Abstract
Simultaneous wireless information and power transfer (SWIPT) is an attractive technique to provide wireless data services and energy charging at the same time. Conventionally, SWIPT is applied to one-Tier networks where a central node is deployed to serve users in the coverage. As the notion of heterogeneous network becomes emerging, it is of paramount importance to investigate effective SWIPT methods in the context of heterogeneous networks. In this work, we consider a two-Tier heterogeneous network where the primary tier performs SWIPT to feed energy to the secondary tier. As a result, the secondary tier can be self-sustainable yet the beamforming weights for data and energy flows need to be carefully designed. We explore the optimal beamforming design based on two optimization formulations including the transmission power minimization subject to the rate requirement and energy requirement, and the rate maximization subject to the maximal transmission power and the harvested energy target. Since both the formulated problems are nonconvex, we apply the semi-definite relaxation (SDR) technique to obtain the optimal solution of the convex formulation. Numerical results are presented to evaluate the performance of the proposed optimal beamforming design in comparison with some benchmark schemes.