# Uplink Interference Reduction in Large Scale Antenna Systems

## TL;DR

This paper demonstrates that Large Scale Fading Decoding (LSFD) significantly enhances uplink performance in massive MIMO systems, even with finite antennas, by reducing pilot contamination and optimizing power control.

## Contribution

It introduces a decentralized LSFD algorithm requiring limited cooperation, achieving over 140-fold increase in outage data rate and further performance improvements through power optimization.

## Key findings

- Over 140-fold increase in 5% outage data rate with LSFD
- Decentralized LSFD requires only neighboring cell cooperation
- Performance improves with user power control optimization

## Abstract

A massive MIMO system entails a large number (tens or hundreds) of base station antennas serving a much smaller number of terminals. These systems demonstrate large gains in spectral and energy efficiency compared with conventional MIMO technology. As the number of antennas grows, the performance of a massive MIMO system gets limited by the interference caused by pilot contamination. Earlier A. Ashikhmin and T. Marzetta proposed (under the name of Pilot Contamination Precoding) Large Scale Fading Precoding (LSFP) and Decoding (LSFD) based on limited cooperation between base stations. They showed that Zero-Forcing LSFP and LSFD eliminate pilot contamination entirely and lead to an infinite throughput as the number of antennas grows. In this paper, we focus on the uplink and show that even in the case of a finite number of base station antennas, LSFD yields a very large performance gain. In particular, one of our algorithms gives a more than 140 fold increase in the 5% outage data transmission rate! We show that the performance can be improved further by optimizing the transmission powers of the users. Finally, we present decentralized LSFD that requires limited cooperation only between neighboring cells.