Energy-efficient CoMP precoding in heterogeneous networks

Heterogeneous networks (HetNets) consisting of macro- and pico-cells can well tackle the contradictory requirements on large coverage of the network and high data rate at the hot spots. In this paper, we study energy-efficient precoding for coordinated multi-point (CoMP) transmission for HetNets. We formulate a problem that maximizes the energy efficiency under the constraints of individual date rate requirement from each user, maximal transmit power of each base station (BS), and zero-forcing (ZF) for a HetNet where the macro-BS cooperates with multiple pico-BSs. We then simplify the problem with the help of the practical topology of HetNets where the macro-BS cooperates with each of the pico-BSs. By introducing the subspace decomposition method and exploiting the feature of HetNets, we obtain the structure of the optimal ZF CoMP precoder. To reduce the computational complexity and hence the circuit power consumed for signal processing, we propose a suboptimal ZF precoder with closed-form expression for the HetNets with isolated pico-cells. We demonstrate the performance of the proposed ZF precoders by comparing with several existing optimal linear precoders.