Synchronous Acquisition Based On Cross-layer Design For Mechanical Vibration Wireless Sensor Networks

Wireless sensor networks(WSNs)have been applied in mechanical vibration monitoring due to the advantages of flexible mobility and convenient deployment.In mechanical vibration monitoring,the accuracy synchronous acquisition of vibration signals between each WSNS node will directly affects the results of vibration signal analysis and processing.For example,the time difference of the vibration data acquisition of each measurement point in experimental modal analysis will lead to serious phase error,which requires that each acquisition node must ensure the synchronized acquisition of dynamic vibration signals.In the mechanical vibration monitoring,the signals require higher precision for synchronous acquisition between nodes due to the high sampling frequency.However,WSNs,as a distributed system,can't provide a unified global clock for each independent acquisition node due to the physical decentralization,nor can they use multi-channel synchronous sampling and holding device to synchronize acquisition of vibration signals for each sensor,just like wired monitoring system.While each node usually controls acquisition by maintaining local clock,which can't ensure the synchronous acquisition.The main reasons for the low accuracy of synchronous acquisition of WSNs nodes in mechanical vibration monitoring are the low synchronization precision of clock,the spatial jitter of sampling trigger,the time jitter of synchronous acquisition,the accumulation of synchronization error with multi-hop and the vulnerability of synchronization accuracy to temperature and other environmental factors.?????The above problems are the key problems that need to be solved urgently for high-precision synchronous acquisition of mechanical vibration signals in WSNs nodes.In this paper,aiming at the above key issues,the synchronous acquisition method of mechanical vibration WSN is deeply studied.The specific research contents are as follows:(1)Aiming at the problem of spatial jitter triggered by multi-hop synchronization in mechanical vibration WSNs,a multi-hop cross-layer synchronization acquisition spatial jitter control method based on beacon transmission offset compensation is proposed.A WSNs platform based on hardware cross-layer design uses a single pulse frame Start of Frame Delimiter(SFD)in multi-hop beacon networks as the key synchronization information to avoid random delay in synchronous information transmission between transport protocol stack and node module and module;adopt the preemptive centralized associated beacon timing allocation method to manage the beacon timing,calibrates the key synchronization information transmission offset through the compensation method of beacon transmission offset captured by synchronization information across layers,and realizes the high-precision synchronization trigger of mechanical vibration wireless sensor multi-hop network.(2)Aiming at the problem of synchronous acquisition time jitter in mechanical vibration WSNs,the mechanism of synchronous acquisition time jitter in mechanical vibration WSNs is analyzed.A synchronous acquisition time jitter suppression method based on cross-layer real-time tracking of synchronous information is proposed.Based on synchronization information cross-layer real-time tracking synchronization error feedback control system,using periodic key synchronization information dynamic feedback and compensating residual synchronization error,the time jitter of vibration data acquisition can be effectively controlled.(3)Aiming at the problem that synchronous acquisition errors of mechanical vibration WSNs accumulate with the number of hops in the network,a method of multi-hop cumulative error control for synchronous acquisition of mechanical vibration WSNs based on regression analysis is proposed.A multi-hardware cross-layer design node architecture is proposed to eliminate the influence of embedded software scheduling delay and improve the real-time performance of synchronous tasks.A mathematical model of random hysteresis for cross-layer transmission over wireless links is established,and the random jitter of synchronization information and the calculation error of transmission delay are calibrated by regression analysis method to restrain the multi-hop accumulation of synchronization error.(4)In order to solve the problem that the crystal oscillator drift of WSNs node caused by the change of ambient temperature is difficult to ensure the synchronous acquisition accuracy between nodes,a synchronous acquisition method of mechanical vibration WSNs with crystal oscillator drift compensation is proposed.Firstly,the drift characteristics of crystal oscillator are studied,a mathematical model is established for the ideal temperature drift characteristics of crystal oscillator,and the thermal hysteresis Considering the complexity of synchronization acquisition algorithm,multi-level hierarchical clock architecture management tasks such as synchronization state monitoring and crystal oscillator compensation are proposed;least square crystal oscillator drift calibration method based on temperature drift model is proposed to suppress crystal oscillator ideal drift characteristics,and variable period fuzzy PID control algorithm is used to suppress crystal oscillator ideal drift characteristics.The non ideal drift characteristics of crystal oscillator maintain synchronous acquisition accuracy under severe temperature drift environment.(5)The system integration of mechanical vibration WSNs is carried out,and the order tracking technology based on mechanical vibration WSNs is realized.Finally,the performance of the monitoring system is tested by experiment and application.Finally,this paper summarizes the research work of this paper and looks forward to the future research direction.