Uplink interference reduction in Large Scale Antenna Systems

Abstract

A Large Scale Antenna System (LSAS) entails a large number (tens or hundreds) of base station antennas serving a much smaller number of terminals, with large gains in spectral-efficiency and energy efficiency compared with conventional MIMO technology. As the number of antennas grows, the performance of an LSAS gets limited by pilot contamination, arising due to the use of same pilot sequences for channel estimation in neighboring cells. Recently A. Ashikhmin and T. Marzetta showed that using proper precoding/postcoding (PCP) and limited cooperation between cells, it is possible to eliminate pilot contamination entirely and get infinite throughput as M → ∞. In this paper, we focus on the uplink of an LSAS and show that even in the case of a finite number of base station antennas, PCP yields very significant performance gain in terms of data transmission rates. In particular, one of our algorithms gives a 140 fold increase in the 5% outage data transmission rates! We also show that the performance can be improved further by optimizing the transmission powers of the users, and present a simple decentralized algorithm in order to solve it.