Design and simulation of integrated navigation system

with satellite correction

A.Petukhov

Kazan State Technical University of A.N.Tupolev's name

14-61, Ak.Korolyova, Kazan, 420039, Russia

 

Navigation systems, basically used on aircrafts and submarines, are widely applied also on other mobile objects. The main goal of such systems is to ensure high precision at any conditions, shocks, while loosing signal etc. At the same time as they become widespread, it is most important to find cheaper and easier technologies. Creation of high-precision, but very expensive instruments can have no prospects.

Due to this, most popular is a combination of few devices, called integrated navigation systems. In integrated systems, quite pure precision of one instrument is compensated with other devices. Connecting together number of instruments makes it possible to increase quality and decrease cost.

This article describes an experience of developing and testing integrated navigation system for small aircrafts. Here, in the developing of initial known statements and introduced main ideas, it is presented some next obtained results. The researches were started in Italy, at Bologna University in Forly in framework of International Inter-University Project "TEAM" by students and post-graduates from Italy, Russia and Canada.

Let consider navigation system, that consists of sensors, computer and input/output devices. Navigation system includes following sensors: Gyro-block - AHRS (attitude and heading reference system); global positioning system - GPS; air data system - ADS.

Each device is connected to a PC via serial ports (COM1, COM2, COM3). Special drivers were designed to achieve information in asynchronous mode. Highest frequency is in AHRS, about 100 Hz. This frequency is used to synchronize whole system, and AHRS timer is used as common timer. ADS frequency is about 1 Hz (time per second), estimation period of GPS varies from seconds to minutes and more due to conditions.

All signals are computed in a PC, which is a special (embedded) computer, based on a Pentium processor about 200 MHz and solid hard disk. Actually, computer doesn't contain any movable parts, which allow to sustain heavy conditions, such as shocks, accelerations, vibration. Software is based on Microsoft Windows NT, modified specially for this particular type of PC.

Two main tasks commonly are solved: estimation parameters of a motion for immediate use; collecting data for later analysis, testing etc.

Each sensor of the whole system is a sub-system, which provide navigation information. Best precision of co-ordinates is provided by GPS, but it is liable to signal lack because of different conditions. Also there is no information if there is no connection to satellites. Most simple and reliable is ADS, but the precision is lowest. AHRS (used as strapped-down inertial navigation system) gives data on highest frequency, but errors grow with square of time.

Profitable combination of benefits of various systems is the goal of integrated systems design.