Energy efficient multi-antenna downlink broadcast transmission

We address the problem of energy efficiency maximization for multi-antenna downlink broadcast systems. The proposed transmission algorithm calculates the optimal pre-coding matrices, power allocation, and solves the user subset selection problem that is most energy efficient while satisfying the Quality of Service constraint of the network. Both zero-forcing beamforming scheme and dirty paper coding scheme for multi-antenna broadcast transmission are considered, and it is demonstrated that significant energy efficiency improvement can be achieved when the transmit power is appropriately adjusted. In most scenarios, it is shown that the optimum energy efficiency is achieved when the base station is transmitting below its maximum throughput capability, hence reducing its transmit power.