Spatial Sharing for Multibeam Opportunistic Beamforming Techniques

Scheduling in a multiantenna broadcast channel, based on partial channel state Information at the Transmitter (CSIT), is carried out through an opportunistic random beam- forming technique. Within a more practical perspective, this paper first presents a transmission strategy where a minimum rate per user is required, which stands as a potential quality of service (QoS) indicator for the system behaviour. The multi- antenna availability provides a spatial resource that can be shared among several users, so that this paper reports the benefits from the spatial sharing, through the optimization of the number of generated beams at the transmitter. Based on the allowed QoS outage, two philosophies are proposed to calculate the optimum number of beams either by instantaneous or statistical design. The benefits from spatial sharing are then tested via simulations in several transmission scenarios.