This dissertation investigates the information-theoretic aspects of communication over fading channels with particular emphasis on Rician channels with no receiver or transmitter fading side information. This work thus leads to enhanced understanding of the potential and limitations of such channels, and the proposal of novel efficient communication schemes.;First, transmission of information over a discrete-time memoryless Rician fading channel is considered where neither the receiver nor the transmitter knows the fading coefficients. The structure of the capacity-achieving input signals is investigated when the input is constrained to have limited peakedness by imposing either a fourth moment or a peak constraint. When the input is subject to second and fourth moment limitations, it is shown that the capacity-achieving input amplitude distribution is discrete with a finite number of mass points in the low-power regime. A similar discrete structure for the optimal amplitude is proven over the entire SNR range when there is only a peak power constraint. This result is extended to Rician block-fading channels by showing that the optimal input can be written as the product of a real nonnegative random variable that has a discrete distribution with a finite number of mass points, and an independent isotropically distributed unit random vector. The Rician fading model with phase-noise, where there is phase uncertainty in the specular component, is also analyzed. For this model it is shown that, with only an average power constraint, the capacity-achieving input amplitude is discrete with a finite number of levels. For the classical average power limited Rician fading channel, it is proven that the optimal input amplitude distribution has bounded support.;The spectral-efficiency/bit-energy tradeoff in the low-power regime is examined when the input has limited peakedness. It is shown that if a fourth moment input constraint is imposed or the input peak-to-average power ratio is limited, then in contrast to the behavior observed in average power limited channels, the minimum bit energy is not always achieved at zero spectral efficiency. The low-power performance is also characterized when there is a fixed peak limit that does not vary with the average power. A new signaling scheme that overlays phase-shift keying on on-off keying is proposed and shown to be optimally efficient in the low-power regime.;Transmission of information over wideband fading channels using M-ary orthogonal on/off FSK (OOFSK) signaling, in which M-ary FSK signaling is overlaid on on/off keying, is considered. (Abstract shortened by UMI.).
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