Research On The Realization Technology Of Cognitive Multi-channel MAC Protocol Based On USRP

With the rapid development and wide application of wireless communication technology, the shortage of spectrum resources is becoming more and more serious. Cognitive radio technology can sense the "spectrum hole" and use that by spectrum access and handoff opportunity without affecting the authorized user communication, so as to effectively improve the utilization rate of the limited spectrum resources, promote the effective integration of the existing heterogeneous wireless networks. Furthermore, cognitive radio networks require the use of multi channel MAC protocol to obtain the communication opportunity based on spectrum hole and effectively solve the problem of communication channel reconstruction when the authorized user appears.The main problems existed in most of the multi-channel cognitive MAC protocol including the precise synchronization of the whole network node which depends on the clock and the need of control channel which available to all or part of the nodes is to realize the negotiation of communication opportunity between the nodes. In practical application, these two requirements are difficult to satisfy. Therefore, the existing literature provides a variety of asynchronous MAC protocols based on channel hopping cognitive convergence which preventing excessive dependence on a particular channel while effectively reducing the requirement of clock synchronization accuracy of the node communication.However, these protocols are mainly focus on the design of channel hopping sequence and only derive the theoretical upper communication convergence delay limit under the condition of asynchronous clock for adjacent node. It fails to optimize the design of the specific details of protocol implementation. In addition, the present study for cognitive MAC protocol based on asynchronous channel hopping are staying in the simulation stage and lack of the experimental demonstration of the physical platform based on verification. Therefore, the emphasis of this dissertation is to design a complete state machine for asynchronous cognitive MAC protocol based on channel hopping, the corresponding performance optimization and the experimental demonstration based on the USRP hardware and GNU software radio platform.First of all, the basic idea of this thesis is to design specific system state machine based on asynchronous channel hopping according to the synchronous multi channel MAC protocol. On the basis of analyzing the theory of this state machine design, it clarify the specific action and transition condition during the implement process of the protocol and elaborate the multiple threads control technology adopted in this thesis, the method of controlling system threads and operation process for every single thread. This has laid foundation for the experimental demonstration and validation for USRP software radio platform.Secondly, based on the asynchronous characteristics of this protocol design, this paper makes a further analyzation of the optimum transmission time selection during each channel hopping slot time for cognitive transmission nodes and proposes a recursive optimization method for sending time based on the Q study. Accoring to the simulation results, this algorithm can effectively reduces the channel hopping gathering delay between both sides and enhances the performance of cognition channel hopping communication.Finally, this paper gives experimental demonstration for the cognitive asynchronous MAC protocol based on channel hopping. Accoring to the test of the USRP software and hardware platform and the test of the protocol function together with the performance has revealed that the system state machine designed in this thesis can realize the basic function of asynchronous cognitive MAC protocol and the test results pointed at the scheme of the protocol implement are basically consistent with the theoretical scope of the asynchronous cognitive MAC protocol performance.