J. Brad Woodfin

In this final entry in the series about our open architecture stratum one server, we call out some of the future investigations we noted that may be worth looking into during the exploration so far.

Multi-Constellation

• Our first iteration of this architecture uses the Meinberg GPS180PEX, which can only see US Global Positioning System satellites.
• There are several competing Global Navigation Satellite Systems (GNSS), including the EU’s Galileo, Japan’s QZSS, Russia’s GLONASS, and India’s NAVIC.
• Using hardware that can process the signals from other constellations increases the robustness of the architecture, due to:

• Greater availability of satellite-based time sources becoming available
• Breaking the dependency upon a single time provider (in the case of GPS, the US Naval Observatory Master Clock which is the source of GPS time)

Multi-Frequency

• The first iteration of the architecture can only receive the GPS L1 Coarse/Acquisition (“L1 C/A”) signal.
• Making it possible for the architecture to receive timing information on at least two different frequencies (e.g., L1 and L5) allows the receiver to compute -- and thus eliminate -- the amount of ionospheric error, which is one of the largest contributors to GPS location/timing errors.

Indoor Reception

• Newer GNSS signals, such as GPS L5 and Galileo E5a/b, were carefully designed to be easier to detect as well as broadcast from the satellites at much higher power levels.
• The improved signal design and strength should make it easier to maintain GPS lock for L5 versus L1 C/A, especially in situations where L1 C/A typically struggles, such as when indoors.

Lowering Price

• At 2,700 USD, the Meinberg GPS180PEX GPS receiver is the single largest factor of the overall cost of the first iteration of the PublicNTP Open Architecture Stratum One platform.
• There are numerous articles on the internet about Raspberry Pi-based GPS receiver solutions that are significantly cheaper than the Meinberg hardware.
• One component typically lacking from the budget GPS receiver solutions is a precise oscillator to allow the system to “freewheel” with very low drift when the GNSS signal is not available.
• We’ve been looking into much cheaper solutions for both halves (GNSS signal reception as well as the precise oscillator). It’s likely that we would have to write an operating system driver to support our oscillator solution, but that’s a challenge the PublicNTP team is eager and well-suited to take on.
• The lower we can push the price point, the more people can take advantage of our work, which makes it a constant goal of the project.

There are many different avenues to improve our first iteration on this platform; these are just the first ones we noted and remembered to write down. :)

We are very interested to see where the network time community takes this, which will likely be well beyond what we have envisioned so far!