Bandwidth Demands Crowd Military Needs

This article first appeared in Defense Technology International.

If a multinational organization that few have heard of, headed by a Russian-educated citizen of Mali, managed to disable the radar of a major U.S. combat system, you would think someone would make a fuss. Apparently not: When the U.S. Federal Communications Commission, acting in accordance with the International Telecommunication Union, inadvertently sold the operating frequency band of the B-2 bomber's Raytheon APQ-181 radar to a commercial user, nobody panicked, even though installing new radar arrays on the 20 surviving jets will cost well over $1 billion.

While more information is stored electronically and shared, the radio-frequency (RF) bandwidth available to share it remains fixed. The pressure is increasing, as consumers trade voice telephones for video smartphones, computer users everywhere demand broadband and new applications emerge. But the concept of network-centric warfare and the wider use of unmanned vehicles are making militaries equally dependent on the availability of wideband wireless.

The B-2 radar is only one capability that has been lost since the information revolution kicked into high gear. The Joint Tactical Information Distribution System, the first attempt to create a network-centric environment (and currently the only way to get AWACS targeting data to an F-22) has "limited supportability outside the continental U.S.," according to a U.S. military presentation, because it was developed in an occupied band.

Global Hawk's satellite data link operates in a non-government fixed satellite service bandi.e., one of the bands used for communications between satellites and fixed ground stationson a limited, noninterference basis. The Situational Awareness Data Link and Enhanced Position Location Reporting System can't be used in Germany or South Korea. Stealth systems present problems, because their emitters hop around the widest possible bandwidth to frustrate tracking.

Another, more subtle problem is getting closer at an alarming rate: encroachment on the spectrum for flight-test telemetry. Although you can fit more memory and processing on the aircraft itself, telemetry is more important than ever to flight testing. To test complex systems efficiently, you need to have the flight-test engineering team monitoring data in real time, so experts on the ground can determine if each test point was good and clear the pilot to proceed to the next. This calls for higher data rates. Another driver for telemetry is testing of increasingly sophisticated unmanned aerial vehicles.

There are two unalterable facts about RF bandwidth. More data takes more bandwidth, counted in hertz, and of course there are more hertz available at higher frequencies. The second law is that the higher the frequency, the harder it is to get range, since it takes more power.

Flight tests can't use a lot of high-technology compression. "This is not a cell phoneyou can't ask the pilot to wait while you redial," says Darrell Ernst of Mitre Corp., a member of a U.S.-European delegation trying to raise international awareness of the bandwidth issue at last month's Aero India show in Bangalore. He reckons that with manageable compression and modulation techniques, 600 MHz. of spectrum will still be needed to fly one test in 2020.

So far, the only space walled off for flight testing is between 5091 and 5150 MHz. in the microwave band. This segment was reserved for the aborted Microwave Landing System project. "If [the flight-test community] can get in there and start using it, we can be established as the primary user and it will be hard for them to throw us out," according to Ernst.

Read the rest of this story, check out a cool JSF pic gallery, see if the DPRK is learning the lessons of Iraq and Afghanistan and take a gander at a HOT F-35 screed from our friends at Aviation Week, exclusively on

-- Christian

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