On the Spectral Efficiency of Noncoherent Doubly Selective Channels

This paper considers block transmissions over single-antenna doubly selective channels that obey a compl exexponential basis expansion model. We consider the noncohe rent case, when the channel fading coefficients are not known at bo th transmitter and receiver. We characterize the spectral efficiency of the channel when the inputs are chosen from continuous distributions. Then, we study several pilot aided transmisions (PAT) over the doubly selective channels. We establish that all the PAT schemes designed to minimize the channel estimation error variance are spectrally inefficient. We also design no vel spectrally efficient PAT schemes.