# Millimeter Wave Beam-Selection Using Out-of-Band Spatial Information

## TL;DR

This paper proposes leveraging sub-6 GHz spatial information to significantly reduce training overhead in millimeter wave beam selection, enhancing high-data-rate communication systems.

## Contribution

It introduces a novel out-of-band aided beam-selection method that uses sub-6 GHz spatial data to improve mmWave link establishment, reducing training overhead by 4 times.

## Key findings

- Out-of-band information reduces beam-selection training overhead by 4x.
- The method improves achievable data rates in mmWave communication.
- Structured precoder/combiner design tailors training to out-of-band data.

## Abstract

Millimeter wave (mmWave) communication is one feasible solution for high data-rate applications like vehicular-to-everything communication and next generation cellular communication. Configuring mmWave links, which can be done through channel estimation or beam-selection, however, is a source of significant overhead. In this paper, we propose to use spatial information extracted at sub-6 GHz to help establish the mmWave link. First, we review the prior work on frequency dependent channel behavior and outline a simulation strategy to generate multi-band frequency dependent channels. Second, assuming: (i) narrowband channels and a fully digital architecture at sub-6 GHz; and (ii) wideband frequency selective channels, OFDM signaling, and an analog architecture at mmWave, we outline strategies to incorporate sub-6 GHz spatial information in mmWave compressed beam selection. We formulate compressed beam-selection as a weighted sparse signal recovery problem, and obtain the weighting information from sub-6 GHz channels. In addition, we outline a structured precoder/combiner design to tailor the training to out-of-band information. We also extend the proposed out-of-band aided compressed beam-selection approach to leverage information from all active OFDM subcarriers. The simulation results for achievable rate show that out-of-band aided beam-selection can reduce the training overhead of in-band only beam-selection by 4x.