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With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is increasing rapidly. Existing spectrum allo-cation policies of the Federal Communications Commission (FCC) prohibits unlicensed access to licensed spectrum, constraining them instead to several heavily populated, interference-prone fre-quency bands, which causes spectrum scarcity. However, it has been shown by several spectrum measurement campaigns that the current licensed spectrum usage across time and frequency is in-efficient. Therefore, a concept of unlicensed users temporarily “borrowing” spectrum from incum-bent license holders to improve the spectrum utilization, called dynamic spectrum access (DSA), is proposed. Cognitive radio is a communication paradigm that employs software-defined radio tech-nology in order to perform DSA and others versatile, powerful and portable wireless transceivers.

Up until now, most existing works have focused on spectrum sensing and spectrum access, but very few have focused on the higher layer, which is very important for cognitive radio networks. In this dissertation, we use the framework of distributed game theory and belief propagation to explore the routing techniques and the security issues in cognitive radio networks. Firstly, a belief-propagation based defense strategy for the primary user emulation (PUE) attack in cognitive radio networks is proposed, which avoids the deployment of additional sensor networks and expensive hardware in the networks used in the existing literatures. The proposed algorithm can provide low computational complexity and fast execution speed, and the framework is flexible to incorporate to defeat various kinds of attacks for future extension. In the next section, a brand new network-layer attack, named routing toward primary user (RPU) attack, is discovered in cognitive radio networks, in which malicious secondary users will try to route the data to those secondary users which are closer to the primary users in order to increase interference to the primary users. This new attack is very difficult to detect because the malicious nodes may claim that those nodes, to which they forward the packets, behave dishonestly and cause problems in the data transmission. Also a belief-propagation based defense algorithm is proposed in which each node keeps a table recording the feedbacks from the other nodes on the route, exchanges feedback information, computes beliefs and detects the malicious nodes based on the final belief values. Simulation results show that the proposed defense strategy against the RPU attack is effective and efficient in terms of significant reduction in the delay and interference caused by the RPU attack. Finally, we propose a distributed routing algorithm using the network formation game to minimize the aggregate interference from the secondary users to the primary users while keeping the delay along the route low. The proposed distributed routing algorithm can avoid the problems in the centralized routing solution, such as the high cost for building the centralized coordinate nodes, high information-gathering delay, and system breakdown caused by the possible failures in the centralized nodes, and is practically implementable. Simulation results show that the proposed scheme finds better routes in terms of interference to the primary users compared to the shortest path scheme, and the distributed solution shows near optimum compared to the centralized solution. The proposed technologies concern-ing the security issues and the routing algorithms in cognitive radio networks can provide a lot of benefits to society, and will assist the public safety, emergency services, and first responders communities in enabling better communications access to the network, which could potentially translate into additional human lives being saved.



Cognitive Radio, Security, Belief Propagation, Network Formation Game, Routing