  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.
