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مدرنیزه شدن و سیر تحولی سیستم های اندازه گیری ماهواره ای

GPS-III-Lockheed-O

Overview of the GPS constellation and modernisation plans

The Global Positioning System (GPS) was the first space-based navigation system that provides location and time information in all weather conditions, anywhere on the earth. The system provides critical capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, and makes it freely accessible to anyone with a GPS receiver.

It currently consists of 3 different generations of satellites (Block IIR, Block IIR-M, Block IIF - in order of deployment).

Every newer generation of satellites shows certain improvements over the older generation, such as longer lifetime, more and stronger signals and better antennas.

GPS satellite Block IIR Block IIR-M Block IIF Block III Total 
In space/Active 12/12 8/7 12/12 32/31 
Signals  L1 C/A, L1P
L2P
L1 C/A, L1P
L2C, L2P
L1 C/A, L1P
L2C, L2P
L5 (I,Q,I+Q)
L1 C/A, L1P, L1C
L2C, L2P
L5 (I,Q,I+Q) 
 
Comment old generation old generation current generation First launch expected in 2017  

 

 

 

 

 

 

 

 

 

 

 

Visualisation of the GPS constellationConstellationGPS.gif

  • Frequencies: L1 (1575.42 MHz), L2 (1227.60 MHz) and L5 (1176.45 MHz)
  • The GPS phase can be measured with a precision of 0.5 mm by Leica GNSS receivers.
  • Tracking more than one code on the same frequency (e.g. L2C and L2P) requires the corresponding number of channels.

For more details see http://www.gps.gov/

Overview of the Glonass constellation and modernisation plans

GLONASS or "GLObal NAvigation Satellite System", is a space-based satellite navigation system used by the Russian Aerospace Defence Forces. It provides an alternative to GPS and is the second navigation system in operation with global coverage and of comparable precision.

It currently consists of 2 different generations of satellites (GLONASS M, GLONASS K1).

GLONASS satelliteGLONASS M GLONASS K1 GLONASS K2 Total 
In space/Active 27/23  2/0  0 29/23 
Signals  L1C/A, L1P (FDMA*)
L2C, L2P (FDMA*)
(L3I,Q,I+Q; CDMA)**
L1C/A, L1P (FDMA*)
L2C, L2P (FDMA*)
L3 (I,Q,I+Q; CDMA)
L1C/A, L1P (FDMA*)
L2C, L2P (FDMA*)
L1C, L1P (CDMA)
L2C, L2P (CDMA)
L3 (I,Q,I+Q; CDMA)
 
Comment current generation
8 satellites still on ground stock
newer generation (10 K1 by 2020)
currently not yet operational
future generation
(4 K2 by 2020)
 

 

 

 

 

 

 

 

  • FDMA stands for frequency-division multiple access, meaning that every GLONASS satellite has a different frequency. Whereas GPS uses CDMA (code-division multiple acces), meaning that every satellite transmits on the identical frequency and differentiates itself by a unique PRN (pseudo random noise) code.

** The GLONASS M satellites launched from 2014 also transmit the L3 signal.

GlonassConstellation.jpg

Visualisation of the GLONASS constellation

  • Frequencies: L1 (1598.0625 - 1605.375 MHz), L2 (1242.9375 - 1248.625 MHz) and L3 (1207.14 MHz)
  • The GLONASS phase can be measured with a precision of 1 mm by Leica GNSS receivers.

For more details see https://www.glonass-iac.ru/en/

Overview of the Beidou constellation and modernisation plans

The BeiDou Navigation Satellite System (BDS) is a Chinese satellite navigation system. It consists of two separate satellite constellations – an initial test system that has been operating at regional scale since 2000, and a full-scale global navigation system that is currently under construction and will be finalised by 2018.

The BeiDou constellation includes 3 different types of satellites, geostationary satellite (GEO), inclined geosynchronous orbit satellite (IGSO) and medium earth orbit satellite (MEO).

BeiDou satellite GEOIGSOMEOTotal 
Altitude (km) 35786 35786 21528  
In space/Active 5/5  8/8 7/7 20
Final constellation 5 3 27 35
Signals B1 (I,Q,I+Q)
B2 (I,Q,I+Q)
B3 (I,Q,I+Q)
B1 (I,Q,I+Q)
B2 (I,Q,I+Q)
B3 (I,Q,I+Q)
B1 (I,Q,I+Q)
B2 (I,Q,I+Q)
B3 (I,Q,I+Q)
 
Comment located over the Indian
Ocean and the Pacific
symmetrical “figure-8”
ground tracks
similar ground track pattern
as the GPS satellites
 

 

Beidou.bmp

Visualisation of the final BeiDou constellation

  • Frequencies: B1 (1561.098 MHz), B2 (1207.140 MHz) and B3 (1268.52 MHz)
  • The BeiDou phase can be measured with a precision of 1 mm by Leica GNSS receivers.

For more details see http://en.beidou.gov.cn/

Overview of the Galileo constellation and modernisation plans

Galileo is the global navigation satellite system that is created by the European Union (EU) and European Space Agency (ESA).

It is currently in the operational deployment phase and consists of IOV (in orbit validation) and FOC (full operational capability) satellites.

Galileo satellite IOV FOC Total 
In space/Active 4/3* 10/6**   14/9
Signals E1
E5a, E5b, AltBOC (I,Q,I+Q)
E6
E1
E5a, E5b, AltBOC (I,Q,I+Q)
E6
 
Comment old generation current generation
24 (+6 spare) planned by 2020
30

 

 

 

 

 

 

 

  • 1 IOV satellite not available since May 2014

** 2 FOC satellites in wrong orbits, 2 FOC satellites under comissioning

30-satellite_Galileo_constellation.jpg

Visualisation of the final Galileo constellation

Each Galileo satellite is equipped with a passive hydrogen maser atom clock, which measures time to within 0.45 nanoseconds over 12 hours.

Highly accurate atomic clock enables extremely stable signal frequencies, producing distance measurements with a high degree of certainty.

  • Frequencies: E1 (1575.42 MHz), E5a (1176.45 MHz), E5b (1207.14 MHz) and E6 (1278.75 MHz).
  • The Galileo phase can be measured with a precision of 0.5 mm by Leica GNSS receivers.

For more details see http://www.gsa.europa.eu/