IEEE Wireless Communications - April 2017 - page 7

IEEE Wireless Communications • April 2017
these problems. This case shows the complex interference reg-
ulatory issues that arise from a combination of a very strong
signal, but unnecessary signal strengths near a transmitter com-
bined with the limitations of practical receivers to deal with
strong adjacent band signals.
A final example of regulation and interference due to high
signals is a long standing concern of possible interference from
the FM audio broadcasting band upper end at or below 107.9
MHz and the aviation safety Instrument Landing System/ILS
band at 108.10–111.95 MHz. While there clearly is a potential
of OOBE interference from FM transmitters at 107.9 MHz near
airports, that can be readily controlled by restricting such loca-
tions. But there is a more complex problem of receiver-generat-
ed intermodulation in the ILS receiver if the ILS frequency has
a 2f
— f
relationship with two nearby FM broadcast stations in
the upper segment of the FM band. This problem is addressed
from the frequency assignment viewpoint in an ITU-R recom-
mendation [3]. The ITU’s aviation counterpart, the International
Civil Aviation Organization, has also addressed it with a mini-
mum standard for ILS immunity to receiver-generated intermod-
ulation from lower adjacent band broadcast signals [4].
Frequency duplex gaps are another issue where regulations
are used to prevent interference. In full duplex systems, such
as mobile radiotelephones, a unit must transmit and receive
on nearby bands using the same antenna or at least antennas
that are physically close. Duplexers or three-way circulators are
used to separate the transmitted power from the unit receiv-
er so that it is not overloaded by a large signal on a nearby
frequency. In creating band plans for such systems, standards
makers and regulators must decide what minimum spacing is
needed. This involves a tradeoff between spectrum efficiency
issues and cost and size issues for the equipment. Duplexers
are basically filters, and their performance generally increases
with improvements in component technology, although there
are some limits imposed by system theory since perfect “brick
wall” filters are not realizable. So one of the challenges for the
spectrum policy maker is how to pick the duplex gap for a new
band knowing both that it is very difficult to change the gap
size once equipment enters the marketplace, and also that per-
formance levels that seem a “push” today may become cost-ef-
fective in a few years as component technology improves and
costs decrease due to production learning curves.
While it is generally simple to understand the technical and
policy issues associated with avoiding cochannel interference,
the corresponding issues related to adjacent channel and near-
by band interference are much more complex. While these situ-
ations could be resolved by the use guardbands, such solutions
decrease spectrum efficiency, which is becoming increasingly
important as demands for spectrum from various radio services
are rapidly increasing.
[1] J. T. Dixon, “UHF-TV Taboos: The FCC Electromagnetic Compatibility Plan for
UHF Television,”
IEEE Trans. Electromag. Comp.
, vol. 6, no. 1, 1964, pp. 29–32.
[2] Declaration of M. J. Marcus, FCC ULS File No. 0006867447, Sept. 11,
[3] Recommendation ITU-R SM.1009-1, “Compatibility Between the Sound-Broad-
casting Service in the Band of About 87–108 MHz and the Aeronautical Ser-
[4] International Civil Aviation Organization, Annex 10 to the Convention on
International Civil Aviation, vol. 1, section 3.1.4 “Interference Immunity Perfor-
mance for ILS Localizer Receiving Systems,” 2006.
[S ’66,M ’72,SM ’01,F ‘04]
Director ofMarcus SpectrumSolutions, Cabin John, Maryland, and adjunct professor
at Virginia Tech’s Bradley Department of Electrical and Computer Engineering. He
retired from the Federal Communications Commission in 2004 after nearly 25 years
in senior spectrum policy positions. While at the FCC, he proposed and directed the
policy developments that resulted in the bands used by Wi-Fi, Bluetooth, ZigBee,
and unlicensed millimeter wave systems. He was an exchange visitor to the Japanese
spectrum regulator and has been a consultant to the European Commission and the
Singapore regulator. During 2012-13 he was chair of the IEEE-USA Committee on
Communication Policy. In 2013 he was awarded the IEEE ComSoc Award for Public
Service in the Field of Telecommunications. He received S.B. and Sc.D. degrees in
electrical engineering from MIT.
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