  Path gain and effective directional gain in azimuth in urban canyons from
actual rooftop base station sites are characterized based on a massive data set
of 3000 links on 12 streets in two cities, with over 21 million individual
continuous wave power measurements at 28 GHz using vertically polarized
antennas. Large street-to-street path gain variation is found, with median
street path gain varying over 30 dB at similar distances. Coverage in the
street directly illuminated by a roof edge antenna is found to suffer an
average excess loss of 11 dB relative to free space at 200 m, with empirical
slope-intercept fit model representing the data with 7.1 dB standard deviation.
Offsetting the base antenna 5 m away from roof edge, as is common in macro
cellular deployments, introduces an additional average loss of 15 dB at 100 m,
but this additional loss reduces with distance. Around the corner loss is well
modeled by a diffraction formula with an empirically obtained diffraction
coefficient. Effective azimuthal gain degradation due to scatter is limited to
2 dB for 90% of data, supporting effective use of high gain antennas in urban
street canyons.
