PERFORMANCE EVALUATION OF 16APSK AND SOQPSK-TG IN THE PRESENCE OF POLARIZATION COMBINING IN AERONAUTICAL TELEMETRY

16-ary amplitude phase shift keying (16APSK) is a candidate modulation for aeronautical mobile telemetry because it has better spectral efficiency and lower sensitivity to adjacent channel interference compared SOQPSK-TG. This paper compares the post-equalizer bit error rate performance of 16APSK and SOQPSK-TG in the aeronautical mobile telemetry multipath channel. The linear polarizations produced by the orthogonal dipoles in the receive antenna feed are combined in two different ways: using a 90◦ hybrid coupler to produce RHCP or LHCP and maximum likelihood combining. The first combining method is the common practice at test ranges and the second combining method is new. The results show the following. First, 16APSK with MMSE equalization outperforms SOQPSK-TG with CMA equalization for the RHCP and LHCP channels. Second, 16APSK with MMSE equalization outperforms SOQPSK-TG with CMA equalization for the maximum likelihood channels at moderate to high signal-to-noise ratios. 

For lower signal-to-noise ratios, SOQPSK-TG shows the best performance. Third, 16APSK with MMSE equalization operating the maximum likelihood combined channel outperforms SOQPSK-TG with CMA equalization operating on the RHCP or LHCP channels.