Why we can have both reliable GPS and more broadband

Radio spectrum is a key resource in today’s information-based society, and it is in everyone’s interest to make reasonable attempts to squeeze the maximum use out of every Hertz of spectrum. The long-standing principle of U.S. spectrum management is that the FCC should make decisions in the “public interest,” although established users of spectrum have more rights of protection than new entrants. 

Unfortunately, in many spectrum struggles over the past few years, incumbent spectrum users with receivers vulnerable to interference from adjacent or nearby band use have insisted on blocking new spectrum use – even when current technology would allow a transition to upgraded receivers with adequate protection. A truism among spectrum managers is “transmitters don’t use spectrum, receivers do.” 

Receiver limitations  – often a simple case of outdated technology – are a major cause of spectrum lying fallow.

For example, UHF TV stations in Washington were assigned channels 14, 20, 26, 32, etc., based on concern that TV sets would suffer interference if more were used. While that was true for 1950s TV sets, it was not applicable for the technology of the past two decades. Eventually, the FCC broke the outdated mold as part of the DTV transition with no problems using available new technology.

The same could be true for the GPS-LightSquared dispute. The FCC first allowed terrestrial use of the band just below GPS, best known as the home of the financially ill-fated Iridium satellite phones, in 2003. In 2004 it authorized LightSquared’s predecessor to use this band for cell phone service, with the limitation that consumer units had to have both bulky Iridium-like circuitry and cell phone circuitry.

The dispute erupted this January, after the FCC relaxed the restriction and dropped the Iridium-like requirement, since users in urban areas would never need it. The GPS industry, supported by DOT and the Air Force, cried foul – arguing that unspecified testing was needed before FCC could make such an authorization (although a careful reading for the FCC order shows that definitive testing is necessary before any practical use of the frequency).

Tellingly, the GPS industry and their supporters were silent on what they have done to improve receiver robustness since 2003, when they were told that terrestrial use of the neighboring band was authorized. 

Are they using the best filter technology currently in production for comparable products such as cell phones?  Do they think it is reasonable to expect that any GPS product ever sold has to be protected forever from any action FCC might take to make the nation’s spectrum resource more efficiently used?

Apparently the general aviation Aircraft Owners and Pilots Association (AOPA) does. For almost two decades now they have blocked FAA action to bring general aviation receivers used in instrument landings into compliance with minimum international standards for immunity to adjacent band FM broadcasters. AOPA feels the burden of any interference problem should be entirely on the neighboring band, so as to allow their members to use outdated receivers indefinitely. The GPS community is following the same pattern here.

A more reasonable solution can be found. On one hand, tight initial restrictions on LightSquared in terms of antenna design and siting would prevent interference to all aviation use and keep terrestrial impact minimal while phasing in more reasonable limits as the GPS receiver population improves.  Conversely, the GPS community has to commit to being a responsible member of the spectrum-using community by employing reasonably available technology to decrease their vulnerability to other types of users.

The radio spectrum is a precious national resource. It must be handled carefully to maximize its utility for both the economy and national defense. That means adapting existing uses as new needs arise and as new technology becomes available. The present stonewalling by the GPS community on their neighbor LightSquared reflects poorly on a community with a proud history of great technical ingenuity that has helped change many aspects of our lives.

Michael Marcus is the founder of Marcus Spectrum Solutions and consults on wireless technology and spectrum policy in the U.S. and abroad.