| With the continuous development of science and technology and information society,target positioning has become a key technology in the emerging applications of wireless sensor networks and the Internet of Things.However,the existing indoor positioning technology has its own shortcomings,none of which can meet the needs of low power consumption,low cost,high precision and large coverage.In order to solve this problem,we hope to introduce the advantages of Lo Ra technology in the field of low power wide area network into the indoor positioning scene.Lo Ra uses Chirp Spread Spectrum(CSS)modulation,and the iot network composed of it has the characteristics of low power consumption,low cost and large coverage,but the current use of Lo Ra network can not achieve high-precision positioning.Previous studies of this research group have shown that the twoantenna base station model using linear frequency modulation signal can realize the positioning system with submeter ranging accuracy,and the research on this positioning model has also made breakthroughs.In order to solve the problem of communication transmission and positioning at the same time,it is necessary to thoroughly master the relevant modulation and demodulation technology.However,there is a lack of in-depth analysis and detailed description of CSS receiver algorithm in various literatures.In this thesis,CSS is selected as the modulation method in indoor positioning scenarios,the modulation and demodulation process and synchronization scheme of CSS are studied,and the detailed algorithm description and performance verification of the physical and mathematical models of CSS receivers are provided,which is conducive to realizing an indoor positioning system with low power consumption,low cost,long transmission distance,high precision and high antiinterference capability is provided.The specific research contents are as follows:(1)This thesis designs CSS frame format that can be extended and applied in indoor positioning scenes,studies CSS communication technology and designs CSS signal modulation and demodulation scheme and mathematical model,including the physical model of CSS modulator and receiver as well as the detailed algorithm flow of signal detection,synchronization and data demodulation.(2)According to the mathematical model of CSS modulation and demodulation scheme,the synchronization process is optimized,and a fine synchronization module is designed based on polyphase filter and frequency offset correction to improve the synchronization accuracy and compensate the carrier frequency offset.In the leading symbol receiving stage of the frame head,the anti-noise performance is improved by the optimization method of average FFT operation,and the error probability of coarse synchronization is reduced.(3)The physical model of the CSS receiver designed in this thesis is given,and the workflow and implementation of each module are described in detail.After considering the influence of sampling frequency deviation on demodulation error,the modulation and demodulation model designed in this thesis is built on the MATLAB software platform and its performance is verified by simulation.The simulation results show that the receiver has good performance,high scalability,high feasibility and good application prospect under the condition of low implementation complexity. |
