# Eliminating Interference in LOS Massive Multi-User MIMO with a Few Transceivers

## TL;DR

This paper demonstrates that in LOS massive MIMO systems, a small number of transceivers can effectively eliminate interference for multiple users by using antenna selection, achieving near-optimal performance with simple linear processing.

## Contribution

It proves that a single extra transceiver chain beyond the number of users suffices for interference elimination, showing near-optimal performance of antenna selection in LOS massive MIMO.

## Key findings

- A single additional transceiver chain reduces interference to desired levels.
- Simple linear receivers achieve near-optimal rates with the proposed antenna selection.
- No complex coding is needed in the downlink, and joint decoding offers minimal gains in uplink.

## Abstract

Wireless cellular communication networks are bandwidth and interference limited. An important means to overcome these resource limitations is the use of multiple antennas. Base stations equipped with a very large (massive) number of antennas have been the focus of recent research. A bottleneck in such systems is the limited number of transmit/receive chains. In this work, a line-of-sight (LOS) channel model is considered. It is shown that for a given number of interferers, it suffices that the number of transmit/receive chains exceeds the number of desired users by one, assuming a sufficiently large antenna array. From a theoretical point of view, this is the first result proving the near-optimal performance of antenna selection, even when the total number of signals (desired and interfering) is larger than the number of receive chains. Specifically, a single additional chain suffices to reduce the interference to any desired level. We prove that using the proposed selection, a simple linear receiver/transmitter for the uplink/downlink provides near-optimal rates. In particular, in the downlink direction, there is no need for complicated dirty paper coding; each user can use an optimal code for a single user interference-free channel. In the uplink direction, there is almost no gain in implementing joint decoding. The proposed approach is also a significant improvement both from system and computational perspectives. Simulation results demonstrating the performance of the proposed method are provided.