Research On Key Technologies Of Shallow Water High-speed Underwater Acoustic Communication Based On Filter Bank Multicarrier

The shallow water is an essential part of our country’s territorial sea.Reliable high-speed shallow water acoustic communication is of great significance to speed up Marine development and utilization,protect territorial sea sovereignty,and perfect offshore defensive deployment.However,shallow water acoustic communication is vulnerable to the time-varying characteristics of underwater acoustic channels,marine environmental noise,multipath delay expansion,and large-scale Doppler effects,which seriously restricts the communication system’s speed and performance.Traditional acoustic high-speed communication waveform uses Cyclic Prefix-based Orthogonal Frequency Division Multiplexing(CP-OFDM).Although the use of the Cyclic Prefix(CP)makes CP-OFDM waveforms capable of resisting InterSymbol Interference(ISI),CP-OFDM as a shallow water high-speed communication waveform also has several drawbacks.First,the longer CP leads to a decrease in the communication system’s frequency band utilization.Secondly,the subcarrier bourbon of the CP-OFDM waveform has high energy,which makes its ability to resist inter-carrier interference(ICI)poor.Finally,due to the nature of multi-carrier random phase superposition,the peaks of CP-OFDM waveforms are relatively high,thus limiting the communication distance of CP-OFDM.This paper focuses on the above problems and researches high-speed and reliable new multi-carrier communication in shallow water.Offset Quadrature Amplitude Modulation-based Filter Bank Multi-Carrier is analyzed with emphasis.The application of FBMC-OQAM in shallow water horizontal communication scenarios is mainly reflected in the following aspects:1.Analysis and research on performance advantages of FBMC-OQAM waveform in shallow water horizontal acoustic channel.Previous studies on the performance of underwater acoustic FBMC-OQAM systems are mainly analyzed under specific channels by Monte Carlo simulation,resulting in no extrapolation of conclusions and no analysis of the cause of dominance and dominant boundaries.Therefore,in view of the performance advantages of underwater acoustic FBMC-OQAM waveforms and performance boundary issues,firstly,this paper establishes a shallow water horizontal acoustic channel model and mainly focuses on considering the environmental noise,the multi-path effect,and the Doppler effect caused by the movement of the transceiver,which seriously affects the performance of the communication system;secondly,on the basis of the established shallow water horizontal underwater acoustic channel model,this paper adopts signal to interference ratio(SIR)and bit error rate(BER)as performance evaluation indicators,deduces the SIR and BER closed-form analytical models of CP-OFDM waveform and FBMC-OQAM waveform,and finally verified the accuracy of the closed-form analytical models through Monte Carlo simulation.Through the closed-form modeling of SIR and BER,this paper reveals the interpretation and boundary of the performance advantage of FBMC-OQAM waveform over CP-OFDM waveform in shallow water horizontal channels with different multi-path delay,which provides the theoretical basis for waveform selection of FBMC-OQAM waveform in various shallow water horizontal communication scenarios.2.Study on PAPR reduction of FBMC-OQAM waveform.Given the nature of the FBMCOQAM waveform and the particular interlaced and overlapping data frame structure,the FBMC-OQAM waveform also has the problem of a high peak-to-average power ratio(PAPR).Therefore,this paper studies the PAPR reduction technique for FBMC-OQAM waveform.Due to the interlaced and overlapping frame structure of FBMC-OQAM,the signal amplitudes on both sides of the frame structure are lower.Therefore,the PAPR reduction method under the phase rotation has a minimal effect on FBMC-OQAM.The clipping method as a pre-distortion class scheme will undoubtedly cause a severe deterioration in communication performance.Therefore,this paper mainly studies the method of PAPR reduction under the companding class.This paper finds that when the number of symbols in a single frame is small,the probability density distribution of signal amplitude in the FBMC-OQAM will follow the Laplace distribution instead of the Gaussian distribution.For the practical design requirements of the frame structure,this paper adopts Laplace distribution to derive the companding gain of FBMCOQAM waveform under two scenarios: single inflection point and double inflection point,and obtain the companding ratio and threshold based on Laplace distribution.This paper finds that compared with the Gaussian distribution,the companding scheme under the Laplace distribution has a significant performance improvement in both the complementary cumulative distribution function of the PAPR and the BER for the FBMC-OQAM waveform.3.Pilot design of FBMC-OQAM underwater acoustic signal and study of receiver preprocessing.In order to track the time-varying underwater acoustic channel while increasing the time-varying tracking capability of channel estimation,this paper designs an auxiliary pilot interleaved placement structure based on the traditional FBMC-OQAM comb-type pilot.The structure avoids introducing auxiliary pilot recursion operation and increases the time-domain pilot insertion density,which improves the time-varying tracking ability.Based on the combtype pilot design,this paper proposes a two-step Doppler compensation scheme combining time domain resampling coarse compensation with fine compensation through measuring pilot phase rotation,which can effectively suppress the bit error rate performance loss caused by the Doppler effect.4.The FBMC-OQAM underwater acoustic channel estimation and channel equalization research.Aiming at the strong frequency selective fading underwater acoustic channel with ambient noise interference,this paper proposes a demodulation scheme based on wavelet soft threshold denoising discrete cosine transform(DCT)domain channel estimation and multiple block multiple tap Minimum Mean Square Error(MMSE)channel equalization.Firstly,considering that traditional interpolation methods are susceptible to ambient noise,this paper presents a discrete cosine transform DCT domain channel estimation technique based on wavelet soft threshold denoising.This scheme reduces the influence of environmental noise on channel estimation at the pilot by using the wavelet soft threshold denoising technique.Then,the noise at the interpolation position is eliminated by combining the DCT-based transformation domain technique to improve channel estimation performance.Secondly,since FBMC-OQAM has poor zero forcing demodulation performance in the face of large maximum multipath delay,this paper adopts a channel equalization method based on multiple blocks multiple tap MMSE.The channel equalization matrix takes complete account of the interference of other subcarrier positions of adjacent symbol blocks to the current subcarrier,effectively improves the performance of FBMC-OQAM waveforms in the face of channels with large maximum multipath delay,and provides an effective demodulation method for the practical application of FBMC-OQAM in shallow water horizontal communication.