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GLONASS Performances
| GLONASS | |
|---|---|
| Title | GLONASS Performances |
| Author(s) | GMV |
| Level | Basic |
| Year of Publication | 2011 |
Equivalent to the Standard Positioning Service (SPS) and the Precise Positioning Service (PPS) of GPS, GLONASS provides a standard precision (SP) navigation signal and a high precision (HP) navigation signal. These signals are sometimes also referred to as Channel of Standard Accuracy (CSA) and Channel of High Accuracy (CHA), respectively.
However, as in GPS there is Standard Positioning Service Performance and the Precise Positioning Standard, in GLONASS there is no document specifying the performances provided by each service.
Is stated[1] that at peak efficiency, the SP signal offers horizontal positioning accuracy within 5–10 meters, vertical positioning within 15 meters, a velocity vector measuring within 10 cm/s, and timing within 200 ns. However these specifications are outdated, based on the performances provided by GLONASS in the year 2000, before starting the Modernization Plan. According to Sergey Revnivykh, the deputy head of the GLONASS Mission Control Center, a GLONASS performance document will be released in the 2012-2013 time frame.[2]
Currently, accuracy comparisons provided by the Russian System of Differentional Correction and Monitoring,[3] show that GLONASS is slightly less accurate than GPS.
GLONASS Availability
The very low number of operational satellites in the constellation (in 2001 there were only seven satellites) along with a ground segment limited to Russian territory, have been the main reasons of GLONASS poor availability performance. The modernization of the Ground Segment, including new monitoring stations (some of them outside Russia) and especially the increase of the number of satellites in the constellation (in the present, GLONASS constellation consists of 27 satellites in orbit although only 23 of them are operational), have led to almost worldwide coverage and 100% availability in the Russian territory.
The table included below, shows the increasing of the number of satellites and the availability performance (calculated as the percentage of time during which the condition PDOP ≤ 6 is valid at mask angles ≥ 5 deg) from the beginning of 2007 to July 2011.[4]
| Date | Operational Satellites in constellation | Integral Availability Global | Integral Availability on Russian territory |
|---|---|---|---|
| 2011/07/06 | 23 | 99.5 % | 100 % |
| 2011/01/01 | 22 | 99 % | 100 % |
| 2010/01/01 | 15 | 73.6 % | 85.3 % |
| 2009/01/01 | 16 | 87.4 % | 96.6 % |
| 2008/01/01 | 12 | 48 % | 57.6 % |
| 2007/01/01 | 9 | 19.2 % | 26.3 % |
GLONASS accuracy
One of the main objectives of the Global Navigation System (GNS) is to ensure GLONASS performance similar to GPS by the end of 2011. GLONASS traditional poorer performance was the culmination of several factors, such as, poor on board atomic clocks or less accuracy in GLONASS broadcast ephemeris.[5] The improvements carried out on the space, ground-based and user equipment segments have paid off, increasing five times the accuracy of GLONASS in the last years.[6] As it is shown in the figure below, in 2006 GLONASS Signal In Space Range Error (SISRE) at 1 sigma was in the order of 25 m and at the moment of this publication, July 2011, the accuracy of GLONASS is 6-7 meters, the same order as GPS.
Furthermore, as stated by Anatoly Shilov at the 5th international forum on satellite navigation, the accuracy of the Russian navigation system is expected to be improved to 2-3 meters in the following years.
Combined Services Performances
Galileo is being designed to be interoperable with other systems and, therefore, it will, in a great many instances, be used as part of a combined service. The identification of combined services is necessary to:[1]
By combining GLONASS with other GNSS systems, such as GPS, GALILEO, COMPASS, SBAS and GBAS improved performance in the following domains can be expected:
- Availability: Using as an example GLONASS in combination with GPS , the number of operational satellites will be in the region of 60. In normal urban environments this would result in an increased availability for 4 satellites from 40% to more than 90%.
- Position Accuracy: Allied to an increased availability in restricted environments (urban) is a better geometry of spacecraft or enhanced positioning performance.
- Integrity: GNSS based integrity systems and techniques, such as SBAS, RAIM and GBAS, would benefit from the addition of new constellations, including GLONASS, in terms of lower achievable protection levels and/or integrity risk.
- Redundancy: By combining services from separate and fully independent systems full redundancy can be achieved. This is particularly important for Safety of Life applications that require full system backup.