Cross-layer Optimization And Undulation Evaluation For Opportunistic Routing In Cognitive Radio Ad Hoc Networks Under Predictable Contacts

With the rapid development of wireless communications technology,spectrum resource becomes scarce.However,the application of cognitive radio(CR)technology with sharable spectrum resource can largely reduce the pressure of spectrum resource shortage.As traditional routing protocols in Ad Hoc networks do not consider the spectrum resource and can not achieve the changeable spectrum resource information.In order to accurately and effectively route,routing protocols must consider spectrum resource information and get the information of neighbors.To solve the problems above,a natural idea occurs,that is,combing CR with Ad Hoc Networks.Then,the cognitive radio Ad Hoc Networks(CRANET)come to appear.Due to the communication opportunities of CUs are dynamic,when the communication opportunities occur i.e.CUs contact.If the contacts are predictable,this CRANET can be called CRANET under predictable contacts.In CRANET under predictable contacts,due to the spectrum resource is dynamically changeable,primary users(PUs)can influence the available frequency bands of cognitive users(CUs).Then,the spectrum resource may be changeable.In addition,spectrum resource management is the function of medium access control(MAC)layer.To make full use of spectrum resource and improve the end-to-end throughput,a cross-layer optimization method is introduced into CRANET under predictable contacts.However,in CRANET under predictable contacts,the contact degree between CUs、signal noise ratio(SNR)for available channels and the queue length of CUs are the main factors for end-to-end throughput.In this context,the routing and channel assignment scheme with the constraints of contact degree and SNR is mainly researched in CRANET under predictable contacts.Furthermore,the assessment criteriathe for undulation of opportunistic routing is also presented in this paper.The main research achievements are as following:(1)In this paper,an analytical model for predictable contacts in the intermittently connected CRANET is proposed.To facilitate the research of contact availability,a classification for predictable contact paradigm of CUs including contact,non-contact and effective contact is given.Then,the probability of continuous effective contact between CUs is defined as contact degree.Subsequently,under the constraint of contactdegree,the concept of continuous effective contact time used to measure the communication duration between CUs is proposed.In addition,the mean value of the continuous effective contact time can be obtained as well.Further,the mean duration for CUs beyond the interference range of PUs is also derived.Simulation results indicate that the presented analytical model for predictable contacts achieves close-to-optimal performance.(2)To identify the set of the forwarding candidate CUs,the selection metric of the possible forwarding candidate CUs is also formulated bearing in mind the joint impact of the queue length and the contact degree on the reliable data packet transfer of CUs.The scheme of the opportunistic routing with autonomic forwarding angle adjustment(FAOR)is developed.This scheme does not only determine the set of the forwarding candidate CUs,but also supports the dynamic calculation and update of the forwarding angle for a CU.Based on the analysis of the FAOR scheme,the joint FAOR and channel assignment(FACA)scheme for CUs is proposed.In addition,the channels are allocated from the available channel set to each link along the optimal opportunistic routing by taking into account the SNR of each idle channel.The forwarding probability of data packet for CUs is derived by employing the metric of expected transmission count to compute the packet loss rate.The end-to-end throughput from the source CU to the destination CU is further modeled as a nonlinear programming problem,in which the constraints including the queue length of CU,the contact degree between CUs,and the channel availability are all taken into account.In the end,the assessment criteriathe for undulation of opportunistic routing is also presented in this paper.