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GNSS Facts

 
Constellation/System:
The NAVSTAR GPS ( Navigation System by Timing and Ranging Global Positioning System) is all weather, continuously available, satellite-based RF positioning system providing highly accurate 3D PVT (Position Velocity & Time)
  • The baseline system is specified for 24 satellites, however the system currently employs 28-31 satellites.
  • The constellation contains 6 orbital planes inclined 55 degrees to the equator. Each plane contains 4-7 active satellites.
  • Satellite altitude is 10,898 nmi. or 20,183 Km or 12,500 statute miles from mean surface of the Earth.
  • Satellites are in 11 hour 58 minute orbital periods (half sidereal day).
  • The system is implemented and operated by the U.S. DoD. FOC (Full Operation Constellation) was declared on 27 April 1995.
 
Navigation parameters are based in the NIMA (National Imagery and Mapping Agency) (formerly DMA) ECEF (Earth Centered Earth Fixed) WGS (World Geodetic System) 1984 datum A worldwide common grid reference system.
  • Transmissions are CDMA spread spectrum signals.
  • Time base for system is UTC (USNO: United States Naval Observatory).
  • The current system consists of Boeing (formerly Rockwell) Block IIA and Lockheed Martin Block IIR and IIR-M satellites.
  • Lockheed Martin Block IIR-M satellites are currently being launched into the GPS constellation.
 
Satellite:
Common features of the Block II/IIA satellites:
  • Run from 700W EOL (End of Life) power source of solar panels and batteries.
  • 12 L-band right hand circularly polarized helical antenna elements form the spacecraft (S/C) phased array antenna.
  • 2 Rubidium and 2 Cesium atomic clocks are onboard II/IIA S/C. 3 Rubidium atomic clocks are on IIR/IIR-M's. UTC time accuracy is better than 30ns.
  • Two Navigation carrier signals for transmission: L1 at 1575.42MHz and L2 at 1227.6MHz. Future (IIF +) L5 signals at 1176.45MHz.
  • 36 available unique PRN (Pseudo Random Noise) codes, 4 of these are reserved.
  • Design lifetime for Block II, IIA S/C is 7.5 years for IIR, IIR-M S/C is 10 years.
 
Signal characteristics:
Message:
  • Navigation message is at 50bps (bits per second).
  • Message structure format, 1500-bit frame (30 second) made up of 5 sub-frames (6 seconds). Each sub-frame is 300 bits long. Superframe consists of 25 subframes (12.5 minutes).
Transmit Power Levels:
 
Receiver Power Levels:
 
-L1 SPS (C/A)
14.25dBW
ERIP 25.0dBW
-L1 (SPS) - 158.50 dBW (-130.00 dBm)
Min. Guaranteed Power
-PPS (PY)
11.25dBW
ERIP 22.0dBW
-L1 (PPS) - 163.50 dBW (-133.50 dBm)
Avg. Receiver Power
-L2 PPS (PY)
6.35dBW
ERIP 17.0dBW
-L2 - 166.00 dBW (-136.00 dBm)
Min. Guaranteed Power
-L5
24.20dBW
ERIP 23.0dBW
-L2 - 157.50 dBW (-127.50 dBm)
Avg. Receiver Power
-M-Code
19.00dBW
ERIP 31.0dBW L1 29.0dBW L2
-L5 - 161.60 dBW (-131.60 dBm)
Min. Guaranteed Power
 
 
-L5 - 157.60 dBW (-127.60 dBm)
Avg. Receiver Power
(all M-Code values estimated)
 
-L5 - 150.00 dBW (-120.00 dBm)
Max. Power Level
  All levels as per ICD-GPS-705  March 20, 2002
 
Carriers:
GPS L1
- Center Frequency 1575.42MHz
- 19cm wavelength (7.48in)
- L1 C/A-Code (Coarse/Acquisition) or SPS (Standards Positioning Services)
- C/A-Code chipping rate of 1.023 Mbps with code period of 1 ms
- C/A-Code bandwidth +/-1.023MHz (to 1st sinc nulls)
- L1 P-Code or Y-Code PPS (Precise Positioning Service)
- P-Code chipping rate of 10.23 Mbps with code period of 1 ms
- P-Code bandwidth +/-10.23MHz (to 1st sinc nulls)
- Bandwidth +/-12MHz (ITU International Telecommunications Union authorized)
 
 
GPS L2
- L2 P-Code or Y-Code PPS (Precise Positioning Service)
- Center Frequency 1227.60MHz
- 24.4cm wavelength (9.61in)
- Bandwidth +/-10.23MHz (to 1st sinc nulls)
- Bandwidth +/-12MHz (ITU authorized)
- Chipping rate of 10.23 Mbps with code period of 7 days
- 267 day pseudo random code generator (divided into 37-7 day segments)
 
GPS L5
- L5 uses codes in-phase (I) and quadrature (Q) I has data message Q does not
- Center Frequency 1176.45MHz
- Bandwidth +/-10.23MHz (to 1st sinc nulls)
- Bandwidth +/-12MHz (ITU International Telecommunications Union authorized)
- Chipping rate of 10.23 Mbps with code period of 1 ms
 
 
GPS M-CODE
- M-Code is a split spectrum signal with a 30MHz bandwidth to 1st nulls
- Center of split spectrum signals are at L1 & L2 band centers

 
WAAS/EGNOS
- 1575.42MHz
 
 
ILAA RTCM Radio Beacons (USCG type Beacons)
-283.5-325.0 KHz
GALILEO
- E1 1575.42MHz
- E2 1561.098MHz
- E5 1191.795MHz
- E6 1278.75MHz
 
 
GLONASS
-L1 1597-1605MHz SPS: bandwidth ~1.022MHz to 1st sinc nulls, centered at each GLONASS L1 SV frequency.
- L2 1240-1260MHz PPS (on L1 & L2) bandwidth 10.22MHz centered at each GLONASS L2 SV frequency.
 

 
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