Page 111 - ITU Kaleidoscope 2016

ICTs for a Sustainable World

spectrum supply exceeded demand, assignment would occur Spectrum sharing is a spectrum utilisation scheme that
in a very straightforward basis; as time went by and allows two or more parties to utilize the same range of
technological advances started to demand more and more frequencies while no exclusivity is granted to any of them. In
spectrum, lotteries and other administrative processes were [10] techniques that facilitate spectrum sharing are primarily
used to assign the spectrum. Soon the flaws of lotteries divided into coordinated, which require coexisting radio-
were revealed and a long held theoretical proposal became frequency (RF) systems exchange information to share the
reality: auctions became the mechanism of choice to assign same frequency band, and uncoordinated, by which RF
radio frequencies to users. Still, assignment entailed systems adjust their operation to coexist with other RF
licensing, so licences would protect the holder from undue systems with little information to share. Coordinated
interference from other spectrum users. Licences were techniques are based on either properties of the
issued on relatively long periods of time, which meant risks communications infrastructure – as in FDMA, TDMA or
associated with technology and policy changes were CDMA - or use channel-based control methods, such as
eliminate in favour of the licensee. CSMA/CA. On the other hand, uncoordinated techniques
include: dynamic channel selection, adaptive frequency hop,
A range of services and applications have benefited from
decisions to exempt users of certain bands from licensing. listen-before-talk, distributed control power, and cognitive
Cordless phones, remote controls and wireless Local Area radio [10].
Networks operate on that basis. The decision to allow for Spectrum sharing started with decisions that split the use of
such commons, especially for Wi-Fi technology, has opened bands, with strong provisions against interference, and has
immense opportunities for innovation in wireless evolved into decisions that have designated some spectrum
communications. Put simply, it reveals the importance of bands as unlicensed and therefore free to be used by any
having tried a non-conventional way of spectrum utilisation. device within technical parameters dictated by standards.
More recently spectrum sharing has found its place into
However, SAs face quite a number of challenges. Spectrum
management needs to embrace new approaches and, in some regulatory frameworks promulgated by some SAs. If policy
cases, a full overturn of traditionally held views. It is the makers and SAs are receptive to spectrum sharing, it may
case of spectrum value maximisation. For example, in the develop as a key spectrum management tool to use, allocate
UK, the Department for Culture, Media and Sport, DCMS, and assign spectrum to achieve the main management
[2] identifies three components of value: private user value, objectives discussed above of value maximisation and
private external value and social value. Private user value, interference minimisation.
also known as the economic value of spectrum is defined as Milgrom et al. [14] argue that a combination of licensed and
the present value of the discounted future profits earned by unlicensed approaches to spectrum assignment may unfold
way of using the spectrum [3], [4]. Value is affected by in innovative services which would in turn lead to increased
revenues, costs and uncertainty. Private external user value social benefits. Licenses provide rights and obligations
refers to the externalities that arise from the use of spectrum whereas unlicensed used of the spectrum, like a no-frills use,
by other users. Social value of spectrum gathers all is subject to the hassles and inconveniences of the commons.
expressions of value that are not directly attributable to Spectrum sharing is not concerned with licensing per se;
economic activities that may profit from spectrum. Most rather it is a spectrum utilisation scheme that erodes
social value resides in the spectrum allocated to defense, exclusivity in spectrum access and utilisation. In recent years
security and public affairs. several technologies such as Software Defined Radio and
Cognitive Radio (CR) have been developed to make shared
4. SPECTRUM SHARING use of the spectrum possible. Such radios are capable of
providing dynamic access to the spectrum, whereby radio
frequency parameters are adjusted dynamically to optimize
The preceding discussion pointed at the need for more
spectrum management flexibility since the "command and spectrum usage. A conspicuous example is IEEE 802.22,
control" or long-term exclusive use approach has proven to also known as Wireless Regional Area Network or WRAN,
be quite a static and rigid management approach. It has been a technical standard that includes CR techniques able to use
argued that such models have contributed to spectrum spectrum allocated to television broadcasters under direct
scarcity [17]. From a technical perspective, a more dynamic coordination of a central database, which keeps up-to-date
spectrum management is possible if and when new information about current band utilisation. WRAN is meant
techniques that enable the redefinition of radio frequency to be deployed in rural, low-density geographical areas
parameters, such as the frequency, modulation or output where broadband access is non-existent. The standard is first
power are allowed to operate. of its kind as it is meant for the opportunistic use of
frequencies associated with TV bands – known as white
The combination of new technology, improved radio spaces- while allowing no interference.
transmission techniques, and flexible and innovative rules on
the use of spectrum facilitate an increasingly attractive Either through new technologies or through purely
aspect of spectrum management which is gathering renewed administrative allowances that make it possible for several
interest and, in a way, being demanded by enthusiasts and users to share a band – shifting the burden of agreeing to
experts: the shared use of the spectrum. interference-free operation onto those users - spectrum

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