Towards More Efficient Wireless Power Transfer for 6G

Sammanfattning: As time is moving forward, the world is becoming more dependent on Internet of Things (IoT) devices. The vision for the future involves IoT devices participating in various aspects of our daily lives, including sensing, controlling, and communicating. Such a future requires a significant number of IoT devices, which raises questions regarding sustainability in terms of battery waste. One promising candidate technology for providing power to IoT devices is Wireless Power Transfer (WPT). WPT can provide a convenient way of powering devices wirelessly, which decreases the need to use batteries. It is known that the efficiency of a WPT system is highly dependent on the waveform used for power transmission, hence it is highly desirable to find waveform designs that enhance the end-to-end efficiency of WPT. In this work, our goal is to find waveforms that maximize the harvested power at the receiver of the WPT system, for a large number of transmitting antennas. We do this by developing a simulation framework using MATLAB, where we can do fast simulations for various system parameters, while taking into consideration the full characteristics of the WPT system. Through our results we concluded that using Maximum Ratio Transmission is a viable waveform design strategy with low complexity. Using a larger number of antennas decreases the distortion caused by the amplifiers at the transmitter and increases the received power. Moreover, due to the receivers non-linearity, for a certain average power, having a waveform with a higher Peak to Average Power Ratio (PAPR) enhances the end-to-end WPT efficiency. However, this is only true up to a certain limit that depends on the rectifier circuit parameters. We also investigated several ways of deciding which subcarriers to use for transmission in the available bandwidth, and found a tone selection scheme aimed at maximizing the PAPR of the signal at the receiver while maintaining high efficiency at the transmitter with minimal distortion.