GPS/MEMS Inertial Integration Methodology and Results

Tom Ford, Jason Hamilton, Mike Bobye and Laurence Day

Abstract:	GPS and inertial systems (INS) provide an obvious synergy whereby low frequency errors in the inertial system are controlled with GPS measurements and at the same time, irregularities in GPS are smoothed or supplemented by continuously available inertial measurements. This technology is well known, and such integrations have been documented since the inception of GPS more than 25 years ago. In that time, inertial systems have evolved from stabilized platforms with spinning mass gyros, to strapdown systems that measure angular change with ring laser or fiber optic gyros to today’s strapdown micro-electrical mechanical systems (MEMS). The MEMS inertial measurement unit (IMU) integrated with GPS, promises to provide a cost effective, low power, low volume position, velocity and attitude system for a myriad of navigation applications. Typical performance for a tactical grade ring laser gyro IMU is 1 deg/hr gyro bias and 1 mg accelerometer bias. The best available MEMS unit currently provides 5 to 10 degrees gyro stability with an industry goal of 1 deg/hr in five years. Other IMU system parameters associated with MEMS are proportionally less certain than those associated with ring laser or fiber optic tactical systems. Therefore, the performance possible with MEMS integrated systems will be proportionally worse than that available from the more mature tactical systems. The system integrator must go to greater lengths to achieve acceptable performance with the MEMS IMUs currently available. This paper describes NovAtel’s experiences in integrating a MEMS IMU (the BAE SiIMU01) with its OEM4-G2 GPS receiver. The performance objective of the system is to provide accuracy over a ten second full or partial outage such that the resulting position at the end of the outage interval can be used to help the GPS carrier positioning software instantly regain carrier ambiguities. The challenge associated with this task is significant and various modeling approaches were used in order to achieve this performance. These approaches are described along with the performance achieved with each of the different modeling methods. In addition, the performance is described during intervals in which only partial satellite coverage is available.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1587 - 1597
Cite this article:	Ford, Tom, Hamilton, Jason, Bobye, Mike, Day, Laurence, "GPS/MEMS Inertial Integration Methodology and Results," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1587-1597.
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