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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)
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The baseline system is specified for 24
satellites, however the system currently employs 28-31 satellites.
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The constellation contains 6 orbital
planes inclined 55 degrees to the equator. Each plane contains 4-7 active
satellites.
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Satellite altitude is 10,898 nmi. or
20,183 Km or 12,500 statute miles from mean surface of the Earth.
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Satellites are in 11 hour 58 minute
orbital periods (half sidereal day).
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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.
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Transmissions are CDMA spread spectrum
signals.
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Time base for system is UTC (USNO: United
States Naval Observatory).
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The current system consists of Boeing
(formerly Rockwell) Block IIA and Lockheed Martin Block IIR and IIR-M
satellites.
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Lockheed Martin Block IIR-M satellites are
currently being launched into the GPS constellation.
Satellite:
Common features of the Block II/IIA satellites:
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Run from 700W EOL (End of Life) power
source of solar panels and batteries.
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12 L-band right hand circularly polarized
helical antenna elements form the spacecraft (S/C) phased array antenna.
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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.
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Two Navigation carrier signals for
transmission: L1 at 1575.42MHz and L2 at 1227.6MHz. Future (IIF +) L5
signals at 1176.45MHz.
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36 available unique PRN (Pseudo Random
Noise) codes, 4 of these are reserved.
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Design lifetime for Block II, IIA S/C is
7.5 years for IIR, IIR-M S/C is 10 years.
Signal characteristics:
Message:
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Navigation message is at 50bps (bits per
second).
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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).
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Transmit Power Levels:
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Receiver Power Levels:
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-L1 SPS
(C/A)
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14.25dBW
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ERIP
25.0dBW
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-L1 (SPS)
- 158.50 dBW (-130.00 dBm)
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Min. Guaranteed Power
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-PPS (PY)
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11.25dBW
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ERIP
22.0dBW
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-L1 (PPS)
- 163.50 dBW (-133.50 dBm)
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Avg. Receiver Power
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-L2 PPS (PY)
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6.35dBW
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ERIP
17.0dBW
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-L2 -
166.00 dBW (-136.00 dBm)
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Min. Guaranteed Power
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-L5
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24.20dBW
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ERIP
23.0dBW
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-L2 -
157.50 dBW (-127.50 dBm)
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Avg. Receiver Power
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-M-Code
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19.00dBW
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ERIP
31.0dBW L1 29.0dBW L2
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-L5 -
161.60 dBW (-131.60 dBm)
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Min. Guaranteed Power
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-L5 -
157.60 dBW (-127.60 dBm)
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Avg. Receiver Power
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(all M-Code values estimated)
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-L5 -
150.00 dBW (-120.00 dBm)
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Max. Power Level
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All levels as per ICD-GPS-705 March
20, 2002
Carriers:
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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)
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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)
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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
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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
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WAAS/EGNOS
- 1575.42MHz
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ILAA
RTCM Radio Beacons (USCG type Beacons)
-283.5-325.0 KHz
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GALILEO
- E1 1575.42MHz
- E2 1561.098MHz
- E5 1191.795MHz
- E6 1278.75MHz
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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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