INS/GPS Integration Architectures

An inertial navigation system (INS) exhibits relatively low noise from second to second, but tends to drift over time. Typical aircraft inertial navigation errors grow at rates between 1 and 10 nmi/h (1.8 to 18 km/h) of operation. In contrast, Global Positioning System (GPS) errors are relatively noisy from second to second, but exhibit no long-term drift. Using both of these systems is superior to using either alone. Integrating the information from each sensor results in a navigation system that operates like a drift-free INS. There are further benefits to be gained depending on the level at which the information is combined. This presentation will focus on integration architectures, including “loosely coupled,” “tightly coupled,” and “deeply integrated” configurations. (Deep integration is trademarked by Draper Laboratory.) The advantages and disadvantages of each level of integration will be listed. Examples of current and future systems will be cited. 1.0 INTRODUCTION INS/GPS integration is not a new concept [Refs. 1, 2, 3, 4]. Measurements of noninertial quantities have long been incorporated into inertial navigation systems to limit error growth. Examples shown in Figure 1 are barometric “altitude” measurements, Doppler ground speed measurements, Doppler measurements to communications satellites, and range measurements to Omega stations.