A Distributed Algorithm for Dynamic Spectrum Access Using Primary-Prioritised Markov Model

The wireless network medium has a large, but finite bandwidth. With increasing wireless network service providers, users, and applications, there is a need to optimise usage of even parts of the spectrum that are licensed. Dynamic spectrum access is an approach that is designed to enable unlicensed users to make use of licensed parts of the spectrum, opportunistically, when they are idle. To achieve this, user-behaviour modelling, spectrum access algorithms and Cognitive Radio (CR) technology will have to be made use of. In this paper, we propose a distributed dynamic spectrum access algorithm based on the primary-prioritised Continuous-Time Markov Chain (CTMC) model of interaction between primary and secondary users. A distributed dynamic spectrum access scheme requires that each secondary user be aware of the statistics - arrival and service rates - of the other secondary users, so as to be able to optimise throughput while maintaining fairness. We formulate heuristics that make use of the estimated stationary idle-probability of the spectrum and the interference which each user experiences, to iteratively update user statistics estimates. Simulations show that the proposed algorithm attains an overall throughput that is better than the persistent form of CSMA when the primary user spectrum utilisation is typical (about 45%).