Overview of low-cost GPS receivers which output raw data

The table below gives an overview of low-cost GPS receivers which output the 'raw' GPS data, such as pseudorange, integrated carrier phase, Doppler shift, satellite ephemeris, and 'processed' data such as position and velocity. These receivers are usually OEM bare board receivers.

The table has been compiled for 'raw data freaks' such as me, people who think they can do a better job with the raw data than the manufacturer  ;-) , or people who like to get down to the basics of (D)GPS.

I invite you to deliver any further relevant rows to the table, fill in missing figures, comment on the numbers, and add other similar receivers.

I am very much interested in cooperating with people in the field of noise/ multipath determination, see below.

Please send your input to samsvl@nlr.nl.

For a detailed explanation of the raw GPS measurements and DGPS, start at Sam Wormley's site, go to Peter Bennett's pages, or try Karen Nakamura 's pages.

Reports on test results can be seen at Waypoint's site.

1 manufacturer Garmin Conexant NovAtel CMC CMC Signav Rojone RoyalTek u-blox Motorola FastraX Ashtech Trimble
  type 25LP Jupiter Superstar II Allstar Superstar MG5001
MG5003
Genius OEM  REB-2100 GPS-MS1 Oncore
M12
iTrax02 G8 LassenSK8
2# channels 12 12 12 12 12 12 12 12 12 12 12 8 8
3# pseudorange Y Y Y Y Y Y Y Y Y Y Y Y Y
4# carrier phase Y Y Y Y Y Y Y Y Y N Y (f) Y
5# Doppler N Y ? Y ? Y Y Y Y Y ? Y Y

6#

iono

N

Y

?

?

?

Y

Y

Y

Y

?

Y

?

Y

7# ephemeris Y Y Y Y ? Y Y Y Y Y Y Y Y
8# position Y Y Y Y Y Y Y Y Y Y Y Y Y
9# velocity Y Y Y Y Y Y Y Y Y Y Y Y Y
10# 1 PPS Y Y Y Y Y Y Y Y Y Y N Y Y
11# 1 PPS acc (ns) 1000 1000 200 200 200 20RMS
100max
0.5 msec ? 180 130 n/a 1000 500
12# clock sync 1 1 1 (3?) 1 1 or 3 3 3? ? 2 or 3 2 (b) ? ? 2
13# clock sync acc ? 200 ? 200 ? N/A ? ? 10 1 ? ? 0.5
14# cold start 300 ? 120 300 120 120 60 60 60 60 50 120 120
15# hot start 15 15 15 30 15 17 8 8 4 15 12 15 20
16# re-acquisition 2 2 1 3 1 1 0.1 0.1 0.1 1 0.1 1 2
17# NMEA-183 out Y Y Y Y Y Y Y Y Y Y Y Y Y
18# DGPS in RTCM RTCM RTCM RTCM RTCM RTCM RTCM RTCM RTCM RTCM N RTCM RTCM
19# DGPS out N N N RTCM (36) N N N N N binary N N N
20# DGPS accuracy 5m RMS 1-5 m 1m CEP 1m CEP 1m CEP 2m CEP 1-5 m 1-5m typical 2 m CEP 1-5m n/a 3m CEP 2m CEP
21 pseudor. noise 0.8 m ? ? ? ? ? ? ? 1 m ? ? ? ?
22 Pr. multip. opt. 2.3 m 2 m ? ? ? ? ? ? 3 m ? ? ? ?
23 Pr. multip. typ. 5 m 2 m ? ? ? ? ? ? ? ? ? ? ?
24 carrier noise 4-8 mm 2-3 mm ? 1 cm ? ? ? ? 5 mm ? ? ? 20 cm(a)
25 Cr. multip. opt. ? ? ? ? ? ? ? ? ? ? ? ? ?
26 Cr. multip. typ ? ? ? ? ? ? ? ? ? ? ? ? ?
27# max alt (km). 18 18 18 18 18 18 18 18 18 18 ? 18 18
28# max speed (m/s) 515 500 514 500 514 515 515 515 515 515 ? 515 515
29# max accel (g) 6 ? 4 4 4 8 4 4 4 4 4 2 4
30# max jerk (m/s3) 60 ? 2 2 2 78 20 ? 20 5 4 ? 20
31# temp range (C) -30/+85 -40/+85 ? -30/+70 -30/+75 -20/+70 0/+70 -10/+70 -40/+85 -40/+85 -40/+85 -30/+80 -10/+60
32# data rate (s-1) 1 1 1 1 to 10 1 1 1 1 1 1 1 1 1
33# Power 3.6 to 6V/
0.115A
5V/0.205A 5V/0.16A
or
3.3V/0.16A
5V/0.24A 5V/0.2A 3.3V/0.16mA
(g)
5V/0.18A 3.3V/0.17A 3.3V/0.15A
(e)
3V/0.075A 2.7V/0.04A 5V/0.14A 5V/0.175A
33# chipset Garmin Zodiac GECPlessey GECPlessey GECPlessey Zarlink (h) SiRF SiRF II SiRF Oncore ? Philips Sierra
34# price (US$) 125 140 150 275 150 199 210 100 152 200(d) ? 140 250

All row numbers marked with a # contain data taken from manufacturers data sheets. Take care in comparing the numbers - the manufacturers may use complete different definitions for their data.

