at UHF, power law with change of slope at breakpoint
at mm wavelengths, breakpoint is outside range of cell and so free-space is assumed.
NLOS, over rooftop paths - diffraction considered dominant mechanism
multi-screen diffraction model if rooftop heights are approximately the same, otherwise method of Rec. P.526 (in which highest edge must be identified)
NLOS, street canyon paths - model given for diffraction and reflection at corners of street crossings.
All methods use the geometric parameters shown in previous slides.
Multipath also contributes as a propagation mechanism; if delays are too large, BER can be unacceptably large due to intersymbol interference.
