Pilot Decontamination via PDP Alignment

TL;DR

This paper proposes a PDP alignment method to orthogonalize uplink pilots within cells and reduce inter-cell pilot contamination in massive MIMO systems, improving channel estimation accuracy.

Contribution

It introduces a novel PDP alignment scheme for intra-cell orthogonalization and inter-cell pilot contamination mitigation in massive MIMO OFDM systems.

Findings

PDP alignment enables more users to be sounded in the same OFDM symbol.

Aligning PDPs reduces pilot contamination by exploiting AoA differences.

Simulation results show PDP alignment outperforms traditional methods.

Abstract

In this paper, we look into the issue of intra-cell uplink (UL) pilot orthogonalization and schemes for mitigating the inter-cell pilot contamination with a realistic massive multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system model. First, we show how to align the power-delay profiles (PDP) of different users served by one BS so that the pilots sent within one common OFDM symbol are orthogonal. From the derived aligning rule, we see much more users can be sounded in the same OFDM symbol as their channels are sparse in time. Second, in the case of massive MIMO, we show how PDP alignment can help to alleviate the pilot contamination due to inter-cell interference. We demonstrate that, by utilizing the fact that different paths in time are associated with different angles of arrival (AoA), the pilot contamination can be significantly reduced through aligning the PDPs of the users served by different BSs appropriately. Computer simulations further convince us PDP aligning can serve as the new baseline design philosophy for the UL pilots in massive MIMO.