On the Spectral Efficiency of Noncoherent Doubly Selective Channels

This paper considers block transmissions over single-antenna doubly selective channels that obey a complexexponential basis expansion model. We consider the noncoherent case, when the channel fading coefficients are not known at both 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 transmissions (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 novel spectrally efficient PAT schemes.