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Questions tagged [gnss]

Questions about Global Navigation Satellite Systems (GNSS), such as existing Global Positioning System (GPS) and GLObal NAvigation Satellite System (GLONASS), but also future such systems in development, like European Galileo, China's Compass or India's IRNSS (Indian Regional Navigational Satellite System).

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What does "Common frequency offset" plot means in gnss raw measurements?

I'm using Google's MATLAB code to analyze raw gnss measurement made with gnsslogger android app. In plots, there is one in particular that I don't understand the meaning, which is "Common ...
allexj's user avatar
  • 59
2 votes
0 answers
24 views

Extract GPS navigation messages from a RINEX navigation file

As a hobby project, I want to implement methods from the "GPS Software Attack" paper, which involves modifying GPS navigation messages. With this goal in mind, I am looking for: Examples of ...
David Khosid's user avatar
5 votes
2 answers
187 views

Is there an authoritative source for which GNSS satellite transmits which signals?

I'm trying to algorithmically predict which signals from which GNSS satellites could be heard by a ground-based receiver (without actually looking at the recieved data; the idea is to be able to also ...
Martin Pecka's user avatar
1 vote
1 answer
213 views

Calculating the elevation and azimuth angles of satellites with location information obtained from sp3 ephemeris files

I'm trying to calculate elevation and azimuth angles of a satellite for a ground GPS receiver. I downloaded the SP3 file for the day '12-01-2015'. The ephemeris files are in the link below. https://...
yysmonyy's user avatar
0 votes
0 answers
18 views

Receiver location calculation based on Rinex navigation and observation files [duplicate]

I am trying to calculate the location of the GNSS receiver using the data available in the Rinex navigation and observation files. As a first step I am trying to calculate the pseudo range using the ...
SAG DAG's user avatar
1 vote
1 answer
278 views

How to download (Assisted GPS) AGPS file on PC?

I am trying to implement GPS receiver in software. Can I use AGPS file for faster locking of GPS satellites? I read somewhere that EPO files exist for Assisted GPS but I can't find any place to ...
Kanika's user avatar
  • 39
3 votes
0 answers
66 views

Dilution of precision in different coordinates

Given the ranges $\rho^{(s)}_{R_x}=\sqrt{(x_{R_x}-X^{(s)})^2+(y_{R_x}-Y^{(s)})^2+(z_{R_x}-Z^{(s)})^2}$ between a receiver $R_x$ and an $s$-th satellite, where $s=1, 2, ... n$, one can construct the ...
Akhaim's user avatar
  • 59
2 votes
2 answers
915 views

How to calculate the ECEF coordinates of a satellite given its elevation and azimuth angle, plus the coordinates of a reference object on Earth

So I am looking for a way to 'reverse engineer' satellite ECEF coordinates given its angles of elevation and azimuth and given the coordinates of an object on Earth serving as a reference ground. The ...
Akhaim's user avatar
  • 59
2 votes
0 answers
326 views

Time parameters in RINEX navigation file

Currently, I am trying to determine the position of a GPS satellite from a RINEX navigation file. I am using RINEX 2.11. Tables A3 and A4 describe how navigation files are structured. In order to ...
alex05's user avatar
  • 21
3 votes
0 answers
77 views

Understanding "classical" algorithms behind RINEX files post-processing

I'm new to this site so I want to apologize beforehand for all the mistakes I could make while writing this. So just to put my situation into context : I am currently an intern in an AI company tasked ...
V. N.P.'s user avatar
  • 31
2 votes
2 answers
84 views

Which is more accurate, the ellipsoidal height from SLR or GNSS?

Satellite Laser Ranging (SLR) and Global Navigation Satellite System (GNSS) both measure the ellipsoidal heights. Which measurement of ellipsoidal height is more accurate?
Astrolien's user avatar
  • 569
2 votes
0 answers
66 views

What is the difference between SBAS and PPP used in GNSS accuracy corrections?

I've found that Satellite Based Augmentation System uses reference stations to compute a model for correction and send them via a master station to a geosynchronous satellite, then to GPS receiver. I ...
Yahya Aouled Amer's user avatar
2 votes
1 answer
379 views

What is "Time To First Fix" in GNSS?

I used an app to test GPS, that shows me TTFF is equal to a few seconds. I want to understand : What is Time To First Fix? Is having internet access useful to improve it?
Yahya Aouled Amer's user avatar
1 vote
1 answer
67 views

Is Satellite Based Augmentation System ,used in GPS, a Differential Technique?

I've read that to get a higher accuracies in GPS, we use differential positioning techniques which compute for satellites errors, using well-known position base station. I want to know if the ...
Yahya Aouled Amer's user avatar
2 votes
2 answers
117 views

Does using multifrequencies totally eliminate the ionosphere delay on GPS measurements?

I've read that the GPS receiver computes the difference in measurement for two GPS satellite signals (in two frequencies L1 and L2), in order to compute the actual delay that the ionosphere causes. ...
Yahya Aouled Amer's user avatar
32 votes
8 answers
11k views

Why does GPS need the fourth satellite?

