PSEUDOLITE APPLICATIONS IN POSITIONING AND NAVIGATION

Global navigation satellite systems (GNSS) introduced revolutionary changes in the positioning and navigation, but it is well known that the precision, reliability, availability and integrity of the results obtained by this technology, largely depend on the number and geometric distribution of the satellites being tracked. This is especially problem in areas with limited sky visibility, such as urban canyons, dam monitoring in valleys, deep open-pit mines, larges construction sites. Furthermore, indoors or underground, such as factory halls, inside buildings and tunnels, positioning is totally disabled due to unavailability of satellite signals. To overcome these severe limitations, additional ranging signals transmitted from pseudolites can be include. Pseudolites (the term derived from pseudo-satellite, often abbreviated PL), are ground-based generators and transmitters of GPS-like signals, for use in the local area. Pseudolites can be used to augment the GNSS satellite constellation in case of inadequate satellites coverage and for improvement the geometry, but also as an independent measurement system which can completely replace the GNSS, such as indoors, underground or on the surface of other planets. The pseudolites may seem like a new measurement technology, but the concept of ground-based transmitters can be tracked back to the early development of GPS, when the pseudolites been designed to test the GPS user equipment. Since than, researches teams around the world continuously improve and develop new pseudolite concepts and hardware, trying to adapt them to the requirements of certain applications. This paper presents the theoretical basis, advantages and disadvantages of pseudolite technology, and its application in some areas of positioning and navigation.