# Coverage Enhancement for NLOS mmWave Links Using Passive Reflectors

## TL;DR

This paper investigates how passive metallic reflectors can significantly improve 28 GHz mmWave signal coverage in NLOS scenarios, using measurements, models, and simulations to quantify gains and analyze environmental impacts.

## Contribution

It introduces an analytical model for NLOS received power with reflectors and demonstrates that appropriately sized reflectors can match LOS signal strength.

## Key findings

- Reflectors can restore NLOS signal power to LOS levels.
- The size of the reflector relative to incident waves is critical for effectiveness.
- Environmental features influence the reflector's impact on coverage.

## Abstract

The future 5G networks are expected to use millimeter wave (mmWave) frequency bands to take advantage of large unused spectrum. However, due to the high path loss at mmWave frequencies, coverage of mmWave signals can get severely reduced, especially for non-line-of-sight (NLOS) scenarios as mmWave signals are severely attenuated when going through obstructions. In this work, we study the use of passive metallic reflectors of different shapes/sizes to improve 28 GHz mmWave signal coverage for both indoor and outdoor NLOS scenarios. We quantify the gains that can be achieved in the link quality with metallic reflectors using measurements, analytical expressions, and ray tracing simulations. In particular, we provide an analytical model for the end-to-end received power in an NLOS scenario using reflectors of different shapes and sizes. For a given size of the flat metallic sheet reflector approaching to the size of incident plane waves, we show that the reflected received power for the NLOS link is same as line-of-sight (LOS)free space received power of the same link distance. Extensive results are provided to study impact of environmental features and reflector characteristics on NLOS link quality.