# Early Warning of mmWave Signal Blockage and AoA Transition Using sub-6 GHz Observations

## TL;DR

This paper demonstrates that lower-frequency sub-6 GHz signals can serve as early indicators of mmWave signal blockage or recovery, enabling proactive mitigation in 5G networks through physics-based simulations.

## Contribution

It introduces a physics-based simulation approach showing sub-6 GHz signals lead mmWave signals in detecting blockages, enabling early warning systems without relying on specific topologies.

## Key findings

- Sub-6 GHz signals lead mmWave signals by several to tens of milliseconds.
- The approach works across various transition scenarios including LoS to NLoS.
- Prediction of AoA and strongest multipath component is feasible using sub-6 GHz observations.

## Abstract

The susceptibility of millimeter-wave (mmWave) signals to physical blockage and abrupt signal strength variations presents a challenge to reliable 5G communication. This work proposes and examines the feasibility of utilizing lower-frequency signals as early-warning indicators of mobile mmWave signal blockage or recovery. A physics-based channel simulation tool incorporating Fresnel diffraction and image sources is employed to demonstrate that sub-6 GHz signals "lead" mmWave signals in reaching a specific signal-strength threshold by several to tens of milliseconds at mobile speeds, suggesting early-warning systems are viable. This predictive approach stems from frequency-dependent properties of diffraction and does not assume a specific topology or mobile and obstacle speeds. Realistic simulations that include transitions from line of sight (LoS) to non-line of sight (NLoS) and reflection scenarios are employed to verify the proposed prediction capabilities. Moreover, prediction of the strongest multipath component and its angle of arrival (AoA) using sub-6 GHz observations is investigated.