Pilot Contamination for Wideband Massive MMO: Number of cells Vs Multipath

TL;DR

This paper introduces a joint channel estimation and beamforming method for wideband massive MIMO systems that leverages multipath characteristics to mitigate pilot contamination, enabling multiple cells to share resources effectively.

Contribution

It presents a novel approach that exploits multipath delay spread to determine the maximum number of cells that can simultaneously estimate channels and perform beamforming without pilot contamination.

Findings

Up to 18 cells can operate simultaneously in a typical LTE environment.

The proposed method outperforms existing techniques in simulations.

The approach is linear, simple, and validated analytically and numerically.

Abstract

This paper proposes a novel joint channel estimation and beamforming approach for multicell wideband massive multiple input multiple output (MIMO) systems. With the proposed channel estimation and beamforming approach, we determine the number of cells $N_c$ that can utilize the same time and frequency resource while mitigating the effect of pilot contamination. The proposed approach exploits the multipath characteristics of wideband channels. Specifically, when the channel has a maximum of $L$ multipath taps, \textcolor{red}{it is shown that $N_c\leq L$ cells can estimate the channels of their user equipments (UEs) and perform beamforming while mitigating the effect of pilot contamination.} In a typical long term evolution (LTE) channel environment having delay spread $T_d=4.69\mu$ second and channel bandwidth $B=2.5$MHz, we have found that $L=18$ cells can use this band. In practice, $T_d$ is constant for a particular environment and carrier frequency, and hence $L$ increases as the bandwidth increases. All the analytical expressions have been validated, and the superiority of the proposed design over the existing ones is demonstrated using extensive numerical simulations both for correlated and uncorrelated channels. The proposed channel estimation and beamforming design is linear and simple to implement.