| With the development of wireless communication,the scarcity of spectrum resource has become increasingly serious.Cognitive radio(CR)technology is one of the most effective means to solve the problem due to its effective improvement of the spectrum utilization.In cognitive radio,how to share the primary user’s spectrum resource without affecting its normal communication is the key issue of CR technology.This thesis aims to exploit beamforming technology to suppress the secondary interference to primary user and improve the spectrum utilization in multiple input multiple output(MIMO)cognitive radio system.In this thesis,we study the robust single-fed electronically steerable parasitic antenna radiators(ESPAR)based beamforming for MIMO cognitive radio network(CRN)with single primary link and multiple secondary users(SUs).Due to the completely-unknown cognitive radio(CR)interference channel for secondary base station(SBS)in the actual scenario,the standard interference temperature can not be used as the metric for interference analysis,therefore,we propose a rank minimization of the secondary transmitted covariance matrix as alternative metric to solve this problem.The computation of the tunable loads and the feeding voltage can be obtained by solving the rank minimization problem which is further relaxed as the log det maximization.Simulation results show that the rank minimization algorithm can effectively suppress the impact of CR interference on the performance of the primary transmission,and validate that the ESPAR antenna array can achieve the similar performance as the conventional antenna array but with compact size and higher energy efficiency. |
