# Communications and Radar Coexistence in the Massive MIMO Regime: Uplink Analysis

## TL;DR

This paper analyzes uplink massive MIMO systems coexisting with radar in the same frequency band, proposing models, receivers, and theoretical bounds to understand and mitigate radar clutter effects, demonstrating capacity restoration with many antennas.

## Contribution

It introduces a comprehensive system model for radar and massive MIMO coexistence, along with novel receiver strategies and theoretical bounds on spectral efficiency under clutter interference.

## Key findings

- Radar clutter effects diminish as antenna count increases.
- Single-user capacity is restored in large antenna regimes.
- Proposed receivers effectively mitigate clutter interference.

## Abstract

This paper considers the uplink of a massive MIMO communication system using 5G New Radio-compliant multiple access, which is to co-exist with a radar system using the same frequency band. A system model taking into account the reverberation (clutter) produced by the radar system onto the massive MIMO receiver is proposed. In this scenario, several receivers for uplink channel estimation and data detection are proposed, ranging from the simple channel-matched beamformer to the zero-forcing and linear minimum mean square error receivers for clutter disturbance rejection, under the two opposite situations of perfectly known ad completely unknown clutter covariance. A theoretical analysis is also given, deriving a lower bound on the achievable uplink spectral efficiency and the mutual information between the input Gaussian-encoded symbols and the observables available at the communication receiver of the cellular massive MIMO system: regarding the latter, in particular, we show that, in the large antenna number regime, the radar clutter effects at the base station is suppressed and single-user capacity is restored. Numerical results, illustrating the performance of the proposed detection schemes, confirm the findings of the theoretical analysis, and permit quantifying the system robustness to clutter effect for increasing number of antennas at the base station.