Aligning technology, business and regulatory scenarios for

Matthias Barrie a,n, Simon Delaea IBBT-SMIT, Vrije Universiteit Brussel, Pleinlaan 9, 104b Delft University of Technology, Faculty of Technology,

a r t i c l e i n f o

Available online 10 April 2012

Keywords:

Cognitive radio

Radio regulations

Spectrum pool

Economic scenarios

spectrum is becoming more and more scarce. Cognitive radio (CR) has been hailed as one of the methods to overcome this

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Telecommunications Policy

Telecommunications Policy 36 (2012) 5465590308-5961/$ - see front matter & 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.telpol.2012.03.001n Corresponding author. Tel.: 32 2 629 11 71; fax: 32 2 629 17 00.E-mail addresses: Matthias.barrie@vub.ac.be (M. Barrie), Simon.delaere@vub.ac.be (S. Delaere), Peter.Anker@telecomabc.com (P. Anker),

Pieter.ballon@vub.ac.be (P. Ballon).Because of the ever growing use of wireless applications and inexibilities in the current way spectrum is allocated,1. Introductionspectrum market scenarios. It can also be concluded that, out of the three proposed

alternatives, the geolocation database is the most likely candidate to be used for CR

purposes. However, although this database is a clear favorite for applications within the TV

White Spaces, spectrum sensing should not be discarded as a potential CR enabler for

highly sensitive applications in high-density radio environments.

& 2012 Elsevier Ltd. All rights reserved.re a, Peter Anker b, Pieter Ballon a

0 Brussel, Belgium, Gaston Crommenlaan 8, 9050 Gent, Belgium

Policy and Management, P.O. Box 5015, 2600 GA Delft, The Netherlands

a b s t r a c t

The amount of wireless and mobile applications and devices is rapidly growing. This

exponential growth might be hindered by a scarcity of suitable radio spectrum, a necessary

but limited natural resource required for all wireless communications. Spectrum scarcity

does not only slow down data growth, but may also disrupt existing communications.

Cognitive radio may provide a solution to these issues, but although the concept seems

promising, few products making use of CR have been brought to the market. This is due to

signicant uncertainties surrounding the appropriate economic scenario for CR, the

regulatory framework and the technology enablers needed for such CR scenario. As

business, regulatory and technical constraints are largely co-determined by each other,

this paper proposes to align them, paving the road for the implementation of specic

economic scenarios with appropriate regulation. First, from the business perspective, a

taxonomy of possible economic scenarios for CR is proposed. Second, for each scenario a

number of regulatory requirements based on a European context and characteristics

are given. In doing so, it is argued that the economic scenarios are inherently distinct so

that CR regulation should be customized for the type of scenario envisaged. Third, from the

technology perspective, this article reviews the possible CR enablers, showing that

spectrum sensing, CPC and geolocation database all have their strengths and weaknesses,

and receive varying support from business and regulators. Based on the analysis it can be

concluded that, although the introduction of CR does not seem problematic for the

unlicensed scenario and the exible operator scenario, more complex measures are

required to enable CR to contribute to the implementation of spectrum poolandcognitive radioURL: www.elsevier.com/locate/telpol

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559 547issue soon after it was rst coined by Joseph Mitola III, as it proclaims the ability of a radio to be aware of its environmentand its capabilities, enabling it to alter its physical layer behavior while being capable of learning from previousexperiences and following complex adaptation strategies (Mitola & Maguire, 1999). These awareness, reasoning andlearning capabilities are basic points of distinction between CR and Software Dened Radio (SDR) as the latter displays alack of these capabilities. The analysis performed in this article will consider CR and not SDR, although in some cases SDRcan be preferred over CR because of cost considerations. CR, however, enables more dynamic sharing situations in whichregulatory requirements are needed. If these situations are to be compared, it is necessary to pick CR as a xed assumption.

Cognitive radios can intelligently optimize their own operations and introduce a shift to more dynamic forms ofspectrum management and access (European Commission, 2011; RSPG, 2010). The latter seems necessary to cope with theexpected scarcity of usable spectrum largely due to a combination of growing demand for spectrum and the classiccommand-and-control approach of spectrum management, which is often cited as an inexible spectrum managementmechanism leading to suboptimal results (Holland et al., 2008; Hoven, Tandra, & Sahai, 2005; Islam et al., 2008; McHenry,Tenhula, McCloskey, Roberson, & Hood, 2006; Renk, Blaschke, & Jondral, 2008).

More than a decade later however, and in spite of very promising theoretical results, the number of actual eld-trials andother experiments is still very limited. Although some trials have been launched in the US, the UK and Ireland (with CR beingtested in the TV-White Space UHF broadcasting bands), there has been little or no market introduction of CR enabled productsso far (Anker, 2010a, 2010b). This reluctance towards actual commercial implementations of CR is due to several uncertainties.

A rst uncertainty slowing down the roll-out of CR is associated with the doubts about the possible economic scenariosand use cases for CR. It can be argued that the majority of scientic, regulatory and industrial attention for CR specicallyin Europe and before the advent of and active lobbying for TV White Spaces by the IT sector has been focused onoperator-centered applications. This has created a somewhat biased view on the viability of CR, since these operators areusually primary users of licensed spectrum, which have exclusive right of use for a set amount of frequencies, and fear thecomplexity and potentially disruptive consequences of the introduction of CR in these frequencies notably secondaryuse of the spectrum by other, possibly competing rms and potential harmful interference to their own networks. As aconsequence, these operators have in many cases been very vocal in voicing their skepticism towards the feasibility, theviability and the added value of introducing CR. However, it is seldom addressed whether the conclusions drawn from suchanalysis are valid for other implementations of CR. This articles hypothesis is that many contexts in which CR technologiesmay be applied are so distinct from a business and regulatory point of view, that any conclusions concerning thecharacteristics and viability of one use case cannot be inferred from the analysis of another. It is therefore essential toestablish which parameters are critical for distinguishing fundamentally different economic scenarios. In Section 2, aclassication of these economic scenarios for cognitive radio, in which use cases can be developed, is proposed.

