Robust coordinated downlink beamforming for multicell-cognitive radio networks

In this paper, we design downlink (DL) beamforming vectors for a multiuser multicell cognitive radio (CR) network with imperfect channel state information (CSI) at base stations (BS). Specifically, we consider deterministic error in both channel gain and channel covariance. Our objective is to minimize the total DL transmit power subject to quality of service (QoS) constraints of each secondary user (SU) and primary user (PU). The optimization problems for both uncertainty models can be transformed into convex semidefinite programming (SDP) from the standard rank relaxation approach. Interestingly, numerical results show that the obtained solutions fulfill the rank constraint and are therefore exact.