On-Off Frequency-Shift-Keying for Wideband Fading Channels

TL;DR

This paper explores the use of On-Off Frequency-Shift-Keying (OOFSK) in wideband fading channels, analyzing capacity, power efficiency, and the benefits of phase tracking and modulation under various power constraints.

Contribution

It provides new capacity expressions for OOFSK with different receiver side information and examines power efficiency under peak and average power limitations, including phase modulation benefits.

Findings

Power efficiency is very low at low SNR with PAR limitations.

Power efficiency improves with smaller SNR under peak power constraints.

Phase tracking and modulation enhance capacity in fading channels.

Abstract

M-ary On-Off Frequency-Shift-Keying (OOFSK) is a digital modulation format in which M-ary FSK signaling is overlaid on On/Off keying. This paper investigates the potential of this modulation format in the context of wideband fading channels. First it is assumed that the receiver uses energy detection for the reception of OOFSK signals. Capacity expressions are obtained for the cases in which 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 a 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. Also studied are the capacity improvements that accrue when the receiver can track phase shifts in the channel or if the received signal has a specular component. To take advantage of those features, the phase of the modulation is also allowed to carry information.