Abstract

Cognitive radio has become a revolutionary technology that enables the functionalities of dynamic spectrum access. These are the radios that can be programmed and configured dynamically and aims at enhancing the efficiency of spectrum usage by allowing unlicensed users to access/share the licensed spectrum. Cognitive radio networks, a network of cognitive radios, are smart networks that automatically sense the channel and adjust the network
parameters accordingly. Therefore, cognitive radio networks raise many challenges such as power management, spectrum management, route management, environment awareness, path robustness, and security issues.

As Cognitive Radio (CR) enables dynamic spectrum access which causes adverse effects on network performance because routing protocols that exists were designed considering fixed frequency band. Also, effective routing in CRNs needs local and continual knowledge of its environment. If licensed user (primary user) requests for its channel which is currently used by unlicensed user (secondary user) then unlicensed user has to return the channel to licensed user. However, unlicensed user has to search for another channel and accordingly it needs to seek for route discovery. So, all these important factors need to be accounted for while performing route management.

In this thesis, QoS based route management technique is proposed. Proposed model makes use of functionalities of profile exchange mechanism and location services. The proposed QoS routing algorithm contains following elements: (a) each licensed user prepares channel property table which lists all the properties of the channel, whereas all the unlicensed users in the network due to cognitive functionality sense the environment and prepare a table which contains identification information of neighbor node and channel present between them. All unlicensed users share their table with central entity. (b) Central entity with the help of received information and location services prepares routing table for all the nodes in the network. (c) Various Quality of Service (QoS) metrics are considered to improve the performance of the network. The metrics include
power transmission, probability of channel availability, probability of PU presence, and Expected Transmission Count. Central entity provides a route to destination based on the QoS level requested by unlicensed users.

Proposed model provides a route with minimum end-to-end transmission power, high probability of channel availability, low probability of PU presence and low value of expected transmission count, to increase life span of users in the network, to decrease the delay, to stabilize wireless
connectivity and to increase the throughput of the communication, respectively, based on the QoS level requested by a secondary user.

Performance of the network is examined by simulating the network in NS2 under simulation environment with the help of end to end delay, throughput, packet delivery ratio, and % packet loss. Proposed model performs better than two other reference models mentioned in the thesis and is shown in the simulation results.