Energy Efficient Downlink Cooperative Transmission With BS and Antenna Switching off

In this paper, we strive to improve the energy efficiency (EE) of downlink base station (BS) cooperative transmission systems by switching off some BSs and antennas and allocating power to the users according to the required data rate and channel of each user. To show the potential of EE gain, we first propose an optimal dynamic switching off scheme using instantaneous channel information that maximizes the EE under per-user data rate and per-BS power constraints. To provide a feasible scheme for practical systems, we proceed to propose a semi-dynamic scheme where the BS-antenna operation pattern selection is based on average channel gains. Low complexity iterative algorithms are provided to find solutions for the dynamic and semi-dynamic strategies. Simulation results with typical circuit power consumption show that the semi-dynamic scheme performs close to the dynamic scheme and both schemes provide a substantial EE gain over the scheme with all antennas at all BSs active, when the data rate requirement is low. By comparing the overall power consumption for the systems of two extreme cases in deploying the active antennas, we find that the scheme only switching off BSs is more cost-effective in terms of energy than the scheme switching off antennas when the data rate requirement is low and the number of active antennas far exceeds that of the users.