V.B. Pudlovskiy – Ph.D. (Eng.), Senior Research Scientist, 

Russian Metrological Institute of Technical Physics and Radio Engineering E-mail: pudlovskiy@vniiftri.ru

Navigation by signals from global navigation satellite systems (GNSS) usually requires that navigation receiver (NR) have pseudorange measurements from four or more navigation satellites (NS) to determine coordinates, object height and to evaluate corrections to the NR time scale relative to the time scale GNSS. The absolute positioning mode based on GNSS signals for an object in motion requires regular evaluation of this correction to the receiver scale due to the low frequency stability of the quartz reference oscillator (QRO) used in the NR.

In difficult conditions for receiving radio navigation signals, for example, in cities with tall buildings, less than four NS of one GNSS are often observed. To provide navigation on the signals of the three satellites, additional information is needed on the exact time scale of the receiver and / or the height of the object.

Currently, several countries, including Russia, have developed subminiature rubidium frequency standards (SRFS) based on the effect of coherent population trapping. SRFS have a frequency instability of no worse than 10-11 and a volume of up to several tens of cubic centimeters, which allows integrating the SRFS in the design of NR.

In order to assess the possibility of determining the coordinates and altitude in the NR using the signals of only three NS, mathematical modeling of navigation sessions was carried out with a forecast of the time scale from the SRFS or QRO.

Based on the simulation results, estimates of coordinate errors and heights for stationary and dynamic objects are obtained using the frequency stability characteristics of real reference generators: type GK-99 and SRFS, developed at the FSUE «VNIIFTRI». The advantages of using the SRFS to estimate the height of an object from the signals of only three satellite are shown for at least 30 minutes.

The use of a highly stable SRFS allows improving the reliability of navigation in difficult conditions for observing GNSS signals, including in a discontinuous navigation field.

1. GLONASS. Printsipy postroeniya i funktsionirovaniya. Pod red. A.I. Perova, V.N. Kharisova. M.: Radiotekhnika. 2010. [in Russian]
2. Accubeat LTD. URL: http://www.accubeat.com/product-item/nano-atomic-clock-nac1 (data obrashcheniya: 15.11.2019).
3. Microsemi company. URL: https://www.microsemi.com/product-directory/clocks-frequency-references/3824-chip-scale-atomic-clockcsac (data obrashcheniya: 15.11.2019).
4. V Rossii sozdan sverkhminiatyurnyy standart chastoty dlya 5G i «bespilotnikov». URL: http://www.vniiftri.ru/ru/news-ru/item/676-vrossii-sozdan-sverkhminiatyurnyj-standart-chastoty-dlya-5g-i-bespilotnikov (data obrashcheniya: 15.11.2019). [in Russian]
5. Sturza M. GPS Navigation using Three Satellites and a Precise Clock / Navigation. Summer 1983. V. 30. № 2. P. 146–156.
6. Krawinkel, Thomas: Improved GNSS navigation with chip-scale atomic clocks. München: Verlag der Bayerischen Akademie der Wissenschaften, 2018 (Veröffentlichungen der DGK, Reihe C, Dissertationen; 823), XV, 97 S. ISBN 978-3-7696-5235-2, https://doi.org/10.15488/4684.
7. Kharisov V.N., Pastukhov A.V. Uproshchennoe modelirovanie priemnikov SRNS na osnove vvedeniya statisticheski ekvivalentnykh korrelyatorov. Radiotekhnika. 2002. № 7. S. 106–112. [in Russian]
8. Pudlovskiy V.B. Metody i algoritmy navigatsionnykh opredeleniy s ispol'zovaniem retranslirovannykh signalov sputnikovykh radionavigatsionnykh sistem. Diss. … k.t.n. MGTU im. N.E. Baumana. M. 2009. [in Russian]
9. Shatilov A.Y. Reference Oscillator Short-Term Drift as it’s Sensed by GNSS Receiver. Proceedings of the 27th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2014), Tampa, Florida. September 2014. P. 2625–2634.