# Cache-Aided Massive MIMO: Linear Precoding Design and Performance Analysis

## TL;DR

This paper introduces a joint caching and massive MIMO transmission scheme that leverages cached files for interference cancellation, leading to significant performance improvements in downlink cellular systems.

## Contribution

It proposes a novel cache-aided massive MIMO scheme that combines caching with advanced precoding, exploiting side information for interference cancellation and performance gains.

## Key findings

- Achieves higher ergodic rates compared to conventional massive MIMO.
- Provides closed-form lower bounds for ergodic achievable rates with MRT and ZF.
- Demonstrates significant rate improvements when user count approaches antenna count.

## Abstract

In this paper, we propose a novel joint caching and massive multiple-input multiple-output (MIMO) transmission scheme, referred to as cache-aided massive MIMO, for advanced downlink cellular communications. In addition to reaping the conventional advantages of caching and massive MIMO, the proposed scheme also exploits the side information provided by cached files for interference cancellation at the receivers. This interference cancellation increases the degrees of freedom available for precoding design. In addition, the power freed by the cache-enabled offloading can benefit the transmissions to the users requesting non-cached files. The resulting performance gains are not possible if caching and massive MIMO are designed separately. We analyze the performance of cache-aided massive MIMO for cache-dependent maximum-ratio transmission (MRT), zero-forcing (ZF) precoding, and regularized zero-forcing (RZF) precoding. Lower bounds on the ergodic achievable rates are derived in closed form for MRT and ZF precoding. The ergodic achievable rate of RZF precoding is obtained for the case when the numbers of transmit antennas and users are large but their ratio is fixed. Compared to conventional massive MIMO, the proposed cache-aided massive MIMO scheme achieves a significantly higher ergodic rate especially when the number of users approaches the number of transmit antennas.