The National Academies of Science has evaluated a steadily growing problem: …
Readers of Ars will undoubtedly be familiar with some of the battles over spectrum allocation for wireless devices and services. As the number of wireless devices and their bandwidth requirements continue an apparently inexorable climb, the fight over who should get which chunk of the radio spectrum has generally played out between big business and public interests. One group that hasn't generally appeared to be taking part in the scrum is the science community, but that's not for lack of interest—the radio spectrum is used for both astronomy and the monitoring of the environment on Earth. Now, a report by the National Academies of Science calls for a greater role for science in spectrum allocation.
The intersection of radio communications and radio astronomy has a rich history—the radiation remnant of the big bang, for example, was discovered accidentally when researchers at Bell Labs noticed that a microwave receiver picked up persistent interference. Radio telescopes have since been used to explore everything from the behavior of neutron stars to the presence of organic molecules in distant dust clouds. Unfortunately, researchers have been compelled to build them in ever more remote locations, due to the interference that arises closer to population centers. As the report notes, however, even those are coming under threat from everything from cell phone signals to aircraft and satellite transmissions.
Because the objects studied by radio astronomers occur at varying distances across the Universe, key diagnostic signals may experience significant redshifts for some objects, meaning that a wide spectrum needs to be reserved in these areas. The faintness of some signals also requires that some objects be imaged for a full day to provide sufficient data, making these observations extremely sensitive to interference.
If anything, the situation with remote Earth sensing is even worse. Signals in the radio frequencies can provide detailed information on things like wind speed, water content, and mineral formations, but these techniques are becoming nearly useless in the areas where we might need some of this information the most: major population centers. In more than one case, we've actually lost the ability to use instruments after we went through the (extremely expensive) step of putting them into space. Right now, there are over 20 satellites in orbit that use passive microwave sensors to study the Earth.
Unfortunately, the spectrum allocation system in the US dates from the 1940s, long before radio astronomy and remote sensing were significant concerns. Still, the system has managed to reserve a bit over two percent of the spectrum below 3GHz for scientific observations, and another four percent is allocated on a secondary basis.
But those allocations haven't been made as part of a systematic attempt to consider what areas of research may require additional areas of spectrum, and a variety of factors are increasing the problems faced by the scientific community. Even licensed devices may interfere with key areas of the spectrum through things like spurious emissions, interference with adjacent channels, and occasional out-of-band emissions. Perhaps more significantly, there has been a proliferation of unlicensed low-power devices, from cordless phones and networking equipment to newer technologies like anti-collision radars used on automobiles. Although these are low power, their collective emissions in densely populated areas can interfere with scientific observations.
Improvements in wireless technology are also causing problems. Scientists have learned to make use of the "white spaces" left between channels to prevent interference with broadcasts, but engineers are increasingly able to fill these with usable signals.
The report makes a large series of recommendations, predicated on the recognition that the problems are entirely one-sided: research uses rely on passive sensing of natural radio sources—they can't possibly interfere with wireless communications. As such, the effort should be made to protect key areas of spectrum for scientific uses, in the same way we protect areas of land in the form of parks. Agencies with key interests in the area, like NASA and NOAA, should become more involved in the spectrum allocation process, and think about future areas of research that will need specific pieces of spectrum. For example, the report notes that researchers have become interested in the Cosmic Dark Ages, when the first stars in the Universe formed and exploded, and imaging that era will require radio frequencies.
For their part, the agencies like the FCC and NTIA could be more aggressive about policing devices or services that bleed over into spectrum they haven't been allocated.
But radio-based communications are clearly here to stay, so the report also suggests that everyone involved look into a number of technological fixes. These include some sorts of active interference suppression for instruments, as well as using technology developed by wireless equipment makers for their own purposes. Devices as simple as WiFi transmitters have the ability to hop frequencies to avoid sources of interference. It should be possible, the authors conclude, to create a cooperative system in which devices coordinate a temporary avoidance of certain areas of the spectrum in order to give scientists a clear window to view the Earth and cosmos.
Listing image by NASA's Astronomy Picture of the Day
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