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Stanford GPS/GNSS Matlab Platform :
Integrated Research Platform
with Unbounded Positioning Database
February 2009
Juyong Do
Stanford University
Stanford GPS/GNSS Matlab Platform
Stanford GPS Matlab Platform (SGMP) is a platform
that enables you to use GPS/GNSS measurements
in various formats for your GPS research activity.
Measurement
GPS/GNSS GPS Simulator
Interface
Measurement
User Interface
Stanford University - GPS Laboratory 2
Key Aspects of SGMP
Everything Matlab
Matlab has been most popular for GPS/GNSS research. So
let’s move everything to the world of Matlab for seamless and
uninterrupted research.
Access to Unbounded Database
Convert positioning database in various formats (NSTB,
NMEA, RINEX…) to a single format in Matlab.
Integrated Platform
SGMP is a platform intended for GPS simulation as well as
measurement interface. Any simulation based on SGMP
format can operate under SGMP platform.
Stanford University - GPS Laboratory 3
Components in SGMP
Measurement
GPS/GNSS GPS Simulator
Interface
Measurement
User Interface
Measurement Interface
Convert various formats to SGMP format.
GPS Simulator
Position estimation, RAIM research…
User Interface
Provides user control.
Stanford University - GPS Laboratory 4
Measurement Interface
An interface to various formats of GPS intermediate
measurements (psuedorange). All supported formats of
measurements are converted to a Matlab format.
NSTB
Database
Measurement
RINEX Interface SGMP
Database Database
NMEA
Database
Extension to other sensors (TV, WiFi, INS…)?
Stanford University - GPS Laboratory 5
Input Formats: NSTB, …
National Satellite Test Bed (NSTB)
A data format for Test Bed Reference Station (TRS) and WAAS Reference
Stations (WRS) data. The recorded data includes GPS measurements;
ephemeris and almanac data; GEO measurement and WAAS broadcast data;
as provided by the GPS receivers at the Reference sites.
Receiver Independent Exchange Format (RINEX)
A data interchange format for raw satellite navigation system data. This allows
the user to post-process the received data (usually with other data unknown to
the original receiver, such as better models of the atmospheric conditions at
time of measurement) to produce a more accurate solution.
National Marine Electronics Association (NMEA)
NMEA 0183 (or NMEA for short) is a combined electrical and data
specification for communication between marine electronic devices such as
echo sounder, sonars, anemometer (wind speed and direction), gyrocompass,
autopilot, GPS receivers and many other types of instruments. It has been
defined by, and is controlled by, the U.S.-based National Marine Electronics
Association.
Stanford University - GPS Laboratory 6
NSTB Stations
Stanford University - GPS Laboratory 7
Output Format: SGMP
info
Structured data tree rx meas tx
rx contains information
and measurements by a aiding
eph
receiver during a specific waas
time frame. almanac
rx.info, rx.meas, and iono
rx.aiding. utc
tms
Field Description
tus
info receiver and data file information
sqm
meas measurements by receiver
aiding aiding information from external sources sqminfo
waasstatus
Stanford University - GPS Laboratory 8
rx.info
rx.info contains receiver specific static information
such as receiver type and the start and end time of
overall data file.
Field Description
id User defined receiver identification number
sitename receiver site name
type receiver type
initpos initial position of receiver in XYZ (meter) and
equivalent to true position for stationary
receiver
gpswk reference time in gps week number
starttow start time of reception in time of week
(second)
endtow end time of reception in time of week
(second)
Stanford University - GPS Laboratory 9
rx.meas.tx
rx.meas.tx contains transmitter specific
measurements for given reference measurement
time.
Field Description
prn transmitter identification number. prn for GPS
satellites
numch number of channels for this transmitter
pr pseudo-range (meter)
cr carrier-range (meter)
dp Doppler (meter/second)
snr signal-to-noise ratio (dBHz)
slip cyclic slip counter (0-7)
Stanford University - GPS Laboratory 10
rx.aiding
rx.aiding contains aiding information provided by
external sources such as GPS satellites and WAAS
satellites. Includes eph, waas, almanac, iono, utc,
tms, tus, sqm, sqminfo, and waasstatus.
Field Description
eph ephemeris and clock parameters from GPS
navigation message
waas WAAS broadcast message
almanac almanac message
iono ionosphere (Klobuchar) message
utc UTC message
tms TMS to TUS message
tus TUS to TMS message
sqm SQM message
sqminfo SQM information message
waasstatus WAAS subsystem status message
Stanford University - GPS Laboratory 11
GPS Simulator
Now We’re Ready to Rock!
