Flexible Pilot Contamination Mitigation with Doppler PSD Alignment

TL;DR

This paper introduces a novel method for mitigating pilot contamination in massive MIMO systems by aligning the Doppler power spectrum densities of users, enabling orthogonal pilot multiplexing even in time-varying channels.

Contribution

It proposes a PSD alignment technique to enable orthogonal pilot transmission in Doppler fading environments, improving channel estimation in massive MIMO systems.

Findings

PSD alignment allows simultaneous pilot transmission without interference.

Analytical formulas quantify the channel estimation MSE improvement.

Simulations confirm effectiveness of the proposed decontamination method.

Abstract

Pilot contamination in the uplink (UL) can severely degrade the channel estimation quality at the base station (BS) in a massive multi-input multi-output (MIMO) system. Thus, it is critical to explore all possible avenues to enable more orthogonal resources for the users to transmit non-interfering UL pilots. In conventional designs, pilot orthogonality typically assumes constant channel gains over time, which limits the amount of orthogonal resources in the case of time-selective channels. To circumvent this constraint, in this paper, we show how to enable orthogonal multiplexing of pilots in the case of Doppler fading by aligning the power spectrum densities (PSD) of different users. From the derived PSD aligning rules, we can see multiple users can be sounded simultaneously without creating/suffering pilot contamination even when these users are experiencing time-varying channels. Furthermore, we provide analytical formulas characterizing the channel estimation mean square error (MSE) performance. Computer simulations further confirm us the PSD alignment can serve as one important decontamination mechanism for the UL pilots in massive MIMO.