A second uncertainty in the implementation process of CR is the regulatory requirements related to the fulllment ofthese economic scenarios and use cases. Building further on the arguments outlined in Section 2, this article argues thatrequirements differ widely between the various economic scenarios discerned. Differences in regulatory approach mayconcern the object of regulation required, the level of governance at which it needs to be decided upon (and, as aconsequence, the specic dynamics related to the policy and regulation making process at that level), and the type ofregulation. In this last category, a distinction can be made between newly created, updated or continuous regulation, andbetween administrative, supporting, competition or research measures. The objective of determining between thesevarious categories is, again, to falsify the assumption that CR regulation is monolithic and inherently complex anddisruptive. To do this, an overview of the regulatory bottlenecks, possible measures and the responsible regulatoryinstances from a European context for different economic scenarios is given in Section 3.

The third uncertainty is related to the choice of a suitable technology for capturing spectrum occupancy informationabout the radio environment, as this kind of information enables a cognitive radio to dynamically adapt and optimize itsoperations (Wellens, Wu, & Mahonen, 2007). These enabling technologies are not the CR technologies responsible for thedecision-making concerning the adaptation of a radios operations and the choice of spectrum access or the learningcapacities, but they are the supporting technologies that obtain and provide crucial spectrum occupancy information usedas a basis for a radio to adapt its behavior and learn. As the decision-making and learning mainly exists of software andalgorithms that can be altered in the course of time (Mitola & Maguire, 1999), it appears that the choice of a CR enablingtechnology is more fundamentally decisive for the business- and regulatory implications than the CR technology itself, asnot only the CR technology has to be in line with the choice of CR enabler, but also an entire infrastructure Fig. 1.

Many technologies are likely candidates to act as the enabling technology of CR, but few of these can provide reliablespectrum occupancy information at a reasonable price tag. Furthermore, stakeholders such as device manufacturers,regional and national regulators and standardization bodies will tend to push forward specic CR enabling technologiesthat would suit their purposes and help achieve their objectives best. An overview of the most important CR enablingtechnology alternatives, considering their main characteristics and their stakeholder support, will be given in Section 4. Inorder to move forward towards commercial implementation, a specic enabler should become widely supported byindustry and regulators, after which it may be further improved to increase its reliability, and economies of scale inproduction may lower deployment cost to an acceptable level.

It is clear that the above uncertainties are highly interrelated. In order for technology, business cases and regulation tomatch, these three elements of CR should be aligned. In other words, technology should fulll industry needs, while beingcompliant to regulation; at the same time, regulation for CR will deliberately or de facto be conceived with specic

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559548Fig. 1. The role of CR enabling technologies within CR.economic scenarios in mind, while disabling others, and will enable the use of certain enabling technologies whileconstraining or even prohibiting others. This article will therefore provide an overview of these three elements and theinuence they have on each other. When the combination of a specic economic scenario, its regulatory requirements andthe chosen CR enabling technology matches without fundamental constraints, a strategic t exists between these domains,signicantly increasing the likelihood of successful adoption of CR in this context. Fig. 2 summarizes the alignmentmethodology throughout this article.

2. Economic scenarios for CR

Cognitive Radio functionalities enabling more dynamic forms of spectrum management and access not only allowfor improvement of current economic scenarios, but may also help create disruptive new scenarios with new actors

Fig. 2. The alignment process of business, regulations and technology levels of CR.

above literature, the categoriesoaches, in order to increase the

9a), EU-projects (IEEE, 2009b;

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559 549SENDORA, 2008) and private initiatives (ARAGORN, 2008) have also made earlier classications of scenarios for cognitiveradio. Such taxonomies are commonly based on three main variables:

1. Regulatory and license rule issue;2. Economical considerations and business models, including the services to be offered;3. Technological opportunities.

As this article argues that both regulations and technology should align with feasible economic scenarios, theclassication developed in this article is focusing on the business domain of CR and is thus constructed with businessparameters. This approach of choosing business parameters, rather than technical parameters that set apart CR scenarios,is rather unique when looking at the mentioned literature. More commonly used, but more technically focused parametersinclude, but are not limited to design parameters (Haykin, 2005), transmission parameters (Sokolowski, Petrova,de Baynast, & Mahonen, 2008), modulation parameters and interface parameters (Mitola, 2006). On the contrary, thetaxonomy presented here is based on three simple business parameters (Barrie, Delaere, & Ballon, 2010), namelyownership, exclusivity and tradability.

The main differentiator between spectrum sensing economic scenarios is ownership. This concept points toownership of a license, which is granted by a regulatory body and authorizes ofcially specied entities (licensees)the operation of (non-specied) devices within a dened geography. The geography is dened by bandwidth,geographic area and time (Industry Canada, 2011). Using this business parameter in the classication, two majorgroups of economic scenarios arise: unlicensed and licensed spectrum economic scenarios. The latter ones includeevery economic scenario in which a regulator has issued licenses for a certain band of spectrum, independent of theway the spectrum is used. Further specifying within the group of licensed spectrum economic scenarios, the exclusivitybusiness parameter addresses the question whether or not frequency bands (in a given geographic and for a speciedamount of time (Hinchman, 1969; Matheson & Morris, 2011) are exclusively assigned to a licensee. A regulator candecide to assign a specic frequency band (specied in geographical area and time) for every licensee and only allowingthat licensee to operate in the band, thus making the frequency band exclusive. If the regulator would decide to groupmultiple frequency bands in a spectrum pool and make it available for multiple licensees, there would be noexclusivity.

