GPS/INS INTEGRATION - SOME CURRENT ISSUES AND DEVELOPMENT PERSPECTIVES

The paper presents a review of the current issues and development perspectives related to the GPS/INS integration. In a short introduction are highlighted the needs in positioning and navigation who concurred to the development of the INS, GPS and GPS/INS systems. Further are presented the INS and GPS specific elements and are identified comparatively theirs operational characteristics. Are exposed, also, the advantages of an integrated GPS/INS architecture in front of single-ended ones and are shown the actual GPS/INS integration architectures. The GPS/INS integration was made in several architectures, known as loosely coupled, tightly coupled and deeply-coupled. The loosely coupled architecture supposes the use of two separate Kalman filters, one for GPS and another one for integration. The second integration architecture, the tightly coupled, is based on a single Kalman filter and uses directly the GPS measurements (pseudo-range and/or pseudo-range rates) to aid the INS. On the other hand, satellite ephemeris data are used to derive pseudo-range from INS. The third and most complex integration architecture, the deeply coupled, uses the data from the INS (the speed solution) to track the satellites with the GPS receiver. Therefore, this architecture combines the GPS navigation and tracking, the INS helping the GPS to reacquire the signal faster when the signal from a satellite is lost. It implies also the use of a single Kalman filter, implementing this time a model to estimate all the states required for GPS/INS integration but also for the satellite tracking. The last section of the paper discuss the limits of the current integration approaches and some developments perspectives.