Development of a Software Defined Radio ( SDR ) for Cognitive Radio ( CR ) Communication Systems

The VHF band is the first choice for the majority of maritime coastal communications because of its affordability, reliability, ease of use and an adequate effective range (up to 30 nautical miles), but expensive satellite links are typically used for all digital communications. However, future navigation and monitoring technologies, such as e-navigation and shipborne personal communications, require high speed (broadband) communication systems, while maintaining affordability. This thesis describes the implementation of a prototype cognitive radio based on software defined radio technology for opportunistic usage of vacant maritime radio spectrum bands, as an alternative to existing expensive satellite links. After an overview on the most recent advances in cognitive radio technology, the target environment and incumbent user’s characteristics is studied and the baseline implementation to address existing issues of maritime communications is presented. The implementation focuses on three essential components: spectrum sensing (a multichannel energy detector), radio transceiver (which uses non contiguous Orthogonal Frequency Division Multiplexing multicarrier modulation) and cognitive medium access control. The implemented cognitive radio uses GNU Radio software for digital signal processing and physical layer design and the Universal Software Radio Peripheral as radio front-end. In order to evaluate the proposed prototype, a set of benchmark simulations based on the expected propagation channel conditions are performed. Then, the prototype is validated in laboratorial tests where it is demonstrated that the system is capable of detecting incumbent user activity and to use vacant spectrum bands without interfering with incumbent users. Finally, some directions towards future work and considerations regarding future implementations are provided.