| Cableway flow measurement uses a metal cableway to control the flow measurement plat-form to move to various underwater measurement points to collect hydrological information,and then the collected data is transmitted to the shore hydrology in the form of switch electrical signals through the loop formed by the cableway and the water body.The station can solve the problem of underwater information transmission.However,the transmission characteristics of the electrical signal in the channel are complex,and the switching electrical signal is affected by many factors during the transmission process,the communication rate is low,the channel noise is susceptible to interference,and the bit error rate is high.Therefore,this graduation thesis proposes to use AC signals for data communication in cableway water channels,to study the transmission characteristics of AC signals in cableway water channels,to analyze communica-tion influence factors and to build a communication system to achieve fast,efficient and stable cableway flow measurement Communication.The main contents of this article include:(1)Clarify the structure of the cableway water loop communication system,analyze the transmission mode of the electrical signal in the channel,test the signal characteristics of the square wave signal and the sine wave signal after the channel is transmitted,according to the attenuated oscillation and sine that appear on the rising and falling edges of the square wave signal The phase shift phenomenon of the wave signal,comprehensively consider the resistance,capacitance and inductance in the water body,propose the equivalent circuit of the cableway water channel,simulate and theoretically analyze the proposed equivalent circuit,and obtain the square wave in the equivalent circuit The damping characteristics of the signal and the amplitude-frequency response and phase-frequency response of the sine wave signal.(2)Use the finite element analysis method to analyze the electrical signal in the channel,establish the cableway water channel model in the finite element simulation software COM-SOL,and use the first boundary condition to simulate the electrical signal transmission path,electric field distribution and electric potential change in the channel,Obtain the transmis-sion process of the electrical signal in the channel intuitively,and simultaneously calculate the equivalent resistance parameter in the channel by simulation,and analyze the attenuation of the low-frequency sine wave signal in the channel in combination with the equivalent circuit.By simulating the movement and environmental parameters of the flow measurement platform The main factors affecting the transmission of electrical signals have been studied,and it is proposed that increasing the plate area can reduce the attenuation of low-frequency sine wave signals in the channel.(3)Build an experimental platform for simulating cableway water channels,conduct signal transmission experiments and collect relevant data,and calculate the equivalent circuit capaci-tance under different conditions through the attenuated oscillation parameters of the square wave signal transmitted through the channel and the equivalent resistance parameters calculated by finite element simulation Inductance value,analyze the influence of plate spacing,plate size and water conductivity on the channel equivalent circuit,build an equivalent circuit model based on the calculated parameters,simulate the equivalent circuit amplitude-frequency curve and phase-frequency curve,and obtain the electrical signal Changes in amplitude attenuation and phase offset are affected by various factors during the transmission process.(4)According to the transmission characteristics of the electric signal in the cableway water channel,the OFDM communication system and the single carrier FSK communication system applied in the channel are proposed,the noise interference in the channel is analyzed,and the channel equivalent circuit is combined to build the communication system model and channel model in Simulink,Simulate the bit error rate performance of the communication system un-der different channel parameters and modulation and coding methods.The simulation results show that OFDM has better communication performance than FSK.By encoding the signal and adopting a suitable modulation method,the OFDM communication system has a bit error rate of less than 10-4in an environment where the signal-to-noise ratio is higher than 18d B.Set up FSK modulation and demodulation circuit to test FSK communication performance in the experimental platform.When the communication rate is 2400bps,the bit error rate reaches the order of 10-3,which can reduce the bit error rate by reducing the communication rate,To prove the feasibility of the proposed communication system. |
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