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4 Technical Aspects of Protection for the Scientific Use of the Radio Spectrum
Pages 86-102

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From page 86...
... on the passive services will likely increase in the upcoming decade thus creating new challenges and hopefully offering new solutions for addressing this changing landscape. Radio spectrum usage can act as a zero-sum game: use by one application can exclude use by a ­ nother.
From page 87...
... Protections such as these are increasingly important as airborne-, ground-, and space-based use of the RF spectrum increase and as the potential for aggregate interference increases due to the proliferation of electronic devices. 4.1  RADIO-FREQUENCY INTERFERENCE 4.1.1  Radio Astronomy Considerations The threshold levels of interference detrimental to radio astronomy3 given in Recommendation ITU-R RA.769 are specified in both power flux density (pfd)
From page 88...
... 6 Appendices 3 and 4 of the ITU Handbook on Radio Astronomy provide a useful guide on converting units used by radio astronomers to those used by others in the radio communications sector. The IUCAF (the Scientific Committee on Frequency Allocations for Radio Astronomy and Space Science)
From page 89...
... Recommendation ITU-R SA.1028 provides the performance criteria for satellite passive remote sensing, and ITU-R SA.1029 provides the interference criteria that are compatible with those performance objectives by defining the maximum permissible interference level within a reference bandwidth that is not necessarily the same as any particular sensor's bandwidth. The ITU further recommends that in shared frequency bands (except absorption bands)
From page 90...
... But most unwanted signals that are not easily recognizable can masquerade as valid scientific data. Because it is not possible for radio astronomy to operate in frequency bands for which there are transmitting antennas within the line of sight, the sharing of primary radio astronomy bands with services using satellite downlink transmissions or aeronautical transmissions is avoided.
From page 91...
... , for a part of the celestial sky that includes the Sun and Cas A, two very strong radio sources. As can be seen in the time stamp of the images in their upper left-hand corner, the top row of images was collected just 10 seconds prior to the bottom row.
From page 92...
... Finally, multiple users may effectively share the same spectral allocation if none need to use it continuously and all are able to coordinate the use of the spectral allocation based on local demand. Thus, while sharing of the radio spectrum is often considered a zero sum game, where use by one service excludes use by another, effective spectrum management includes consideration of location and time, as well as the specific spectral allocation.
From page 93...
... In the case of terrestrial mobile transmitters, it is often useful to use the Monte Carlo method to determine how the flux density at the observatory or Earth station varies with the size of the coordination zone, using the criteria in Recommendation ITU-R RA.1513 for the percentages of time for which flux density in excess of the detrimental thresholds can be allowed. If it is necessary that a transmitter be sited within the coordination
From page 94...
... Should such assignments result in harm ful interference to these observatories, the situation will be remedied to the extent practicable." SOURCE: Reprinted from FCC Online Table of Frequency Allocations, 47 C.F.R.
From page 95...
... 4.2.3  Temporal Separation A third strategy for mitigating interference between active and passive users of the radio spectrum is with dynamic frequency allocations based on local demand. For example, with increasing demand for
From page 96...
... For example, the IEEE Geosciences and Remote Sensing Technical Committee on Frequency Allocations in ­ emote R S ­ ensing (FARS) has created a geographic database that can be accessed through the Internet that combines satellite observations of the RF spectrum with ITU and FCC regulations.
From page 97...
... 4.3.2  Filtering in Radio Astronomy Receivers As explained in §4.2.2, the ability of passive services to employ filtering of sufficiently high order to mitigate the deleterious effects of emissions outside the radio astronomy band is severely limited by the need to achieve an extremely low noise figure. The requirements for a filter designed to mitigate out-ofband emission effectively must take into account (1)
From page 98...
... 4.3.4  Transmitter Beamshaping In the case of transmitters in fixed terrestrial locations, it is often possible to place a null in the radiation pattern in the direction of a radio astronomy observatory. This technique has been used on numerous occasions to protect radio telescopes at Green Bank, West Virginia, within the National ­Radio Quiet Zone.
From page 99...
... There is no EESS allocation near 6.8 GHz, and subsequent use of this spectral region, primarily by the fixed service, mobiles service, and fixed-satellite service, in accordance with the national and international allocations, has caused the band to be unusable for passive microwave measurements over land in much of the world's developed regions without the application of RFI mitigation. Over the oceans, the ITU recognizes the passive microwave EESS usage between 6.425 and 7.075 GHz through Radio Regulation 5.458, but offers no formal protection other than asking administrations to keep the EESS needs in mind.
From page 100...
... Because radio telescopes are generally located in remote areas and are somewhat shielded by the surrounding terrain from ground-based RFI, protection to the RAS while needed over very broad bands, is only necessary for relatively small geographic areas surrounding each operational radio telescope. While radio astronomy needs protection over large segments of the radio spectrum, some degree of time sharing with active users, enabled by the Internet and dynamic frequency allocation, may be possible to make more efficient use of the overall spectrum (See Section 4.2)
From page 101...
... However, frequency coordination must take into account the rapid timescale at which radio telescopes operate. Most modern radio telescopes are equipped with multiple receivers and instruments,
From page 102...
... Thus, dynamic scheduling and frequency coordination must take into account both the local spectral environment and also those of the associated facilities in order to enable productive scientific use of the radio spectrum.


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