Study Of Distributed Cognitive Radio Access Technology

The exponential progress of wireless devices has resulted in a over crowed spectrum, and radio resources has become the most valuable resource. However, the traditional spectrum allocation approach leads to under-utilization. Cognitive radio is regarded as a solution to this problem, which can use the spectrum dynamically and improve the spectrum utilization remarkably. Opportunistic spectrum access (OSA) is one key technique of cognitive radio and this paper focuses on OSA in distributed environment.OSA allows cognitive radio users (CRU) to use the spectrum which primary users (PU) don't use at this moment, and return it to primary users when needed. OSA brings challenge to the design of access algorithms, especially in distributed environment. How to choose the channel to access in order to reduce the collision between CRUs and avoid interference with PUs is the principal problem of OSA.In this paper, we propose access algorithms and protocols which can be applied to the dynamic environment and provide the simulation results.This paper first introduces the cognitive radio concepts, and then the recent works on opportunistic spectrum access techniques. According to the research status on opportunistic spectrum access, the possible issues in OSA and the purpose of our studies are concluded in follow.In a distributed network, the cognitive radio users can't sense full spectrum due to hardware constraints and they can only choose one or several channels to sense. We propose an access algorithms based on Partially Observable Markov Decision Process (POMDP) in Chapter 3, which includes one-decision strategy and N-decision strategy.In Chapter 4, we propose an access algorithm based on No-regret learning, which can avoide the collision of cognitive users in a distributed way. And simulation results show this algorithm is quick-converged and practical.A multi-channel MAC protocol based on packet reservation is proposed in Chapter 5, which considers the negotiation between sender and receiver. This protocol can avoid the collision of control message and data transmission between CRUs, and solve the hidden terminal and exposed terminal problem effectively.Finally, we sumarize this paper and point out the future research direction of OSA algorithms and protocols.