Decentralized spectrum allocation schemes for cognitive radio networking

This thesis presents simulation and an experimental investigation of a decentralized spectrum allocation algorithm for secondary user co-existence in a cognitive radio network. Conventional centralized approaches use a Base Station (BS) or a centralized server with a global view of spectrum availability to carry out spectrum allocation. To keep this global view updated in real-time requires significant amount of signaling between the users and the BS, requiring additional spectrum. On the other hand, a decentralized spectrum allocation has the advantage of low-overhead for control information signaling and is typically more appropriate for ad-hoc network deployments. Various frameworks for decentralized resource allocation have already been proposed (Game theoretic framework, markov decision theoretic framework etc.). However, a full system implementation of any such technique has not been attempted.;Inspired by the TCP congestion control mechanism, an Additive Increase Multiplicative Decrease (AIMD) based decentralized spectral allocation algorithm is proposed. It leads to a network-level fairness and efficient spectral usage in a cognitive radio network. A network consisting of only secondary users is considered for this problem and each secondary user uses a Non-Contiguous OFDM (NC-OFDM) transceiver system for data transmission. The GNU Radio-USRP2 cognitive radio platform is used for implementation purposes. This thesis also presents an experimental evaluation of an active interference suppression scheme used along with NC-OFDM to enhance the spectral quality of the transmitted waveform and, thereby, improving the overall spectral efficiency of the network. The RF transmission quality of the IA-PFT based NC-OFDM transmission using GNU Radio-USRP2 has been verified with reference to simulation results. Some system level throughput measurement results for Primary-Secondary Co-existence experiments are also discussed in the thesis. The functioning of the decentralized spectrum allocation algorithm has been validated using MATLAB simulations.