Directional channel modelling for millimetre wave communications in urban areas

Integrating Kirchhoff approximation (KA) and a ray‐tracing (RT) algorithm, this study develops a new directional three‐dimensional channel model for urban millimetre‐wave small cells. The authors study the path loss, spatial correlation, coverage distance, and coherence length for line‐of‐sight (LOS), obstructed LOS, and non‐LOS (NLOS) scenarios in urban areas. Exploiting physical optics and geometric optics solutions, closed‐form expressions for spatial correlation are derived. It is deduced that LOS availability, frequency, and surface roughness scale highly impact spatial diversity. In addition, using antenna arrays of moderate gain at both sides of the link, even under NLOS conditions, a typical urban cell size of 200 m is achievable.