The Effect of Time Synchronization on Real Time Implementation of Integrated GPS/INS Systems

A. Moussa, A.S. Ali, N. El-Sheimy

Abstract:	Integrated Global Positioning System (GPS) and Inertial Navigation System (INS) systems have been widely applied in different positioning and navigation applications. The evolution of low cost sensors encouraged the fabrication of low cost navigation systems to satisfy different personal and portable navigation applications. Accurate time synchronization of measurement data from multiple sensors is needed in order to be able to process the GPS/INS data in the integration filter. Inaccurate time synchronization of the sensor measurements adds more randomness to the system and therefore it causes less data fusion performance. Practically speaking, it’s difficult for a system to reach perfect time synchronization due to a number of limitations such as analog to digital conversion delay, data buffering requirements, and signal conditioning latency. Low cost sensors are more susceptible to these limitations. Designing a GPS/INS integration module faces a tradeoff between meeting the accurate synchronization requirement and the cost and simplicity of the hardware design. Regarding the tremendous amount of GPS/INS integration modules produced every year for vehicle and pedestrian purposes, a significant attention should be paid to the effect of synchronization accuracy on the performance of such modules. The study of inaccurate time synchronization effect can clarify how much synchronization inaccuracy the system can accept and also can help designers to reach a suitable compromise between cost and performance to offer simpler and more economic integration systems. In this paper, the effect of time synchronization inaccuracy on the integration solution is investigated. Inertial sensors measurements of field test are processed to simulate different levels of time synchronization accuracy and GPS signal outage conditions. These processed measurements are integrated using Loosely Coupled Extended Kalman Filter (LCEKF) to estimate the navigation solution. A comparison of the integration results of different levels of synchronization accuracy is presented. The results of the presented test with low cost GPS and IMU units show that a synchronization inaccuracy of up to 400 ms has only a sub meter degradation effect on the position solution, which is acceptable for many applications which use low cost units. This recommends adopting more flexible, simpler, and more economic designs for (GPS/INS) integration modules used in these applications.
Published in:	Proceedings of the 2010 International Technical Meeting of The Institute of Navigation January 25 - 27, 2010 Catamaran Resort Hotel San Diego, CA
Pages:	43 - 48
Cite this article:	Moussa, A., Ali, A.S., El-Sheimy, N., "The Effect of Time Synchronization on Real Time Implementation of Integrated GPS/INS Systems," Proceedings of the 2010 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2010, pp. 43-48.
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