Channel Performance Metrics and Evaluation for XR Head-Mounted Displays with mmWave Arrays

TL;DR

This paper introduces six metrics to evaluate mmWave channel performance in XR HMDs, demonstrating that multiple arrays or distributed infrastructure significantly improve stability and capacity during HMD rotation.

Contribution

The paper develops and applies six novel channel performance metrics specifically for mmWave XR HMDs, analyzing their impact through real-world data and providing design recommendations.

Findings

Single array performance is poor due to narrow FoV.

Multiple arrays improve channel stability and capacity.

Distributed AP infrastructure offers an alternative solution.

Abstract

Millimeter-wave (mmWave) technology holds the potential to revolutionize head-mounted displays (HMDs) by enabling high-speed wireless communication with nearby processing nodes, where complex video rendering can take place. However, the sparse angular profile of mmWave channels, coupled with the narrow field of view (FoV) of patch-antenna arrays and frequent HMD rotation, can lead to poor performance. We introduce six channel performance metrics to evaluate the performance of an HMD equipped with mmWave arrays. We analyze the metrics using analytical models, discuss their impact for the application, and apply them to 28 GHz channel sounding data, collected in a conference room using eight HMD patch-antenna arrays, offset by 45 degrees from each other in azimuth. Our findings confirm that a single array performs poorly due to the narrow FoV, and featuring multiple arrays along the HMD's azimuth is required. Namely, the broader FoV stabilizes channel gain during HMD rotation, lessens the attenuation caused by line of sight (LoS) obstruction, and increases the channel's spatial multiplexing capability. In light of our findings, we conclude that it is imperative to either equip the HMD with multiple arrays or, as an alternative approach, incorporate macroscopic diversity by leveraging distributed access point (AP) infrastructure.