Despite the breakthrough earlier this year when the US Departments of Transportation (DoT) and Defense (DoD)agreed to allow commercial users access to parts of the military global-positioning system (GPS), the two sides are now deadlocked over the choice of a frequency for a new dedicated civilian GPS signal.

Concerns are growing that if the problem is not resolved swiftly, Europe and Japan may begin to "lose faith" in GPS as an international standard, says National Oceanic and Atmospheric Administration (NOAA) Capt Lewis Lapine, who is chairing the GPS Interagency Advisory Council (GIAC).

In February, the DoD and DoT agreed to allow civil users uninterrupted access to the so-called "carrier phase", a portion of the L-2 military GPS signal, in addition to the existing downgraded L-1 civilian signal. The aim was to agree to a second dedicated civil frequency, known as the L-5, with a coarse acquisition code and navigation message which is considered essential for critical civilian uses of GPS, including aircraft precision approaches.

A detailed plan for providing the critical second civil frequency was promised within a year of the February accord, but seven months later no progress has been made, say participants of a technical session sponsored by the GIAC.

Progress towards L-5 is "deadlocked" over the fact that none of the GPS frequencies was "mutually acceptable to all federal agencies", says Lapine. Also unresolved was how the provision of the L-5 signal would be funded.

"We need to get this issue clarified," adds Lapine. The apparently simple impasse is an embarrassment to the Clinton Administration, which has called for establishment of a second civil frequency as part of a broader programme to maintain US leadership in aviation and satellite technology.

"The Europeans and the Japanese are watching this L-5 decision. If we can't get our act together, they will have no confidence that [GPS] will be a worldwide system. They are losing faith in our ability to get the decision made," warns Lapine.

The L-5 frequency is considered necessary for carrying out precision approaches together with the US Federal Aviation Administration's planned wide-area augmentation system. This now requires the L-1 and a portion of the L-2 military frequency. The L-5 would also provide redundancy against jamming, which continues to worry GPS sceptics.

Source: Flight International