The tradability business parameter questions whether or not it is permitted for licenses to switch ownership forexample between different operators. If tradability is allowed, an operator can buy (e.g., for the remainder of the license) orlease (for periods varying from milliseconds to years) a licensees frequency band. However, if tradability is either notallowed, or impossible, the use of the frequency band is restricted to the licensee itself.transmutability of the taxonomy.A number of standardization efforts (ETSI, 2009; IEEE, 2009c; ITU, 2009; IEEE, 200in the proposed taxonomy below will be linked to one or more of the above sharing appr

use and Cooperative sharing. As the sharing approach is an important differentiator in thespectrum assignment on two sharing parameters: primary sharing versus secondary sharing and non-cooperative sharingversus cooperative sharing (or alternatively coordinated sharing versus uncoordinated sharing (Hooli et al., 2004),(e.g., third-party CR service providers), new roles and interactions. Though all easily classied as CR/SDR, such scenariosare highly heterogeneous, ranging from CR for Body Area Networks over optimization of small-scale in-houseentertainment systems to infrastructure sharing between large cellular network operators. To bring order into thisdiversity of possible deployments, this article proposes to classify them into a taxonomy of mutually exclusive, higherlever categories. Such a taxonomy is particularly relevant in the context of this paper, because belonging to a specicscenario has clear and distinct implications not only relating to the technology used but also with regard to the regulatoryrequirements for enabling the business case for CR deployment in question. As an example, CR used to facilitate spectrumsharing between multiple licensed mobile operators cannot and should not be regulated in the same way as CR used toavoid interference between multiple unlicensed short-range radio access technologies in hospitals. It is important tounderstand that fundamental differences exist in how CR is used in these distinct settings, which have wide technological,business and regulator consequences. The classication of distinct economic scenarios proposed here will therefore serveas a basis to identify the regulatory requirements for CR in Section 4.

Buddhikot (2007) has made efforts in constructing a taxonomy of spectrum access models. The models identied in thistaxonomy differ from each other based on the level of spectrum access increase in the scenario. A command-and-controlmodel will yield the lowest increase in spectrum access, followed by an exclusive use model, in which dynamicuse by secondary users is a possibility. Even more spectrum access increase is possible when spectrum is shared viaunderlay or overlay in a shared use of primary licensed spectrum model. The highest degree of spectrum accessincrease, however, is found in the commons model. The author states that, from a spectrum access increase perspective,it is a good evolution to be moving away from a command-and-control model. However, he states that targeting acomplete commons model may not be realistic and hybrid models may very well prove to be more pragmatic options forthe future.

Other taxonomies include the work of Weiss and Lehr (2009) which have based their categorization of dynamic

resulting in four spectrum assignment approaches: Unlicensed, Secondary Spectrum Markets, Easements & Opportunistic

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559550A possible fourth parameter, which is also proposed in Barrie et al. (2010), is technology neutrality in spectrum bands.Some frequency bands may be open to a variety of radio access technologies, while others only allow one specictechnology. It is obvious that the latter case limits the efcient use of spectrum, but in terms of regulatory requirements, atechnology neutral band would pose more issues because of the increased complexity. However, this technology neutralityparameter does not set apart the economic scenarios, but rather divides each possible economic scenario in a technology

Fig. 3. Identication of economic scenarios for CR, based on three parameters.neutral fraction and a non-technology neutral fraction. Furthermore, including this parameter would double the number ofeconomic scenarios and create overlaps in the regulatory requirements. Therefore, this parameter is discarded in furtheranalysis in this article.

Based on the other three parameters, four categories of scenarios, in which CR can be of use, can be distinguished Fig. 3.

2.1. Unlicensed spectrum

In the unlicensed scenario there is no ownership of a license involved. Sharing of spectrum would occur in adecentralized and horizontal way. Examples of economic scenarios are mostly found in the ISM bands. In this scenario, CRcan be of value by reducing interference between networks of various radio access technologies in high-density radioenvironments.

2.2. Spectrum pool

In a scenario where licenses are issued, but no exclusive frequency bands are assigned to every licensee, then thoselicensees will have to share spectrum from a spectrum pool, while using CR to nd available spectrum and avoidinterference. Sharing of spectrum would occur in a coordinated and horizontal way.

2.3. Spectrum market

This scenario represents settings in which licenses are issued, specic bands are exclusively assigned to every singlelicensee and tradability of the rights to access these exclusively assigned bands is allowed. The spectrum trades in thisspectrum market should be regarded as cooperative, coordinated and vertical spectrum sharing, involving permanent(in case a licensed spectrum block is reserved for a specied amount of time for secondary usage) or dynamic and exible(in case primary and secondary user utilize frequencies from the same licensed spectrum block, but not both at the sametime) license transfer in return for economic compensation (Caicedo & Weiss, 2011; Weiss & Lehr, 2009).

2.4. Flexible operator

In this economic scenario, a licensee cannot trade its exclusive right to operate within a specic band. CR could still beof use by taking place within this operators frequency band to dynamically coordinate radio signals of multiple radioaccess technologies.

The benet, but also the downside, of taxonomies such as the proposed one above is the simplicity of the model. Thissimplicity enables to regulate groups of cases, rather than case by case, but the risk exists of wrongly including some caseswithin an economic scenario group. In order to minimize these case-inclusion errors, while still providing the highest levelof simplicity, this research uses the basic principles of the clustering method used in, amongst others, statistics,

set the grounds for further research and study. With this typology in mind, this article will now evaluate regulatory

disputes, it may be necessary to introduce a unique identier for all cognitive radios that is sent alongside with the

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559 551message with all radio transmissions. This will require that regulators are actively involved in the standardization of CRtechnology (Anker, 2010a, 2010b) Table 1.

In conclusion, in this rst scenario the regulatory measures that need to be taken are primarily limited to updates ofcurrent technological requirements and spectrum etiquettes, followed by the enforcement of the rules by monitoring anddispute resolutions. CR implementation in this scenario thus does not pose any real regulatory obstacles.

Table 1Regulatory issues and measures for CR implementation in an unlicensed scenario.

Issue Measure Responsible instance Measure type

Tragedy of the commons

and spectrum congestion

European decisions and recommendations

(eg., CEPT rec. 70.03)

European instance Continuous: administrative

Update technical requirements Standardization body Update: technical

Update etiquette rules Standardization body Update: technical

Monitor etiquette rules National regulator Continuous: administrative

Update dispute resolutions National regulator/standardization body Update: administrative/technicalrequirements for the different CR economic scenarios, based on the EU regulatory contextalthough an analysisperformed for a different region is likely to yield similar results.

