Frequency-domain on-off accumulative transmission over frequency-selective fading channels

In this paper, we propose a new cross-layer technique that utilizes frequency-domain on-off accumulative transmission (OOAT) in the physical layer to achieve collision-tolerance in the media access control (MAC) layer. The frequency-domain OOAT is developed for wideband systems operating in frequency-selective fading channels. The available spectrum is divided into a large number of orthogonal non-overlapping sub-channels. To achieve collision tolerance, each symbol is transmitted over a set of randomly chosen sub-channels to reduce the probability of collision. Spreading the signal over the frequency-domain also enables frequency diversity, and further improves system performance. Performance of the proposed scheme is analyzed and a performance bound, matched filter bound, is derived. Simulation results show that the proposed scheme can support more active users simultaneously than sub-channels, and it achieves a higher spectral efficiency compared to conventional MAC schemes.