NMBEnet: Efficient Near-field mmWave Beam Training for Multiuser OFDM Systems Using Sub-6 GHz Pilots

TL;DR

This paper introduces NMBEnet, a deep learning-based method that uses sub-6 GHz uplink pilots to efficiently perform near-field mmWave beam training in multiuser OFDM systems, reducing pilot overhead and improving accuracy.

Contribution

The paper proposes a novel neural network architecture, NMBEnet, that leverages correlations in multiuser OFDM signals to enhance near-field mmWave beam training accuracy using sub-6 GHz pilots.

Findings

NMBEnet reduces pilot overhead in near-field mmWave beam training.

The neural network improves beam training precision by exploiting signal correlations.

The method is effective in high user density scenarios.

Abstract

Combining millimetre-wave (mmWave) communications with an extremely large-scale antenna array (ELAA) presents a promising avenue for meeting the spectral efficiency demands of the future sixth generation (6G) mobile communications. However, beam training for mmWave ELAA systems is challenged by excessive pilot overheads as well as insufficient accuracy, as the huge near-field codebook has to be accounted for. In this paper, inspired by the similarity between far-field sub-6 GHz channels and near-field mmWave channels, we propose to leverage sub-6 GHz uplink pilot signals to directly estimate the optimal near-field mmWave codeword, which aims to reduce pilot overhead and bypass the channel estimation. Moreover, we adopt deep learning to perform this dual mapping function, i.e., sub-6 GHz to mmWave, far-field to near-field, and a novel neural network structure called NMBEnet is designed to enhance the precision of beam training. Specifically, when considering the orthogonal frequency division multiplexing (OFDM) communication scenarios with high user density, correlations arise both between signals from different users and between signals from different subcarriers. Accordingly, the convolutional neural network (CNN) module and graph neural network (GNN) module included in the proposed NMBEnet can leverage these two correlations to further enhance the precision of beam training.