Modeling and analysis of cooperative spectrum sensing is an important aspect in cognitive radio systems. In this paper, the problem of energy detection (ED) of an unknown signal over Nakagami-m fading is revisited. Specifically, an analytical expression for the local probability of detection is derived, while using the approach of ED at the individual secondary user (SU), a new fusion rule, based on the likelihood ratio test, is presented. The channels between the primary user to SUs and SUs to fusion center are considered to be independent Nakagami-m. The proposed fusion rule uses the channel statistics, instead of the instantaneous channel state information, and is based on the Neyman-Pearson criteria. Closed-form solutions for the system-level probability of detection and probability of false alarm are also derived. Furthermore, a closed-form expression for the optimal number of cooperative SUs, needed to minimize the total error rate, is presented. The usefulness of factor graph and sum-product-algorithm models for computing likelihoods, is also discussed to highlight its advantage, in terms of computational cost. The performance of the proposed schemes have been evaluated both by analysis and simulations. Results show that the proposed rules perform well over a wide range of the signal-to-noise ratio.
In a multi-hop mobile ad hoc network (MANET), mobile nodes communicate with each other forming a cooperative radio network. Security remains a major challenge for these networks due to their features of open medium, dynamically changing topologies, reliance on cooperative algorithms, absence of centralized monitoring points, and lack of any clear lines of defense. Most of the currently existing intrusion detection algorithms designed for these networks are insecure, inefficient, and have high rates of false positives. In this paper, a new approach has been proposed to bring out the complementary relationship between key distribution and intrusion detection for developing an intrusion detection protocol for ad hoc networks. The redundancy of routing information in ad-hoc networks is utilized to develop a highly reliable protocol that works even in presence of transient network partitioning and Byzantine failure of nodes. The proposed mechanism is fully cooperative, and thus it is more robust as the vulnerabilities of the election algorithms used for choosing the subset of nodes for cooperation are absent. Simulation results show the effectiveness of the protocol.
A normal factor graph (NFG) based approach for cooperative spectrum sensing in cognitive radio over time varying and frequency non-selective fading channels is presented in this paper. An NFG based representation of a distributed cognitive radio system is first presented and then a Sum-ProductAlgorithm (SPA) based analysis is developed for inference. The spectrum sensing problem is modelled as a distributed binary hypothesis testing problem. A Neyman-Pearson (NP) based likelihood ratio test statistic is derived for optimal sensing. As exact theoretical analysis of the system level probability of detection and probability of false alarm is very difficult, we provide an approximation which performs satisfactorily in the moderate to high signal-to-noise ratio (SNR) regime. The proposed NFG based spectrum sensing approach is computationally scalable to large networks and performs well under time varying channel conditions. Extensive simulation results are provided to validate our proposed approximation.
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