In just more than a month, users of global positioning system applications will face a challenge in many ways similar to the highly publicized millennium bug.
“It’s serious enough to be called a `dress rehearsal’ for the Y2K bug-yet few people know about it,” said John Lovell, director of quality at Trimble Navigation Ltd., a manufacturer of GPS-based products.
The problem stems from a date field that was restricted by the developers of the GPS system in order to allow for more functionality, much like how many early computer programmers restricted their date field to only two digits to conserve then-precious memory.
The GPS system keeps track of time in two ways-weeks and seconds. Each Saturday at midnight GPS time (about 8 p.m. EDT) the system’s week counter increments by one.
The GPS week number count began at about midnight on Jan. 5, 1980, and it will roll over to zero when the count tries to increment from 1023 to 1024 at about midnight GPS time on Aug. 21. The system will roll over once about every 20 years.
The phenomenon, which is referred to as “GPS Week Number Rollover” or “GPS End-Of-Week Rollover,” is compared with a car’s odometer rolling over from 99,999 to zero.
“It’s different from Y2K because it will affect everyone at exactly the same time,” said Lovell.
In an article about the problem, Lovell writes, “If a GPS receiver has difficulty determining the correct date at, before, during and after this rollover, it may process data incorrectly. In fact, users who depend on GPS for geographic locations on land, at sea or in the air could face serious safety hazards.”
Experts on the matter aren’t sure how the rollover will affect GPS receivers, but they offer several scenarios.
“The best-case scenario is that nothing will happen at all,” said Lovell. Most newer GPS receivers are expected to handle the rollover without any problems, he said.
If problems do occur, they could range from receivers displaying the date as 1980 to some interruptions in service up to a half hour while the receiver sorts itself out.
“The worst-case scenario is that the receiver will put out incorrect information,” said Lovell. Receivers also might stop working completely.
The Department of Defense has said the date changes are unlikely to affect the operation of GPS satellites or the Defense Department’s ground control center, but no guarantees can be made for GPS receivers used in commercial and consumer applications. Older GPS receivers are of particular concern.
In the wireless industry, GPS clocks are used to synchronize Code Division Multiple Access networks. If the GPS clocks begin to function improperly, communications could be interrupted. However, many vendors appear to have addressed the potential problem.
Sam Gronner, a spokesman for Lucent Technologies Inc., said, “We have thoroughly tested our systems, and we have notified our customers that when the rollover occurs, there should be no issue whatsoever with our network synchronization.”
GPS locations also are instrumental to the growing telematics industry, which provides location-based information and emergency services to automobiles.
Most GPS receiver manufacturers have provided software upgrades that should enable many older receivers to function properly when the rollover occurs.
Still, Trimble is encouraging people to take potential problems seriously.
“We’re recommending, if possible, that in situations where life or significant property damage is at stake, that people evaluate the use of the GPS receiver,” said Lovell. “And we’re recommending that if loss of life could occur, that they not rely on GPS receivers at that time.”
