Medium Access Control Protocols with Efficient Enhancement for Cognitive Radio Networks
【摘要】：Cognitive radio (CR) is a new technology invented to improve the spectrum utilization by using the white space spectrum that is licensed to different services, but not used in a spe-cific time and space. One of the major aspects of the spectrum allocation in distributed cog-nitive radio networks is how professionally the spectrum is administered and how the sec-ondary user's link (SUL) protected. These functions are medium access protocols responsi-bility; thus, our objective in this thesis is to develop various medium access control (MAC) solutions for this new technology.
In the previous works, some of the proposed MAC protocols reactively access the spectrum, thus, SUL terminated upon detecting the primary user (PU) signal. This approach is susceptible to detection errors, such as, miss detections and false alarm. Furthermore, the collision probability and data loss is highly expected since the channel is released subsequent to the PU's arrival.
In this thesis, we propose a proactive cognitive MAC protocol to attain compensation to the suspended secondary link and avoid collision with PU. This goal is achieved by re-serving an alternative backup channel to reconstruct the SUL before forced termination oc-curred. The novel idea of this protocol is the channel selection method according to various factors such as the channel's current states, release time, occupation ratio, residual free time and physical specification factors. The protocol provides proactive reliable SUL maintenance and reduces disruption to both primary and secondary users. It also gives solutions for both large and small data packets size. The protocol operates over a separate common control channel and multiple data channels; hence, it is able to send the channel reservation informa-tion in the control channel simultaneously with the current data transmission to achieve ef-fectively a quicker and smoother channel switching.
In addition, and due to nodes coordination and neighboring discovery necessity, we propose a synchronized cognitive MAC protocol for decentralized networks and GPS re-ceiver capabilities are utilized to provide prominent neighboring discovery, data rate estima-tion and synchronization. The protocol simulates the impact of adding GPS information, and effectively improves the network performance as demonstrated by the analysis and simula-tion.