Underlay Spectrum Sharing Techniques With In-Band Full-Duplex Systems Using Improper Gaussian Signaling

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. To tackle this problem, we use the so-called improper Gaussian signaling. Particularly, we assume a system with a SU pair working in a half-duplex mode that uses improper Gaussian signaling while the FD PU pair implements the regular proper Gaussian signaling. First, we derive a closed form expression and an upper bound for the SU and PU outage probabilities, respectively. Second, 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 (CSI). Moreover, we provide the conditions to reap merits from employing improper Gaussian signaling at the SU. Third, we design the SU signal parameters based on perfect knowledge of its direct link instantaneous CSI and investigate all benefits that can be achieved at both the SU and PU. Finally, we provide some numerical results that demonstrate the advantages of using improper Gaussian signaling to access the spectrum of the FD PU.

Overlay Spectrum Sharing using Improper Gaussian Signaling

“…On the other hand, the secondary network uses IGS scheme to reduce its interference on the primary network. The results in [10]- [16] demonstrated benefits for adopting IGS as long as the PT link is not fully loaded especially when the secondary network exists near the receivers of the primary network. The merits can be reaped using global knowledge of instantaneous CSI [10], [11], [14] or even using average CSI [12], [13], [15], [16].…”

“…On the other hand, IGS scheme achieves superior rate improvements for systems not supported with interference cancellation techniques and deal with interference as noise. IGS scheme is employed in different interference scenarios such as two user single input single output interference channel [6], k-user multiple input single output interference channel [7], full duplex relaying [8], alternate relaying [9] and underlay cognitive radio [10]- [16].…”

“…IGS scheme has proved its superiority in enhancing the underlay cognitive radio performance through reducing the interference effect on the primary user [10]- [16]. In underlay cognitive radio system, there is no access on designing the licensed network signals or systems.…”

“…Furthermore, a common and reasonable assumption of the primary network is the operation as if there no other user shares the spectrum. Thus, the primary network is assumed to employ PGS scheme since it accesses its dedicated licensed channels [10]- [16]. On the other hand, the secondary network uses IGS scheme to reduce its interference on the primary network.…”

“…Moreover, IGS grants performance improvement for secondary networks when they share the spectrum with half-duplex transmissions [10], [12] or full-duplex transmissions [14]- [16]. As for overlay cognitive radio, to the best of authors' knowledge, IGS scheme has not yet been implemented.…”