Countdown to the GPS Timepocalypse

A bug that is about to hit older GPS hardware that has echoes of the year 2000. People who are old enough to have experienced the transition from the 1990s to the 2000s will probably remember the dreaded "Year 2000 Bug" supposedly ringing the knell of civilization. With short-sighted software engineering that only recorded two digits a year, we were told that date calculations would fail massively in software that went from the electrical network to digital watches at all. Massive remediation efforts were undertaken, companies rehired programmers whose obsolete skills were suddenly coveted again, and ultimately nothing happened.

Another era awaits us, much less known but potentially deeper and more insidious. Saturday, April 6, 2019 – it's tomorrow – GPS receivers could have software problems due to the rotation of their time counters. This could result in minor inconvenience to a major confusion, with an external chance of chaos. Some alarmists even say they will not fly this weekend, for fear of the consequences.

So what are the actual potential consequences and what is the problem with GPS in the first place? Not surprisingly, it all comes down to basic math.

History of the era

GPS satellites are essentially very precise clocks in orbit, transmitting navigation messages at a speed of 50 bits per second. The navigation messages include a time stamp and orbital information for each satellite, which the GPS receivers below can use to determine their position. Each full navigation message has a length of 37.5 kilobits, which means that a full page of GPS data takes 12.5 minutes to transmit.

The navigation message is divided into 1500-bit frames, each divided into five 300-bit subframes whose transmission takes 6 seconds. Each 300-bit sub-frame is then divided into ten 30-bit words. The first 30-bit word of each subframe is a telemetry word, encoding certain information about the health of the satellite. The telemetry word is followed by a 30-bit TOW (Time of Week) word, which codes the number of the week and the time of that week. The calculation of GPS time is a bit strange because of the gymnastics needed to code the number of seconds of a week (604,800) in the 17 bits available in the word TOW after taking 13 bits for parity and d & rsquo; Other uses. The word TOW actually represents the number of 1.5-second periods of a week, divided by four, because there are four 1.5-second periods within six seconds required to transmit each sub-frame .

Despite appearances, the complexity of temporal coding of the spatial side of the GPS system is not the cause of the impending problem, although it is related. The problem is the way in which time data is interpreted by GPS receivers and, like the Y2K bug, comes down to decisions made by software engineers. Of the 17 bits devoted to the coding of the word TOW, the week counter uses 10 bits. This means that satellites can count to 1024 weeks, or about 19 years and 8 months, before the meter goes back to zero. At the present time, the week counter corresponds to all units: 1111111111. On Saturday, April 6, the week counter will be incremented, returning to 0000000000. That's where the problem lies.

Been here, do this

Now, this is not the first time this has happened. The GPS system had been operating in various forms since the late 1970s, for strictly military purposes, and opened to the civilian market in 1983, in part as a result of the destruction of Korean Airlines Flight 007 by Soviet anti-aircraft defenses, which claimed that the airline was a spy plane. The beginning of the GPS era was fixed on January 6, 1980, from that moment. This means that the first turnaround took place on August 21, 1999 – 1024 weeks after the start of the clocks.

The clever reader will notice that the world did not end at the last reversal of the weekly GPS meter. This time, this time, will definitely be a non-event. Probably, but there are two or three factors that complicate things this time around. First, in 1999, very few GPS receivers were in civilian hands. Whereas Magellan introduced the first portable GPS receiver, the Magellan NAV 1000, in 1989, and some mobile phones were equipped with receivers as early as 1999, the problems encountered with the nascent system when the date turned for the first time did not occur. were just not so huge. treat.

The year after the first rollover, the US Department of Defense made the decision to broadcast navigation messages with maximum localization accuracy. For the first time, everyone could have achieved centimeter accuracy with the right equipment, and the GPS industry took off. In 2001, the dashboard browsers Garmin and Tom Tom became the flagship application of GPS. Cell phones turn into smartphones soon after and begin to integrate GPS receivers and navigation software. In 2017, the global market for GPS receivers was estimated at nearly $ 38 billion. So there are many GPS receivers, far more than in 1999.

Back to the future?

So, what will happen with your GPS? Probably nothing. GPS manufacturers have been experiencing this reversal for some time and virtually all receivers manufactured over the past decade are already able to handle it. Older devices, like my old Garmin eTrex Legend, which once was a source of fun for family geocaching in 2003, but has been sitting in a drawer for years, are in danger of collapsing on Saturday.

The way in which the end of the second GPS era will manifest itself on specific devices depends entirely on how the manufacturer coded the thing. Some will interpret the report as a 19.7-year-old leap forward or downstream. The navigation itself should not be affected, even if time goes by, or just for a moment if it is. Non-navigational GPS receivers, such as the GPS timebases used to synchronize mobile phone services, may have a bigger problem, but again, if the devices are new or they have have been corrected, this should not be the case.

So, relax and go about your business knowing that when ten turns become ten zeros on Saturday, there will be practically nothing. If you are so inclined, you might want to hook up your car GPS and see if any updates are needed, but other than that, you're probably all good. And if you really want to spend some time worrying about the bearings, think about it: there are 19 years left to wait until we have to deal with the Year 2038 problem.