The strong increase in the number of devices and systems deployed for consumer, commercial, and industrial uses has fueled an interest in learning how the radio spectrum is actually used. While the various efforts of the active and passive user communities have been useful in confirming the sparse time-frequency utilization of the spectrum, most existing studies are of limited usefulness because of their limited sensitivity, time resolution, and frequency resolution. Useful spectral monitoring for RAS applications requires continuous time-frequency resolution on the order of 1 kHz and 1 microsecond, with sensitivity sufficient to detect signals approaching the levels already known to be potentially harmful to radio astronomy as determined in ITU-R Recommendation RA.769. For air- and spaceborne EESS applications, an adequate spatial resolution would be critical, as discussed in §4.1.

The major drivers for more intensive spectral use will come from newly deployed 3G and 4G cellular systems, new technologies for unlicensed devices (Wi-Fi, etc.), changes to the regulations, and the availability of advanced technologies such as cognitive radios. It should be expected that the use of the 700 MHz, 1710-1755 MHz, 2110-2180 MHz, and 2495-2690 MHz spectral bands will be greatly increased due to 3G and 4G cellular deployments. Unlicensed devices will continue to proliferate in the 5 GHz, 70-90 GHz, and 3.1-10.6 GHz (ultrawideband) spectral bands. The onset of agile, frequency-hopping radio technology will create challenges: the prediction of open spectral bands will become more difficult. Regulatory agencies determine the appropriate technical parameters for operation in each spectral band, but these rules are in constant flux. The agencies need to enhance their role with respect to the passive services to include interference metrics, an extension of enforcement technology, and the inclusion of passive systems in their databases (e.g., the FCC’s Universal Licensing System).

4.3
UNILATERAL MITIGATION TECHNIQUES

A variety of techniques have been developed to reduce the impact of RFI on EESS and RAS observations. This section presents a review of unilateral methods. These methods apply to situations in which the EESS or RAS operator has no ability to influence the behavior of the sources producing the interference. This is the most common situation, but at present the performance achieved by the majority of the unilateral methods has been documented only anecdotally and so remains to be completely quantified.25 Following the review of specific unilateral mitigation

25

International Telecommunication Union, “Techniques for Mitigation of Radio Frequency Interference in Radio Astronomy,” Document 7D/142-E, January 23, 2007; A.J. Boonstra, “Radio Frequency Interference Mitigation in Radio Astronomy,” PhD Thesis, Delft University of Technology, Dept. EEMCS, June 2005, ISBN 90-805434-3-8.



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