multiple-input multiple-output (MIMO) measurements in the 20-GHz band, and evaluates the basic performance of massive MIMO systems when considering 100 elements at a base station (BS) and seven user equipment units. First, it is shown that zero forcing (ZF) is essential as a transmission scheme in massive MIMO systems, whereas the maximum-ratio combining method cannot reduce interference effectively in such systems. In addition, it is shown that analog-digital hybrid beamforming can be used to reduce the calculation complexity and improve hardware implementation. Next, we compared the Shannon capacity with the achievable bit rate (ABR), using ZF for seven-user MIMO transmissions with 100 elements at the BS. When the number of degrees of freedom in the array antenna is guaranteed, the ABR is almost the same as the Shannon capacity. Moreover, multiuser transmission is realized by linear decoding. Thus, decoding methods such as ZF are effective in massive MIMO systems.