Yanyshyn V. Radio frequency spectrum management models and algorithms in cognitive radio networks.

The thesis solves an actual scientific problem - development of effective radio frequency spectrum management methods and algorithms in cognitive radio networks for the quality of service improving. The basic functions of cognitive radio, radio frequency spectrum management schemes and features of the network architecture of the cognitive network are analyzed. A study of the efficiency of spectrum scanning by one cognitive user and using the method of cooperative scanning was conducted. The intellectual computer model of the cognitive network management system with the possibility of wide and flexible adjustment of input parameters, choice of radio frequency spectrum management methods, and with the possibility of further improvement and scaling is developed. Improvement of spectral scanning method and estimation of spectral power density based on energy detection using the Welch periodogram was contributed. The model for assessing the efficiency of spectrum selection methods based on the introduced new performance indicator - the duration of the adoption of a system solution (radio channel designation) for the algorithms for balancing the input load has been improved. The simulation system model has been proposed to calculate main system operational parameters and integrated in simplified model of cognitive radio network with one primary system and one secondary cell. The model uses queueing systems to evaluate how effects on the total system configuring time of the secondary connections on sensing errors, multiple interruptions and capacity of channel. Based on the results, when using load-balancing methods, the total system configuring time can be reduced from 20% and even up to 50%. The advanced algorithm of the proactive protocol of spectrum transmission for service with the use of statistical data about system operation and preliminary forecasting of the frequency channel status was proposed, which allowed to improve the bandwidth of the cognitive radio system by 25% and almost halve the likelihood of a collision between the primary and cognitive users. The simulation was conducted for estimating the bandwidth of a cognitive radio network on the basis of an intellectual simulation model with the use of advanced methods for managing the radio frequency spectrum under the system's operation in conditions close to real. Based on the results of the simulation, it is determined that even with the maximum load of the primary network, the average total bandwidth of the cognitive radio network model with improvements is increased by 7-12%.