Research On Underwater Acoustic Channel Modelling And Communication Scheme For Large Storage Tank

China is a large country in energy. With the rapid development of national economy, the demand for oil in our country is growing. As the most important facilities in oil storage, the safety of large-scale storage tank has been paid close extensive attention as its number increases fast. The leakage accident of an oil tank may cause huge economic losses, even pose a threat to people’s personal and property safety. The background of this paper is the application of an oil storage tank bottom corrosion on-line detection system based on cruising wireless sensor nodes. Underwater acoustic communication technique and scheme within the storage tank are researched in this paper. The study includes the following aspects:(1) The underwater acoustic channel model of oil storage tanks is built. The underwater channel impulse responses of confined spaces with different shapes and sizes are clarified. The characteristic of multipath signal in storage tank is discussed and compared to multipath signal in the sea. All these studies provide the theoretical foundation for the construction of underwater acoustic communication scheme suitable for storage tanks.(2) Direct at the characteristic of underwater channel and demand of underwater communication in storage tanks, direct sequence spread spectrum OFDM(orthogonal frequency division multiplexing) scheme is proposed. The anti-multipath property of spread spectrum OFDM(SS-OFDM) is analyzed. The channel coding scheme of spread spectrum OFDM is dicussed. The computer simulation and experimental results showed that spread spectrum OFDM has more reliable transmission performance than conventional OFDM scheme in storage tanks.(3) In the detection process, the cruising sensor nodes need to send the collected corrosion acoustic emission data back to central control station, which requires the transmission speed as high as possible. The spread spectrum process reduces the spectrum efficiency of SS-OFDM system. Due to the spread sequence is short in the application, a mapping sequence spread spectrum OFDM(MSSS-OFDM)system is proposed. The simulation and experimental results verified the MSSS-OFDM system can improve the system transmission rate by twice.(4) The influence of Doppler frequency shift on underwater acoustic communication system is analyzed. A Doppler factor estimation method based on the maximum correlation peak shift is proposed. Two-step compensation method is adopted in the Doppler shift compensation process. The proposed method is characterized by light computational load, therefore it can meet the needs of real-time processing. The experimental results verified that the proposed estimation and compensation methods can effectively eliminate the influence of Doppler shift induced by the motion of cruising sensor nodes.