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In this paper we address the problem of neighbor discovery in cognitive radio networks. Cognitive radios operate in a particularly challenging wireless environment. In such an environment, besides the strict requirements imposed by the opportunistic co-existence with licensed users, cognitive radios may have to deal with other concurrent (either malicious or selfish) cognitive radios which aim at gaining access to most of the available spectrum resources with no regards to fairness or other behavioral etiquettes. By taking advantage of their highly flexible radio devices, they are able to mimic licensed users behavior or simply to jam a given channel with high power. This way these concurrent users (jammers) are capable of interrupting or delaying the neighbor discovery process initiated by a normal cognitive radio network which is interested in using a portion of the available spectrum for its own data communications. To solve this problem we propose a Jamming Evasive Network-coding Neighbor-discovery Algorithm (JENNA) which assures complete neighbor discovery for a cognitive radio network in a distributed and asynchronous way. We compare the proposed algorithm with baseline schemes that represent existing solutions, and validate its feasibility in a single hop cognitive radio network

In this paper we propose a Dynamic Spectrum Access scheme which allows the users to opportunistically and efficiently access the channels available for communications. It addresses the following important aspects of opportunistic spectrum access: 1) implementation of the control channel, 2) multi-channel medium access control, 3) primary user detection, and 4) secondary reuse of spectrum unused by primary users. The main features of the scheme are that it is completely distributed, it does not need dedicated spectrum resources for control purposes, but rather leverages on a virtual control channel which is implemented using Network Coding techniques, and it exploits a cooperative detection strategy to identify unused spectrum. Due to these aspects, our proposal represents a significant improvement with respect to existing Dynamic Spectrum Access solutions. We carry out an evaluation study of the proposed solution to assess its performance with respect to different system and scenario parameters; the obtained results show that the proposed solution is feasible, capable of providing satisfactory performance, and suitable for implementation in real systems