Opportunistic Ambient Backscatter Communication in RF-Powered Cognitive Radio Networks

In the present contribution, we propose a novel opportunistic ambient backscatter communication (ABC) framework for radio frequency (RF)-powered cognitive radio (CR) networks. This framework considers opportunistic spectrum sensing (SS) integrated with ABC and harvest-then-transmit (HTT) operation strategies. Novel analytic expressions are derived for the average throughput, the average energy consumption and the energy efficiency (EE) in the considered set up. These expressions are represented in closed-form and have a tractable algebraic representation which renders them convenient to handle both analytically and numerically. In addition, we formulate an optimization problem to maximize the EE of the CR system operating in mixed ABC-and HTT-modes, for a given set of constraints, including primary interference and imperfect SS constraints. Capitalizing on this, we determine the optimal set of parameters which in turn comprise the optimal detection threshold, the optimal degree of trade-off between the CR system operating in the ABC-and HTT-modes and the optimal data transmission time. Extensive results from respective computer simulations are also presented for corroborating the corresponding analytic results and to demonstrate the performance gain of the proposed model in terms of EE.

I. Introduction

The need for efficient utilization of spectrum resources has become a fundamental requirement in modern wireless networks due to the witnessed spectrum scarcity and the ever-increasing demand for higher data rate applications and Internet services. In this context, an interesting proposal has been the development of cognitive radio (CR) networks [2], which can adapt their transmission parameters according to the characteristics of the communication environment. Cognitive radios have been shown to be efficient in increasing spectrum utilization due to their inherent spectrum sensing (SS) capability [3]. In this regard, dynamic spectrum access (DSA), where the secondary users (SU) can opportunistically access the underutilized frequency bands, is the standard solution for the realization of DSA [4], which is envisioned to be an integral part of future communication systems [5]. In order to realize DSA, three strategies have been proposed, namely the underlay, the overlay and the interweave. In the underlay technique, the SUs coexist with a PU provided that the interference level at the PU remains below a certain threshold [6]. In the overlay paradigm, the SUs would be allowed to share the band with PU by exploiting the knowledge of its message and codebook in order to reduce interference. Finally, in the interweave technique, the SU can only access the licensed spectrum of the PU when it is idle [7].