  In this paper, we consider a green cloud radio access network (C-RAN) with
simultaneous wireless and power transfer ability. In order to reduce the energy
consumed for updating the chanel state information (CSI), energy users are
divided into two different groups, including the free charge group and the MIMO
group. Then a semi-definite programming problem is formulated under the
constraints of energy and information transmission requirements. To minimize
the total energy consumption, two algorithms are developed to authorize the
energy users into two group divisions in single time slot. Then the algorithms
are extended to long term scenarios consisting training and long term stages,
the CSI of free charge energy users are not required during the long term
stage. Simulation and numerical results are presented to demonstrate the
efficiency of the proposed algorithms in significantly reducing the energy
consumption of C-RAN systems.
