Transmit beamforming optimization for energy efficiency maximization in downlink distributed antenna systems

In this paper, the energy efficient joint transmit beamforming is studied in the downlink of a single-cell multiuser distributed antenna system (DAS). A new power consumption model is defined at first, in which the backhauling power is taken into account. Then, we formulate a fractional optimization problem to maximize the system energy efficiency under the constraints of the maximum transmit power per distributed antenna unit (DAU) and the minimum rate requirement per user. The parametric equivalence method is employed to deal with the non-linear fractional objective, with the Dinkelbach's algorithm applied for searching the optimal parameter. Since the backhauling power is entangled with the structure of the beamformers, we firstly assume that each user is jointly supported by all DAUs. Moreover, due to the co-channel interference among users, the successive convex approximation method is employed. Finally, we use the weighting factor iteration to enhance the sparsity of the beamformers with the aim of minimizing the total power consumption while maintaining the achieved rate of each user. Simulation results show that our proposed joint transmit beamforming algorithm greatly improves the system energy efficiency.