Theoretical error performances of communication systems with doubly selective (time-varying and frequency-selective) fadings and fractionally spaced (oversampled) receivers are analyzed. Closed-form error probability expressions of MPSK, MASK and MQAM systems are derived as tight lower bounds of the symbol error probabilities. The effects of receiver oversampling, Doppler spread and fading power delay profile are quantified in the error probability expressions. Simulation results show that the new analytical results can accurately predict the error performances of MLSE and MAP equalizers in a wide range of SNR. Moreover, it is discovered that significant performance gain can be achieved by fractionally spaced receivers over symbol spaced receivers for systems experiencing fast time-varying fading, whereas the effects of Doppler spread are overlooked by most previous works.
['Jingxian Wu', 'Chengshan Xiao']
On the error performance of linearly modulated systems with doubly selective Rayleigh fading channels