Avionics Navigation Systems, 2nd Edition

6 Terrestrial Integrated Radio Communication–Navigation Systems

6.1 INTRODUCTION

Since the 1970s, many radio communication and navigation systems have used the same portion of the frequency spectrum and common technology, such as time synchronous operation, digital modulation, spread spectrum wave forms, coding and user-borne clock oscillators. Synchronous operation, in conjunction with signal time-of-arrival measurement, has lead to a direct method for measuring the range between transmitter and receiver locations in systems using this technology. For these reasons, integrated relative and absolute communication–navigation systems, which provide both digital communication and navigation functions by means of the same wave form, have been widely developed. These systems typically use the content of digital data and the time of arrival of the messages measured by the receiver, to determine the receiver platform's position, through some form of multilateration. In general, the positions are determined in a relative sense within an arbitrary grid, although the unit positions can be referenced to an absolute, geodetic coordinate system, such as latitude, longitude, and altitude, through the use of reference stations whose positions are independently known in the absolute coordinate system. In addition, the position data may be combined in a Kalman filter with dead-reckoning sensor data, such as from an inertial platform, for the purpose of position extrapolation and calibration of ...