An analysis of FQPSK and SOQPSK in frequency selective multipath

The performance of FQPSK and SOQPSK-TG in frequency selective multipath is analyzed in this paper. It is shown that these waveforms, called the advanced range telemetry (ARTM) tier-1 waveforms, behave the same in the presence of multipath interference. In the presence a strong specular multipath reflection with relative amplitude |Γ| > 0.5, the phase averaged bit error rate exhibits a floor at approximately 10^-2. When the amplitude |Γ| is less than 0.5, the loss in performance relative to the AWGN case is approximately (1 - |Γ|)^-4√(|Γ|). 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. Given the bandwidth of the ARTM tier-1 waveforms is half that of PCM/FM, the time-varying multipath interference effects the waveform half the time thus improving the overall link availability.