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GNSS - Global Navigation Satellite Systems

May you please explain RTK Network Performance?

Please reference this document to view more information.

What are Satellite Based Augmentation Systems (SBAS)?

SBAS provide orbit and clock corrections for the GPS satellites and an Ionospheric model. These were initially developed for civil aviation use to augment L1 Coarse Acquisition Code receivers, but have since been developed for alternate markets such as offshore and agriculture. Correctional data are transmitted on the GPS L1 frequency from Geo-stationary communication satellites. Examples include the Wide Area Augmentation System (WAAS) for USA and Puerto Rico, the European Geostationary Navigation Overlay Service (EGNOS) for Europe, the Multi-Function Satellite Augmentation System (MSAS) and the Satellite Navigation Augmentation System (SNAS) for China. Corrections can be received outside their network but should only be used within their designated operational area due to accuracy and reliability measures. All NavCom / Deere receivers are capable of receiving and using WAAS/EGNOS signals. NavCom has also developed a commercial SBAS system known as StarFire that is available globally and is more accurate.

Why does NavCom provide two dedicated SBAS channels?

SBAS signals can be seen from multiple satellites, with two dedicated channels, NavCom has the ability to lose lock on one and still track the other without a new search. Having dedicated channels means you never give up a GPS channel to access WAAS, EGNOS or other L1 based SBAS signal.

Leap Second Change June 30, 2015. What do I need to know?

A global leap-second time change will occur at 0:00:00 on July 1st. GNSS broadcast, reference, and rover systems need to apply this change at exactly the same moment in order to function properly. Unfortunately, GPS and GLONASS broadcasters handle the time change differently. More information is available at this link.

 

Here is how NavCom products are impacted:

 

  • No software update for discontinued products. All discontinued products operate on GPS only and there is no performance impact as the GPS leap second functions correctly

    Multi-hertz NMEA data will have a 1-second timing change at the time of transition and will revert back 1-second to June 30, 23:59:59.x at the next fractional epoch reporting UTC time (i.e. for 10Hz data this will 59.1 seconds).

 

  • Sapphire, SF-3040 and SF-3050 products
    • New software is available (v3.5.8 or later) which has a fix for the GLONASS leap second under most conditions as described below:
      • RTK
      • NavCom or 3rd –Party Base providing RTCM 3 (1001 to 1012msgs) and proprietary (x5B and 5E) formats operate correctly for GPS and GLONASS with the new firmware. RTCM 3 messages provide specific data related to the leap second event.
      • CMR/CMR+, RTCM 2.2, and 2.3 (Type 18/19 and 20/21) do NOT operate correctly for GLONASS. These public RTK correction protocols do not specifically address the leap second transition and are subject to each manufacturer’s interpretation of the transition. Internal testing demonstrates issues with a number of competitive receivers.
        • Customers need to turn GLONASS off prior (23:59:00 or earlier) to the UTC date change from 6/30 to 7/1. GLONASS may be turned on again after 00:00:01 UTC on July 1st. If after turning GLONASS on the receiver does not use GLONASS in RTK, cycle power to the receiver.
        • If the receiver is operated in GPS only mode, it is not impacted by the leap second change in any RTK format.
      • StarFire and SBAS modes are not impacted
    • Fielded software performance (v3.4.12)
      • RTK
        • Proprietary (x5B and 5E) formats operate correctly for GPS and GLONASS
        • With RTCM2.2/RTCM2.3/CMR/CMR+/RTCM3 the rover may lose GLONASS ambiguity for seconds or even longer.
          • Customers need to turn GLONASS off prior (23:59:00 or earlier) to the UTC date change from 6/30 to 7/1. GLONASS may be turned on again after 00:00:01 UTC on July 1st. If after turning GLONASS on the receiver does not use GLONASS in RTK, cycle power to the receiver.
          • If the customer is using both a NavCom base and rover and RTCM 3 (1001 to 1012) correction formats, rovers are expected to function correctly.
      • If the receiver is operated in GPS only mode, it is not impacted by the leap second change in any RTK format.
    • StarFire and SBAS modes are not impacted

StarFire Frequency Change, June 2015. What do I need to know?

Net 2 of the StarFire system underwent a frequency change in late 2014. No new software was made available at that time and customers with recent software realized an automatic transition to the new frequencies from the over-the-air StarFire almanac for current generation products (legacy products require manual tuning). The Net 1 frequencies take place in June 2015. Similarly, automatic transition to the new frequencies from the over-the-air StarFire almanac will take place. With all the new StarFire frequencies reassigned, new software (v3.5.4 or later) for current generation products contains an updated default frequency table (legacy products require manual tuning). Customer Support has produced a detailed Troubleshooting Guide for customer who choose to remain on older firmware. The old frequencies are scheduled to terminate in mid-July 2015.