While the simultaneous power and information transfer in a multi-user network extends the functionality of a traditional base station (BS) in accordance with the requirements of future communication systems, it gives raise to the problems regarding information security. This stems in the fact that the energy harvesting (EH) nodes can also act as potential eavesdroppers. Hence, in this work we address the network requirements for a full duplex (FD) BS regarding uplink (UL) and downlink (DL) information rate and power transfer to EH nodes, under the constraints regarding the information security. An optimization problem for minimizing the total power consumption is then formulated for a network with multiple antenna BS and multiple antenna EH nodes. Due to the non-convex nature of the resulting problem a semi-definite-relaxation framework is proposed in order to approach an optimal solution. Furthermore, for a simpler setup where the EH nodes are equipped with a single antenna, it is shown that an easier problem formulation is possible. A sub-optimal approach is also provided which reduces the DL beamforming design into a power adjustment problem with a reduced complexity. The numerical results investigate the performance of the proposed methods under different system parameters.
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