Research On Spectrum Handoff In Cognitive Radio Networks

The low spectrum utilization caused by the static spectrum allocation scheme, has been one of the main barriers of the development and application of wireless communication. As a kind of intelligent spectrum sharing technology, cognitive radio could relieve the problem of limit spectrum resource and improve the spectrum utilization effectively by using the underutilized spectrum resource on time domain, frequency domain and space domain. Based on the national science foundation project which named"the research of the topology management of Mesh network, MAC mechanism and adaptive resource allocation of cognitive radio", the paper shows the research and analysis on the spectrum handoff technology of cognitive radio. The main content includes the analysis of theory model and multi attribute handoff mechanism.1)The paper introduces and summarizes the research background, the basic concept, the key technology and the current research situation of cognitive radio firstly, and then analyzes the requirement, concept, trigger scene, the current typical spectrum handoff mechanism, the key technology, the handoff flow and the existing shortage of spectrum handoff based on the background of cognitive radio.2)Next, the research and analysis on the model of spectrum handoff theory are showed. In the cognitive radio system with multi-channels and finite user population, the Markov model is used to describe the state of spectrum access. And then the handoff performance of cognitive users based on different channel bandwidth and different access schemes of primary users including random access scheme, real-reservation access scheme, pseudo-reservation access scheme and non-random access scheme is given. The simulation results show that when the channel bandwidth is larger, the increase rate of the blocking probability, the forced termination probability will grow up faster with the increasing the number of cognitive users, while the average number of cognitive user in one channel will increase slowly; besides, the blocking probability, the forced termination probability and the handoff probability will grow up as the number of cognitive users increases. The random access scheme shows the highest handoff probability, the real-reservation access scheme shows the highest blocking probability and forced termination probability and the non-random access scheme has the maximum channel utilization.3)A kind of multi-attribute spectrum handoff mechanism is proposed. For meeting the QoS requirement of cognitive users, the mechanism analyzes the available, SINR, the channel capacity, the delay characteristics and bit error characteristics of idle channels, and adopts the AHP(Analytic Hierarchy Process) algorithm to select the global optimum switchable channels based on the match rules of the multi target QoS requirement. By establishing the system model of multi attribute spectrum handoff mechanism and simulating the handoff process using the time stepping method, the simulation analyzes the statistic parameter performance with different number of cognitive users and compares with the random handoff mechanism. The results show that the times on switching success, switching failure, the discarded services and the collision with primary users will trend to increase as the number of cognitive users increase, and the multi attribute handoff mechanism has higher reliability and transmission efficient.