I am currently working on a GPS project, so I am doing some research about the subject. I understand that the GPS receiver knows its location by calculating its distances from 3 satellites, and by ...
Yahya Aouled Amer's user avatar
3 votes
1 answer
129 views

Precise Orbit Determination (POD) vs GNSS accuracy; seeking references

Precise orbit determination provides performances that are not currently achievable with GNSS systems. I cannot find information of the reason for this. I imagine different possibilities: Use of ...
AUP's user avatar
  • 51
4 votes
1 answer
301 views

Can the James Webb Space Telescope's position be determined using GNSS? And if not, how is this done?

As far as I know, the recently launched James Webb Space Telescope will be positioned at 1,500,000 km of the Earth, orbiting Sun-Earth L2 Lagrange point at roughly 4x the distance between the Earth ...
swiss_knight's user avatar
3 votes
0 answers
150 views

Are LHCP L-Band antennas for Cubesats available?

I am designing a cubesat to carry out GNSS reflectometry or GNSS-R. To collect the earth reflected signals, I need a nadir pointing array of patch antennas, with Left Hand Circular Polarisation (LHCP) ...
Luke O's user avatar
  • 31
7 votes
2 answers
1k views

How is the ambiguity in code phase resolved in GNSS code-based positioning?

For positioning using GNSS, a typical introduction text (example PDF) introduces the concept of pseudo ranges as roughly being the time between transmission of a GNSS signal by the satellite $s$ and ...
Ludo's user avatar
  • 14.4k
4 votes
2 answers
3k views

Ephemeris time and clock corrections in RINEX navigation files

RINEX (Receiver INdependent EXchange format) is a set of file formats to distribute satellite navigation systems data, including GNSS. One of these standards, navigation files, provide positional ...
Rafa's user avatar
  • 1,750
3 votes
1 answer
1k views

Obtaining position of GPS and GLONASS satellites from RINEX navigation files

I am currently trying to understand the best way to use the available information in RINEX navigation files for GPS and GLONASS satellites. My main goal currently is to calculate the position at epoch ...
Rafa's user avatar
  • 1,750
3 votes
1 answer
52 views

generated error terms for positioning based on a pre defined target accuracy level

I would like to ask a question about accuracy level and precise point positioning or PPP. I'd like to design a system such that when the desired accuracy level is provided as an input, the ...
user42663's user avatar
3 votes
1 answer
162 views

Lunar satellite navigation system

Inspired by some questions: Are People Actually Serious About Mining The Moon? How to estimate that receiving GNSS signals Earth while orbiting the Moon will still provide locations to about 200 ...
Fred's user avatar
  • 13.1k
7 votes
0 answers
773 views

Are software defined GNSS (GPS) receivers legal under ITAR and other export regulations?

With the latest update to ITAR rules, it looks like covered GNSS receivers are defined as follows: (2) Global Navigation Satellite System (GNSS) receiving equipment, as follows: (i) GNSS receiving ...
Manuel Menzella's user avatar
4 votes
1 answer
215 views

How to estimate that receiving GNSS signals Earth while orbiting the Moon will still provide locations to about 200 meters of uncertainty?

IEEE Spectrum's Can Astronauts Use GPS to Navigate on the Moon? NASA Scientists Say Yes says: Kar-Ming Cheung and Charles Lee of NASA’s Jet Propulsion Laboratory in California did the math, and ...
uhoh's user avatar
  • 149k
7 votes
0 answers
375 views

Interpolating precise ephemerides of GPS satellites

My objective is to obtain at least a sub-meter position accuracy by interpolation of the GPS ephemerides. There is conflicting research outside, where some authors state that a simple Lagrange or ...
Samuel Low's user avatar
3 votes
2 answers
2k views

Delay-Doppler maps in space science

Maybe this question might be more physics related, but I've read about mostly in context of space science: What is a delay-doppler map (DDM)? I can find it in exploration of asteroids (e.g. (...
sequoia's user avatar
  • 311
45 votes
3 answers
9k views

What is GPS' 19 year rollover and does it present a cybersecurity issue?

The NPR new item and audio podcast The Global Positioning System Resets talks about a 19 year cycling of something in the GPS system, but it's not clear what it is. Every 19 years, the Global ...
uhoh's user avatar
  • 149k
2 votes
3 answers
915 views

Does GPS spoofing ever come from space? How are spoofings usually detected?

