Sensing-Throughput Tradeoff for Cognitive Radio in TV White Spaces

Cognitive Radio (CR) dynamically finds the spectrum opportunity i.e. spectrum hole in space-time-frequency and code to do its adaptive transmission without harming the incumbent or the Primary User (PU). TV white spaces (TVWS) are the unused or underutiliised bands in the UHF and VHF part of the band which according to Federal Communication Commission (FCC) can be exploited if the secondary user (SU) with CR capabilities can adequately accommodate the transmission without introducing the harmful interference to incumbent or Primary Users (PU). TV band offers excellent building penetration and less propagation losses when compared to ISM bands of 2.4GHz and 5GHz. The focus of this article is to study cooperative sensing-throughout trade-off for SU with CR capabilities in TVWS. It is shown that with M cognitive users in cooperation we can get increased throughput with increase in sensing time for a fixed probability of false alarm and target probability of detection.

I. Introduction

Cognitive Radio (CR) has emerged as one of the promising solution to deal with the problem of spectrum scarcity. More specifically it addresses the inefficient utilisation of the exclusive and static allocation of spectrum. Moreover recent example is the inefficient utilisation of the VHF/UHF TV band which give rise to notion of TV white space. TVWS are the underulitilised bands in VHF/UHF band ranging from 54–698 MHz in US and 470-790MHz in Europe[1]. Apart from TV users this band is also used by variety of program making and special event (PMSE) users such as wireless microphone whose operating bandwidth is 200 KHz which is much smaller than 6 MHz TV band signal. Due to favourable propagation characteristics at this band it's becoming increasingly common to develop low-cost and flexible wireless communication systems in this band. There has been recent surge in wireless standards that has been proposed for TVWS, for example WRAN IEEE 802.22, IEEE 802.11af and IEEE 802.15.4m etc. Few of the fundamental requirements of CR are the implementation of efficient sensing algorithm, detection and sharing of spectrum, maximum PU protection and increased SU throughput [2]. Therefore, in this paper we have revisited cooperative spectrum sensing and throughput tradeoff for SU from TV band perspective. It has been shown analytically and with the help of simulation results that we can get increased throughput for a given sensing time when there are cognitive users in cooperation. Fig. 1.

Cognitive radio network scenario