Full-Duplex Communication in Cognitive Radio Networks: A Survey

Wireless networks with their ubiquitous applications have become an indispensable part of our daily lives. Wireless networks demand more and more spectral resources to support the ever increasing numbers of users. According to network engineers, the current spectrum crunch can be addressed with the introduction of cognitive radio networks (CRNs). In half-duplex (HD) CRNs, the secondary users (SUs) can either only sense the spectrum or transmit at a given time. This HD operation limits the SU throughput, because the SUs cannot transmit during the spectrum sensing. However, with the advances in self-interference suppression (SIS), full-duplex (FD) CRNs allow for simultaneous spectrum sensing and transmission on a given channel. This FD operation increases the throughput and reduces collisions as compared with HD-CRNs. In this paper, we present a comprehensive survey of FD-CRN communications. We cover the supporting network architectures and the various transmit and receive antenna designs. We classify the different SIS approaches in FD-CRNs. We survey the spectrum sensing approaches and security requirements for FD-CRNs. We also survey major advances in FD medium access control protocols as well as open issues, challenges, and future research directions to support the FD operation in CRNs.

I. Introduction

The advances in information and communications technologies over the past decade have enabled seamless connectivity among several entities and electronic devices. In order to keep up with this progress and enhance the consumer experience, service providers have started to introduce next-generation data-intensive applications. At the same time, a massive increase in the global subscription of wireless services, such as broadband, cellular, television, and navigation, is under way. Overall, there is an ever-increasing demand for uninterrupted ubiquitous connectivity and higher data rates. It has been predicted that by 2019, the global wireless data traffic will see a tenfold increase compared to the traffic in 2014 [1]. This exceptional growth has motivated the development of next generation wireless technologies, such as femtocells [2], [3], exploitation of millimeter wave spectrum [4], multiple-input multiple-output (MIMO) systems [5], [6], and dynamic spectrum sharing using cognitive radio (CR) [7]–[9].