Rendezvous in cognitive radio ad-hoc networks
Hossain, Md Akbar
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Cognitive radio (CR) is a promising technique to enhance the spectrum utilisation by enabling the CR users to opportunistic access the spectrum holes or channels. CR ad hoc network is a multi-channel environment where channel status changes over time depending on primary users’ (PUs) activities. Analogous to control channel establishment in traditional multi-channel ad hoc network, rendezvous in CR ad hoc network is one of the most important processes for a pair of unknown CR users to initiate communication. Most of the existing research have utilised a common control channel to achieve rendezvous. This utilization generates channel saturation, extreme transmission overhead of control information, and a point of vulnerability. The traditional designs for rendezvous protocols do not support an ad-hoc CR network model. Therefore, this thesis is focused on improving control channel establishment to solve the rendezvous problem and support further CR ad-hoc networks. This thesis proposes a new channel hopping (CH) scheme called extended torus quorum channel hoping (ETQCH) for asymmetric and asynchronous pair wise RDV in CR ad-hoc networks. The ETQCH employs channel ranking information for allocating more slots to high-rank channels than low-rank ones. The system dynamically updates the CH sequence by replacing channels from both the licensed and unlicensed bands to protect intermittent PUs. Channel hopping sequence scheme is a mathematical concept to guarantee overlap between two CR users. A successful RDV establishment depends on successful channel probe or control packet exchange which is a MAC layer issue. Therefore, a new MAC protocol named cognitive radio rendezvous (CR-RDV) MAC is proposed to facilitate the multiuser contention in CR ad-hoc networks. CR-RDV is developed by re-deﬁning the traditional backooﬀ procedure and incorporating a sensing period immediately after the request-to-send; the incumbent PU’s transmission is protected and blocking problems are resolved. The analysis and simulation results show the potential to minimise service interruption, block node problems, and eﬃciently utilise dynamic radio resources. The thesis also provides a guideline for CR system planners to design and deployment of dense networks with active PUs.