The GLObal NAvigation Satellite System (GLONASS), being deployed by the Russian Federation, has much in common with the U. S.' Global Positioning System (GPS) in terms of the satellite constellation, orbits, and signal structure. Both systems are owned and operated by their respective defense departments, and offer precise, global, and continuous position-fixing capabilities. Both transmit spread spectrum signals at two frequencies in the L-band (1.2 GHz and 1.6 GHz), and have pledged to make a partial set of signals available for civil use without any user fees for the next 10 years, or more.
The 24 GLONASS satellites are deployed in three orbital planes; GPS uses 6 planes. The GPS satellites transmit at the same carrier frequency using codes that are orthogonal; GLONASS satellites transmit the same code but at different frequencies.
Unlike GPS, GLONASS has disavowed any plans to degrade the signals available for civil use. The differences in the quality of the position estimates available from GPS and GLONASS are mainly due to this purposeful degradation of the GPS signals, a policy known as Selective Availability (SA). (Beginning in the year 2000, the President will make an annual determination on the continued use of SA.)
Like GPS, GLONASS offers two levels of service. The Channel of Standard Accuracy (CSA), available to all civil users, shall provide horizontal position accuracy of 60 m with 0.997 probability, and vertical position accuracy of 75 m with 0.997 probability. The Channel of High Accuracy (CHA) shall be available only to the authorized users.
GLONASS is still under development. In January 1996, for the first time, the system had a full constellation of 24 working satellites. The year 1996 was also important for user equipment as new GLONASS receivers began to come into the market. However, no satellites were launched in 1996, and so far in 1997. The number of satellites in the constellation now stands at 16. To our knowledge, GLONASS has not announced plans for declaration of readiness for operational use.
This MIT Lincoln Laboratory Web site offers information on the status of GLONASS and the quality of its positioning capability based on continuous monitoring of the GLONASS signals. The information includes constellation status; recent health and availability of the satellites; summary of position estimates obtained from GPS, GLONASS, and the combined set, GPS+GLONASS, over the previous day.
To learn more about GLONASS, refer to:
P. N. Misra, "Integrated Use of GPS and GLONASS in Civil Aviation," Lincoln Laboratory Journal, Vol. 6, No. 2, Summer/Fall 1993.
GLONASS Interface Control Document, International Civil Aviation Organization (ICAO), GNSSP/2-WP/66, Montreal, Canada, 14 November 1995.
P. Daly and P. N. Misra, "GPS and Global Navigation Satellite System (GLONASS)", Chapter 9 in Global Positioning System: Theory and Applications, Vol. II, published as Vol. 164 of Progress in Astronautics and Aeronautics, American Institute of Aeronautics and Astronautics (AIAA), Washington, DC, 1996, pp. 243-272.
S. Feairheller et al, "The Russian GLONASS System," Chapter 10 in Understanding GPS Principles and Applications, Elliott D. Kaplan (ed.), Artech House, Boston, MA, 1996.
P. Misra, M. Pratt, R. Muchnik, B. Burke, and T. Hall, "GLONASS Performance: Measurement Data Quality and System Upkeep," Proc. ION GPS-96, Kansas City, MO, 17-20 September 1996.
T. Hall, B. Burke, M. Pratt and P. Misra, "Comparison of GPS and GPS+GLONASS Posistioning Performance", Proc. ION GPS-97, Kansas City, MO, 16-19 September 1997.