Research On Underwater Acoustic Communication Technology And Its Implementation For Micro AUVs

With the rapid development of science and technology,underwater cable-less submersible,also known as autonomous underwater vehicle(AUV),is increasingly used in the development of marine resources.AUV can use underwater acoustic communication without restriction of control cables,greatly increasing the flexibility of underwater operations.Among them,micro-sized autonomous underwater vehicles(uAUVs)with a size less than 2 m can perform surveying,searching,rescuing and reconnaissance tasks in narrower restricted waters because of their high flexibility,easy operation and low cost,which has become a hot research direction of AUV.At present,uAUVs mainly use optical or radio as the main means of communication,requiring the submarine to float to the surface first and transmission distance is limited;underwater acoustic communication,as the only effective means of underwater data transmission,can meet the communication needs of uAUVs.Unlike the general acoustic communication machine or the special AUV underwater acoustic communication system,due to the strict limitation of the size,load and cost of uAUVs,higher requirements and challenges are put forward for the design,implementation and engineering integration of the supporting underwater acoustic communication system.In the popular application scenarios of uAUVs,Direct Sequence Spread Spectrum(DSSS)technology is the most reliable method of communication so far,which is suitable for important control instructions to aircraft.The high-speed transmission efficiency of Orthogonal Frequency Division Multiplexing(OFDM)technology is suitable for large data transmission.However,due to the low transmission speed of underwater acoustic wave,Doppler spread will occur in uAUVs mobile communication process,which lead to frequency offset of received signal,thus affecting carrier recovery of communication system.In addition,uAUVs work in confined and narrow areas,which will inevitably lead to serious multipath expansion,reduce synchronization accuracy and increase inter-symbol interference(ISI)during demodulation.Based on the requirement of uAUVs underwater acoustic communication,combined with DSSS and OFDM technology,we search for the low complexity hardware implementation scheme of Doppler suppression and synchronous detection technology.Finally,a micro underwater acoustic modem is designed.The main work of this paper is arranged as follows:1.Aiming at the low complexity requirement of Doppler estimation and compensation for the limited computing power processor mounted on uAUVs,the direct hardware compensation of Doppler is implemented by ADC with adjustable sampling rate,and piecewise convolution technology is used to improve the system's synchronous detection performance for the long time delay expansion caused by working in restricted waters.2.Considering the requirement of uAUVs for small size,low cost and load of underwater acoustic communication system,the embedded software and hardware of underwater acoustic MODEM are designed by using low power MCU.3.The design system is validated by sea test and lake test.