UK radio disturbance caused by satellite network bug
An error with the Global Positioning System (GPS) network has been blamed for causing problems with digital radio broadcasts last week.
The US Air Force said that removing a satellite from service had caused a software error.
A BBC spokesman confirmed that the decommissioning of a GPS satellite led to difficulties for listeners receiving digital radio signals.
The BBC understands several other satellites were affected.
"I live on the Worksop side of Sheffield and for the past two days the reception of the BBC National Ensemble [BBC radio stations] has been virtually non-existent indoors," wrote Darcy72 on Digital Spy's online forums last week.
In a response to the reported issues, the BBC said: "The outages were caused by a rogue GPS satellite (SVN23), which was taken out of service in the evening of 26 January."
The BBC has now learned that the problem occurred after a decommissioned satellite caused software problems which affected several other satellites.
DAB transmitters must broadcast at exactly the same frequencies and, in order to synchronise, they lock on to GPS satellite signals.
The GPS signals themselves broadcast the time and are supposed to be accurate to within a few nanoseconds.
However, on 26 January, one of the GPS satellites - named SVN23 - orbiting the Earth was decommissioned.
This unexpectedly caused problems for the whole network.
"While the core navigation systems were working normally, the co-ordinated universal time timing signal was off by 13 microseconds which exceeded the design specifications," said the US Air Force in a statement.
"The issue was resolved at 06:10 MST, however global users may have experienced GPS timing issues for several hours."
In fact, as a result of the problem, some GPS positioning would have been thrown off by nearly 4km.
The time discrepancy was picked up by the Metsahovi Radio Observatory in Finland.
It is not yet clear whether other systems around the world, such as navigational tools, were affected.
The BBC is still chasing the US Air Force for further details about the incident.
"They knew they were decommissioning it so shouldn't they have been aware this would happen?" questioned Prof Danielle George, a radio engineer at the University of Manchester.
"It was decommissioned after 25 years - actually it should have just had a seven-and-a-half-year lifespan so it lasted a lot longer than it should have done."
Depending on GPS
Prof George added that had there only been a problem with one satellite, DAB transmitters would probably not have experienced difficulties.
"They shouldn't have seen an issue with that because as far as I understand the way they work is they need two frequencies to lock and there are a number of GPS [signals] to look at," she told the BBC.
"This should be treated as a warning of what could go wrong," said Martyn Thomas, a fellow at the Royal Academy of Engineering who has criticised technological reliance on GPS.
"The world is dependent on GPS for a vast range of critical applications from navigation to financial trading, and precision docking of oil tankers to high tech farming."
In the future, Prof Thomas said, it was "essential" that there was back-up.