Enhanced GPS: The tight integration of received cellular timing signals and GNSS receivers for ubiquitous positioning

GNSS receivers have been developed over 40 years with increasing levels of integration and performance, and are now able to operate in much more severe signal-degraded environments than before. Despite this, the goal of ubiquitous positioning with GNSS-only receivers is still far away, and GNSS receivers generally need support by combining, loosely or tightly, with other positioning systems. This paper describes the Enhanced GPS system (EGPS), a system that tightly couples timing measurements and timing-based positioning made using cellular network signals, with GNSS receivers in cellular telephones. The system is able to achieve a near ubiquitous positioning capability, along with improvements in time to fix.