Adaptive Loop Aiding for Performance Improvement in Weak Signal Environments

Use of loop aiding for facilitating the operation of GPS receivers in weak SNIR environments has been widely researched in recent years. Locata, a terrestrial radio navigation system working on similar principles as GPS, can also make use of loop aiding techniques with some additional advantages. Locata employs dual-frequency and dual-antenna transceivers (LocataLites) allowing a Locata rover receiver to track four signals from each LocataLite. This paper proposes that the carrier tracking loops (CTL) tracking these signals adaptively aid each other to maintain lock in weak signal and moderate dynamics environment. Performance of this proposed scheme is evaluated and an analytical description and test results of the proposed scheme are presented. Results show that the proposed scheme allows tracking with a loop bandwidth (LBW) of 0.5Hz, operating at 20dB-Hz. A relationship between the aided loop’s total phase jitter and the quality of the signal tracked by the aiding loop is also identified and analysed. Using an analytical approach, it is also shown that a lower bound on the aided loop’s expected performance is predictable. It is also established that, by using inter-loop aiding, the Locata system gains more than similarly aided GPS receivers.