Based On The Measurement Of Wlan Wireless Network Node Time Synchronization

With the development of science and technology, the needs and applications ofdistributed measurement are increasing.The main technologies used in distributedmeasurement are wired distributed measurement systems and sensor networks.However, the cable distributed measurement system makes wiring and installation ofmulti-channel measurements become very inconvenient, and the low data rate ofwireless sensor networks can not meet the throughput requirements of real-time andmulti-channel measurement. Traditional wireless distributed systems of WSN andZgbee have some problems such as lower data transfer rate and inadequate timesynchronization accuracy. This paper introduces the WLAN technology to wirelessdistributed measurement and makes an in-depth study of time synchronization in theWLAN wireless distributed systemThis thesis uses the IEEE1588precision time synchronization protocol to solve thetime synchronization problem in the WLAN wireless distributed measurement systemand make an in-depth study of its time synchronization on a WLAN measurement node.The main contents are as follows: For the reaseach on time synchronization of wirelessdistributed measurement systems, this thesis analysis the precision of IEEE1588Precision Time Protocol based on the application layer, driver layer and MAC layer.This thesis mainly bases on the application layer, layer-driven synchronization model.Wireless data transmission technology is a prerequisite for the implementation of thetime synchronization of wireless distributed measurement system. This thesis describesthe establishment of hardware platform and software environment of wirelessmeasurement node. This thesis makes a detailed study of the application layertimestamp of WLAN distributed measurement system. This paper also gives the PTPsoftware implementation process, including the best master clock algorithm, applicationlayer timestamp obtain and clock servo module. A detailed study of the implementationprocess of the driver layer timestamp of the WLAN distributed measurement node ismade too. This thesis gives and implements the methods of how to obtain timestamps in driver layer and how the PTP protocol in application layer can access these timestamps.This paper also gives the test results of a model constituted by a single wirelessnode and a laptop connected by the Ad Hoc. The test results show that the timesynchronization accuracy of IEEE1588protocol based on the application layer timestamp can reach950μS, and its convergence time is400S. But the fluctuations of thetime deviation vary fast, that is Allan variance curve variation fast. The accuracy of thedriver layer timestamp is much better than the accuracy of the application layertimestamp; it can reach20μS, and its convergence time is also400S. Driver layertimestamp synchronization is more stable, Allan variance curve fluctuation much flat.