Spectrum Sharing in the Cognitive Radio Communication Networks

Abstract

Thesis Summary Cognitive Radio (CR) is a technology which can solve the scarcity and inefficient of spectrum usage. It achieves this target by enabling the primary users and cognitive users share the same spectrum under the condition that the cognitive user must minimize the power interference produced on the primary user through using multiple antennas for the transmitters and receivers. Thus, this thesis introduces the interference management problem for underlay spectrum sharing approach of the MIMO cognitive and primary users. This study has been introduced for two different cases: single unlicensed users and multiple unlicensed users. In case of single unlicensed user, the interference management problem of a CR networks has proposed for minimizing the interference power introduced to the licensed receiver while satisfying capacity and power constraints for unlicensed user transmission. A solution for the interference management problem of a single primary user and cognitive user in MIMO system is proposed. The problem was formulated as interference minimization problem under both transmission capacity and transmit power constraints for obtaining a closed form solution. Low complexity algorithm is proposed for designing the optimal covariance matrix based on the Lagrangian duality method which convey the cost function and its constraints into a weighted sum form. Numerical results are performed to corroborate our theoretical results, where a near optimal capacity and interference power are achieved with a low complexity. This study has been extended for multiple cognitive users where the competition over the utility maximization between the secondary transmitters is occurred. This problem has been modeled as a cooperative and non-cooperative game where game theory is an effective mathematical tools for analyzing the confliction between secondary transmitters to achieve the optimal behavior derived algorithm. Numerical results approved the effectiveness of the cooperative scenario that minimizes the network interference power.