Date Added: May 2012
The authors consider a pair of Secondary nodes (SU) coupled, in Z-topology, with multiple pairs of Primary nodes (PU). The secondary (cognitive) transmitter is combining Beamforming with Orthogonal Space-Time Block Coding (BOSTBC) and operates under Quality-of-Service (QoS) constraints that must be guaranteed for the Primary Receivers (PURx). The cognitive link is designed assuming imperfect Channel State Information (CSI) for all links, available at the SU Transmitter (SUTx). Under this premise they characterize the optimal design in terms of CSI quality and interference and evaluate their impact on the performance of BOSTBC transmission in underlay cognitive networks.