GNSS

DOT releases Complementary PNT Action Plan

The U.S. Department of Transportation (DOT) has unveiled its Complementary Positioning Navigation and Timing (CPNT) Action Plan, which contains steps the department is taking to drive CPNT adoption across the United States transportation system and within other critical infrastructure areas.

In 2020, the U.S. DOT Volpe National Transportation Systems Center conducted field demonstrations of various PNT technologies that could offer complementary service if GPS is disrupted. The department was able to gather information on PNT technologies at a high technology readiness level that can work in the absence of GPS.

The U.S. DOT have selected 11 candidate technologies to demonstrate positioning or timing functions:
• Two vendors demonstrated low-Earth orbit satellite PNT technologies — one L-band and one S-band;
• two vendors demonstrated fiber-optic timing systems, both based on the White Rabbit Precision Time Protocol;
• one vendor demonstrated localized database map matching database, inertial measurement unit, and ultra-wideband technologies; and,
• six vendors demonstrated terrestrial radio frequency PNT technologies across low frequency, medium frequency, ultra-high frequency, and Wi-Fi/802.11 spectrum bands.

Five of the selected technologies were demonstrated at Joint Base Cape Cod in Massachusetts, and six were demonstrated at NASA Langley Research Center in Virginia. The demonstrations were scenario-based implementations modeled on critical infrastructure use cases under different operating conditions.

Two central recommendations from the demonstration were made: the U.S. DOT should develop system requirements for PNT functions that support safety-critical services; and the U.S. DOT should develop
standards, test procedures, and monitoring capabilities to ensure that PNT services, and the equipage that utilize them, meet the necessary levels of safety and resilience identified in recommendation one. www.transportation.gov

Russia launches Glonass-K2

The Russian Federal Space Agency has launched one of its Glonass global positioning satellites, Glonass-K2 No. 13 (Kosmos 2569), into medium-Earth orbit (MEO) on August 7. It was launched to improve the accuracy of the Russian dualuse GNSS. The K2 satellites are the fourth iteration in satellite design for GLONASS.

The new generation of satellites provide navigation accuracy of less than 30 cm and feature an unpressurized satellite bus (Ekspress-1000) manufactured by ISS Reshetnev. The satellites also use a novel navigation signal, code-protected selection, to transmit three signal types, including two in the L1 and L2 ranges for military users, and one channel in the L1 range accessible to the civilian users.Each K2 satellite weighs 1,645 kg and has an operational lifetime of 10 years. www.russianspaceweb.com

I/NAV improvements are now available to all Galileo Open Service users

The Galileo OS has been upgraded with three new features added to its I/ NAV message, one of the four message types broadcast by Galileo satellites. Collectively referred to simply as I/NAV improvements, these features are now available to all Galileo Open Service users. Starting on 12 August 2023, the gradual process of upgrading the operational Galileo FOC constellation satellites has been finalized, and the I/NAV improvements are openly accessible through the I/NAV message carried by the E1-B signal. In simple terms, in case you have experienced delays when turning on your GNSS device, the I/NAV improvements can reduce them significantly. Let’s have a look at the features more in detail.

The Reed Solomon Outer Forward Error Correction (RS FEC2) increases demodulation robustness at all times and therefore enhances the sensitivity. It also improves the overall time to retrieve Clock and Ephemeris Data (time to CED) thanks to the broadcast of additional, redundant CED information, while allowing for the device to restore potentially corrupted data bits autonomously.

The Reduced Clock and Ephemeris Data (RedCED) allows for a fastinitial positioning, albeit with lower than nominal accuracy, by decoding one single I/NAV word, while waiting to receive the four I/NAV words carrying the full-precision CED.

The combination of these two features allows not only to obtain a first coarse position solution much faster (RedCED), but also to reduce significantly the time required to obtain a first full accuracy solution (RS FEC2). This translates into a much-reduced Time to First Fix (TTFF) for the OS users, particularly when operating in harsh environments.

The improvements also benefit applications working in assisted GNSS (A-GNSS) mode, through the Secondary Synchronisation Pattern (SSP). In A-GNSS mode, when navigation data is received from nonGNSS channels and the receiver’s knowledge of the Galileo System Time is affected by a relatively large error, typically in the order of a few seconds, the clock uncertainty must be resolved quickly and stably.

With the I/NAV improvements, receivers will be able to do this via the new SSP feature, thus reducing the TTFF also in A-GNSS mode. www.euspa.europa.eu