Underwater Acoustic Transmission Module Design

With the development of science and technology,mankind's demand for oil and natural gas is increasing.The deep sea has rich oil and gas resources,so deep sea drilling is becoming more and more important.However,there are many emergencies in deep sea drilling,one of which is gas invasion.In order to control sudden events caused by gas invasion during the drilling process,it is necessary to transmit data of real-time monitoring gas invasion to the sea surface,so that people can deal with it in time.In this paper,underwater acoustic communication technology is used to transmit data from the detection terminal to the sea surface.Digital modulation technology is the most widely used in underwater acoustic communication,and MFSK is one of them.MFSK not only has the stability of FSK communication,but also has the advantage of high spectrum utilization.The demodulation of MFSK does not require the restoration of the local carrier.digital demodulation can be used and the performance is stable.MFSK modulation is a good method to achieve medium and low rate underwater acoustic communication.The traditional underwater acoustic communication system has the characteristics of large power consumption,high complexity and high price.This article from the perspective of low-cost and low-power realizes two underwater acoustic communication transmitter modules based on MFSK modulation.One is the underwater acoustic transmission module based on the Nios II's SOPC structure and the other is the underwater acoustic communication transmitter module based on FPGA and MSP430structure.Because MFSK belongs to the multi-carrier modulation,in order to simplify the system,this article adopts DDS technology to achieve carrier switching of different frequencies.In order to reduce the bit error rate and complexity,a synchronization signal is added to each byte of data in the processing of synchronization.In processing the inter-code interference,a DC signal with zero amplitude is added between adjacent carriers.The underwater acoustic communication system design based on MFSK modulation in this paper mainly includes scrambling code?descrambling code?module,interleaving?deinterleaving?module,convolutional code?Viterbi decoding?module,and 4FSK modulation and demodulation module.Besides,these modules are implemented by FPGA and simulated by Modelsim.This paper introduces and implements the related technologies of two kinds of underwater acoustic communication transmitter modules and gives related circuit diagrams.This paper also detailly describes the design of the DAC circuit,the low-pass filter and the design of the amplifier circuit.This article also discusses the advantages and disadvantages of the two schemes from the perspectives of development,power consumption and cost.In the end,this paper verifies the feasibility of the program with experiment and performs a system test and achieves communication rate of 6.15 kbps and error rate of 10^-5.