Performance Analysis of Dynamic Spectrum Access Networks under Primary User Emulation Attacks Z. Jin, S. Anand and K. P. Subbalakshmi Department of Electrical and Computer Engineering Stevens Institute of Technology, New Jersey, USA Email: {zjin, asanthan, ksubbala}@stevens.edu Abstract— Primary user emulation attack (PUEA) is a denial of service (DoS) attack unique to dynamic spectrum access (DSA) networks. While there have been studies in the literature to detect and mitigate PUEA, the impact of PUEA on the call blocking and call dropping probabilities of users in secondary networks has not been studied. We present the first analysis to study the impact of PUEA on the secondary users in terms of call blocking and call dropping. We propose a three dimensional continuous time Markov chain (3D-CTMC) to model the channel occupancy in DSA networks. We use the 3D-CTMC to determine the call blocking and call dropping probabilities for secondary users. We validate our analysis with simulations. Results indicate that while PUEA does not affect the call blocking probability, it can increase the call dropping probability of secondary users by more than one order of magnitude. We also evaluate the call dropping performance of some of our previously proposed protocols to mitigate PUEA. We show that our protocols can improve the call dropping performance by about 40% for high traffic loads of malicious users and can provide almost the same performance as that of a system with no PUEA, when the malicious user traffic is low. Keywords – Dynamic spectrum access (DSA), primary user emulation attack (PUEA), call blocking, call dropping, Markov model I. I NTRODUCTION Dynamic spectrum access (DSA) [1] is viewed as a solution to address the current under-utilization of spectrum resources in wireless systems. Unlicensed “secondary users” are allowed to access the spectrum bands when they are not in use by licensed “primary users”. However, the spectrum bands must be made available to the primary users whenever they wish to access them. Therefore, secondary users must keep sensing the spectrum and evacuate the spectrum upon sensing primary transmission. This evacuation policy could lead to denial of service (DoS) attacks (unique to DSA networks), called primary user emulation attacks (PUEA). In such attacks, a set of malicious secondary users transmit spurious signals that have similar characteristics to those from primary transmitters. This leads good secondary users who follow the spectrum evacuation etiquette, to unnecessarily evacuate the spectrum band and make an attempt to use an alternative spectrum band for communication. The good secondary user leaves the system if it cannot occupy any other spectrum band. There are several studies in literature that deal with de- tection and mitigation of PUEA [2]-[9]. Some of these in- clude isolation of malicious users using directional anten- nas for secondary users 1 [2] or underlying sensors [3]. In [5], we proposed a Wald’s sequential probability ratio test (WSPRT) to enable each individual node to detect PUEA. We then proposed a Neyman-Pearson composite hypothesis test (NPCHT) [6] and compared the performance of the NPCHT and the WSPRT in terms of their ability to mitigate PUEA. In [7], we proposed a centralized protocol in which secondary users convey their individual PUEA detection decisions to a centralized controller. The centralized controller, in turn, uses the decisions obtained from all the secondary users to come up with a decision on behalf of the entire network, that helps the secondary users further mitigate PUEA. We then developed a distributed protocol [8], in which the secondary users exchange their individual spectrum decisions on PUEA with their one-hop neighbors. The decisions made by all one- hop neighbors were shown to enable the secondary users to better mitigate PUEA. Thomas et al [9] presented a Bayesian game framework to mitigate PUEA. Additional description and references on PUEA in DSA networks can be found in [4]-[9]. The mechanisms described thus far, however, do not evaluate the effects of PUEA on the performance of secondary network as a whole. The secondary users affected by PUEA will have to find an alternate spectrum band for transmission, or leave the system when alternate channels are not available. Thus, PUEA may result in increased blocking of new calls for secondary users or increased dropping of ongoing secondary calls. It therefore becomes essential to study the effects of PUEA on the call blocking and call dropping performances of secondary users in a DSA network. In this paper, we present the first analysis of the effect of PUEA on the call blocking and call dropping probabilities for secondary users in a DSA network. We pro- pose a three dimensional continuous time Markov chain (3D- CTMC) to model the channel occupancy in a DSA network. Each state in the Markov chain is a three tuple (s, m, p), which denotes the number of channels in the system that are occupied by secondary, malicious and primary users, respectively. We solve for the steady state stationary probability of the 3D- CTMC and use the solution to determine the call blocking and call dropping probabilities for the secondary users in the presence of PUEA. We validate our analysis by comparison 1 Henceforth, throughout this paper, “secondary user” indicates “good secondary user” unless explicitly specified otherwise. 978-1-4244-5638-3/10/$26.00 ©2010 IEEE This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE Globecom 2010 proceedings.