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StarFire

What is StarFire™?

StarFire is the World's first commercial Global Satellite Based Augmentation System (GSBAS). StarFire uses a global tracking network of approximately 60 reference stations and software originally developed by NASA's Jet Propulsion Laboratory to calculate very precise and accurate real-time orbits and clocks for all the GPS satellites. These are transmitted via Geo-Stationary communication satellites to StarFire receivers who use the corrections with NavCom's geodetic quality L1/L2 engine measurements and proprietary StarFire positioning algorithm. Real-time positioning accuracy is typically a decimeter horizontally and two decimeters vertical. Performance may be better depending upon the local conditions.

Why is WAAS and EGNOS performance much better with NavCom receivers than other receivers?

NavCom manufactures dual frequency GPS receivers. The GPS frequency measurements on both L1 and L2 allow the ionospheric errors to be corrected prior to navigation. This technique is much more accurate than using the WAAS or EGNOS ionospheric models. NavCom's rover positioning algorithm for StarFire has been adapted to work with WAAS and EGNOS corrections providing greatly enhanced positioning performance. NavCom has also implemented a patented method which allows for the repression of high-frequency noise associated with these types systems, named Refraction Corrected Phrase (RCP). In addition, NavCom's patented multi-path suppression and high quality of measurements result in superior position accuracy.

What is StarFire convergence?

Upon power-up, a StarFire receiver initializes, locks on to the available GPS satellites, the local StarFire communication satellite and starts NavCom's proprietary StarFire positioning algorithm. Positioning accuracy will typically be sub-meter with decimeter accuracy performance available within 30-45 minutes. This is a function of the tropospheric conditions, number of GPS satellites available and inter channel calibration of the receiver.

What is StarFire Quickstart?

NavCom offers the unique feature called QuickStart where an accurately known ITRF05 position can be used to initialize StarFire navigation and eliminate the convergence period. This is typically a position previously surveyed and converted to ITRF05 prior to initialization. For example, vehicular installations can be initialized using the last position from when it was parked and powered down.

What is RTK Extend™?

RTK Extend uses StarFire to provide RTK-quality positioning when the RTK communication link has been temporarily lost. This can mean greater survey efficiency by eliminating the need to stop the survey or relocate the RTK base station for better communication coverage.

How does RTK Extend™ work?

A StarFire-licensed receiver with the RTK option enabled is equipped with an RTK communication link and placed in the 'RTK Extend Base' mode. Both RTK corrections and the offset between the StarFire and RTK solutions are transmitted to multiple roving StarFire receivers (the base will be navigating at the same time as it is computing corrections). When the RTK communication link is blocked at the StarFire rover, the unit initializes the StarFire positioning algorithm based upon the last good RTK-based position along with the last StarFire position offset at the base station. This offset is computed by taking a delta between the locked RTK base coordinate and the StarFire navigation result. Its best performance is after steady-state navigation is achieved at the base. RTK-quality positions are maintained for up to and beyond 15 minutes after a RTK communication dropout. If the RTK data link is not restored, the StarFire rover accuracy will migrate to its typical decimeter performance.

Does StarFire use a bi-directional communication system?

No. StarFire receivers are receive-only. This reduces their power consumption and the network costs, savings of which are passed to the end user.

How do I license my StarFire receiver to work with StarFire corrections?

Every StarFire user must complete a StarFire End User License Agreement (EULA) and subscribe to one of the flexible licensing plans via their local NavCom distributor. Once confirmed, a license file is provided for upload into the StarFire receiver via the supplied control software. The license and expiration date can be confirmed using the same software program.

Where are StarFire corrections available?

Everywhere. StarFire corrections are valid for anywhere in the world. NavCom distributes these via three Inmarsat geo-stationary communication satellites which provide near-global coverage. Reception of these L-Band signals is through the tri-band antenna of the StarFire receivers No other equipment is necessary. The two Polar Regions are not visible from the Inmarsat satellites and for these regions, dedicated satellite phones have been used as data links for StarFire corrections. For StarFire users operating in high latitudes or on a dynamic platform with antenna sway, NavCom offers a separate, low elevation L-Band antenna coupled with a dual RF input receiver which yields enhanced performance in these regions.

How frequently do the StarFire correction updates need to be received?

