A Case for Line-Of-Sight Blockage Detection as a Primitive in Millimeter-Wave Networks

Millimeter-wave is the core technology for current wireless standards to enable multi-Gbps throughput and ultra-low latency connectivity. However, designing reliable mmWave networks that provide high quality of service is challenging because of the extreme sparsity of the mmWave channel and frequent unavailability of the Line-Of-Sight (LOS) path. To this end, we propose a primitive to detect the state of the LOS path across the entire mmWave frequency band in afrequency-agnostic manner. The primitive leverages two key observations: under open LOS, the path is correlated between any two mmWave frequencies; and under the blockage, such correlation disappears. Such a primitive allows a mmWave picocell to achieve the latency of handover below sub-millisecond consistently, change its PHY, MAC, and Network layer policies at run-time adaptively, and ensure the link doesn't suffer from outage proactively. We have validated this primitive on three distinct mmWave frequency bands: 24 GHz; 77 GHz; and 122 GHz, and in the future, we propose to extend the validation to several mmWave frequencies, up to 300 GHz. We also discuss the system-level challenges pertaining to design and implementation of such a primitive for a practical, flexible mmWave networking stack.