Robust beamforming for multi-cell downlink transmission

For coordinated transmissions in multi-cell downlink channels, the base stations are required to acquire and share their channel state information (CSI). Acquiring CSI is often prone to errors and a globally-optimal coordination is not possible when the acquired CSI is imperfect. However, when the errors in the acquired CSI are guaranteed to lie within bounded regions, any quality-of-service (QoS) measure of interest will also lie within a bounded region. Motivated by this premise, by employing the notion of robustness in the worst-case sense, some worst-case guarantees on QoS can be offered. We assume that CSI perturbations belong to known hyper-spheres and aim to design linear transceivers that optimize the minimum worst-case rate of the network. We offer centralized (fully cooperative) and distributed (limited cooperation) procedures imposing different levels of complexity and information exchange among the base stations.