Optimal total-downlink-transmitting-power and subchannel allocation for green cellular networks

Femtocells can be employed as the low-power “green” wireless-access points to extend the macrocell network coverage and enhance the quality-of-service inside homes. In this paper, we focus on the joint subchannel allocation and transmitting-power control for femtocells during the downlink transmissions. Our objective is to minimize the total transmitting power across femtocell access points (FAPs) to facilitate “green” mobile communications. We would like to minimize the following criteria: (1) each user´s received signal-to-interference-plus-noise ratio (SINR) per subchannel and (2) the number of subchannels each femtocell user requires to maintain a reliable quality-ofservice (QoS). Meanwhile, the interference of the users in the underlying femtocells to users in other macrocells should also be restricted. Thus, a new pertinent optimization problem is formulated as a mixed integer nonlinear program (MINLP), which is very complicated to solve in practice. In our work, a reformulation-linearization technique (RLT) based on a branchand-bound framework is invoked to simplify the aforementioned MINLP. Finally, simulation results are demonstrated for the effectiveness of our proposed new scheme.