iTrack: Tracking Indicator LEDs on APs to Bootstrap mmWave Beam Acquisition and Steering.

We present iTrack, a system which steers mmWave beams at mobile devices by tracking the indicator LEDs on wireless APs to passively acquire direction estimates, and demonstrate that iTrack acquires and maintains beam alignment at the narrowest beamwidth level even in case of device mobility, without incurring any training overhead. Our implementation on custom dual-band hardware testbed shows that iTrack acquires direction estimates within 4.5 degrees of the ground truth and achieves beam steering accuracy of more than 97% while in tracking mode, without incurring any in-band training or feedback.