On Polarization, Combining, and Equalization in Aeronautical Mobile Telemetry

In this article, we explore the relationship between an equalizer and a combiner operating on the available polarization states of a received signal in aeronautical mobile telemetry. The maximum likelihood combiner is derived and shown to be equivalent to summing the outputs of two filters matched to the channels in the horizontal and vertical polarization states. For historical reasons, current systems combine right-hand and left-hand circularly polarized antenna feed outputs using a maximum ratio combiner. To compare the two combining approaches, the aeronautical telemetry multipath channel is extended to include polarization state information. The channel extension is used in computer simulations. The simulations results for SOQPSK-TG with a constant modulus algorithm equalizer show that the postequalizer bit error rate for the two approaches is the same.