Multiband Spectrum Access: Great Promises for Future Cognitive Radio Networks

Cognitive radio has been widely considered as one of the prominent solutions to tackle the spectrum scarcity. While the majority of existing research has focused on single-band cognitive radio, multiband cognitive radio represents great promises towards implementing efficient cognitive networks compared to single-based networks. Multiband cognitive radio networks (MB-CRNs) are expected to significantly enhance the network's throughput and provide better channel maintenance by reducing handoff frequency. Nevertheless, the wideband front-end and the multiband spectrum access impose a number of challenges yet to overcome. This paper provides an in-depth analysis on the recent advancements in multiband spectrum sensing techniques, their limitations, and possible future directions to improve them. We study cooperative communications for MB-CRNs to tackle a fundamental limit on diversity and sampling. We also investigate several limits and tradeoffs of various design parameters for MB-CRNs. In addition, we explore the key MB-CRNs performance metrics that differ from the conventional metrics used for single-band based networks.Comment: 22 pages, 13 figures; published in the Proceedings of the IEEE Journal, Special Issue on Future Radio Spectrum Access, March 201

Full-Duplex Cognitive Radio: A New Design Paradigm for Enhancing Spectrum Usage

With the rapid growth of demand for ever-increasing data rate, spectrum resources have become more and more scarce. As a promising technique to increase the efficiency of the spectrum utilization, cognitive radio (CR) technique has the great potential to meet such a requirement by allowing un-licensed users to coexist in licensed bands. In conventional CR systems, the spectrum sensing is performed at the beginning of each time slot before the data transmission. This unfortunately results in two major problems: 1) transmission time reduction due to sensing, and 2) sensing accuracy impairment due to data transmission. To tackle these problems, in this paper we present a new design paradigm for future CR by exploring the full-duplex (FD) techniques to achieve the simultaneous spectrum sensing and data transmission. With FD radios equipped at the secondary users (SUs), SUs can simultaneously sense and access the vacant spectrum, and thus, significantly improve sensing performances and meanwhile increase data transmission efficiency. The aim of this article is to transform the promising conceptual framework into the practical wireless network design by addressing a diverse set of challenges such as protocol design and theoretical analysis. Several application scenarios with FD enabled CR are elaborated, and key open research directions and novel algorithms in these systems are discussed

On the technical challenges of cognitive radio in TV white spaces

Cognitive Radio (CR) has been considered as a powerful technique to increase the spectral efficiency by enabling unlicensed users to access unused spectrum opportunistically. Cognitive Radio has two important paradigms to efficiently utilise spectrum which are spectrum sensing and spectrum database. In spectrum sensing unlicensed users sense the spectrum and to detect the availability of under-utilised channels before transmission and access the channels when idle or tolerable interference to primary user (PU) is guaranteed. For the later case i.e. database paradigm of CR unlicensed users can acquire the availability of channels through spectrum database before accessing the channels. In this work, spectrum sensing part of the CR has been focused. In cognitive radio SU should yield maximum throughput and guarantee maximum PU protection. Sensing-throughput tradeoff has been studied for both single cognitive radio and cooperative cognitive radio with different fusion strategies. In cooperative cognitive radio OR and Optimal fusion strategies yielded maxim throughput than the AND strategy. Thereafter, the problem of throughput has been compared for both half-duplex cognitive radio and full-duplex cognitive radio for a given target probability of detection. It was found that there is an optimal sensing time at which a CR yields maximum throughput for a given target probability of detection. Much of the initial discussion is based on half-duplex communication cognitive radio (HDC-CR) using HDC-SS scheme. It is of special interest to derive the PD, PFA mathematical expressions for full-duplex communication cognitive radio (FDC-CR) which uses full-duplex spectrum sensing scheme to do sensing and transmission at the same time. It was found that the FDC-CR yields higher throughput for SU than the HDC-CR since FDC-CR performs sensing and data transmission at the same time therefore it gets increased data transmission time for secondary user

Listen-and-Talk: Protocol Design and Analysis for Full-duplex Cognitive Radio Networks

In traditional cognitive radio networks, secondary users (SUs) typically access the spectrum of primary users (PUs) by a two-stage "listen-before-talk" (LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before transmitting in the second. However, there exist two major problems: 1) transmission time reduction due to sensing, and 2) sensing accuracy impairment due to data transmission. In this paper, we propose a "listen-and-talk" (LAT) protocol with the help of full-duplex (FD) technique that allows SUs to simultaneously sense and access the vacant spectrum. Spectrum utilization performance is carefully analyzed, with the closed-form spectrum waste ratio and collision ratio with the PU provided. Also, regarding the secondary throughput, we report the existence of a tradeoff between the secondary transmit power and throughput. Based on the power-throughput tradeoff, we derive the analytical local optimal transmit power for SUs to achieve both high throughput and satisfying sensing accuracy. Numerical results are given to verify the proposed protocol and the theoretical results