ملخص البحث :

The Cognitive Relay Network is an emergent technology to deal with the scarceness and authority conditionality of frequency spectrum by dynamically assigning spectrum to unlicensed users with relaying. This new technology changes the model of conventional wireless system design by allowing unlicensed user with ability to sense, adapt and share the dynamic spectrum through relay nodes. The resource allocation (RA) of Cognitive Relay Network such (power allocation, sub-carrier allocation), interference management and relay selection are the important challenges because the adaption is operating under consideration of all constraints that prevent harmful the licensed user. In this thesis, CRN models with an objective function of maximizing secondary users overall transmission rate are proposed. These CRN models adopted on OFDM as modulation scheme with multiple secondary users to enhance the spectrum efficiency, the model formulation schemes are supposed on a group of small cells within one macro cell in a heterogeneous cellular system with cross-tier interference. Genetic Algorithm (GA) is used to solve the optimization problems. The results showed high ability of this algorithm to effectively determine the sub-channel (subcarrier) and power assignment, and increase the total capacity for the secondary network. The highest total transmission data rates obtained from these system models are (16.9715,17.0391,5.0686) bit/sec/Hz. The results are simulated by using the commercial package soft MATLAB 2018b.