History of Cognitive Radio

History of Cognitive Radio
The cognitive radio is an emerging new technology, which is far from mature in terms of real applications
in current wireless systems and networks. Today, to implement a practical cognitive radio, many hurdles
should be overcome, and it is still too early to tell what a cognitive radio should look like for different
wireless applications. Therefore, the history of cognitive radio technology is still relatively short.
Mitola’s work
A comprehensive description of the term cognitive radio was first discussed in a paper written by J.
Mitola III and Gerald Q. Maguire in 1999 [793]. In 2000, J. Mitola III wrote his PhD dissertation
[794] on cognitive radio as a natural extension of the SDR concept. When addressing the broad
issue of wireless personal digital assistants (PDAs) in his dissertation, Mitola mentioned that the term
cognitive radio identifies the point at which wireless PDAs and the related networks are sufficiently
computationally intelligent regarding radio resources and related computer-to-computer communications
to (a) detect user communications needs as a function of use context, and (b) to provide radio
resources and wireless services most appropriate to those needs.
FCC’s initiatives
In 2002, the FCC’s Spectrum Policy Task Force Report [797] identified that most spectra go unused
most of the time, as shown in Figure 9.2. Consequently, it was then realised that spectrum scarcity is
driven mainly by archaic systems for spectrum allocation and not by a fundamental lack of spectra.  How to open up additional spectra, whether it should be licensed or unlicensed, and the economic
implications of these decisions, have been topics of considerable debate [798]. Cognitive radio technology
offers a possible solution based on a more sophisticated or intelligent system for allocating
spectra that can dramatically increase the amount of spectra available to network operators and individual
users. In particular, on December 20, 2002, it was stated in FCC’s “Notice of Inquiry” (NOI)
titled “Additional Spectrum for Unlicensed Devices Below 900 MHz and in the 3 GHz Band” (FCC-
02-328) that it opens the question of using fallow TV band channels for unlicensed services on a
noninterference basis. In the NOI, the FCC states that specifically, an unlicensed device should be
able to identify unused frequency bands before it can transmit, that is, by using Dynamic Frequency
Selection (DFS) and Incumbent Profile Detection (IPD) algorithms.
On November 13 of 2003, FCC issued NOI and “Notice of Proposed Rulemaking” (NPRM) titled
“Establishment of an Interference Temperature Metric . . .” (FCC-03-289), in which it proposed an
interference temperature model for quantifying and managing interference. The interference temperature
is calculated by Tint = N+I
kB . It also stated that for an interference temperature limit to function
effectively on an adaptive or real-time basis, a system (cognitive radio) would be needed to measure,
and a response process would also be needed.
In another NPRM and order titled “Facilitating Opportunities for Flexible, Efficient, and Reliable
Spectrum Use Employing Cognitive Radio Technologies” (FCC-03-322), issued by FCC on December
17, 2003, it was stated that a wide ranging NPRM exploring a broad range of issues related to cognitive
radio technology will be required. It pointed out that the FCC wants to push for advances in technology
which support more effective spectrum use. Among these advances are cognitive radio technologies
that can possibly make more intensive and efficient spectrum use by licencees within their own
networks, and by spectrum users sharing spectrum access on a negotiated or an opportunistic basis.
The FCC’s action sparked a lot of response from both industry and academia, and some research
activities on cognitive radio [798–801] in the last few years. However, the most important event in
the development of cognitive radio happened in 2004, when the FCC issued yet another NPRM that
raised the possibility of permitting unlicensed users to temporarily “borrow” spectrum from licensed
holders as long as no excessive interference was seen by the primary user [795]. Devices that borrow
spectrum on a temporary basis without generating harmful interference are commonly referred to as
“cognitive radios” [796]. Basic cognitive radio techniques, such as DFS and transmit power control
(TPC), already exist in many unlicensed devices. However, to make a practical cognitive radio terminal,
we have to deal with many serious challenges.
