Research On Underwater Acoustic Cooperative Detection Based On Single Carrier Frequency Domain Equalization

Human exploitation of marine resources cannot be separated from the support of underwater acoustic communication and other infrastructure. However, the underwater acoustic channel which leads to the low link reliability of underwater acoustic communication is one of the most complex wireless communication channels. The proposed cooperative communication provides an opportunity to solve this problem because of one of its advantages in improving the reliability of the link.A single antenna structure is used in cooperative communication so it is not limited to the size and volume of the terminal. The cooperative communication technology is very flexible and can be combined with other technologies so it is very suitable for application in underwater acoustic communication. However, the underwater acoustic channel delays spreading for a long time and the equalization technology is adopted in order to eliminate Inter Symbol Interference(ISI). The traditional time domain equalization is to achieve a certain performance that the required tap length is related to the delayed spreading time so the complexity is high. OFDM technology has a certain ability to inhibit ISI, but it has the disadvantage of high peak to average ratio. Considering the complexity and the peak to average ratio, this paper adopts the single carrier frequency domain equalization system because it has the advantages of low peak to average ratio and low complexity. There are a lot of contents in underwater acoustic cooperative communication. The technology of underwater acoustic cooperative detection has been studied in this paper only from the angle of information detection including the combination process and the node selection problem.Firstly, the main characteristics of underwater acoustic channel have been analyzed including the change of sound velocity, acoustic propagation loss, ocean noise, multipath effect and Doppler effect. An underwater acoustic channel model based on the characteristics of the channel is established and the influence of the underwater acoustic channel on the underwater acoustic cooperative detection is analyzed.Secondly, based on the single carrier frequency domain equalization in underwater acoustic cooperative communication system, the adaptive combining method for the signal from each node is studied when the relay node works in amplify and forward mode. Adaptive combining can adaptively adjust the combined coefficients according to the Steady-state Mean Square Error(SMSE) of the signal. The adaptive combining which can achieve similar performance with the Maximum Ratio Combining(MRC) has the simple form and low computational complexity. Based on that, joint adaptive combination and frequency domain Doppler compensation for underwater acoustic cooperative communication is proposed and compares with the existing methods by simulation.Finally, the problem of node selection in underwater acoustic cooperative communication system is studied, and a relay node selection scheme based on SMSE is proposed. In this scheme, the output SMSE in frequency domain is used as an index to select nodes because the SMSE is an important parameter influencing the performance of frequency domain equalization detection. The smaller SMSE is, the better detection performance is. The advantages and disadvantages of the relay are determined according to the SMSE value of each node signal processing. And the implementation of the scheme does not need to assume that the channel state information of each node is known, eliminating the processing of channel estimation which can reduce the complexity of the implementation to a certain extent. In addition, the system capacity and performance are further improved by the combination of node selection and power allocation.