Research On The Key Technology Of Through–metal-wall Wireless Communication Based On The Ultrasonic Transducers

In modern defense and industrial equipment,the need for through-metal-structure wireless communication is gradually becoming indispensable.In those circumstances which are surrounded by metal barrier,effective data transmission cannot be achieved by traditional electromagnetic telecommunications due to Faraday shielding.For the advantages of strong penetrance and good convergence,it's ideal to transmit the picture,voice and video through metal wall in the form of ultrasonic waves without physical penetration.In this paper,the key technologies of ultrasonic wireless communication is deeply studied,which is divided into two parts: low-speed communication and high-speed communication.The main content of this paper include:(1)This paper introduces the key technologies of high reliable half-duplex communication.There are the digital amplitude modulation when the data transmits from the transmitter to the receiving end and the data transmission based on impedance modulation from the receiving end to the transmitter.The system general design is discussed,while the information coding and decoding methods are designed according to the information type.(2)In order to improve the bit rate of communication,the technology based on echoes canceling is studied.The channel's characteristics is measured in detail by the voltage transfer function and impulse response.The response signal is used for system identification,and then a more accurate model of the ultrasonic channel is built.A pre-distortion equalizer is directly derived based on the identified model.The simulation result indicate that data rates on the order of 100 Kbps at least.However,this techonology's realiability is decreased in engineering application because of the shortcomings include the high precision for system identification and less resistance to interference.(3)The through-metal-wall ultrasonic high-speed communication technology based on OFDM is studied.Then the modulation scheme is designed based on the real channel.An algorithm which realize frame synchronization,frequency offset estimation,phase tracking is proposed.The system parameters consists of subcarrier,cyclic prefix and symbol length are determined based on the pulse response result.Convolutional coding,punching,and intertexture are applied for improving the system's reliability.Through the comparison for BPSK and QPSK in different SNR environment,simulation results illustrate that this technology can improve the data rate on the order of 1Mbps by overcoming the ISI.(4)The half-duplex low-speed communication system is built and its performance is tested by transmitting temperature and picture at 10 Kbps steadily with low bit error rate.After develop the principle experimental system,it is verified that OFDM modulation scheme can effectively improve the data rate to 1Mbps.Based on experiment,the scheme designed in the test is feasible.