Optimization Algorithm For Channel Rendezvous In Cognitive Radio Networks

With the popularity of wireless devices,cognitive radio networks(CRNs),allowing dynamic access of spectrum resources which greatly improves the utilization of spectrum resources,have been widely used in numerous fields.In cognitive radio networks,Channel rendezvous is a fundamental process for two secondary users(SU)to find a common available channel and subsequently establish a link between them to communicate.This paper introduces the three widespread methods of channel rendezvous called the common control channel algorithm,cluster algorithm and channel hopping algorithm,respectably,and then briefly analysis its basic ideas,scope of application,pros.and cons.while have an elaboration on channel hopping scheme.The channel hopping scheme can be classified according to the number of users participating in the channel rendezvous and the network model the scheme adapted.The metrics are unified mathematically for the first time,and the currently available representative algorithms are compared in term of the given mathematical metrics.The related research working on rendezvous schemes are analyzed deeply,and the main challenges as well as fundamental principles of channel hopping are proposed.A new rendezvous algorithm named Adjusted Disjoint Finite Cover Rendezvous(ADFC-CH)is proposed,which can be used in more general cognitive radio networks such as synchronous clock,heterogeneous model,symmetric role,and anonymous information.The relationship between the concept in mathematics called Disjoint Finite Cover(DFC)and rendezvous process is built in ADFC-CH.The ADFC-CH produces a channel sequence by constructing the DFC of time slot which is a function of network size called LOCK.Obviously,the proposed algorithm is fit for the diversity of the network requirement through adjusting the size of the LOCK.Simulation results show that ADFC-CH can achieve better performance over the exiting channel hopping protocols such as SSB,L-DDP and DSCR.Most of previous works assume that the user can find a set of available channel after spectrum sensing stage and the status of all channel are stable all the time.However,this assumption may not be true in reality and we use the concepts of Markov process,Jenkins Hash and Josephus recursive to design a fair channel hopping protocol with dynamic channel state.Two protocols(FCH_S,FCH_A)are proposed for synchronous clock and asynchronous clock network model,respectively.With the help of Markov process,the channel activity model is built and thanks to the feature of Jenkins Hash and Josephus recursive the fairness of protocol is guaranteed.We assume that a secondary user,SU_A,rendezvous with SU_B,which channels'available probability are p_a and p_b respectively.Based on this assumption it can be proved that expect rendezvous time for FCH_S and FCH_A are 1/p_ap_b,and 1/p_a+1/p_b-1.Simulation results show that FCH_S and FCH_A can achieve better performance over the exiting channel hopping protocols such as H.Tan.Open problems in channel hopping rendezvous schemes design are discussed so as to point out future research trends and focuses.