Multi-Antenna System And Indoor Positioning System Based On Backscatter Communication Technology

The Internet of Things technology(IOT)has been regarded as the third wave in the field of information technology.Radio frequency identification(RFID)technology has been extensively studied as a key technology of the IOT.However,the traditional RFID system must be equipped with a dedicated reader and communicate through a dedicated radio frequency signal,which results in a short communication distance of the system and cannot be directly connected to other networks.In this regard,the academia has proposed some new backscatter technologies in recent years to improve the performance of RFID systems by multiplexing existing signals in the environment as carrier signals.At the same time,in the field of positioning system,various indoor positioning technologies newly proposed by academia,but lack versatility.The methods of Observed Time Difference of Arrival(OTDOA)and Timing Advance + Angle of Arrival(TA + AOA)supported by 3GPP LTE are all based on the time delay estimation algorithm.Non-line-of-sight(NLOS)propagation brings large positioning error in indoor environment.These problems,combined with the development direction of the industry,this article studies the new backscatter system and the indoor positioning system based on it.First,this article introduces a full-duplex backscatter system based on Wi-Fi signals.Different from traditional RFID systems,Wi-Fi access point are used as readers,and tags communicate with readers by reflecting and modulating Wi-Fi signals.Due to the particularity of the excitation signal,the interference cancellation technology of the full-duplex system is used to eliminate environmental interference,and a method based on maximum ratio combining(MRC)is used for demodulation.On the basis of constructing the system model,the workflow of both parties of communication is summarized,and the communication protocol is planned.Finally,the performance of the system is verified through experimental simulation.Experimental results show that the system is stable.Moreover,by reducing the modulation rate of the tag,the decoding performance can be greatly improved.Faced with the explosive growth of information,in future applications,the requirements for tags' transmission rate will also increase.In order to improve the throughput of the system,a multi-antenna system is proposed based on the Wi-Fi backscatter system.Aiming at the different antenna distribution modes of SIMO,MISO and MIMO,three system models are established respectively.Due to the change in the number of antennas,there are also differences in the signal demodulation methods.Based on these differences,the workflows of the two parties of communication are planned.Finally,through experimental simulation,the improvement of the system performance of the multi-antenna system is verified.The experimental results show that the SIMO and MISO systems further reduce the bit error rate based on the single antenna system,and the MIMO system doubles the system throughput.In addition,this article also attempts to apply the new backscatter technology to indoor positioning systems.Considering the ease of maintenance and low cost of passive tags,the tag is used to construct a line-of-sight transmission environment,and a delay estimation algorithm with lower requirements on the terminal and the environment is used for user positioning.The work model of the positioning system and the communication process between the user and the passive tag are described in detail,and a fairly complete system design is presented.Finally,simulation experiments verify the feasibility and stability of the system,and the performance of this scheme is improved compared with OTDOA.