Spectrum-Aware Dynamic Channel Assignment in Cognitive Radio Networks Yasir Saleem, Adnan Bashir, Ejaz Ahmed, Junaid Qadir, Adeel Baig School of Electrical Engineering and Computer Science National University of Sciences and Technology Islamabad, Pakistan {08bitysaleem, 08beeadnanb, ejaz.ahmed1, junaid.qadir, adeel.baig}@seecs.edu.pk Abstract—During the past few years, cognitive radio networks (CRNs) have emerged as a solution for the problems created due to fixed spectrum allocation such as inefficient usage of licensed spectrum. CRNs aim at solving this problem by exploiting the spectrum holes (the spectrum not being used by primary radio nodes at a particular time) and allocating the spectrum dynamically. In this paper, we address the problem of dynamic channel assignment for cognitive radio users in multi-radio multi- channel cognitive radio networks (MRMC-CRNs). We propose an efficient spectrum-aware dynamic channel assignment (SA-DCA) strategy for such networks. SA-DCA utilizes available channels and assigns them to multiple radio interfaces of cognitive radio nodes based on primary radio unoccupancy, minimum interference to primary radio nodes, maximum connectivity and minimum interference between cognitive radio nodes. We perform simulations in NS-2 and compare the performance of SA-DCA with two related strategies. Simulation results show that SA-DCA assigns channels efficiently and results in significantly reduced interference to primary radio nodes and increased packet delivery ratio in MRMC-CRNs. I. I NTRODUCTION In recent days, most wireless networks follow fixed spec- trum allocation policy which results in only 15% - 85% spectrum usage with high variance in time [1]. Due to the inefficiency of fixed spectrum access schemes, cognitive radio technique has been proposed for utilizing the spectrum op- portunistically. Unlicensed devices can use licensed spectrum as approved by Federal Communications Commission (FCC). In cognitive radio networks, there are two types of users, one is Primary Radio (PR) user, which operates in its licensed spectrum band and the second is Cognitive Radio (CR) user, which operates either in unlicensed spectrum band or in the licensed spectrum band of PR nodes while ensuring that it does not interfere with PR nodes [1]. If CR node is using licensed spectrum band of PR node and PR node arrives at that time, then CR node has to vacate this spectrum by selecting another spectrum from the spectrum pool [2]. This is known as spectrum handoff [1]. The diversity in number of channels for the usage of CR nodes is one of the known issues of wireless networks, thus while selecting spectrum from the spectrum pool, CR nodes must ensure connectivity by selecting those spectrum bands which are also available to its neighborhood and should not result in disconnected network. There are many factors that make CRNs dynamic including PR activity, diversity in number of available channels and interference due to spatial re- use of a channel within interference range of other transmitting nodes. Due to these dynamic factors, channel assignment in CRNs becomes complex. For channel assignment, mainly two types of methodologies can be adopted, one is centralized and the other is distributed. In centralized channel assignment, there is a central entity generally known as spectrum administrator which is respon- sible for gathering the information about free spectrum bands in the network and assigning them to CR nodes. However this approach is not feasible for dynamic multi-hop networks because an attack on spectrum administrator such as Denial of Service (DoS) attack [8] will jam the whole network and thus due to one controlling entity, the whole network will suffer. Therefore, a distributed approach is preferred over centralized one. In distributed channel assignment, there is no centralized entity, thus all nodes sense the free spectrum bands individually and share this information with their neighbors and then take decisions themselves about which spectrum bands to assign based on the sensed and shared information. In this paper, a distributed spectrum-aware dynamic channel assignment (SA-DCA) scheme for MRMC-CRNs is proposed. In this scheme CR nodes first check for PR activity on all channels and if there is no PR activity, they will calculate the channel quality for all channels which gives the value for maximum connectivity and minimum interference between CR nodes. Minimum interference between CR nodes is calculated by considering the channels assigned to other CR nodes. After calculating the channel quality, best channels will be assigned at multiple radio interfaces of CR nodes. Our goal is to minimize the interference to PR nodes, maximize the connectivity and to minimize the interference between CR nodes due to channel reuse. Our work is different from previous work because it caters dynamic conditions along with handling multiple radio nodes. The organization of the paper is as follows. Section II describes the related work. Section III describes the network model and assumptions. In Section IV, we describe spectrum- aware dynamic channel assignment (SA-DCA), our proposed solution. Performance analysis is presented in Section V and we conclude the paper in Section VI. 978-1-4673-4451-7/12/$31.00 ©2012 IEEE