Unlike conventional Ground Based Augmentation Systems (GBAS) which determine highly temporal signal corrections, StarFire corrections are derived for satellite key parameters of orbit and clock. This is a more fundamental method of correction and as a result the accuracy degrades much more slowly with time. Excluding any sudden GPS satellite anomalies, the last set of valid corrections will provide decimeter accuracies for up to and beyond 10 minutes. This is a setting made allowable to the user, which permits many accuracy tolerances dependant upon the application.

To which datum are StarFire corrections referenced?

StarFire uses the latest realization of the International Terrestrial Reference Frame (ITRF). In other words, the StarFire corrections are based upon ITRF05, and adjusted on a daily basis (at UTC midnight) to account for minute shifts in velocities attributed to continental shifts on a global basis.

What is the relationship between StarFire positions (ITRF05) and WGS84?

The latest realization of the WGS84 Datum, as used by the GPS satellites, is based upon ITRF2000 at a different epoch from StarFire. The difference is sub-decimeter. It is important to understand that ITRF differs from WGS84, and one should never assume that they are equivalent in terms of truth reference.

Why does there exist a difference between my StarFire converged position and my known WGS84 position?

The WGS84 Datum has undergone a number of revisions and realizations. A bias may be seen between WGS84 positions and StarFire (ITRF00) positions depending on the equipment, methodology and time when the known WGS84 position was determined. For example, early WGS84 positions were based on Transit doppler receivers, which had an accuracy of about 10m (depending on observation time). It should be noted that the original WGS84 Datum definition DMA TR8350 defined the Datum with an accuracy of +/- 1.5m. Accurate ITRF coordinates for a static location can be determined by recording several hours of L1 and L2 GPS data and processing these at the SOPAC SCOUT site for global locations or the NGS OPUS site for USA only.

http://sopac.ucsd.edu/

http://www.ngs.noaa.gov/OPUS/

Why is a Tide model used in StarFire receivers?

StarFire is an absolute space-based positioning system. The Earth's crust flexes during the day with sea, solar and lunar gravity induced tides resulting in the distance from the earth's surface to the center varying. These variations are well known, principally affecting the height and can be corrected for by the Sinko model which is within the StarFire positioning algorithm.

What is SureNav™?

With so many navigation choices available within NavCom receivers, we produced the SureNav concept. Multiple sources of correction data including StarFire corrections can be input into a receiver at the same time. With SureNav, you can be Sure that the output navigation position will be the best available, coupled with NavCom’s robust confidence statistics which are based upon the navigation inputs to depict the performance level at any moment in time.

What is StarFire Over IP?

This feature allows users to access StarFire corrections over the Internet, giving them access to the same reliable five centimeter global positioning accuracy without the need for a base station. Users are now also able to access StarFire corrections even in those situations when satellite delivery might be unavailable, such as deep urban canyons or very high latitude locations. Furthermore, the automatic failover capabilities in our StarFire enabled products allow the user to switch seamlessly from satellite to internet delivery of StarFire service and thereby maintain the maximum possible uptime.

 

  • Not available on Sapphire-integrated systems which do not support an IP interface with Ntrip 2.0 (or later) protocol)
  • SF-3040 requires software development by 3rd party
  • SF-3040 in a LAND-PAK System requires either NavCom FieldGenius v6.0.3.1 or later, or NavCom SurvCE software (available in early 2013 with this specific feature)

How it works:
The receiver acts as an Ntrip client and initiates an Ntrip session including automatic authentication (no user parameters required).
  • Requires the unit be licensed for StarFire operation
  • Requires the unit to be optioned for StarFire over IP and StarFire Enabled
  • Ntrip mountpoint and IP address is only provided to customers who are activated for this service. This information is provided at the time the software option is provided to the customer or from Customer Support  
  •  NavCom FieldGenius and NavCom SurvCE are preconfigured to connect to the correct IP address
  • The method that the GNSS receiver is connected to the internet is the customer’s responsibility. The connection can be made through a 3G modem, VSAT, Iridium, direct connection to the internet, etc. The connection can be made using StarUtil 3000 and the command line interface (Input Terminal). An Application Note is available to detail the mechanics of making the connection.

 

Data management
  • Packet size is currently at 787Bytes max with GPS and GLONASS corrections
  • The service is offered with three different delivery modes to help customers manage their data costs: 1-second (streaming); 15-seconds; 60-seconds
  • Packet size for different rates are the same size
  • Convergence time and accuracy is the same for all delivery rates, whether over the air or via IP

How do I get StarFire Over IP? StarFire Over IP Licensing
  • Receiver needs StarFire over IP and StarFire Enable options
  • Standard receiver StarFire license authenticates both services