3.1. Unlicensed spectrum

Although the unlicensed spectrum is free to use by anyone, there is still a limited set of rules to adhere to. Especiallyspectrum etiquette rules try to avoid interference by limiting transmit power and eld strengths of the wireless devices(FCC, 1998; Hateld, 2003). Today, relatively few problems exist in the unlicensed bands. However with the rapid growthin wireless data demand, requiring ever increasing bandwidth, the likelihood of a tragedy of spectrum commons, in whichover-utilization of the common spectrum leads to congestion and, thus, a destruction of the value of the common good forsome or even all users, also increases. Such a situation could in fact be reinforced by CR, as devices will be able to detectand subsequently reserve available spectrum for their own (over-) use. To avoid this, strict technological restrictions thatlimit frequency hoarding can be set by CEPT decisions. In the meantime, standardization bodies (e.g., ETSI) can align withthe CEPT decision by standardizing the CR hardware accordingly. To enforce these rules, a regulator can closely monitor ifthe CR hardware that is brought on the market complies with the rules, to minimize interference. To ease the settlement ofdemographics and marketing segmentations. An important notice when clustering is the internal coherence and theexternal isolation between clusters (Milligan, 1980). Translated to CR regulations this means that the ideal level of detail ofthe CR taxonomy is achieved when all cases within a certain economic scenario can be covered by the same regulations,with these regulations being as distinct as possible from regulations of another economic scenario. As will become clear inSection 3, unlike most taxonomies, the proposed taxonomy in this article meets such requirements.

3. Regulatory bottlenecks and requirements for CR

As different economic scenarios for CR exist, different regulatory issues exist. This section will identify these roadblocksthat hamper CR implementation, while proposing the regulatory measures to overcome these roadblocks. Furthermore, foreach regulatory measure, the responsible regulatory instance will be provided.

As a means to broaden possible analysis of the regulatory requirements for CR, the different regulatory measures will becategorized based on two parameters: the stage in which the regulatory process takes place and the type of regulatorymeasure needed. First, three stages can be identied, distinguishing between measures that create a regulatory context,initiate a regulatory process or develop regulatory frameworks (Creation measures), measures that enhance alreadyexisting rules (Update measures) and measures that continuously enforce rules and exercise control and coordination overregulatory processes (Continuous measures). Second, different types of measures can be identied: these may be of atechnical nature, refer to administrative procedures, be intended to support the industry, to safeguard competition or to

3.2. Spectrum pool

Pooling is already a common practice in a number of bands (Anker, 2010a, 2010b), CR further enables it as thetechnology will also make more efcient arrangements possible, because it allows for dynamic arrangements in whichaccess to the pool is based on the actual demand for spectrum (Anker, 2010a, 2010b). As this would entail dynamicspectrum sharing, the same principle of tragedy of the commons, as described in the above (unlicensed) scenario, isequally possible in such a spectrum pool. In some cases, membership in such a spectrum pool can be controlled and thiscontrol will alleviate most of the issues associated with the tragedy of the commons. However, such membership control isnot a denite guarantee that there will no longer be occurrences of malicious use of the pools resources. To identify whatis normal behavior and what can be categorized under malicious behavior, etiquette rules can be formulated. If certainmembers of the spectrum pool consistently neglect these rules, the regulator can take action by removing the membershipof these members.

Consequentially, the same regulatory measures (displayed in gray in Table 2) can be proposed to counter this hoardingbehavior.

Apart from measures to guard from the tragedy of the commons, various other issues can be identied. First of all, forsome spectrum uses, pooling is not yet common (e.g., in standard 3 G bands, every mobile operator has its own exclusivepart of spectrum). To create a spectrum pool for these uses, there is the practical problem of nding the necessaryfrequencies to serve as such a spectrum pool. Finding a trans-frontier spectrum pool would be even more difcult becauseharmonization would be needed. It is up to the national regulators to search for appropriate spectrum to allocate to the

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559552spectrum pool.Because it is unlikely that regulators would nd empty frequency bands, they would need to cope with a second issue:

freeing up spectrum and resolving issues concerning existing licenses. Because these historically granted licenses havedifferent durations, expiration dates, technological requirements and required fees to be paid, it will be difcult to initiatea smooth transition from exclusive licensing to a common spectrum pool. Further research by national regulators, giventhe national context, is therefore needed to identify appropriate parts of spectrum, together with a suitable time window(e.g., when most licenses expire) in which such a transition would be possible.

Even if a regulator were able to cope with these organizational issues, it would still need to gather licensees to populatethe spectrum pool. It is not unthinkable, however, that many operators would resist this idea as they are unwilling to sharewith competitors what is for them a valuable resource; radio spectrum. Possible incentives for these operators could belower license fees and the mere fact that by using CR, they could benet extra available bandwidth in the spectrum pool.

Even if licensees are incentivized, the regulator should still be careful in which licensees are brought together in thespectrum pool. If these licensees provide the same kind of services, chances are high there will be coinciding peaks indemand for spectrum. As a result, the users from the pool would not experience any additional exibility gains during peakhours because of the simple reason that all users would be looking for extra spectrum at the same time. Outside peakhours there would be an abundance of unutilized spectrum, but there would be no demand for it. By diversifying thespectrum pool with licensees providing different sorts of services, regulators could tackle this problem.

A fth issue that the national regulator should tackle is the threat of unfair distribution of spectrum. By issuing a use-it-or-lose-it rule, the regulator can guarantee that blocked spectrum is actually used to deliver services to end-customers.

A last issue for the national regulator could be the choice out of a diversity of CR technologies (e.g., sensing, geolocationdatabase, beaconing) available. It is highly desirable to use a unied CR enabler throughout the same pool and therefore,choices have to be made, based on European recommendations.

Table 2Regulatory issues and measures for CR implementation in a spectrum pool scenario (parts in gray are similar to unlicesed scenario).

