Noncoherent detection of π/4-QPSK systems in a CCI-AWGN combined interference environment

The performance of π/4-QPSK modems in a cochannel interference (CCI) and additive white Gaussian noise (AWGN) environment is studied. Three differential detection models are described and modified to improve the BER (bit error rate) performance of the detector: (1) baseband differential detection, (2) IF (intermediate frequency) band differential detection, and (3) FM-discrimination detection. Computer simulation results show that, if optimal filter separation is used, the three differential detection schemes can achieve optimal performance for differential detection. The simulation results also show that, for a stationary environment without Rayleigh fading at 15-dB signal-to-interference ratio (CIR), the BER is only 1.3-dB degraded at P _e=10^-2 compared to an AWGN-only environment. If CIR decreases to 9 dB, however, the eye-diagram closes and an error floor of 10^-3 occurs even without noise. The impact of random FM on differential detection is also studied