Positioning performance of chip-scale atomic clock GNSS augmentation systems

Abstract

Current GNSS (Global Navigation Satellite System) receivers include an internal quartz oscillator, such as TCXO (Temperature Compensated Crystal Oscillator) or similar, limited by its frequency stability and a poor accuracy, being one of the main sources of uncertainty in the navigation solution (also multipath and ionosphere effects are an important error sources.) Replacing the internal TCXO clock of GNSS receivers by a higher frequency stability clock such a CSAC (Chip Scale Atomic Clock) can improve the navigation solution in terms of availability, positioning accuracy, tracking recovery, multipath and jamming mitigation and spoofing attacks detection. For achieving these benefits, the deterministic errors from the CSAC need to be modelled, by determining and predicting the clock frequency stability in the positioning estimation process. The procedure of calculating a position without the need of estimating continually the clock error parameter is also known as clock coasting. The presented research shows the potential of the clock coasting method in order to be able to obtain position with only three satellites, improve the vertical positioning accuracy and increase the navigation solution availability.

Research on a chip scale atomic clock driven GNSS/SINS deeply coupled navigation system for augmented performance

“…When no less than four satellites in view, the GNSS receiver is able to determine its three‐dimensional positions and velocity, and clock offset and drift stably. Most GNSS receivers usually employ a low‐profile, and low‐accurate and low‐cost temperature compensated crystal oscillator (TXCO) as a local clock or frequency reference, which offers an inexpensive but sufficient local clock reference for navigation solutions determination [2, 3]. However, it will be preferable to employ a considerably more stable clock than TXCO as a receiver clock reference, for such a precise local clock enables the receivers to output moderate navigation solutions with only three available satellites in view.…”

Research on a chip scale atomic clock aided vector tracking loop

“…Atomic clocks provide the most accurate frequency reference for humans so far [9–14]. The frequency accuracy of the atomic clock (10–11 s) is several orders of magnitude higher than that of crystal oscillators (10 −6 s).…”

“…With the fast development of Micro‐Electro‐Mechanical Systems (MEMS) technology, a commercial Chip Scale Atomic Clock (CSAC) product which has considerately better size and power consumption with lower cost is available now. More specifically, CSAC (SA.45s) has 120 mW power assumption, 40.6 × 35.5 × 11.4 mm physical size and 1.5 × 10–11 s stability [9–14]. Therefore, it is possible to integrate a CSAC into a receiver substituting the traditional Temperature Compensated Crystal Oscillator (TCXO).…”

“…Several works have been carried out for utilising a CSAC as the local time or frequency reference in STL GNSS receivers for robust navigation solution. The results show that dilution of precision (DOP) values could decrease, especially the vertical DOP (VDOP) values [9–14]. Moreover, when the visible satellites amount is 3, the STL GNSS receiver can still produce moderate navigation solutions.…”

“…To our best knowledge, research on CSAC influence on VTL has not been reported. In some work, the CASC is employed as a frequency reference for intermediate frequency (IF) signal collecting [9–15].…”