No abstract

Reliable detection of primary users (PUs) is an important task for cognitive radio (CR) systems. Cooperation among a few spectrum sensors has been shown to offer significant gain in the performance of the CR spectrum-sensing system by countering the shadow-fading effects. We consider a parallel fusion network in which the sensors send their sensing information to an access point which makes the final decision regarding presence or absence of the PU signal. It has been shown in the literature that the presence of malicious users sending false sensing data can severely degrade the performance of such a cooperative sensing system. In this paper, we investigate schemes to identify the malicious users based on outlier detection techniques for a cooperative sensing system employing energy detection at the sensors. We take into consideration constraints imposed by the CR scenario such as the lack of information about the primary signal propagation environment and the small size of the sensing data samples. Considering partial information of the PU activity, we propose a novel method to identify the malicious users. We further propose malicious user detection schemes that take into consideration the spatial information of the CR sensors. The performance of the proposed schemes are studied using simulations.

No abstract

We present a randomized distributed algorithm that in radio networks with collision detection broadcasts a single message in O(D + log 6 n) rounds, with high probability. This time complexity is most interesting because of its optimal additive dependence on the network diameter D. It improves over the currently best known O(D log n D + log 2 n) algorithms, due to Czumaj and Rytter (Broadcasting algorithms in radio networks with unknown topology. In: Proceedings of the symposium on foundations of computer science, pp [492][493][494][495][496][497][498][499][500][501] 2003), and Kowalski and Pelc (Broadcasting in undirected ad hoc radio networks. In: Proceedings of the ACM SIGACT-SIGOPS symposium on principles of distributed computing, pp [73][74][75][76][77][78][79][80][81][82] 2003). These algorithms where designed for the model without collision detection and are optimal in that model. However, as explicitly stated by Peleg in his 2007 survey on broadcast in radio networks, it had remained an open question whether the bound can be improved with collision detection. We also study distributed algorithms for broadcasting k messages from a single source to all nodes. This problem is a natural and important generalization of the single-message broadcast problem, but is in fact considerably more challenging and less understood. We show the following results: If the network topology is known to all nodes, then a k-message broadcast can be performed in O(D + k log n + log 2 n) rounds, with high probability. If the topology is not known, but collision detection is available, then a k-message broadcast can be performed in O(D + k log n + log 6 n) rounds, with high probability. The first bound is optimal and the second is optimal modulo the additive O(log 6 n) term.

No abstract