Spatial optimization for maximum throughput in multibeam opportunistic schemes

Scheduling in a downlink channel based on partial channel state information at the transmitter (CSIT) is carried out through a multibeam opportunistic beamforming technique. A practical transmission strategy is presented where a minimum rate per user is required within a given time interval, to satisfy maximum delay restrictions for the user´s application. The proposed strategy achieves these quality of service (QoS) restrictions at the same time as an opportunistic user selection is performed, so that the system multiuser gain is extracted while the QoS is satisfied. The system minimum-guaranteed throughput is then formulated in a closed form expression, and a throughput maximization is performed through the optimization of the number of transmitting beams, therefore exploiting the system spatial capabilities in the most convenient approach.