Channel Identification And Equalization Of Ultrasonic Through-Thick-Metal-Wall Communication

This paper presents the design of an ultrasonic through-metal-thick-wallcommunication system, which utilizes the strong penetrating capability ofultrasonic wave in the rigid body, and overcomes the shortcomings of thedecreased quality or complete blocking of the traditional radio frequencycommunication caused by skin effect of electromagnetic wave in the metalsurface.According to ultrasonic transducer working mechanism and ultrasonicpropagation characteristics in metal channel, the channel ARX transfer functionmodel of ultrasonic through-metal-thick-wall communication is established, andthe main path transfer function and the echo path transfer function are obtained.Based on input and output data of ultrasonic through-metal communicationprocess, the model parameters are estimated using the least squares complexexponent method （LSCE）, and the model orders are identified using the finalprediction error （FPE）criterion. According to the characteristics of metalchannel echo, based on the experience of the traditional digital communication toeliminate intersymbol interference, an equalizer is inserted before the transferfunction in the main path. Simulation results show that the design of the echocancellation equalizer is effective.Based on the DDS technology, digital output of pulse signal and equalizerwaveform is implemented. After the D/A conversion and low pass filtering,analog small signal is obtained, which drives the ultrasonic probe with goodimpedance matching after voltage amplification and power amplification. Afteramplification and band-pass filtering, the small signal at the receiving probe isconditioned into digital pulse signal through comparison circuit, and then is sentto FPGA I/O port and converted to binary data stream, which are sent to theRAM memory in the form of bytes after FPGA processing.Experimental results indicate that data transfer rate with equalizer reaches20kbps by cancelling ultrasonic metal channel echo，twice that without equalizer,which proves that the design of channel model and equalizer model are correct.