Improving Performance of Millimeter Wave Beamforming using Inaudible Acoustic Side-Channel

Abstract

Millimeter wave networks promise to offer ultra-fast internet download speed, but the access points or base stations must always align the beams precisely to client devices. Efficient beam alignment for mobile users therefore is considered one of the most challenging problems facing millimeter wave networks. Existing approaches that use in-band beam alignment suffers from long alignment delays and low communication performance, especially when large number of mobile clients are connect to the access point. In this research, we explore the benefits of out-of-band inaudible sound assisted beam alignment to reduce the outage probability, thereby improving the performance gain of antenna in millimeter wave beamforming.

In particular, this thesis makes three fundamental contributions. First, we analytically study the beam alignment performance of 802.11ad in the presence of multiple devices while rotating with an applicable angular velocity. We come up with a probabilistic model for required number of beacon intervals to complete antenna training in multi-users scenario for 802.11ad. Second, we propose to take advantage of inaudible sound as a side channel to detect the direction of client and assist beam alignment in millimeter wave access points. Using a combination of experimental and simulation analysis of the inaudible sound spectrum available in typical mobile phones, we demonstrate that the use of 50 Hz and 50 ms sound chirps with an array of two microphones provide efficient and reliable detection of direction. Moreover, we design a filtering approach using FDM channel access to correctly assign the sound source corresponding to the estimated angle on the receiver side. Third, we conduct a comprehensive simulation in order to evaluate the performance of the proposed sound assisted beamforming on the gain of antenna. \deleted{Initially, the proposed analytical model is validated by the developed simulation platform.} We show that our proposed algorithm achieves a significant 11 dB average gain of antenna for AP with 64 antenna sectors serving 10 users moving with walking speed of two different mobility model compared with IEEE 802.11 ad. This improvement is the result of using the proposed contention-free out-of-band sound channel to remove the existing contention-based channel access for beam alignment.

We believe that our findings in this thesis shed new light on the fundamental benefits of out-of-band beamforming in crowded millimeter wave network.