The Operation of Dual Polarized QAM Systems in the Presence of Depolarization Crosstalk and Differential Fading

The performance of dual-polarized -QAM systems is studied. By assuming coherence between the crosstalk and the desired signal, results are obtained for systems up to the modulation level of 64 QAM in each channel. Both balanced systems, with equal modulation levels in each channel, and unbalanced systems, with different modulation levels in each channel, are considered. Graphs are presented which show possible design tradeoffs to improve performance and suggest methods of system optimization. Each system is found to have an optimum value of relative transmitter power in the two channels. Analyses include the application of empirically based channel models giving relations between depolarization crosstalk, coplanar path attenuation, and differential fading levels.