Overview

GNSS and inertial technologies have a complicated mutual history.

Once competitors for navigation and positioning applications, they now appear ever more frequently in complementary roles — often within the same solution or system design.

Employing motion sensors (ac­celerometers), rotation sensors (gy­roscopes), and a processing unit that integrates and processes the sensor data, an inertial navigation systems(INS) continuously calcu­lates position, heading, and speed of a moving vehicle, vessel, or aircraft based on dead-reckoning principles.

Before GPS satellites were ever launched, triple redundant INS had be­come state-of-art technology in com­mercial and military aircraft. With a set of initial coordinates, pilots could guide their aircraft from one waypoint to the next using an INS to determine aircraft position and velocity.

More recently, automotive engi­neers have incorporated low-cost inertial technology into car and truck design to improve vehicle stability and control, and to aid on-board nav­igation systems.

One strength of an INS is its auton­omy. Once an INS has been initialized it can operate without depending on external references or information. On the other hand, its dependence on relative positioning makes inertial navigation subject to internal error sources, which may be undetectable without outside aid.

Indeed, the ascendancy of GNSS technology over earlier technologies was foreshadowed in the 1983 KAL 007 incident and its aftermath when a commercial airliner flew off course over Soviet airspace and was shot down. Shortly after the incident, U.S. President Ronald Reagan announced that, following its completion, the Global Positioning System would be made available for civilian use, free of charge, in order to avoid similar navi­gational errors in the future.

Widespread adoption of GPS even­tually revealed the practical limitations of this new technology, too — par­ticularly in places that block or reflect satellite signals: underwater, under­ground, in steep terrain and urban “canyons,”and inside buildings.

Inertial technology is unaffected by such factors. Consequently, interest in bringing these two technologies to­gether is growing among engineers on both sides of the GNSS/INS divide.

To help explain the state of play in GNSS/INS integration, we turned to Dr. Andrey Soloviev, a part-time research faculty at the University of Florida, Research and Engineering Education Facility, and president of Qunav, a small R&D business enter­prise. Previously he served as a senior research engineer at the Ohio Univer­sity Avionics Engineering Center.