Sharing the Licensed Spectrum of Full-Duplex Systems using Improper Gaussian Signaling

TL;DR

This paper explores spectrum sharing in in-band full-duplex primary systems using improper Gaussian signaling, demonstrating its potential to improve secondary user performance while maintaining primary user quality-of-service.

Contribution

It introduces a novel application of improper Gaussian signaling in spectrum sharing with full-duplex primary users, deriving outage probability bounds and optimizing secondary user parameters.

Findings

Improper Gaussian signaling reduces secondary user outage probability.

The derived bounds for primary user outage are tight.

Numerical results show the advantage of improper signaling in spectrum sharing.

Abstract

Sharing the spectrum with in-band full-duplex (FD) primary users (PU) is a challenging and interesting problem in the underlay cognitive radio (CR) systems. The self-interference introduced at the primary network may dramatically impede the secondary user (SU) opportunity to access the spectrum. In this work, we attempt to tackle this problem through the use of the so-called improper Gaussian signaling. Such a signaling technique has demonstrated its superiority in improving the overall performance in interference limited networks. Particularly, we assume a system with a SU pair working in half-duplex mode that uses improper Gaussian signaling while the FD PU pair implements the regular proper Gaussian signaling techniques. First, we derive a closed form expression for the SU outage probability and an upper bound for the PU outage probability. Then, we optimize the SU signal parameters to minimize its outage probability while maintaining the required PU quality-of-service based on the average channel state information. Finally, we provide some numerical results that validate the tightness of the PU outage probability bound and demonstrate the advantage of employing the improper Gaussian signaling to the SU in order to access the spectrum of the FD PU.