The FCC is proposing specific rulemaking in the unlicensed arena related to cognitive technology
as follows:
• Opening three new bands to unlicensed operation based on DFS and TPC protocols (interference
temperature NPRM), which include 6525–6700 MHz (175 MHz), 12.75–13.15 GHz
(400 MHz), and 13.2125–13.25 GHz (37.5 MHz);
• Allowing six times more transmitter power for cognitive radio devices (under Part 15.247 and
Part 15.249) where the ISM band is lightly used (cognitive radio NPRM);
• DFS thresholds at which frequency change is required: For Tx power levels < 23 dBm:
−62 dBm; For Tx power levels > 23 dBm: −64 dBm; DFS threshold averaging time varies
with rule: unlicensed national information infrastructure (U-NII) is 1 μs, new interference temperature
bands: 1 ms; DFS thresholds are referenced to the output of an omni-directional
antenna.
• The definition of an unoccupied band: RSL < −83 dBm measured in a 1.25 MHz bandwidth
using an omni-antenna.
• Minimum TPC backoff from maximum allowed Tx power: −6 dB, triggered by a vendor
specific criterion for link quality. Related IEEE standards
On the other hand, the standardization work done by the Institute of Electrical and Electronics
Engineers (IEEE) has also been carried out parallel to the FCC’s action. Recent IEEE 802 standards
activity in cognitive radio includes a recently approved amendment to the IEEE 802.11 operation, or
the IEEE 802.11h, which incorporates DFS and TPC protocols for 5-GHz operations under the IEEE
802.11a standard [449–451].
Because 802.11a wireless networks operate in the 5-GHz radio frequency band and support as
many as 24 nonoverlapping channels, they are less susceptible to interference than their 802.11b/g
counterparts. However, regulatory requirements governing the use of the 5-GHz band vary from
country to country, hampering 802.11a deployment. In response, the International Telecommunication
Union (ITU) recommended a harmonized set of rules for WLANs to share the 5-GHz spectrum
with primary-use devices such as military radar systems. Approved in September 2004, the IEEE
802.11h standard defines mechanisms that 802.11a WLAN devices can use to comply with the ITU
recommendations. These mechanisms are DFS and TPC. WLAN products supporting 802.11h have
already been available in the second half of 2005. DFS detects other devices using the same radio
channel, and it switches the WLAN operation to another channel if necessary. DFS is responsible for
avoiding interference with other devices, such as radar systems and other WLAN segments, and for
uniform utilization of channels.
Among other activities carried out by the IEEE is 802.18 SG1, which was established at the
Albuquerque Plenary in November 2003, and focused on creating the following: (1) Recommendations
for a rule making proposal to the FCC on TV band use by unlicensed devices. (2) A Project
Authorization Request (PAR) and associated five Criteria documents to create a network standard
aimed at unlicensed operation in the TV band. In “Reply to Comments of IEEE 802.18” prepared by
Carl R. Stevenson (carl.stevenson@ieee.org) in May 2004, it indicated clearly that IEEE 802.18 supports
the opportunistic use of fallow spectrum by licence exempt networks on a noninterfering basis
with licensed services using cognitive radio techniques. IEEE 802.18 supports the FCC’s approach
to rural applications of cognitive radio technology as a means to increase the coverage area of wisps
and other unlicensed services in the ISM bands.
Earlier similar works
It has to be noted that, although the terminology of “cognitive radio” was only proposed recently,
the concept of intelligent radio is not completely new. Many previously carried out researches on
wireless communications and networks bear some similarity to what a cognitive radio does. The
first example of such research is the collision avoidance protocol used in IEEE 802.3 standard or
Ethernet standard: carrier sense multiple access (CSMA).2 The basic idea for CSMA is to sense
before transmitting, which works in a very similar way to what a cognitive radio unerringly does.
This polite radio transmission etiquette forms the core of today’s cognitive radio technology.
Another example of similar research is the so-called “dynamic channel selection/allocation,”
which has been extensively used in user traffic channel assignment schemes in mobile cellular systems.
A new mobile terminal will be assigned a traffic channel with an available idle channel from the
traffic channel pool. Its utilization will be released back to the pool when its transmission ends, thus
making it available to others’ use. Naturally, the intelligence level possessed in a cognitive radio will
be much higher than that available in all previous wireless applications.