Research On Simultaneous Wireless Information And Power Transfer Based On AMPSK Modulation

Simultaneous Wireless Information and Power Transfer(SWIPT) is a frontier research direction, which is formed by the mixture of communication technology and power transmission technology. SWIPT aims at harvesting energy from the Radio Frequency signal to prolong the lifetime of mobile device, and realizing high-speed reliable point-to-point communication over the wireless channel at the same time.This paper discusses the theoretical concept and application fields of SWIPT in detail, and proposes a feasible analysis model and reference design. This proposal neither relies on two signals to transport information and power respectively, nor transports information and power in the Time-Division way. By using a novel sine-like modulation scheme-AMPSK, the reference design of SWIPT system could realize the transmission of information and power at the same time in real meaning by occupying only one modulated carrier.Firstly, the architecture of the SWIPT system based on AMPSK modulation is presented, which mainly consists of AMPSK modulation module, Wireless Power Transfer(WPT) system, and Power splitting system, rectifying circuit, demodulation circuit.Secondly, according to the modulation principle and the characteristic of power spectrum of AMPSK signal, the advantages of AMPSK signal in SWIPT are discussed. Experimental and theoretical estimation of power spectrum of AMPSK signal illustrates that the power of AMPSK signal highly concentrates on the frequency of its carrier. Such a sine-like modulated waveform has an excellent energy-carrying ability that is suitable for SWIPT. According to the characteristic of SWIPT application, two kinds of impacting filtering mechanism for AMPSK signal are summarized, namely phase matching mechanism and carrier suppression mechanism. Based on carrier suppression mechanism, the principle of resonant coherent demodulation scheme for AMPSK signal is derived, and a complete structure of resonant coherent demodulation circuit is presented. This circuit reflects a reversed-phase carrier to demodulate the input AMPSK signal, by using only a λ/4 microstrip open stub.Thirdly, chapter 4 analyzes the near-field WPT at first. In order to extend the effective region of the conventional magnetic coupled WPT, two resonant compensating capacitors are added to transmitter coil and receiver coil, respectively. It is pointed out that the key point to achieve a long-distance efficient power transmission is to keep the transmitter coil and the receiver coil resonant at the frequency of carrier with a high quality factor. On this basis, the difference and connection between the magnetic coupled WPT and the coupled resonant WPT is explored. Then, the antenna design of the rectenna of far-field WPT is presented in section 4.3, and the free space attenuation of microwave power of far-field WPT is estimated according to the parameters of these antennas. Section 4.4 and 4.5 discuss the Power splitting method for the receiver of SWIPT system, two special cases of power splitting, namely, time-domain splitting and frequency-domain splitting are proposed. According to each case above, reference design and performance analysis by computer simulation are given. The close-form equation of diode conversion efficiency is derived based on modelling and analysis for the diode rectifying circuit in section 4.6. Then a printed microstrip rectifying circuit is presented. By comparing the simulational results with the model caculations, the key factors which affect conversion efficiency are discussed.Finally, in order to verify the feasibility of SWIPT, some experiments are conducted. One experiment that based on the conventional magnetic coupled WPT proves the feasibility of simultaneous information and power transfer. Another one proves that adding resonant compensating capacitors to transmitter coil and receiver coil will extend the effective region of conventional magnetic coupled WPT system significantly.