GPS World

Tag: loss of lock

  • Unicore’s position accuracy matters for all farm tasks

    Unicore’s position accuracy matters for all farm tasks

    Photo: Unicore
    Photo: Unicore

    Although GNSS has been applied in agriculture for many years, farmers still encounter challenges caused by GNSS. No matter the farm task — planting, spraying, harvesting or specialized applications such as robotic grass mowing — position accuracy matters.
    Here are the most common issues farmers have and how Unicore’s products help.

    • Under canopy. They are unable to get a fix under heavy foliage canopy because the real-time correction signal is interrupted or “shaded out” by the canopy. Unicore is launching two new modules that will help mitigate this problem.
    • Loss of lock. At times, the receivers lose lock or get large position errors when the ionosphere’s effects are severe. Driven by a full-constellation and full-frequency RTK engine, Unicore’s RTK algorithm takes advantage of triple and quad frequency observables, effectively mitigating ionospheric residuals.
    • Loss of 4G signals. RTK can provide real-time centimeter-level high-precision positioning, which requires real-time base station data. In practical applications, radio or wireless network communication is often interrupted. During the interruption of the base station data, RTK’s positioning accuracy decreases quickly. Unicore’s RTK KEEP technology can maintain the centimeter-level positioning accuracy for more than 10 minutes after the interruption.
    • Lack of CORS stations. It is challenging to provide a stable high accuracy position for an ultra-long baseline. With the mitigation of ionospheric and tropospheric delays, Unicore products’ RTK baseline can be extended to up to 50 kilometers.

    The UM980 is Unicore’s new-generation high-precision RTK positioning module, supporting full constellation and full-frequency. Relying on the strengths of high reliability, precise positioning accuracy and low latency, UM980 is not only well suited for high-precision surveying and mapping, but also a good choice for rover or base station receivers in agriculture.

    The UM982 is a dual-antenna high-precision positioning and heading module. Since its master and slave antennas can simultaneously track all the frequencies of all the GNSS systems, the UM982 performs fast on-chip RTK positioning and dual-antenna heading solutions without the need to initialize the IMU. Featuring great positioning performance and stability, the UM982 is a perfect choice for high-precision agriculture applications, such as drones, autonomous tractors and autonomous lawnmowers.

    Both products will be available in June 2022.

  • Capt. Sullenberger, PNT board against Ligado decision

    Capt. Sullenberger, PNT board against Ligado decision

    Opposing the FCC’s Ligado Decision

    Not surprisingly, the primary topic at the July 1 meeting of the National Space-based Positioning, Navigation and Timing Advisory Board was the Federal Communications Commission (FCC) decision on Ligado Networks.

    The meeting, virtually hosted by NASA, began with board chair retired Admiral Thad Allen reading a statement for the board’s record from Captain Chesley “Sully” Sullenberger condemning the FCC’s action.

    In it Captain Sullenberger cited many of the issues the board’s vice chair, Brad Parkinson, discussed later in the meeting. Sullenberger’s statement is available here.

    In his presentation, Parkinson called the FCC decision “a grave error.” He outlined his rationale in 21 information-packed slides.

    Parkinson summarized his presentation up front with three points:

    1. Repurposing the Mobile Satellite Services (MSS) radio spectrum is very high risk and brings virtually no near-term benefit to the United States.
    2. The risks affect much more than the Department of Defense: high-value civil applications are also in jeopardy.
    3. Any such repurposing should have been subject to a formal rulemaking process.

    At the end of the presentation, the board voted unanimously to adopt the presentation, with slight modifications, as a reference document for posting on the board’s website.

    The group had previously made strong recommendations to the Departments of Defense and Transportation to oppose any such action by the FCC. Both departments have done that and are continuing to do.

    Hazardous information versus losing lock

    One slide in Parkinson’s presentation included a Department of Transportation (DoT) depiction how of Ligado transmissions would cause several types of receivers to “lose lock.” This graphic was used in a recent DoT presentation to the FCC.

    DOT briefing to FCC: “Concerns Over Ligado Order & Authorization,” June 2020. (Slide: DOT)
    DOT briefing to FCC: “Concerns Over Ligado Order & Authorization,” June 2020. (Slide: DOT)

    Heretofore DoT has usually discussed the points at which Ligado transmissions would cause a 25% increase in the noise floor for receivers. This is an important metric as tests have shown that beyond that point many receiver types begin to give hazardously misleading information. DoT officials have used the example that the 1dB limit is like putting a load limit on vehicles crossing a bridge so that the bridge never reaches its breaking point. An important consideration with a safety-of-life application like GPS.

    The National Space-Based PNT Advisory Board. (Board photo)
    The National Space-Based PNT Advisory Board. (Board photo)

    A receiver often gives inaccurate positioning and timing data, possibly hazardously misleading information, before it “loses lock” and stops providing any information at all. It is more difficult for a receiver to “acquire lock” than to track satellites and provide information, so equipment is rarely able to function again until it moves out of the area of interference.

    When asked why DoT would bother to show such information to the FCC, one official suggested that loss of lock was more in line with the criteria the Commission used in making the Ligado decision. The hope was that, by showing that even this flawed standard had significant impacts which the FCC perhaps did not fully recognize, further technical discussions and reconsiderations could be realized.

    Other Topics

    While discussion of the FCC’s decision took the most time in the on-line meeting, several other issues were discussed as well.

    Colonel Curtis Hernandez from the National Security Council briefly described development of a new space-based PNT policy to replace NSDP-39 which was put in place by President Bush in 2004.

    He was not able to provide any specifics as it is a draft and still under consideration. Answering a question, he did say that the draft policy outlined the responsibilities of various departments, including for interference detection and monitoring.

    Adam Balkcum from the Office of Science and Technology Policy discussed his office’s nascent efforts to investigate non-GNSS PNT as directed by the recent Executive Order on Responsible Use of PNT. The question of whether this includes possible PNT services from low earth orbit and geostationary satellites remains an open one.

    Other presenters included:

    • Seth Jonas of the National Security Council staff on the recent Executive Order on Responsible Use of PNT,
    • Andrew Hansen of the Volpe Transportation Systems Center who spoke about efforts to monitor for GPS interference, especially in the post-FCC Ligado decision environment, and
    • NASA’s Chris Bonniksen discussed issues with operating and funding the agency’s Global Differential GPS system.

    The agenda for the meeting and presentations are available here, as will be the meeting minutes once they have been finalized.