The Research On Key Technologies Of Media Access Control For Blind Rendezvous Based Cognitive Radio Networks

With the rapid evolution of wireless networks and the explosive growth of wireless services, the spectrum scarcity problem caused by traditional static spectrum allocation policy becomes more and more serious, which significantly restrains the occurrence and prosperity of innovative wireless applications. In order to change the current situation that the spectrum resource is extremely under-utilized, allowing unlicensed users(a.k.a.secondary users, SUs) to temporarily use the licensed band without interfering with licensed users(a.k.a. primary users, PUs) gradually becomes the consensus of spectrum management agencies all over the world. Cognitive radio is just the technology converting the concept of consensus into reality, which is widely regarded as the most promising technology to improve the spectrum utilization. Consequently, based on this technology,the corresponding cognitive radio networks(CRNs) is the current hot research area.Due to dynamic channel availability caused by PU activity, how to establish common control channel(CCC) is known as the main challenge to achieve networking and practical deployment of CRNs. In recent years, the concept of blind rendezvous spawns a large number of research work on channel-hopping sequence(CHS) based rendezvous schemes. Although these CHS based rendezvous schemes avoid the drawbacks of conventional approach to CCC establishment, they bring new problems into networking protocol design, as well as performance analysis and optimization.Being oriented to CHS based rendezvous schemes, this thesis studies the key problems related to the medium access control(MAC) layer. A survey is given on the related concept and the concrete implementation schemes of blind rendezvous. In particular,the design principle and the concerned performance of existing CHS based rendezvous schemes are summarized. According to this new approach to CCC establishment, we analyze and conclude the emerging problems in MAC protocol design, as well as performance analysis and optimization. The main contributions are summarized as follows.(1) We design two CSMA/CA MAC oriented to CHS based rendezvous schemes:one is a non-cooperative MAC named CH-CSMA/CA MAC, the other is a cooperative MAC named Co CH-CSMA/CA MAC. By expanding the freezing mechanism of backoff counter, CH-CSMA/CA MAC tailors the IEEE 802.11 distributed coordination function(DCF) to slotted operation manner. To handle the false collision caused by rendezvous de-synchronization, an enhanced virtual carrier sensing(EVCS) mechanism is proposed.By comparison with conventional VCS mechanism, the EVCS mechanism can reduce the waste of reserved channel resource, which not only decreases the packet delivery delay but also increases network throughput by at least 69.6%. As CH-CSMA/CA MAC is unable to discern the false collision, the proposed Co CH-CSMA/CA MAC employs a cooperative control feedback mechanism designed by using correlation-based signal detection, which can help senders to discern false collision and avoid backoff misbehavior to extend backoff counting-down process. By using the developed classic Bianchi model to analyze the behavior of these two MAC protocols and verify the analysis, we reveal the fundamental cause, the trade-off between backoff counting-down process and true collision, of the result that CH-CSMA/CA MAC and Co CH-CSMA/CA MAC are suited to SU-dense and SU-sparse CRNs, respectively. In addition, we discuss the impact of false collision detection precision and pseudo-noise sequence(PNS) length on performance of Co CH-CSMA/CA MAC, which indicates that the MAC performance cannot be improved by increasing the detection precision of false collision through extending the PNS length.(2) Existing CHS based rendezvous schemes emphasize on the access negotiation problem in multi-channel MAC of CRNs but ignore the access control problem, which causes that the concerned rendezvous delay performance cannot reflect the real delay of link establishment. To this end, we analyze the delay of link establishment(i.e., channel access delay) when SUs use their local CHSs for saturation transmission. Our analysis is the first one that considers the aggregate impact of CHS based rendezvous schemes,PU activity and multi-user contention on channel access delay. By jointly employing the developed classic Bianchi model and the absorbing markov chain model, we carry out our analysis and verify it by simulation results. In order to measure the impact of multiuser contention, a new performance metric named the probability of seizing transmission opportunity is proposed, and we discuss the impact of packet length changed by packet aggregation on this performance metric and MAC performance. Simulation results indicate that packet aggregation cannot ensure the improvement of network throughput due to its increased channel access delay.(3) In the CRN where CHS based rendezvous schemes are employed, the success of packet transmission has to meet that a sender locates the channel of its receiver successfully and transmits without collision. However, existing transmission coordination schemes only consider the performance of locating the channel of receiver during link establishment. To defeat this drawback, we propose a state-based transmission coordination(STC) scheme, which jointly considers the impact of locating the channel of receiver and multi-user contention on link connectivity. In comparison with existing transmission coordination schemes, STC scheme has a little performance loss in locating the channel of receiver, but it can mitigate multi-user contention, which can further improve MAC performance effectively. Simulation results indicate that STC scheme can search the balance between performance loss of locating the channel of receiver and performance improvement of the probability of seizing transmission opportunity, which implies that the STC scheme can adapt to different network scenarios and has the merit of optimizing MAC performance.(4) When link disconnection is caused by jamming attack, it is time-inefficient to recover the link by only relying on existing CHS based rendezvous schemes, as there exist a large number of channels and PU activity in CRNs. To improve the efficiency of link recovery, we propose a neighbor cooperation based fast link recovery(NC-FLR)scheme, which supplies the cooperation opportunity brought by CHS diversity for neighbors to help SU senders efficiently find their intended receivers and accelerates the speed of reconstructing link for existing CHS based rendezvous schemes. This neighbor cooperation method for link recovery can achieve the effect of “multi-radio virtualization”,i.e., a sender borrows the neighbors’ radios and uses multiple radios to find its receiver.When only a neighbor takes part in the cooperation, the link recovery delay of the optimal CHS based rendezvous scheme can even be decreased by nearly 30%.In summary, being oriented to CHS based rendezvous schemes, this thesis systematically studies the problem of protocol design, as well as performance analysis and optimization related to MAC layer, which lays the foundation of upper-layer protocol design.Our work has significance of theoretical guidance and practical value to further promote the advancement of networking and deployment for CRNs.