Precoding for MIMO Uplink Transmission Over EM-Lens-Based Correlated Channels

In multiple-input/multiple-output (MIMO) systems, advanced equalization or precoding schemes are not only known for providing interference mitigation, but they also have been proven to exploit the MIMO channel's diversity. However, in the case of massive MIMO, the computational complexity of such schemes make them unfeasible. To solve this problem for the uplink scenario, an electromagnetic (EM) lens may be employed at the receiver. It effectively focuses the received power onto a smaller number of antennas. Hence, the application of techniques known from classical (non-massive) MIMO systems is enabled in MIMO systems with a large number of antennas. However, building such EM-lens-enabled systems comes with a drawback. Due to physical limitations, it may be impossible to space the antenna elements in a way to provide spatially decoupled channels at the receiver, which results in a performance loss. In this paper, this issue is addressed by first extending the EM-lens-enabled system to include multiple antennas at the transmitter. Following this, different equalization strategies for this scenario are assessed. The performance of the proposed strategies is evaluated by means of numerical simulations. To this end, different levels of spatial channel correlations are considered for both uncoded and coded transmission.