Sum rate optimization for SWIPT system based on zero-forcing beamforming and time switching

Because of power consumption in free space, the received radio frequency signal is weak, which leads to a lack of energy collection in simultaneously wireless information and power transfer system, namely SWIPT system. The PS receiving mode is commonly used in SWIPT system, but the circuit design of PS receiving mode is complex, and the power of received radio frequency signal is small. If the power is divided once again, it must lead to a less energy collection. Meanwhile, less energy collection will affect information transmission, and it's not benefit to the improvement of system sum rate. Aiming at above problems, this paper proposes a system sum rate optimization problem based on zero-forcing beamforming and time switching mode for SWIPT system. Beamforming technology is suitable for multi-antenna system, which can not only increase the signal intensity in the direction of antenna array, but also can reduce the intensity of interference signal. As a result, the system sum rate of communication network is improved. The receiving TS mode means that a unit time is divided into two time slots, one is energy time slot, and the other is information time slot. In the two time slot, the received radio frequency signal is all used for information demodulation or energy collection. In this paper, a system sum rate optimization problem is established, it's a complex problem and it can be solved by Lagrange relaxation method. The simulation results show that when transmission power of base station is certain, the method proposed in this paper can make the SWIPT system's sum rate and power collection increase, so as to optimize the rate-energy (R-E) curve.