Energy efficient joint user scheduling and transmit beamforming in downlink DAS

This paper studies the energy efficient joint user scheduling and transmit beamforming in the downlink of a single-cell distributed antenna system. Due to the distributed nature of antenna units, traditional power consumption model cannot be applied without the backhauling power taken into account. Therefore, under the constraints of the minimum rate requirement of each user and the transmit power budget of each distributed antenna unit, we maximize the system energy efficiency through making a tradeoff between the transmitting power and the backhauling power. By employing the parametric equivalence method to deal with the fractional objective and the \(\ell _1\)-norm relaxation method to cope with the user scheduling problem, the energy efficiency maximization is turned into a standard difference of convex program and then solved via the successive convex approximation method. Finally, the optimal sparse transmit beamforming vectors are obtained during the weighting factor iteration process, with the aim of minimizing the total power consumption while maintaining the achieved rate of each user. Extensive simulations are conducted to demonstrate the effectiveness of proposed scheme. Simulation results show that energy efficiency can benefit from not only the user scheduling but also the transmit beamforming optimization.