## 1 Introduction  
Based on convenience and safety, wireless power transfer (WPT) technology has been developed rapidly in the field of electric vehicles [1; 2; 3], urban rail transit [4], motor control [5; 6], LED [7], and so on. Along with the development and optimization of new devices [8; 9], topology and coil structure [10; 11], the performance of WPT system has greatly improved. For WPT system, bidirectional power transfer can improve the energy utilization and increase the interaction between the power grid and electrical equipment, such as vehicle-to-grid (V2G), autonomous underwater vehicle, implantable medical devices [12; 13; 14]. However, for the industrial applications, it is necessary to monitor the actual working state of the devices, and the information transfer needed [15]. Reliable communication between the primary and secondary side plays a critical role in wireless transmission systems. If communication between the two sides is provided, it is easier to implement system requirements in specific applications, such as output voltage feedback control, load detection and status monitoring. [PERSON] [16] proposed a simultaneous wireless information and power transfer technology (SWIPT) for the first time, giving a trade-off method between signal capacity and energy efficiency suitable for discrete channels and Gaussian channels. Subsequently, [PERSON] et al. [17] proposed a circuit model that uses a coupled inductance circuit to achieve the simultaneous transmission of short-range wireless information and energy, and applied the water injection algorithm to the SWIPT system to achieve the optimal distribution of information energy power. In view of the fact that the actual hardware may not be able to demodulate information and receive energy at the same time, [PERSON] et al. [18] proposed a dynamic power allocation method, and on this basis, proposed a separate and integrated receiver. The authors in [19; 20; 21] further studied the receiver models suitable for SWIPT, including models such as time allocation and power allocation. Power and information are transmitted in different time period, which reduces the power transmission time to a certain extent and affects the power transmission performance. In addition, in order to ensure the reliability of power transmission, the time allocated for signal transmission is relatively short, which mainly limits the signal transmission rate. There are many ways to achieve information transmission in SWIPT system, including radio frequency (RF), dual channel mode, and shared channel mode. For Bluetooth, WiFi, NRF2401 and other RF system, the structures are simple and the transmission speed is stable. However, the reliability and stability of the system may decline in complex electromagnetic environment [22]. The dual-channel technology employs additional information transmission coils. Due to the coupling between the coils, system analysis, and design become complicated. Shared channel technology has the advantages of high integration, stable and reliable information transmission [23; 24; 25]. In shared channel technology, signal transmission modes can be divided into power modulation mode and carrier modulation mode [26; 27; 28]. For the power modulation mode, the information transfer can be realized by the voltage regulation, frequency modulation or tuning. In the SWIPT system, adding a voltage regulation circuit in the main circuit, the information is modulated on the power carrier by changing the input voltage [29]. The frequency modulation method changes inverter operating frequency that makes the system be in a resonant or non-resonant state. The information is obtained by detecting the voltage amplitude envelope [30; 31]. The tuning method affects the current by changing the compensation parameters of the circuit, thereby achieving information transfer [32]. These modulation methods have simple structures and principles, so they are easy to implement. However, the information transfer data are limited by the power transfer rate.