Petri Mähönen is the head of the Institute for Networked Systems at RWTH
Aachen University in Aachen, Germany. Janne Riihijärvi works as a senior
research scientist in the institute.
The debate over radio spectrum regulation has become one of the most intense and crucial telecommunications policy debates. Radio spectrum, in the sense of availability of radio frequencies for wireless data communications, is scarce. Wireless technologies have inherent limitations. Understanding the current radio spectrum use in different environments is important and harder than it might sound. First, as is now well understood, not all spectrum that is allocated is actually used. Second, spectrum measurements and realistic usage models are harder to make than people assume. Third, while regulatory databases and similar sources, such as white space databases, contain a lot of information how spectrum might be used, inevitable errors in propagation models significantly limit the value of this information. Finally, for unlicensed frequency bands and user-deployed networks, particularly emerging femtocells, there really is no substitute for in situ measurements.
The policy debate needs to be quantitative and data driven, and several research groups around the world have been conducting different types of measurement campaigns on spectrum use for quite some time. Measurement campaigns by the Shared Spectrum Company are early examples, while longer-running efforts include the Spectrum Observatory of the Illinois Institute of Technology, as well as our own efforts in this domain. However, most existing campaigns have focused on measurements at a single location. Such measurements are invaluable to gauge the promises of new technologies, but ultimately lack statistical coverage. They also cannot support regulatory enforcement, national security applications, or dynamic radio environment based optimization.
As part of the recently concluded European research project FARAMIR, we collaborated with industry and academic research groups to carry out extensive measurements on spectrum use across different urban and rural regions. During this work, we spent a week collecting measurements in different regions of London, UK, ranging from downtown shopping streets and tourist haunts to outer suburbs. Some 150 different locations were covered during the week, and at each location several hundreds of received power measurements were taken on different frequency bands. The first results were presented recently in the IEEE DySPAN 2012 conference in Seattle. Our measurements show that while the cellular bands are, as expected, practically fully utilized in urban environments, the usage of many other bands was significantly lower. Further, even the usage of cellular bands varied highly across the different measurement locations, falling to surprisingly low levels outside dense population centers. These results indicate that while availability of cellular spectrum in urban region is indeed limited, there seems to be little shortage of available frequencies in rural settings especially if low power transmitters are used. Overall the dynamics of spectrum use were observed to be very complicated as can be seen from the example below, illustrating spectrum use on the 900 MHz GSM downlink band at a location near Oxford Street in downtown London.
In addition to the results from our own analysis, we will gradually make the raw data from our measurements available to the research community. Last week we released the first data sets from the London measurement campaign, as well as our earlier comparison measurements of spectrum use across several different European cities. All of these data sets as well as documents describing results from our analysis can be obtained from the website of the FARAMIR project. In the future all the publicly available measurement data from the Institute for Networked systems will be made available through iNets Measurement Data Archive (currently under construction). We believe that sharing data from such measurement campaigns is key to developing global understanding on spectrum use, thereby providing solid foundation for making policy decisions for future spectrum use.
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