Underwater Acoustic Communication Technology For Data Recovery Of Seabed Base Observation Network Based On USV

Recent developments in the field of sea bed observation platforms are the result of the national strategy of enhancing the ocean based research and ensuring the maximum use of ocean for building a strong nation.Despite of many advancements,there is still room for improvement in the field of data recovery technology.Underwater acoustic communication is the most effective method for long distance underwater communication.It has become the key development direction of seabed-based observation data recovery technology.With the recent developments in the field of Unmanned Mobile Platforms,the use of Unmanned Surface Vehicle(USV)with embedded underwater communication equipment has emerged as a new and effective method for seabed-based data recovery network.Its key features include easy integration,fast distribution and low cost.In addition,it can effectively improve the timing of underwater data recovery and can also reduce the risks involved in offshore operation.An USV navigates on the sea surface.Because of its small size and less draft,its operation is severely influenced by sea state and other environmental factors.Hence,the communication equipment fitted onboard an USV should be able to nullify the adverse effect of sea state on its smooth operation.Seabed-based observation network is usually located in shallow water where the environmental conditions are complex and unpredictable.Moreover,the multipaths is observed due to reflections both from sea surface and bottom.One of the core tasks of Unmanned Underwater Vehicle with data recovery unit is to deal efficiently with the changing environmental conditions while ensuring the timely detection and smooth reception of varying communication signals.Some of the practical degrading factors include self-noise interference,random platform movements and other related effects.The practical problem for an USV with underwater communication equipment is to finish communication parameter configuration at physical level to reduce the rate of error and ensure effective communication.Another problem is to design network MAC Protocol to reduce the overall energy consumption of seabed-based observation network and to extend its service life while ensuring data transfer throughout.Based on the above problems,with prime focus on the marine environment-channel characteristics-underwater sound signal processing,this paper sets forth relevant theories and simulation analysis of random interface fluctuations,spatial and temporal characteristics of sound field,underwater acoustic communication system and analysis&design of seabed-based network MAC protocol.Moreover,it provides the theoretical and technical support for seabed-based data recovery system of an USV for underwater acoustic communication based on many lake and sea trials.This paper covers the following four aspects:1.Research and analysis of random interface fluctuation characteristics in underwater acoustic communication.Random motion of the sea surface greatly effects the underwater acoustic communication of USV navigating on the sea.Practically,it is hard to describe this effect quantitatively.Firstly,taking into consideration the wind speed,wind direction and real-time depth of water observed by USV,we establish a wave spectrum model bearing in mind the influence of shallow water sea bottom and data of onboard CORS-GPS.Finally,we calculate the average acoustic reflection coefficient of random fluctuation interface which is then used for simulation analysis of vertical and horizontal channels influenced by interface fluctuation.Simulation result shows that the horizontal channel is affected more by random interface fluctuation and its characteristic signal space-time fluctuation is noteworthy in bad sea conditions.Hence,vertical channels should be given priority over horizontal in data recovery.We used wave spectrum of USV to describe real-time state of sea surface fluctuations and to count&calculate the average acoustic reflection coefficient which is then used for analysis of spatial and temporal distribution of sound field distribution and for parameter configuration of underwater acoustic communication system parameter configuration.2.Research and analysis of characteristic of spatial and temporal distribution of sound field of underwater acoustic communication signals.Under the influence of shallow water random fluctuation interface,spatial and temporal characteristics of sound field distribution has severe effect on system performance.The major focus of this paper is spatial and temporal variation range of signal-to-noise ratio in underwater acoustic communication.Sound field is divided into signal field and noise field to study and analyze spatial and temporal distribution.This paper analyzes the influence of the signal interference caused by sea surface reflection of signal field.After the analysis by sound field interference theory and experimental data,this paper explains the problem of time domain signal distortion and frequency selective fluctuation caused by multipath propagation in underwater acoustic communication.It also covers signal intensity variation with horizontal distance,signal frequency and deployment depth.Moreover,it conducts verification of simulation by comparison with the real data of the Yellow Sea.In terms of noise field,this paper analyzes the spatial and temporal distribution of noise fields under the influence of random sea surface fluctuation.The spatial and temporal distribution of wind-induced noise field is mainly considered.The analysis of experimental data reveals that the time fluctuation of noise basically conforms to the Gauss distribution,and the spatial fluctuation consistency is high.The sound pressure level of offshore surface noise is slightly higher than that of seabed noise.This paper explains the time-varying-air-varying acoustic channel structure from the perspective of sound field.It is found that the communication signal fluctuation is inversely proportional to the frequency,bandwidth,and deployment depth,and positive proportional to the horizontal distance between the transmitter and the receiver.This rule can be used to guide the parameter configuration and network protocol optimization of USV underwater acoustic communication system.3.Research on underwater acoustic communication system for USV based on joint environment-channel sensing.Based on the analysis of the fluctuation characteristics of random interface and acoustic field,a model for evaluating the quality of underwater acoustic communication of USV is proposed for the first time.The evaluation of current channel characteristics is based on real-time sensing of the environmental parameters of USV and the channel sensing parameters.System configuration of parameters such as speed,course of USV and depth of modem.Using PN-vector-OFDM high-speed coherent underwater acoustic communication technique,the effective communication rate is considered as the evaluation index,and the parameters such as vector length,modulation mode,signal length and protection interval are configured.Under the constraints of effective communication rate,the seabed-based observation network data are efficiently recovered.The effectiveness and robustness of the underwater acoustic communication system are verified by two field experiments.4.Analysis and design of data recovery protocol for seabed-based observation network.Starting from the physical layer and combining with the measured marine environment parameters of USV,the sparse and clustered seabed-based network protocols are designed respectively.The energy optimization analysis and data recovery efficiency of both the protocols are also studied.In terms of energy optimization,sparse seabed-based network protocol design is considered.According to the current seabed-based state and underwater acoustic communication capability,the parameters such as USV speed,duty cycle,communication data frame length and interval distance are reasonably optimized.In terms of data recovery efficiency,the protocol design of cluster seabed-based observation network is considered.The problem of node clustering and path planning for USV data recovery is also discussed.The parameter design of cross-layer protocol is analyzed in detail and a multiple access to cross-layer adaptive slot time division protocol is proposed,which improves the data recovery efficiency of cluster network.