GPS Simulator is a block allocated for signal
processing functionalities based on data from
Measurement Interface. A sample program is
provided which can be modified according to user’s
needs.
GPS Simulator
PosFix
Engine
SGMP Multipath
Database Simulation
RAIM
Evaluation
Stanford University - GPS Laboratory 12
Example: Position Fixes
Position Estimation
"Acv EPak 1330 1514 00 0.mat" at (41.0, -124.1, 56.2m) "Acv EPak 1330 1514 00 0.mat" at (41.0, -124.1, 56.2m)
2 15
East (m)
100.0% success with 1.0m (2drms)
0
10
-2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
5
North (m)
5
0
North (m)
-5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0
10
Up (m)
0
-5
-10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
2 -10
Clock (us)
1
0 -15
-15 -10 -5 0 5 10 15
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
East (m)
Time (hour)
Stanford University - GPS Laboratory 13
Example: Position Fixes (cont’d)
"Acv EPak 1330 1514 00 0.mat" at (41.0, -124.1, 58.7m)
30
"Acv EPak 1330 1514 00 0.mat" at (41.0, -124.1, 56.2m) (, ) = -0.0 0.5
20
East
10
6 0
-1.5 -1 -0.5 0 0.5 1 1.5
4
20
2
(, ) = 0.0 0.6
Up (m)
North
0 10
-2
-4 0
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-6
30
4
2 2 (, ) = -0.0 1.5
20
0 1 Up
0
-2 -1
10
North (m) -4 -2
East (m) 0
-5 -4 -3 -2 -1 0 1 2 3 4 5
Position error (m)
Stanford University - GPS Laboratory 14
How it works: Setting Up
Go to waas.stanford.edu
Download and unzip SGMP.zip
You’ll see following directories created under
/SGMPrelease:
• /SGMPrelease/document
• /SGMPrelease/measurement interface
• /SGMPrelease/simulator
• /SGMPrelease/user interface
Stanford University - GPS Laboratory 15
How it works: Parsing
Getting NSTB Data
• Go to http://www.nstb.tc.faa.gov/DisplayNSTBDataDownload.htm
• Download and unzip NSTB files
• Move the unzipped NSTB files to /SGMPrelease/measurement
interface/data/nstb
Parsing
• To parse all NSTB files, use /SGMPrelease/measurement
interface/batchparseNSTB.m
• To parse a NSTB file, use /SGMPrelease/measurement
interface/parseNSTB(filename, starthour, endhour, crccheck)
ex) rx = parseNSTB( 'Acv_EPak_1330_1514_00', 1, 5, 0);
%parse NSTB file from 1 hour to 5 hour without CRC checking
Stanford University - GPS Laboratory 16
How it works: Positioning
Positioning
• After parsing NSTB files to SGMP files (located under
/SGMPrelease/measurement interface/data/parsed), we
are ready to rock!
• Start Matlab and go to /SGMPrelease/simulator/
• Execute batchPosfixSGMP.m
• Alternatively, use posfixNSTB(filename)
Results
• Go to /SGMPrelease/simulator/result/posfix/
• Check out *.mat, *.fig, or *.eps files for results
Stanford University - GPS Laboratory 17
Summary
SGMP (Stanfor GPS/GNSS Matlab Platform) is a
Matlab based platform providing access to multi-
format positioning database.
SGMP enables you to tap into existing and ever-
growing database regardless of formats.
Standardized format (SGMP) opens door to
research collaboration and connection b.t.
generations of students.
Stanford University - GPS Laboratory 18
What’s next…
Measurement Interface
• Support for NMEA, RINEX, …
• Extension to other sensors such as TV, WiFi,…
GPS simulator
• Add more blocks (RAIM simulation, differential
positioning,…)
• For example, NSTB provides dual frequency code and
carrier measurements. Lots of possibilities.
User Interface
• Implement a “Per”-friendly GUI?
Stanford University - GPS Laboratory 19
Reference
1. NstbDataFormat1103.doc Description of NSTB
format
2. www.nstb.tc.faa.gov/DisplayNSTBDataDownloa
d.htm NSTB data files are provided.
3. www.mathworks.com/access/helpdesk/h
elp/techdoc/ref/struct.html Matlab
structure type is described.
4. SGMP.zip
Stanford University - GPS Laboratory 20
Thanks!
Thanks to Euiho and Grace for their earlier
works for NSTB data.
Thanks to Todd, Juan and Per for their inputs to
SGMP.
Thank you, everyone!
Stanford University - GPS Laboratory 21
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