Error rates of Nyquist-shaped QPSK in cochannel interference and fading

The use of linear modulation schemes such as quaternary phase shift keying (QPSK) in wireless communication systems has recently received much attention. This is mainly because linear modulation schemes are more spectrally efficient than constant envelope modulation schemes such as Gaussian minimum shift keying modulation (GMSK). The increasing demand for spectrum resources has also motivated interest in using coherent demodulation. We analyze the performance of QPSK in the presence of cochannel interference. Three approaches that can be used for analysing the cochannel interference are investigated. These are a precise method based on the average probability of error, a sum of sinusoids (sinusoidal) model, and a Gaussian interference model. The system performance is assessed in terms of the average bit error rate. The examples consider the outdoor microcellular fading environment. In this environment, the fading experienced by the interfering signals may be represented by a Rayleigh fading model while the fading experienced by the desired signal may be represented by a Ricean or a Nakagami fading model