Impact of Microwave Depolarization During Multipath Fading on Digital Radio Performance

Experimental data describing the statistics of microwave depolarization during multipath fading have been obtained from a propagation experiment conducted near Atlanta, Georgia. The experiment included 6- and 11-GHz reception on a 26.4-mile path, and 11-GHz reception on a 15.9-mile path. A theoretical model, suggested by T. O. Mottl, indicates that the interference occasioned by depolarization for a given copolarized signal level is Rice-Nakagami distributed. The theoretically calculated distribution agrees well with the data. The cross-polarization interference consists of a signal-level-dependent component as well as a residual that is independent of the in-line signal level. The residual is Rayleigh distributed with an rms value about 40 dB below the nonfaded in-line signal level, and limits the multipath fade margin of a cochannel dual-polarized digital radio to approximately 30 dB. Calculated multipath outage probabilities for cochannel, dual-polarized, 11-GHz, quaternary-coherent-phase-shift-keyed digital radios with and without space-diversity protection are presented.