Extraordinary though satellite navigation may be, GPS and other satellite-based constellations are limited when there is not a line-of-sight or near-line-of-sight path to at least three (and preferably more) satellites. These systems also do not provide sufficiently accurate and reliable altitude information for most applications, especially indoors. Finally, power consumption is an issue for user equipment.
It has been easy to overlook these limitations as the enormous benefits of GNSS have become pervasive, but the increasing demand especially for indoor geolocation now requires a robust solution designed for the indoors and urban canyons. Support for Terrestrial Beacon System (TBS) location technologies was incorporated in Release 13 of the Third Generation Partnership Project (3GPP). These technologies are complementary to GNSS, and provide a comprehensive solution to these limitations.