| With the rapid development of Low Power Internet of Things(Low-power Io T)technology,various kinds of miniature medical robots have been widely used in intelligent medical scenarios.However,for implantable medical robots or implantable health sensors,the remote control and wireless communication performance of these devices are fundamentally limited by the battery life of the wireless devices.Due to the need to manually replace the battery,the implantable devices cannot operate continuously,which brings a great limitation to the development of the application of implantable devices.The Wireless Powered Communication System(WPCS)is an important strategy to solve this problem.However,the existing solutions of downlink(DL)energy transmission of WPCS can only achieve low energy transmission efficiency,or require the implantable devices and radio frequency(RF)source to remain relatively static,which cannot solve the problem of efficient wireless power supply of implantable devices in the moving state.In addition,due to the large channel fading of implantable devices in the human body,the Uplink(UL)signal-to-noise ratio is low,and subtle changes in the channel will increase the packet error rate of data frame decoding,which cannot meet the demand of the Uplink reliability communication of implantable devices.Therefore,this thesis considers the implantable WPCS assisted by backscattering technology,and designs an efficient downlink energy transmission scheme and a reliable uplink communication scheme suitable for the implantable devices under the moving environment by utilizing the coupling relationship between the energy of backscattering devices and communication.(1)To solve the problem of low energy transmission efficiency of implantable devices in moving scenarios,this thesis proposes to deploy multiple RF sources around the implantable devices,and adopt beamforming scheme to make the energy of multiple RF sources superposition at the receiver,thus improving the energy transmission efficiency.In order to solve the problem of channel estimation when the channel fading is large in human body with beamforming technology,the channel fading is reduced by nonlinear backscattering tags to measure the Channel State Information(CSI)of implantable devices.After obtaining CSI,the transmitter achieves efficient downlink power supply by means of Phase Alignment(PA).Based on the above scheme,a backscattering hardware prototype is designed and the energy supply efficiency of the system for the implantable device in motion is evaluated.The experimental results show that the energy supply efficiency of the proposed scheme is nearly 10 times higher than that of the existing implantable wireless power supply schemes when the motion speed exceeds 100cm/s.(2)Aiming at the problem of packet error rate caused by subtle channel changes in uplink wireless communication of implantable devices,a Polar Code coding scheme suitable for implantable WPCS is designed in this thesis to improve communication reliability through low power coding.Firstly,in order to accommodate the limited power consumption of implantable devices,this thesis designs an optimization algorithm of the storage matrix based on the capacity polarization order of the polarization channel,which effectively reduces the storage resource utilization rate of the encoding.Then,in order to solve the problem that the implantable device is difficult to adjust the transmission rate according to the channel quality,in this thesis,the Frozen Bit Error Rate(FBER)in the polarization code is used to select the coding rate to adapt to different channel states.,so as to ensure the transmission reliability and transmission rate.This thesis evaluates the performance of the encoding scheme in an implanted device scenario.Experimental results show that the proposed scheme achieves a 2.6-fold performance improvement when the packet receiving rate of the communication link constructed by the existing common Internet of Things coding method is only 30%. |
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