Issue Measure Responsible instance Measure type

Spectrum pool creation Search and allocate appropriate bands National regulator Continuous: research, Creation:

administrative

Historic licensing Appropriate timing of pool creation and

possible compensations

National regulator Creation: administrative

Unwilling users Incentivize (e.g., reduced license fee) National regulator Creation: administrative

Coinciding peaks Diversify pool National regulator Creation: administrative

Unfair distribution Monitor and regulate fair distribution

(e.g., use-it-or-lose-it)

National regulator Continuous: administrative/

competitive

Diversity of CR technologies Introduce unied CR technology National regulator Creation: administrative/

technical

Tragedy of the commons and

spectrum congestion

European decisions and recommendations European instance Continuous: administrative

Update technical requirements Standardization body Update: technical

Update etiquette rules Standardization body Update: technical

Monitor etiquette rules National regulator Continuous: administrative

Update dispute resolutions National regulator/

standardization body

Update: administrative/

technical

transfers (Bauer, 2002; ECC, 2002). While for permanent transfers, CR is not really necessary as interference with primaryl guarantees of non-interference in case the spectrum trades arey information needs to be acquired instantaneously by secondaryies, similar to CR operations in TV White Spaces.pean countries, there has been little activity so far. Nonetheless,ce spectrum in a more efcient manner. Therefore, regulators can

Research by Caicedo and Weiss (2011) has pointed out that in order for spectrum trading to blossom, a sufcient

spectrum through the introduction of property rights that give enough exibility in the use of spectrum and by removing

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559 553the barriers to instant trading (Anker, 2010a, 2010b). Many additional administrative measures are proposed and most ofthem are responsibilities of the national regulator. An important factor to consider here, however, is the fact that thesemeasures are only needed if the regulator itself would create, host and manage a spectrum market. According to the RSPGpaper on cognitive technologies (RSPG, 2010), a market managed by the regulator would be recommended, but otheroptions with operators and third parties running a spectrum market themselves, are possible as well. In this case many ofthe measures below will not be necessary, while extended monitoring of the activities of these spectrum market hostswould become even more important.

Althoug it is clear that many regulatory issues remain to be solved, the revision of the European regulatory frameworkof 2009 already removes the main obstacles for spectrum trading. In this framework spectrum trading and the principle ofamount of market participants (which they estimate at a minimum of ve to six active spectrum users) needs to bepresent. In order to reach this critical mass, the authors state that the barriers to market entry for new service providersneeds to be lowered and the marketplace needs to be liberalized.

One way of lowering the markets entry barriers is by removing the administrative obligations prior to a trade.Automatic approval of a trade will make trading more useful in case of urgent peaks in demand. Furthermore, shortertime-spans of spectrum trading should be considered, with dynamic real-time trades being the ultimate goal.

Another way of reducing the reluctance to trade is to provide information on spectrum ownership. This way, buyers andsellers can get into contact and entries of new market participants are facilitated. This practice has already been adoptedby the Federal Communications Commission (FCC), which releases US ownership information through its SpectrumDashboard.

Like in the other scenarios, spectrum hoarding is a problem in a spectrum market as well. Appropriate use-it-or-lose-itmeasures (Anker, 2010a, 2010b) are the recommended way to bring unutilized spectrum back to the market.

Preferably, regulators are also involved in the creation of a standardized marketplace (Quasar, 2010). The benet of acentralized marketplace is the control possibilities a regulator has. It is up to the regulator to what extent control over themarket is exercised and which of the following roles is taken up (Quasar, 2010):

Monitor spectrum usage (use-it-or-lose-it) Monitor trading Monitor contractual agreements Admissions or exclusions to the spectrum market Certifying trading agencies or spectrum brokers Overall guarantee of fair trading.

Similar to the spectrum pool scenario, the choice of a CR enabler has to be taken (based on European research andrecommendations (CEPT, 2008, 2011)) by the national regulator in order to guarantee that one unied CR technology willbe used in the spectrum market to base decisions on the same spectrum occupancy information.

Table 3 clearly shows that there are some regulatory roadblocks that need to be considered before CR can live up to itspotential to facilitate the existence of a spectrum market. The main task of the regulator is to facilitate this market forfurther incentivize trading in various ways.

spectrum trading is a valuable principle in using scarAlthough trading is already allowed in many Euro

users devices in order to move to unutilized frequenc

dynamic. In such a situation, local spectrum occupanc

users is not an issue here, CR does provide additionaIn conclusion, this CR implementation encounters signicantly more regulatory roadblocks for this scenario. Most ofthe issues are organizational in nature, ranging from the creation of the spectrum pool to the management of it. While insome cases, most of these identied issues exist (e.g., in cellular bands, where pooling is not yet a common practice), notall regulatory measures are needed for every pooling scenario. For example, in cases where pooling has already beenimplemented (Darpa, 2012), none of the creation measures will need to be carried out. Even though there is a likely chanceof CR implementation in the latter cases, it is still rather unlikely that CR will be used for enabling a dynamic spectrumpool for mobile network operators (e.g., providing 3 G) in the near future, given the amount of necessary measures andtheir nature.

3.3. Spectrum market

CR can be used to nd available spectrum from other licensees and use it without interfering primary operations.In return, primary users may be compensated. These are the basics of secondary use and dynamic spectrum trading in aspectrum market scenario. Spectrum trades can involve permanent license transfers or dynamic and exible license

Table 3Regulatory issues and measures for CR implementation in a spectrum market scenario.

admissions to market

Exclusive technology licensing Technology neutral licensing National regulator Creation: administrative/technical

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559554technology and service neutrality is introduced (EC, 2009). This principle allows for the denition of (tradeable) exible certifying broker

guarantee fair trading

Diversity of CR technologies Introduce unied CR technology National regulator Creation: administrative/technical

Table 4Regulatory issues and measures for CR implementation in a exible operator scenario.

Issue Measure Responsible instance Measure typeIssue Measure Responsible instance Measure type

Reluctance to trade Introduction of exible property rights National regulator Creation: administrative

Propose incentives for trading:

auto-approval

shorter time-spans

real-time

European Instance Continuous: research, creation: administrative

Provide ownership information National regulator Continuous: support

Implement European proposed incentives National regulator Creation: administrative

No current market Create standardized marketplace National regulator Creation: administrative

Unfair trading Monitor market:

spectrum usage

trades/agreements

National regulator Continuous: administrative/competitivespectrum usage rights, which is necessary to enable future trades.

3.4. Flexible operator

In a exible operator scenario, CR is not used for trading or sharing of spectrum, but more to optimize a licenseesoperations, by using its limited frequency band as efcient as possible, while switching to the most appropriate radioaccess technologies (RATs) at specic locations. To ensure the possibility of switching between RATs, national regulatorscould proactively issue technology-neutral licenses.

However, no real constraint for CR use in a exible operator scenario can be identied. As technology neutrality isintroduced in the revision of the regulatory framework, CR technology can likely be used to facilitate this scenario in thenear future, while of course respecting the current regulatory framework (EC, 2009; Hoven et al., 2005) Table 4.

