Toolbox for precise GNSS velocity estimation with time-differenced carrier phase technique

User Manual

Written by:

Pierluigi FredaAntonio AngrisanoSalvatore Gaglione

Salvatore Troisi

July 2014

Parthenope University of NaplesDepartment of Science and Technology

Italy

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Table of Contents

1. Introduction.......................................................................32. Programming Language....................................................33. Run the Program................................................................33.1 Input................................................................................................................................43.2 Functions.........................................................................................................................63.3 Output.............................................................................................................................64. Example Test.....................................................................75. Support..............................................................................8

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1. IntroductionThe toolbox for precise velocity estimation is based on the TDCP (Time-Differenced

Carrier-Phase) technique, which consists in differencing successive carrier phases,

enabling accuracies at mm/s level. As described in the paper “The Time-Differenced

Carrier Phases Technique for Precise GNSS Velocity Estimation” the use of different

broadcast ephemeris sets to calculate the satellite positions and clock offset, produces a

discontinuity in the TDCP measurements that affects the velocity estimation. To

overcome this drawback, the same ephemeris set is used to obtain the satellite clock

bias at consecutive epochs.

This manual describes all the steps to use the associated software.

2. Programming LanguageThe source codes are developed in MATLAB® Version 8.0.0.783 (R2012b) under OS

X Mavericks Version 10.9.4 and can be run on Windows too.

MATLAB® is a high-level language and interactive environment for numerical

computation, analysis and visualization of data. MATLAB enables to analyse data, and

develop algorithms to create models and applications. The language, tools and

mathematical functions built-in allow to explore different approaches and to reach a

solution faster than using traditional programming languages. Many applications

developed under MATLAB are portable and can be readily run on Windows,

Macintosh, and Unix/Linux operating systems (OS).

3. Run the ProgramThis toolbox consists of:

- “Test_Data” (folder) is a data set for a demo program processing.

This folder contains two file .mat.

The first is“NAPO078.mat” that includes the variables DOY (Day of The Year),

XYZ_station (approximate user coordinates), dt_data (data-rate), eph_GPS

(broadcast ephemeris), iono_corr (ionospheric corrections transmitted by the

navigation message), leap_sec (leap second), observation (observation data),

GDOP and user_position include respectively GDOP values, ECEF user

position and user clock offset previously estimated.

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The second is “solution_nap.mat” that includes the true user position.

- “Library” (folder) includes a set of MATLAB m-files (function);

- “main_TDCP” (.m) is the main program.

3.1 InputThe software “main_TDCP.m” accepts in input the following variables:

- leap_sec

o it is the number of leap seconds and is a scalar

- observations

o it contains the measurements

- dt_data

o it is data interval and is a scalar

- eph_GPS

o it contains the GPS ephemerides

- iono_corr

o it contains the parameter to implement the Klobuchar model

- DOY

o It is the day of the year and it is a scalar

- GDOP

o It contains the GDOP values at each considered epoch

- user_postion

o it contains the user coordinates in ECEF frame at each epoch

The format of the variable “observation” is described below

FORMAT “observation”week toe SV prn C1 L1

The format of the variable “eph_GPS” is described below

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FORMAT “eph_GPS”

eph_GPS(1,:) SVprn

eph_GPS(2,:) week

eph_GPS(3,:) toe

eph_GPS(4,:) af0

eph_GPS(5,:) af1

eph_GPS(6,:) af2

eph_GPS(7,:) IODE

eph_GPS(8,:) crs

eph_GPS(9,:) deltan

eph_GPS(10,:) M0

eph_GPS(11,:) cuc

eph_GPS(12,:) ecc

eph_GPS(13,:) cus

eph_GPS(14,:) roota

eph_GPS(15,:) toe

eph_GPS(16,:) cic

eph_GPS(17,:) Omega0

eph_GPS(18,:) cis

eph_GPS(19,:) i0

eph_GPS(20,:) crc

eph_GPS(21,:) omega

eph_GPS(22,:) omegadot

eph_GPS(23,:) idot

eph_GPS(24,:) CodesOnL2

eph_GPS(25,:) week_toe

eph_GPS(26,:) L2Pflag

eph_GPS(27,:) SVaccuracy

eph_GPS(28,:) SVhealth

eph_GPS(29,:) tgd

eph_GPS(30,:) IODC

eph_GPS(31,:) TTimeMsg

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eph_GPS(32,:) Fit_IntervalThe format of the variable “user_position” is described below

FORMAT “user_position”X [m] Y [m] Z [m] cdtu [m]

Additional details about the parameters included in the described variables can be

found in:

IS-GPS-200: Navstar GPS space segment/navigation user interfaces, Revision D,

ARINC Research Corporation, El Segundo, CA, 2004

and

Gurtner, W. (2001): RINEX: The Receiver Independent Exchange Format Version

2.10, 2001.

3.2 FunctionsBelow the list of functions and a brief description:

- “ecef2enu_velocity.m” convert geocentric (ECEF) to local (ENU) velocity

coordinates;

- “enu2altaz.m” convert local (ENU) to altazimuth coordinates;

- “iono_correction.m” calculates the ionospheric corrections for single frequency,

using Klobuchar model;

- “Matrix_rot.m” compute a rotation matrix;

- “orbital_propagator.m” calculates ECEF satellite coordinates and velocity;

- “tropo_correction.m” computes an estimation of the tropospheric delay using

the model described in MOPS/WAAS or Saastamoinen model;

- “vel_phase.m” calculates ECEF user velocity with carrier-phase measurement.

3.3 OutputThe result of velocity estimation are displayed in the Workspace files named

RESULTS and SOLUTION_AVAILABILITY. This MATLAB files are organized in

the following format.

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FORMAT “RESULTS”Horizontal mean error

[m/s]

Horizontal max error

[m/s]

Horizontal RMS[m/s]

Vertical mean error

[m/s]

Vertical max error

[m/s]

Vertical RMS[m/s]

FORMAT “SOLUTION_AVAILABILITY”Number of epochs used

% number of epochs used

4. Example TestThe example data provided with the software were collected at the GNSS permanent

station placed in Naples, Italy, on 19 March 2014; the data section has a duration of 8

hours and a data-rate of 1 second.

The GNSS station is equipped with a Topcon NET-G3 double frequency receiver

connected to a GPS Topcon CR-G3 antenna, as shown below.

The visibility during the test was excellent, there were always at least eight GPS

satellites in view and the corresponding GDOP was always below 2.4.

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The positioning results, using pseudorange measurements were always within 12

meters horizontally and vertically.

5. SupportAny suggestions, corrections, and comments about this toolbox are sincerely welcomed

and could be sent to:

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Pierluigi Freda

Email: pierluigi.freda@gmail.com

Antonio Angrisano

Email: antonio.angrisano@uniparthenope.it

Salvatore Gaglione

Email: salvatore.gaglione@uniparthenope.it

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