Published in IET Communications Received on 28th November 2008 Revised on 10th November 2009 doi: 10.1049/iet-com.2009.0430 ISSN 1751-8628 Throughput analysis of non-persistent carrier sense multiple access combined with time division multiple access and its implication for cognitive radio H. Li D. Grace P.D. Mitchell Department of Electronics, The University of York, Heslington, York, YO10 5DD, UK E-mail: hl527@york.ac.uk Abstract: This study analyses a cognitive radio scenario based on non-persistent carrier sense multiple access (CSMA) and time division multiple access (TDMA) systems sharing a single-channel wireless network. TDMA users are considered as primary users who can access the channel at any time, and non-persistent CSMA users are considered as secondary users who can share the channel when it is free. New expressions for the individual and aggregate throughput performance of this combined system have been developed, and the system performance is evaluated for a variety of proportions of non-persistent CSMA and TDMA traffic levels. Simulation and analytical results are presented and the ways in which both schemes suffer negative effects as a result of the interaction are shown, primarily caused by increased number of collisions arising from the other scheme. 1 Introduction Ever since radio communication was invented in the early 19th century, the application of wireless communication has been widely and rapidly exploiting the limited radio spectrum [1]. In order to secure the best use for society, users are currently assigned a license to use the specific radio spectrum band, and users without a license cannot use the band which has already been assigned to licensed users [2]. However, the Ofcom spectrum framework review in 2004 [3] showed that the demand for some spectrum bands have exceeded supply, but despite this there still remains a large portion of unused spectral bands within the entire spectrum. This implies that the shortage of spectrum comes from current spectrum policies that allow little sharing, since regulators grant licenses that only offer exclusive access to spectrum. This causes spectrum to sit idle even when licensed users are not active [4]. Cognitive radio (CR) [5] promises to increase spectrum usage by supporting secondary users to share licensed bands. However, to date few realistic demonstrators have been developed, and most of the development is being tackled by research projects, for example, a survey of NeXt generation CR wireless networks [6] explains the important functions of CR, such as spectrum management, spectrum mobility and spectrum sharing. A study of CR technology for Ofcom [7] discusses the issues surrounding the commercial exploitation of CR, such as the potential applications, the key benefits and challenges, the regulatory and security issues and the expected spectrum efficiency from CR. Considering the features of CR technology, spectrum sharing is one of the most important parts of CR technology, supporting user access to the licensed spectrum as a secondary user when and where channels are detected idle [8]. However, the interference between primary users and secondary users is a crucial issue that may have a negative effect for both types of users, thereby limiting the spectrum sharing. Therefore as a precursor to the development of more sophisticated multiple access schemes for CR [9, 10], the purpose of this paper is to develop a model describing the basic interaction characteristics of CR and primary user interaction modelled by two traditional schemes when operating in combination, sharing the same spectrum within the same geographical area. Specifically, these are contention-based non-persistent carrier sense multiple access (CSMA) used to describe the behaviour of a CR that has the 1356 IET Commun., 2010, Vol. 4, Iss. 11, pp. 1356–1363 & The Institution of Engineering and Technology 2010 doi: 10.1049/iet-com.2009.0430 www.ietdl.org