Differentially amplitude and phase encoded QAM on Rayleigh fading channels

Quadrature amplitude modulation (QAM) is an effective technique to achieve a high bit-rate transmission without increasing the transmission bandwidth. Due to the limitation on available spectrum, research in digital mobile data communications have considered employing QAM as the fundamental modulation format. This paper evaluates the bit error probability (BEP) of differentially amplitude encoded (DAPE) QAM over nonselective Rayleigh fading channels with switched diversity reception. The QAM transmitter employs a multiamplitude star constellation and modulates the information onto the amplitude ratio and phase difference between the transmitted signals in two consecutive signalling intervals. At the receiver, the amplitude ratio and phase difference between the received signals in two successive signalling intervals, corresponding to the diversity channel with the largest amplitude in the previous interval, are compared with preset thresholds for data demodulation. An exact closed form expression of BEP is given for a general system format and for channels with fading fluctuations. The results show how the DAPE QAM can be optimized and how fading fluctuations and the order of the switched diversity affect its performance.