Research On Underwater Acoustic Communication Technology Based On OFDM Coding

In the exploit of offshore oil resources,the prevention and control of the overflow and blowout of deep oil-gas wells is an important work in the process of oil drilling.The underwater overflow monitoring device is located at 1²km below sea level,which by detecting the change of the flow velocity of oil-based drilling fluid and the change of gas content in the underwater pipeline,the early water overflow monitoring and warning is realized,and the longer warning time is won for the well control.In order to transmit the data from the monitoring device to the base station at high speed and reliably,this paper studies the channel characteristics of the underwater acoustic channel and designs a low cost and low power underwater acoustic communication scheme based on OFDM coding.This paper starts with the communication sonar equation,analyzes the characteristics of the ocean channel in detail,and puts forward some countermeasures.Secondly,the implementation and key technologies of underwater acoustic communication based on OFDM system are discussed in detail,it includes using the way of adding zero in the frequency domain and taking its real part to carry out the OFDM modulation;using the cyclic prefix whose length is 2⁴ times as much as the root mean square of the channel delay to fight the ISI;using deep clipping method to reduce the peak to average power ratio of OFDM system;and using CAZAC sequence to solve the problem of time and frequency synchronization in OFDM.Nextly,this paper uses the BELLHOP model for modeling and analyzing the ocean channel,and obtains the oceanic acoustic line and channel unit impulse response and the coherent propagation loss graph,which provides reference for the selection of central frequency,bandwidth and receiver location.The communication algorithm based on OFDM is simulated and instantiated by MATLAB and ModelSim.It demonstrates the feasibility of the scheme and the balance selection between SNR,bit error rate and power consumption is proposed.The SNR of the receiver should not be less than 10dB,and16²0dB should be selected.Then,the OFDM communication in the ocean channel condition with vertical distance 1490m and 5 level clear wind is simulated by MATLAB.Under the condition of transmitting acoustic power 185dB,the center frequency is 20kHz and the bandwidth is 8k Hz,the image transmission with a bit error rate of 0.648%and a communication rate of 12.698kbps is achieved.Finally,this paper builds the software and hardware experiment platform,completes the hardware design of MSP4305438A and FPGA as control and digital signal processing.Last but not least,the OFDM communication experiment is completed under the narrow and strong multipath interference pool channel.In the case of effective data communication rate is 15.87kbps,the bit error rate is 9.8%,and in the case of effective data communication rate is 10.58kbps,the bit error rate is 6.7×10^-4.