Performance of π/4-QDPSK in a Rayleigh/lognormal/delay spread/AWGN-cochannel interference environment

The performance of π/4-QDPSK system is presented in a fast Rayleigh fading/slow lognormal shadowing/delay spread/AWGN channel in the presence of cochannel interference. The performance of the system is measured in terms of symbol error rate (SER). The system was simulated using two-ray model for normalized value of Doppler shift (0.001), degree of shadowing (σ=6), and several values of time delays and carrier-to-interference ratios. It is seen that the system performance is limited by the presence of cochannel interference. When cochannel interference is negligible, the system performance is dominated by the ratio between the main path signal and the delayed path signal, and the differential time delay between them. It is observed that the shadowing degrades the system performance at low CNR but not at high CNR (i.e., CNR>50 dB). The irreducible symbol error rate (ISER) does not vary significantly as the differential time delay between the two path varies