# MilliSonic: Pushing the Limits of Acoustic Motion Tracking

## TL;DR

MilliSonic introduces a novel acoustic motion tracking system that achieves sub-millimeter accuracy with a single beacon and small microphone array, enabling high-precision VR/AR applications and concurrent multi-device tracking.

## Contribution

A new localization algorithm that achieves sub-millimeter accuracy in multipath environments using only a small microphone array and a single beacon.

## Key findings

- Achieves 0.7mm median 1D accuracy and 2.6mm 3D accuracy for smartphones.
- Enables concurrent tracking of up to four smartphones without accuracy loss.
- Outperforms state-of-the-art systems by 5x in accuracy.

## Abstract

Recent years have seen interest in device tracking and localization using acoustic signals. State-of-the-art acoustic motion tracking systems however do not achieve millimeter accuracy and require large separation between microphones and speakers, and as a result, do not meet the requirements for many VR/AR applications. Further, tracking multiple concurrent acoustic transmissions from VR devices today requires sacrificing accuracy or frame rate. We present MilliSonic, a novel system that pushes the limits of acoustic based motion tracking. Our core contribution is a novel localization algorithm that can provably achieve sub-millimeter 1D tracking accuracy in the presence of multipath, while using only a single beacon with a small 4-microphone array.Further, MilliSonic enables concurrent tracking of up to four smartphones without reducing frame rate or accuracy. Our evaluation shows that MilliSonic achieves 0.7mm median 1D accuracy and a 2.6mm median 3D accuracy for smartphones, which is 5x more accurate than state-of-the-art systems. MilliSonic enables two previously infeasible interaction applications: a) 3D tracking of VR headsets using the smartphone as a beacon and b) fine-grained 3D tracking for the Google Cardboard VR system using a small microphone array.