Scheduling in a Broadcast (BC) channel based on partial Channel State Information at the Transmitter (CSIT) is carried out in an opportunistic way, where several orthogonal beams are randomly generated at the Base Station transmitter to simultaneously deliver several users with their intended data. Within a more practical perspective of the opportunistic systems, this paper first presents a transmission scheme where a minimum rate per user restriction is required for each scheduled user. This minimum rate is demanded by each user to properly decode and manage its received signal, which stands as a possible Quality of Service (QoS) indicator for the system behaviour. Then, the paper considers an imperfect CSIT situation where robust schemes are required to meet the QoS restrictions. Two robust opportunistic transmission philosophies are presented through a power allocation over the transmitting beams, and they are efficiently solved via convex optimization tools.
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