NGS Real Time Network

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NGS Real Time Network Status Future Prospects
Neil Weston NGS Convocation, 2005 Silver Spring,
MD
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Main Concepts

• Modify CORS sites for real time data transmission
• GPS receiver data
• Transmission via the Internet
• Standardized protocols and formats
• Not a navigation service!

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CORS Site Modification

• Receiver modifications
• Firmware
• Multiple satellite systems
• Data interval
• Communications / Network modifications
• Routers
• Increased bandwidth
• Internet
• Software

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Network Design Issues

• What format?
• What stations?
• What software?
• What distance?
• What data rate?
• What latency?

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Formats

• RTCM-SC104
• Versions 2.0, 2.1, 2.2, 3.0
• Type 1 Fixed GPS corrections (1 sec)
• Type 3 GPS reference station parameters (10)
• Type 16 GPS special message (30,60)
• Type 18 RTK uncorrected carrier phases (1)
• Type 19 RTK uncorrected pseudoranges (1)
• Type 22 Extended station parameters (15)
• Type 59 Proprietary messages (1)

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Formats cont.

• Raw
• Topcon/Javad Compact (1)
• Ashtech MBEN (5) / PBEN (5) / SNAV
• Thales ASCII
• SP3 ASCII
• Trimble RT17, concise
• Leica LB2
• RINEX
• BINEX

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CORS Stations

• NDGPS
• WAAS
• PBO Network
• Other contributors sites

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Software

• NTRIP - Networked Transport of RTCM via Internet
  Protocol (version 1.5)
• NTRIP is an RTCM standard
• Application-level protocol streaming Global
  Navigation Satellite System (GNSS) data over the
  Internet
• Based on hypertext transfer protocol (HTTP/1.1)
• Simultaneous connections from PCs, laptops,
  receivers to a broadcast host
• Streams data to stationary and mobile users

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Software cont.

• NTRIP Three major components
• NtripClients acts as an HTTP client
• NtripServers acts as an HTTP client
• NtripCasters HTTP server

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DGPS/ RTK Data Rates

• DGPS 0.5 kbits/sec
• RTK 5 kbits/sec
• Much less demanding than Internet radio,
  teleconferencing 128 kbits/sec

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Administration of NtripCaster

• Logs
• Sourcetable
• Configuration file
• User registration

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NTRIP Pros / Cons

• RTCM standard
• Open documentation
• Software components developed under GNU General
  Public License
• Communications through a HTTP port
• Workload on server side
• Not supported by mobile IP provider

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Data Rate / Latency

• Modified CORS Stations 1 second interval
• Latency Not more than 1 to 2 seconds
• Most third party software packages buffer the
  data before processing begins

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NTRIP Consequences

• Easy to become a provider
• Drivers available for real time software
  development
• End of special hardware for receiving RTCM / RTCA
• Support for networking software
• Lots of potential for mass-usage
• Sites, networks and coverage will grow
• Many third party client and server applications
  already exist

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NTRIP Demonstrations

• www.euref-ip.net2101
• RTK station
• RINEX test station
• Erlanger
• alt.ngs.noaa.gov2101
• NGS_GRD
• NGS_LAB
• How you can listen

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Conclusion

• Streaming GNSS data over the Internet is feasible
• No significant lack of performance compared to
  other transportation media
• Advantages for user / service providers
• Developments for various products
• Promising solution for GIS
• Faster data access

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References

• NTRIP BKG GPS/GLONASS Data Center
• http//igs.ifag.de/index_ntrip.htm
• RTCM Radio Technical Commission for Maritime
  Services
• http//www.rtcm.org