Paternity Suit - Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design

Paternity Suit

Don’t be misled by the title. This is not another round of speculation about who should be proclaimed the rightful “Father of GPS.”

Don’t be misled by the title. This is not another round of speculation about who should be proclaimed the rightful “Father of GPS.”

Rather my comments have to do with the ancestry of GNSS signals and the increasingly crowded path ahead. The subject comes come to mind now for several reasons: the imminent arrival of a spate of new signal designs from all four GNSSs and several regional systems, problems with the navigation payload on the GPS III, wide acceptance of the original GPS C/A-code in consumer equipment, and the general question of whether “modern” is necessarily better.

Every generation seems obliged to tell those coming after it that things were simpler in the old days. In the case of GNSS, this is demonstrably true: one system, GPS; two transmit frequencies, L1 and L2; and three signals, P-code (on L1 and L2) and C/A-code (L1 only).

Those days are gone.

The company building the navigation payload for the GPS Block III satellites has eight signals that must be broadcast on three frequencies. That probably contributes to all of the satellite production delays and also fuels suggestions that the hoary C/A-code should be phased out to free up space and power for more modern signal designs.

Meanwhile, receiver manufacturers are trying to figure out which of the new Galileo, BeiDou, GLONASS, and regional systems’ signals they should adopt — as well as when and how they should incorporate them into their products. In its many variations, we are frequently reminded these days that “the best is the enemy of the good,” a sentiment traced back to a poem by Voltaire.

In the title of his article in this issue about the robust presence of the original civil GPS C/A-code in the midst of latter-day entrants, Frank van Diggelen asks, “Who’s your Daddy?” (For those unfamiliar with this bit of American slang, perhaps Wikipedia says it best: it is an expression “commonly used as a boastful claim of dominance over the intended listener.”)

In fact, Frank is only pointing out the reality of — and debt owed to — the C/A-code’s historical precedence, its persistent utility, and its incorporation into more than one billion GNSS receivers in use today.

The original designers of the first GPS civil signal got a lot right, which subsequent signal designs have built on. But innovations have also been introduced into more recent GNSS signal designs.

These are not simply attempts to improve on perfection. The C/A-code hails from a technological era in which electronics, computing power, battery designs, applications, and many other factors were less advanced than they are today. Or than they will be tomorrow.

Every parent hopes that his or her offspring will go farther and accomplish more while still recognizing the assets and values that they inherited. So it should be with technologies and their progenitors, too.

Tradeoffs inevitably occur in changing or adding features to GNSS signals. Ultimately, the marketplace — including the installed base of receivers and already satisfied users — will decide which of these have more utility and, therefore, are worth paying for. Regulatory mandates may influence the outcome, but end users and equipment manufacturers will have the most to say about it.

And that is also as it should be.


One final note: Dean Bruckner, who wrote a letter to the editor that we published in our last issue, asks that I mention that his remarks reflected his personal opinion, not any institution with which he is affiliated. And while we’re at it, I should state that the sentiments expressed in these “Thinking Aloud” commentaries are mine alone, and should not be taken to reflect the opinions of the magazine’s editorial advisors, authors, and advertisers — or my parents or children, for that matter.