The BBC News article Study maps 'extensive Russian GPS spoofing' says: (GPS spoofing) involves the state using strong radio signals to drown out reliable navigation data, says non-profit C4ADS. The ...
uhoh's user avatar
  • 149k
1 vote
0 answers
77 views

Examples of both hardware and software GNSS recievers

I am writing an essay titled: Critically evaluate the positional fixing capabilities of current smartphone technologies for real world GIS data collection I am wanting examples of both hardware and ...
Tom Haywood's user avatar
4 votes
1 answer
400 views

Celestrak GLONASS TLE's showing satellite numbers not listed in the GLONASS constellation, others missing

For a project, I'm retrieving TLE information live from https://celestrak.org/ and using them to simulate satellite orbits. The TLE's for the GLONASS constellation (https://celestrak.org/NORAD/...
Brian C. Peters's user avatar
5 votes
1 answer
310 views

Why the PRN obtained from Android is different from calculated by TLE

I want to use TLE data to calculate the azimuth and elevation of every GPS satellites at user's location. In order to verify the correctness of TLE calculation, I wrote an Android app that can be ...
AndyShan's user avatar
12 votes
2 answers
2k views

What is this gap in the GNSS satellite trajectories?

I've recently bought a USB-connected multi-constellation GNSS-receiver with a U-blox 8 chip in it. I've downloaded the U-center software that can display a lot of details about the received signals. ...
Bart Noordervliet's user avatar
3 votes
1 answer
196 views

Current status of the use of GPS multi-antenna time differentials for satellite attitude determination?

I am certain that I read a year or three ago about an unmanned satellite that was going to be testing a method of attitude determination that relied upon two (or more) separate antennas on one ...
uhoh's user avatar
  • 149k
5 votes
1 answer
1k views

Is two-way communication really required to use BeiDou GNSS?

The BBC's How China's GPS 'rival' Beidou is plotting to go global mentions a scenario where end-users can send signals to other Earth locations using BeiDou and later says: But despite its ...
uhoh's user avatar
  • 149k
12 votes
1 answer
858 views

Why do GPS (but not GLONASS or Beidou) satellites have increasing eccentricity over time?

When comparing GPS, Beidou, Galileo, GLONASS, and potentially other GNSS, we can see that the eccentricities of GPS spacecraft are increasing with time (i.e. apogees increasing and perigees decreasing)...
costrom's user avatar
  • 1,053
4 votes
1 answer
315 views

What function do the GEO satellites have in the BeiDou system?

As the title asks: the Compass/BeiDou-2 system constellation includes five satellites in GEO, while most of their satellites are in MEO at about half the altitude. Do these provide a ranging signal, ...
D.H.'s user avatar
  • 191
11 votes
1 answer
894 views

Does the "17" really mean anything with respect to GNSS orbits being rational factions of a sidereal day?

This answer to Why are orbital periods different for different GNSS positioning system constellations? suggests that the orbital periods of the four large GNSSS constellations are linked to the ...
uhoh's user avatar
  • 149k
7 votes
1 answer
334 views

How might excluding the UK from Galileo set the European programme back years and cost the EU billions?

edit 1: More here: Brexit 'will force Airbus work on Galileo out of UK' and now here: Brexit: UK wants £1bn back from EU if it is excluded from Galileo edit 2: And now more here: UK rebuffed over ...
uhoh's user avatar
  • 149k
6 votes
1 answer
529 views

What is the magnetic equatorial anomaly and how is GAGAN unique in its ability to compensate?

ISRO's GPS Aided GEO Augmented Navigation system (GAGAN) (see ISRO and Wikipedia) is the first GPS augmentation system designed to deal with ionospheric effects near the geomagnetic equator. From ...
uhoh's user avatar
  • 149k
2 votes
2 answers
583 views

3D modelling of satellites around the earth

I want to find and see "GPS satellites in view" for different orbits missions. For example I want to see the observable GPS satellites for a specific satellite in GEO, for this purpose I need a ...
S.P's user avatar
  • 23
9 votes
1 answer
1k views

Radiation pattern and signal strength of navigation satellite antennas

Where can I find the actual radiation pattern and signal strength of transmitting antennas used by GNSS navigation satellites/constellations (GPS, GLONASS, IRNSS, etc)?
akum's user avatar
  • 328
43 votes
3 answers
28k views

Why are the GPS constellation satellites in such a high orbit?

Most satellites are in Low Earth Orbit. Some other satellites are in Geostationary Orbit because their function requires it. The GPS (and other GNSS, e.g. GLONASS) satellites are in a much higher ...
Max Q Lagrange's user avatar
19 votes
2 answers
2k views

Do any spacecraft use GNSS for attitude determination?

In principle, by placing a GNSS-receiver on all extremities of a spacecraft (or aircraft, for that matter), one can determine the orientation of the satellite. Google lists some studies, but have ...
gerrit's user avatar
  • 11.7k
22 votes
2 answers
1k views

How far up have satellites used a GNSS for positioning, and how does the precision degrade with altitude?

GNSS satellites (at least GPS ones) are in Medium Earth Orbit (MEO). LEO satellites can use GNSS for positioning. Is this still possible for satellites in elliptical, such as Molniya, orbits? For ...
gerrit's user avatar
  • 11.7k
11 votes
1 answer
398 views

In LEO, what is the precision of GNSS-based position compared to traditional methods?

GNSS satellites (at least the GPS ones) are in MEO, so LEO spacecraft can use GNSS for their positioning. I've read that it's quite low-cost compared to the alternatives. How does the precision of ...
gerrit's user avatar
  • 11.7k