Downlink Precoding for FBMC-based Massive MIMO with Imperfect Channel Reciprocity

TL;DR

This paper introduces a practical downlink precoding method for FBMC-based massive MIMO systems that compensates for imperfect channel reciprocity and CSI errors, improving performance over traditional OFDM benchmarks.

Contribution

A novel two-stage precoding approach for FBMC massive MIMO that accounts for and mitigates imperfect channel reciprocity and CSI inaccuracies.

Findings

Effective compensation for reciprocity calibration errors.

Significant performance gains over OFDM-based systems.

Robustness to practical channel estimation imperfections.

Abstract

In this paper, a practical precoding method for the downlink of filter bank multicarrier-based (FBMC-based) massive multiple-input multiple-output (MIMO) is developed. The proposed method includes a two-stage precoder consisting of a fractionally spaced prefilter (FSP) per subcarrier for flattening/equalizing the channel across the subcarrier band, followed by a conventional precoder whose goal is to concentrate the signals of different users at their spatial locations. This way, each user receives only the intended information. In this paper, we take note that channel reciprocity may not hold perfectly in practical scenarios due to the mismatch of radio chains in uplink and downlink. Additionally, channel state information (CSI) at the base station may not be perfectly known. This, together with imperfect channel reciprocity can lead to detrimental effects on the downlink precoder performance. We theoretically analyze the performance of the proposed precoder in the presence of imperfect CSI and channel reciprocity calibration errors. This leads to an effective method for compensating these effects. Finally, we numerically evaluate the performance of the proposed precoder. Our results show that the proposed precoder leads to an excellent performance when benchmarked against OFDM.