So, first, who needs three more worldwide satnav systems, when we already have GPS? Why do these others want to spend billions just to keep up with the U.S.? There are two reasons: one political and the other practical. Politically, GPS has become a (not the) dominant technology in almost every part of human life around the world, in government, national security, industry and private life, with more than a billion receivers being used daily for thousands of applications, from simple to critical. But if you were Chinese, Russian or European, would you want to leave key control of your economy in U.S. hands? Yes, the U.S. has promised never to restrict or turn off GPS but, nevertheless, major nations still feel uncomfortable about extensive dependence on a foreign country.

The practical reasons are twofold. Additional satellite systems are operationally beneficial to users. More GNSS satellites–within limits–provide greatly enhanced performance. GPS works well with 24 satellites, but it would work much better with 50, except that 21 is actually all the DOD needs, and it can’t afford to build and launch more just to improve things for civilians. The other reason is that satnav will be a huge money maker for other nations: just think of the growing Chinese market for GNSS receivers embedded in personal cellphones alone.

Seamless Intersection

So how will GPS users use foreign satellite systems? Interestingly, you won’t know when you are using them. Unlike, say, the frequency selections for NDB or VOR or VHF, your GNSS receiver won’t have a switch to choose GPS or Galileo or any of the others. Just as your current receiver automatically selects the four GPS satellites that are in the optimum geometric configuration for the most accurate position fix, your future GNSS receiver will select the four satellites–which could even be one from each of the four different constellations–that will provide the most accurate result.

The seamless transition from one to another brings in two new buzzwords–compatible and interoperable–that seem similar but are distinctly different. Think of them this way. In male/female relationships, for example, compatible means you have much in common and get along well together. So while each of the four GNSS constellations operates in different groups of frequencies, their satellites are designed not to interfere–in other words, be compatible–with satellites of the other constellations. Owners of the different systems have now accepted and accomplished that compatibility.

But compatibility is not enough. Those signals also need to be interoperable, which takes things in that relationship a big step further. The four different constellations use different transmission formats to send their data, and before any of them can be used in combination with those of a different constellation they have to be converted via software to, shall we say, consummate things to achieve full interoperability. That conversion is fairly complex, but all GNSS providers are committed to developing solutions and that work is under way. Note also that while each constellation’s satellites transmit within different allocated groups of frequencies, some of those are encrypted for its operator’s special services. GPS, for example, transmits highly classified signals on its unique M-Code frequency, available only to the U.S. military and some allied military forces. Consequently, the separate GNSS providers will each offer only two, internationally common, frequencies–the so-called L1 and L5 frequencies–for interoperability.

However, that process has hit a stumbling block. It turns out that while the first interoperable technique–to make Europe’s Galileo interoperable with GPS–was apparently agreed by an international GNSS expert panel, a UK government affiliate has claimed that it has intellectual property rights to the technique that forms the basis of the chosen solution. Somewhat embarrassingly to the Brits, the claimant is a commercial subsidiary of the UK Ministry of Defense (MoD) and, making things more complicated, the subsidiary was established as an arm’s length company to sell commercial applications of their development activities. Legally, it also appears that the MoD’s hands are tied, and it can’t tell the subsidiary to withdraw the applications that it has already submitted in the U.S., Europe, Australia and elsewhere.

U.S. officials are extremely put out over this, arguing that GNSS technology was never intended to be patentable for the purpose of imposing any sort of user fee, either on the systems’ signals or on the receiving equipment. One senior U.S. official has reportedly expressed concern about even discussing current and future U.S. development concepts at forthcoming international technical meetings unless new rules are firmly established.

Fortunately, perhaps, this situation has arisen early enough to nip the patent question in the bud, and it seems likely that the weight of opinion of the international GNSS partners and the user community will cause the UK company to withdraw. But the situation has shown that rules of conduct once felt unnecessary are always valuable to have in the background. Equally fortunately, it appears that the GNSS development community has not slowed its activities, and that interoperability is still an essential goal.

GPS III Launch Delay

Separately, an unrelated concern has arisen in the progress of the USAF GPS III program: the launch of that system’s first satellite has been delayed for 12 months, from 2014 to 2015. GPS III employs completely new-design GPS space vehicles that will progressively replace all the earlier GPS II variants now in orbit. GPS III will have increased power, thus improved interference and jamming resistance, and the new L5 frequency will, in combination with the L1 frequency common to all previous GNSS satellites, significantly reduce ionospheric effects that can create accuracy errors.

In itself, the GPS III delay would not be of real concern. However, in examining past GPS satellite orbital performance, a 2011 report from the Government Accountability Office (GAO) pointed out the risk that several earlier satellites were now down to “single thread” operation of critical systems, compared to their triple-redundancy configuration when launched, with the loss of their final “threads” being impossible to predict with any accuracy. The GAO’s concern was underlined by doubts expressed by a former USAF GPS program director that the current batch of GPS-11F replacement satellites–two of which are already in orbit–were unlikely to have the expected orbital longevity of their predecessors, bringing the possible risk of a total system “brownout” before sufficient GPS III space vehicle replacements could be launched. On this, only we–and the USAF–can wait and see, since the GPS launch philosophy has traditionally been one of “launch on replacement only,” and not on anticipated failures. o