4. Technologies for enabling cognitive radio

The cognitive radio concept refers to all radios that are context aware, have (local) spectrum occupancy informationand are able to (re)-act upon this. Of course the information on which these radios base their decisions, needs to beobtained in some way. Without this information, no intelligent decisions and resulting adaptive behavior by the CR radiosis possible. It is apparent that this information is a crucial precondition for CR. Three main technological concepts havebeen put forward to provide radios with this kind of information: spectrum sensing, geolocation databases and beaconing.Regulators throughout the world1 have started evaluating these three concepts in order to determine their relative valueas well as the regulatory conditions under which they could be introduced.

Recently, industry and regulators have indicated their preference towards particular systems for enabling CR. This doesnot necessarily mean that other technologies have no value, but it does mean that the chances of actual implementationare higher for the preferred technologies than for ones (currently) discarded by regulators. In this sense, adoption oftechnology and its standardization and harmonization process is to an extent a virtuous circle: the technology in which theinitial belief is the highest will have the most development opportunities, with the highest chances of success as a result.

1 For example, Ofcom in July 2009 (Gonc-alves & Pollin, 2011).

o astronomy, but it falls short on the rstchnology to exploit white spaces needs tocumbent broadcast service. As spectrum

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559 555sensing in its current stage of development fails to do so, alternative technologies may need to be considered.Finally, the EUs Radio Spectrum Policy Group came to similar conclusions, considering that sensing may not be reliable

enough to adequately protect incumbent users. This is particularly the case when a wider range of frequencies or a widerrange of applications needs to be taken into account. Therefore, the RSPG came to the conclusion that a case-by-caseapproach is needed, which takes account of the existing spectrum usage (RSPG, 2011).

4.2. Beaconing/CPC

An alternative to spectrum sensing could be beaconing, that is through the use of a cognitive pilot channel (CPC).Although these two technologies are not the same, this research treats them as one category of CR enabling technologies,since they both enable terminals to switch between radio access technologies and frequencies on the basis of spectruminformation obtained through a common beacon or pilot channel (Bourse et al., 2007). A beacon differs from a pilotchannel in that it is part of an incumbent protocol and only provides information on the spectrum occupancy by theprimary user. The CPC is an in-band or out-band channel that provides all necessary spectrum availability information andtechnical conditions to the CR terminal.

A major strength of this technology is undoubtedly the fact that terminals will not encounter the hidden node problem,as could be the case when using spectrum sensing methods. In this case, terminals focus on aggregated spectrumoccupancy data rather than on single quick scan of the local environment. Not only is the information provided toterminals richer, it is also constantly accessible using a permanent channel. However, the latter also poses some issues, as achannel needs to be found and reserved to transmit and receive information. Furthermore, it is recommended toharmonize this channel across regions, so terminals all around the world know where to tune in to get the rightinformation. On a technical level, the complexity of the system can be regarded as a roadblock for its implementation and afactor that substantially increases the cost of a cognitive pilot channel network deployment. Besides this, on a morepractical level, some questions still need answering with regard to ownership of CPC networks. This important gatekeeperrole could be taken up by the regulator, by one or a group of mobile network operators or even by a third-party. As aconsequence, not only the technical side of a CPC is complex, but also the organizational aspects surrounding it.twobeconditions and further research is needed on the last condition. A suitable teable to avoid interference to any other (primary) operation, especially the inThe report concludes that spectrum sensing could succeed in protecting radi Protect Aeronautical radio navigation in the 645790 MHz frequency band.Therefore, it is recommended to not only look at the characteristics of the enabling technologies, their strengths andweaknesses, but also to evaluate current trends, support from regulators, standardization bodies, academia and themarket. The strengths and weaknesses part of the analysis will address the technology-specic characteristics, while theopportunities and threats are linked to non-technical factors.

4.1. Spectrum sensing

In its Report on Cognitive Technologies (RSPG, 2010, p. 9), the Radio Spectrum Policy Group denes spectrum sensing asfollows: [Spectrum sensing] provides a real-time map of the radio environment. The main focus is on identifying unusedareas in the intended frequency range that can be used by [Cognitive Radios].

A strength of state-of-the-art spectrum sensing technology is its ability to scan the entire radio spectrum, resulting in awide set of spectrum occupancy information. Furthermore, current spectrum sensing technology is able to sense very fastand requires low power amounts making it possible to implement the feature into terminals. As more and more terminals,wireless and mobile devices, are expected to be interlinked in the future, the multitude in data these could provide isanother potential benet of the technology. A third advantage of spectrum sensing is its potential to provide very location-specic spectrum occupancy information as the data is captured from the terminal itself. However, the latter characteristicalso constrains the reliability of spectrum sensing technology, due to various physical effects such as the so-called hiddennode problem, fading, and shadowing and noise uncertainty. For this reason, the FCC removed spectrum sensing as anobligatory technology in its unanimous decision on TV White Space regulations in September 2010 (FCC, 2011). Thereliability issue was, however, not the only reason for this decision, as the cost of implementing sensing on a large scale forthe purpose of enabling CR was also considered too high.

The FCCs judgement is more or less in line with the ndings of the European regulators, according to ECC report 159(ECC, 2011). In this report, CEPT thoroughly addressed the way forward for secondary use of TV White Spaces in Europe,assessing both geolocation databases and spectrum sensing, based on some preset goals. In particular, CEPT concluded thatthe technologies under consideration should:

Protect Broadcast service Protect Program Making and Special Events (PMSE) Protect Radio Astronomy in the 608614 MHz frequency band

. This is partly due to recent stepse spectrum in the context of ones and wireless microphone users)stimation that costs will be lower

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559556than that of competing solutions, as current infrastructure is used to update and access the database information. Somesources even claim that geolocation database services could be provided to users for free, using a Google-type model ofgetting revenues out of advertisements (Daily Wireless, 2011). It comes as no surprise that Google was one of the databaseadministrators appointed by the FCC in January 2011.

