The capacity and power efficiency of OOFSK signaling over wideband fading channels

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. It is assumed that the receiver uses energy detection for the reception of OOFSK signals. Capacity expressions are obtained when the receiver has perfect and imperfect fading side information. Power efficiency is investigated when the transmitter is subject to a peak-to-average power ratio (PAR) limitation or a peak power limitation. It is shown that under PAR limitation, it is extremely power inefficient to operate in the very low SNR regime. On the other hand, if there is only a peak power limitation, it is demonstrated that power efficiency improves as one operates with smaller SNR and vanishing duty factor.