IEEE Signal Processing Magazine - January 2018 - 139

PLM, Amateur Others: 30-54 MHz
TV 2-6, RC: 54-88 MHz
Air Control, Aero Navigation: 108-138 MHz
Fixed Mobile, Amateur, Others: 138-174 MHz
TV 7-13: 174-216 MHz
Maritime Mobile, Amateur, Others: 216-225 MHz
Fixed Mobile, Aero, Others: 225-406 MHz
Amateur, Fixed Mobile, Radio Location: 406-470 MHz
TV 14-20: 470-512 MHz
TV 21-36: 512-608 MHz
TV 37-51: 608-698 MHz
TV 52-69: 698-806 MHz
Cell Phone and SMR: 806-902 MHz
Unlicensed: 902-928 MHz
Paging, SMS, Fixed, BX Aux, and FMS: 928-960 MHz
IFF, TACAN, GPS, Others: 960-1,240 MHz
Amateur: 1,240-1,300 MHz
Aero Radar, Military: 1,300-1,400 MHz
Space/Satellite, Fixed Mobile, Telemetry: 1,400-1,525 MHz
Mobile Satellite, GPS, Meteorological: 1,525-1,710 MHz
Fixed, Fixed Mobile: 1,710-1,850 MHz
PCS, Asyn, Iso: 1,850-1,990 MHz
TV Aux: 1,990-2,110 MHz
Common Carriers, Private, MDS: 2,110-2,200 MHz
Space Operation, Fixed: 2,200-2,300 MHz
Amateur, WCS, DARS: 2,300-2,360 MHz
Telemetry: 2,360-2,390 MHz
U-PCS, ISM (Unlicensed): 2,390-2,500 MHz
ITFS, MMDS: 2,500-2,686 MHz
Surveillance Radar: 2,686-2,900 MHz
0

25

50
Spectrum Occupancy (%)
Chicago

75

100

New York City

FIGURE 1. The spectrum occupancy measurements in New York City from 30 August to 3 September 2004 and Chicago, Illinois, from 16 to 18 November
2005. (Image courtesy of SSC [5].)

meet its specific radio-sensitivity requirements and wide-band
frequency agility [10]. The CR cycle includes two major functionalities: spectrum sensing and spectrum access. Through
spectrum sensing, CRs collect information about the status of the surrounding spectrum's occupancy, i.e., the PUs'
activity, allowing for the adapted exploitation of the vacant
spectral bands. To minimize the interference caused to PUs,
the spectrum-sensing task performed by a CR should be
reliable and fast [11]-[13] and obey the requirements of the
IEEE 802.22 protocol, which is described in "IEEE 802.22
Standard for WRAN."
For the past ten years, CR and its challenges have been thoroughly reviewed in the literature. Several works [14]-[19] focus
on spectrum-sensing and survey-sensing techniques, along with
their performance and limitations. These techniques are essen-

tially energy detection, matched filter, and cyclostationary
detection. Collaborative CR networks, where different users
share their sensing results and cooperatively decide on the
licensed spectrum occupancy, have also been proposed to overcome practical propagation issues, such as path loss, channel
fading, and shadowing. Other works [17], [20] deal with spectrum access, which uses the information gathered from spectrum sensing to plan the spectrum exploitation by unlicensed
users. This functionality includes spectrum analysis, spectrum
access, and spectrum mobility [21]. It ensures coexistence with
PUs and other CRs by minimizing interference for the former
and sharing the spectrum with the latter.
In this article, we focus on the issue of spectrum sensing from
the analog-to-digital interface point of view, which has so far
received little attention. Our motivation stems from one of the

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