Not only does there seem to be enough engagement from private companies to make this CR enabling technology work,also the technical requirements of the database seem fullled. The ECC report 159 (ECC, 2011) clearly favors thegeolocation database over spectrum sensing, when matching the CR enabling technologies with the technical protectionrequirements, being the protection of priority services within the same frequency bands (for white spaces beingbroadcasting, PMSE, radio astronomy and aeronautical radio navigation). In the US, the FCC has equally favored thegeolocation database in its decision on White Spaces of September 23, 2010, obliging White Space Devices to use thegeolocation database to protect primary users in the television bands.

Even though regulators and the private sector seem relatively enthusiastic about the geolocation database, some issuescan also be identied, particularly for what concerns its implementation. In FCCs white space regulations, the chosenadministrators can decide on the details of the development of the database. Although such exibility is generally positive,it leaves open many questions: Who will pay for the database? Who can access the database? How will the database get itsinput and how frequently will these updates occur? How can it be guaranteed that the database is permanently available ifit is owned by a third-party? Is it necessary for the regulator to monitor and intervene in the operations of a third-partydatabase service provider? Furthermore, how realistic is the threat of monopolization of the geolocation database andwhat are the consequences? Clearly, further research on these organizational topics is needed.

On a more technical level some issues also still remain. One of these concerns the reliability of the system; an Ofcomconsultation document, for example, has recently warned that the database could result in errors of up to 100 m. Forlocations with high-density radio communications, such as stadiums, airports, hospitals and events, such accuracy of ageolocation database may not be sufcient. As a result, Ofcom has now set up a working group to specify the requirementsto be met by geolocation database providers and providers that wish to be accredited by the UK regulator (Ofcom, 2011).Another technical issue could concern the interoperability of the databases in terms of the sharing of data and thestandardization of information models and interfaces if several of these databases are commercially launched. Regulatorsare currently working towards addressing these issues (RSPG, 2011). In doing so, they will need to:

indicate how the database should be certied or accredited; provide information on actual spectrum usage; provide information to database managers on algorithms to calculate white spaces.

The development of the database technology itself can be left to the research community and industry, however it isrecommended that any solution be standardized at least on a regional (in this case European) level, for example, by ETSI.This process could be supported by the regulators by giving ETSI relevant information on the data elements needed todescribe actual spectrum usage, expected behavior of the equipment and the radio characteristics of the radio devices(RSPG, 2011).

4.4. Which CR enabling technology?

The adoption of a CR enabling technology is dependent on the technical capabilities, as well as the cost for thestakeholders (primary user, secondary user and third parties such as brokers) (Weiss & Altamaimi, 2011). If one considersadoption from a technical perspective only, one can argue that each economic scenario has different needs, and thusrequires different technical capabilities of the CR enabling technologies. In this case is clear that an unlicensed economicspe(Necic frequency band (UHF) and associated set of primary users (mostly TV broadcasterul, 2011; Microsoft White Space Research, 2011; Spectrum Bridge, 2011) and to the etowards commercial use of the database concept for allowing access to TV White Spac

Beyond doubt, the geolocation database is the most debated alternative in recent monthsAlthough the CPC has been and in modied form is still being evaluated by standardization bodies such as ETSI RRSand IEEE SCC41 1900.4 (Delaere, 2010), major issues remain in relation to the technology. Neither FCC (2011), nor CEPT(Holland et al., 2008) have acknowledged a CPC as an option to enable CR in the near future. Therefore, the CPC/beaconingwas not considered in ECC report 159 (ECC, 2011) on the technical and operational requirements of CR enablers in WhiteSpaces. The RSPG notes that beacons can be sent as part of the normal transmissions from a digital device. It is up to thestandardization bodies to implement this technology (RSPG, 2011).

4.3. Geolocation database

A third potential technology to serve as a CR enabler is the geolocation database. There is a wide variety of forms ofsuch a geolocation database, but they all have the common idea of collecting, storing and distributing spectrum availabilityand occupancy information with the related technical parameters and conditions for secondary use of that spectrum.

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559 557scenario for CR has different requirements than a spectrum market scenario, in which primary and secondary use isallowed. The unlicensed scenario, for example, a factory scenario in which machine-to-machine communications are used,will require highly localized information since coordination is needed between a large amount of terminals in a verylimited space. On the other hand, in a TV-White Spaces scenario, reliability is the most important requirement, especiallyfor the primary user who wishes to avoid interference at all cost. One can therefore distinguish between two groups ofscenarios with distinct technological needs: on the one hand the open/unlicensed spectrum scenarios (which will likely bebetter served by spectrum sensing based enablers) and, on the other hand, more licensed spectrum oriented (e.g., Telco-centered) scenarios (spectrum market/spectrum pooling/exible operator where a highly reliable geolocation databasewill be better suited.

For the licensed scenarios, the geolocation database indeed seems to be the preferred CR enabler, at least for the nearfuture. As mentioned, its rst implementation is expected to serve for opportunistic use of TV White Spaces. Not onlyregulators (ECC report 159 (ECC, 2011) and FCC White Space regulations, Ofcom consultation November 2010), but alsoindustry seem enthusiastic about the database concept, as shown by the recent market introductions and the level ofinterest for starting the databases in the US. Little support is found for the CPC approach while spectrum sensing can fornow at least not achieve an adequate level of reliability at a sufciently low cost. On the other hand, the geolocationdatabase still needs to prove its value in the coming years; moreover, should the database concept extend its reach intoother frequency bands and services, allowing for more disruptive forms of Dynamic Spectrum Access, it will have toresolve technical and organizational challenges similar to that encountered by spectrum sensing and Cognitive PilotChannels. Furthermore, the three approaches have characteristics that suit different specic applications and economicscenarios of cognitive radio, which certainly are not limited to TV White Spaces.

Although technical capabilities in specic situations and spatial-temporal environments are a major factor in theadoption of a CR enabling technology, Weiss and Altamaimi (2011) rightfully point out that the costs of CR enablingtechnologies should be taken into the equation as well. From their interesting ndings, they conclude that differentstakeholders within the same spatial-temporal environment each have different preferred CR enabling technologies basedon the costs. This can be explained by the fact that primary users, as well as secondary users, try to limit their contributionto the investment in a CR enabling technology. As a result, primary users will try to avoid cooperative solutions, in whichthey would have to contribute to the spectrum information gathering and communication with the secondary users. Viceversa, secondary users would prefer these cooperative solutions to additional spending on sensing engines or databases.

