TABLE OF CONTENTS This chapter describes the terrestrial radio navigation systems in use or under development at the time of this writing. Terrestrial radio navigation history is summarized in Section 1.3.1.
Section 9.1 describes the point-source systems: nondirectional beacons (NDBs), VOR, and DME, while Section 9.2 describes Loran. These long-range navigation systems predate GNSS and now act as a backup, as they don't share the common failure modes of the different GNSS systems. They only provide horizontal position fixes, as the signal geometry (see Section 7.1.4) in the vertical axis is generally poor because the transmitters and receiver are usually close to coplanar.
Section 9.3 describes the instrument landing system, which is dedicated to aircraft landing. Section 9.4 reviews a number of relatively new techniques, designed to operate primarily in urban areas and indoors, where GNSS performance is poor. These include use of mobile phones, signals of opportunity, and UWB positioning. Sections 9.5 and 9.6 discuss relative navigation and tracking, respectively, while Section 9.7 discusses sonar positioning for use underwater.
Point-source navigation systems can provide horizontal positioning using measurements from only one station, though multiple stations may be used. NDBs, VOR, and DME are described [1, 2].
Nondirectional beacons broadcast omnidirectional signals between 150 and 1,700 kHz. Some NDBs also broadcast radio stations or transmit LADGNSS information (see Section 8.1.2). Using a direction-finding receiver, a bearing to the beacon, accurate to about 5 , may be measured. A rough position fix may be obtained from two NDBs. Alternatively, an aircraft...