Noise- and multipath measured values are 1 sigma values, unless other identified.

NOTES

  1. Receiver type
  2. Number of parallel channels
  3. Pseudorange is the primary measurement of the receiver; it is the range between the satellite and the receiver, plus a number of errors.
  4. Integrated carrier phase is another range measurement, again with a number of errors.
  5. Doppler is the instantaneous frequency difference between the receiver's internal oscillator and the received carrier from the satellite.
  6. The Iono parameters allow the receiver to calculate an estimate for the ionospheric delay, which can be applied as a correction to the measured pseudorange.
  7. Ephemeris is the parameters to allow the receiver to calculate the satellite's position. The ephemeris data are a part of the 'navigation message'.
  8. No comment.
  9. No comment.
  10. 1PPS is the ability of the receiver to output a discrete pulse on the full GPS second.
  11. 1PPS accuracy is the possible deviation of the 1PPS pulse from the GPS time.
  12. 'Clock sync' is the receiver's ability to 'measure' the raw data exactly on the full GPS second.
    1. Type 1 receivers keep their internal clock continuously synced to the GPS time.
    2. Type 2 receivers reset their clock once it has drifted away a few milliseconds from GPS time.
    3. Type 3 receivers let their internal clock drift away from GPS time for ever (usually they reset their internal clock after power-up once the first valid position calculation is completed).
  13. This number gives the possible deviation of the raw data measurement time from the full GPS second, for type 1 in nanoseconds, for type 2 in milliseconds, and for type 3 not applicable.
  14. Cold start: the time the receiver requires from power up to the first position solution, while starting without initial position, time, almanac and ephemeris.
  15. Hot start: the time the receiver requires from power up to the first position solution, starting with initial position, time, almanac and ephemeris.
  16. Re-acquisition: the time the receiver requires to track again a satellite, which was lost shortly before.
  17. No comment.
  18. The ability of the receiver to process differential corrections in the mentioned format.
  19. The ability of the receiver to generate differential corrections (reference station) in the mentioned format.
  20. The DGPS accuracy as specified by the manufacturer. Sometimes it is not clear how this number is defined by the manufacturer, e.g. 2D or 3D, CEP/SEP or RMS.
  21. Pseudorange noise is determined largely by the quality of the receiver. It can be determined with a so-called Zero Base Line (ZBL) test: connect two identical receivers to one antenna via an antenna splitter. Subtracting a pseudorange as measured by receiver A from a pseudorange to the same satellite as measured by receiver B cancels all common errors, the noise contribution remains. For a more detailed description go to noise.
  22. The quality of the antenna, the location of the antenna and the quality of the receiver determine multipath. Multipath may very well be the largest error for DGPS. Multipath can be determined with a Short Base Line (SBL) test: place two receivers, each with their own antenna, close to each other. Subtracting pseudoranges as above and correct for receiver noise (from the ZBL) gives an indication of the multipath error. Using a high quality antenna (e.g. with choke rings) in a flat area without obstructions should result in a minimal multipath error. For more details go to multipath.
  23. A typical multipath error can be determined using a 'normal' antenna (as recommended by the manufacturer) in your 'normal' working area. Minimal multipath error can be in the sub-meter range for a high quality receiver, typical multipath can be in the order of many meters, even tens of meters.
  24. As in 20, but applied on the integrated carrier phases.
  25. As in 21, see above.
  26. As in 22, see above.
  27. US export restrictions limit most receivers to 60000 ft or 18000 m.
  28. US export restrictions limit most receivers to 999 kts or 515 m/s.
  29. This is the acceleration at which the tracking loops of the receiver loose lock on the satellite, important for high-dynamic applications.
  30. The rate-of-change of the acceleration at which the tracking loops loose lock.
  31. The operating temperature range. Sometimes, extended ranges are available as an option.
  32. The maximum rate (samples/second) at which the receiver can deliver data. If more than once per second, this is usually an option.
  33. The typical power consumption.
  34. This is the chipset that forms the heart of the receiver, and determines to a large extent its quality.
  35. An estimate of the price for one receiver, based on info that I collected from various sources.
  36. But at a price: USD 2000 !!!!

  1. Firmware version 7.52 has been updated with a new TSIP message called 0x6F. This packet contains filtered pseudoranges, and integrated carrier phases. Unfortunately the carrier phases have been truncated to the integer value, which equals to one wavelength or 20 cm.
  2. The Oncore's clock is offset by 20 kHz, which theoretically means that a clock reset is carried out every 89 sec.
  3. Deleted.
  4. Price for the option with 1PPS and raw data US$ 290 (as per 12 Jan 98).
  5. In the 'trickle power mode' the power drops down to 100 mA for 1 Hz rate, to 60 mA for 0.5 Hz rate and to 36 mA for 0.25 Hz rate.
  6. Carrier phase output can be provided as an option. Contact Ashtech at http://www.astech.com.
  7. MG5001 is powered by 3.3 to 5.5 VDC, MG5003 by 3.3VCD +/- 10%
  8. Aka Mitel, aka GECPlessey.

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