  Millimeter-wave communication with high throughput and high reliability is
poised to be a gamechanger for V2X and VR applications. However, mmWave links
are notorious for low reliability since they suffer from frequent outages due
to blockage and user mobility. Traditional mmWave systems are hardly reliable
for two reasons. First, they create a highly directional link that acts as a
single point of failure and cannot be sustained for high user mobility. Second,
they follow a `reactive' approach, which reacts after the link has already
suffered an outage. We build mmReliable, a reliable mmWave system that
implements smart analog beamforming and user tracking to handle environmental
vulnerabilities. It creates custom beam patterns with multiple lobes and
optimizes their angle, phase, and amplitude to maximize the signal strength at
the receiver. Such phase-coherent multi-beam patterns allow the signal to
travel along multiple paths and add up constructively at the receiver to
improve throughput. Of course, multi-beam links are resilient to occasional
blockages of few beams in multi-beam compared to a single-beam system. With
user mobility, mmReliable proactively tracks the motion in the background by
leveraging continuous channel estimates without affecting the data rates. We
implement mmReliable on a 28 GHz testbed with 400 MHz bandwidth and a 64
element phased-array supporting 5G NR waveforms. Rigorous indoor and outdoor
experiments demonstrate that mmReliable achieves close to 100% reliability
providing 1.5 times better throughput than traditional single-beam systems.
