Aeronautical telemetry using offset QPSK in frequency selective multipath

The impact of frequency selective multipath fading on the bit error rate performance of ARTM Tier-1 waveforms (FQPSK and SOQPSK) is derived and analyzed. In the presence of a strong specular reflection with relative magnitude |Γ₁|, the ARTM Tier-1 waveforms suffer a loss in performance of (1 - |Γ₁|)^-4√|Γ₁| for |Γ₁| < 0.5 and a relatively high error floor at approximately 10^-2 for |Γ₁| ≥ 0.5. The ARTM Tier-1 waveforms possess twice the spectral efficiency of PCM/FM, but exhibit a greater loss and higher error floors than PCM/FM for the same multipath conditions and signal-to-noise ratio.