Downlink Beamforming and Admission Control for Spectrum Sharing Cognitive Radio Mimo System

We investigate the problem of multiuser downlink beam-forming and admission control considering a scenario where licensed, or primary, users and cognitive radios, or secondary users, are transmitting concurrently over the same band. The primary users share a common receiver and the interference on this receiver from secondary users should be strictly limited to a certain level. Each secondary link is assumed to have a minimum quality of service (QoS) requirement that should be satisfied together with the interference limit constraint, otherwise the secondary link is not admitted. Under those constraints, downlink beam-forming and admission control for secondary users are investigated for two main optimization objectives. First, we maximize the number of admitted secondary links. Second, we maximize the sum throughput of the admitted secondary links. our main design objective is to minimize the transmit power of the SU-transmitter while simultaneously targeting a lower-bound on the received signal-tointerference-plus-noise-ratio(SINR) for the SU’s and imposing on upper limit on the interference power(IP) at the PUs.