The above shows that the adoption of a CR enabling technology is dependent on at least four factors: technicalcapabilities, spatial-temporal environment/scenario, type of stakeholders involved and the system cost. So although thegeolocation database seems preferable for TV White Spaces, it is still too early to consider the geolocation database as theone and only valuable CR enabler in all situations.

5. Conclusions

With the objective of contributing to Cognitive Radio implementation, this paper has broken down the feasibility ofcommercial CR introduction into a set of constituent requirements. Only tting combinations of technology, economicscenarios and regulation have a chance of commercial introduction and may prove to be sustainable in the long term.

Four majors groups of economic scenarios have been identied in this article, each requiring distinct regulatorymeasures in order to overcome obstacles associated with the implementation of the scenarios. Although the introductionof CR does not seem problematic for the unlicensed scenario and the exible operator scenario, more complex measuresare required to enable CR to contribute to the implementation of spectrum pooland spectrum market scenarios.

The dynamic spectrum pool scenario poses signicant administrative problems. First of all, the historic licensing makesthe creation of a dynamic spectrum pool difcult as appropriate spectrum needs to be found. Second, regulators wouldneed to nd a balanced mix of motivated licensees that could participate in this spectrum pool. Third, harmonization of thespectrum pool would be an even bigger task. Even though a spectrum pool could very well be a solution to cope withgrowing demand for spectrum, these regulatory roadblocks make it very hard for such a spectrum pool to be realized inthe near future.

The amount of regulatory issues that need to be resolved for introduction of cognitive radio in a spectrum marketscenario is also considerable. Although regulators worldwide have acknowledged that spectrum trading may allow for amore efcient use of spectrum, many issues still need to be resolved. Apart from the organization and monitoring of amarket, spectrum trading has to be incentivized by facilitating measures such as automatic approval of trades, theprovision of spectrum ownership information and the implementation of a real-time spectrum market. Although these areconsiderable hurdles, regulatory advances may well resolve many of the above issues, making CR widely available for avariety of applications.

As for the question, which is the most adequate technological enabler to support the envisaged business cases, analysisof the various CR enabling technologies has shown that out of the three proposed alternatives, the geolocation database isthe most likely candidate to be used for CR purposes. However, although this database is a clear favorite for applicationswithin the TV White Spaces, spectrum sensing should not be discarded as a potential CR enabler for other situations, suchas highly sensitive applications in high-density radio environments. Also, stakeholders involved and system costs shouldbe taken into the equation when selecting the appropriate CR enabling technology.

Hoven, N.,Tandra, R., & Sahai, A. (2005). Some fundamental limits on cognitive radio. Proceedings of the Forty-second Allerton Conference onCommunication, Control, and Computing held in Monticello, IL, USA, 2830 September 2005 (pp. 131136). Retrieved from /http://www.eecs.

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559558berkeley.edu/tandra/pub1.htmS.IEEE (2009a). Draft Standard for Wireless Regional Area Networks Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer

(PHY) Specications: Policies and Procedures for Operation in the TV Bands (IEEE P802.22/D2.0). Retrieved from /https://mentor.ieee.org/802.11/dcn/09/11-09-0934-00-tvws-draft-par-and-5c.docS.

IEEE (2009b). Wireless Coexistence: White Space Coexistence use Cases. Retrieved from /https://mentor.ieee.org/802.19/dcn/09/19-09-0031-02-tvws-tvws-coexistence-use-cases-user-experience.docS.By further focusing on economically viable use cases, and prioritizing regulatory reforms along the lines of such usecases, while choosing the most appropriate CR enabling technology for them, it can be hoped that Cognitive Radio willnally evolve towards sustainably viable deployment, and in doing so realize the promise of enabling unprecedented newlevels of system diversity and spectrum efciency that will benet many sectors and segments of peoples lives.

Acknowledgment

The ndings presented in this article are based on research performed in the IWT ESSENCES-project. Contributions fromcolleagues and project partners are acknowledged.

References

Anker, P. (2010a). Cognitive radio, the market and the regulator. Proceedings of the IEEE Symposia on New Frontiers in Dynamic Spectrum AccessNetworks (DYSPAN) held in Singapore, 69 April 2010.

Anker, P. (2010b). Does cognitive radio need policy innovation? Competition and Regulation in Network Industries, 11, 226.ARAGORN, (2008). Adaptive recongurable access and generic interfaces for optimisation in radio networksARAGORN (Document number 5.1 (a)). EU

project 216856. Retrieved from /http://www.ict-aragorn.eu/leadmin/user_upload/deliverables/Aragorn_D5_1.pdfS.Barrie, M., Delaere, S., & Ballon, P. (2010). Classication of business scenarios for spectrum sensing. Proceedings of the IEEE 21st International Symposium

on Personal Indoor and Mobile Communications conference (PIMRC10) held in Istanbul, Turkey, 2630 September 2010 (pp. 26262631). Retrievedfrom /http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5671782S.

Bauer, J.M. (2002). A comparative analysis of spectrum management regimes. Quello. Working Papers. Retrieved from /http://www.ictregulationtoolkit.org/en/Publication.2298.htmlS.

Bourse, D., Agusti, R., Ballon, P., Cordier, P., Delaere, S., Deschamps, B., et al.. (2007). The E2R II Flexible Spectrum Management (FSM) Framework andCognitive Pilot Channel (CPC) ConceptTechnical and Business Analysis and Recommendations. E2R II White Paper. Retrieved from /https://ict-e3.eu/project/white_papers/e2r/7.E2RII_FSM_CPC_UBM_White_Paper_Final[1].pdfS.

Buddhikot, M. (2007). Understanding dynamic spectrum access: models, taxonomy and challenges. Proceedings of the IEEE DySPAN 2007 held in Dublin.Retrieved from /http://www.bell-labs.com/user/mbuddhikot/psdocs/ModelsTaxonomy-MilindDyspan07.pdfS.

Caicedo, C. E., & Weiss, M. (2011). The viability of spectrum trading markets. IEEE Communications Magazine, 49(3), 4651 Retrieved from /http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F35%2F5723785%2F05723799.pdf%3Farnumber%3D5723799&authDecision=-203S.

CEPT. (2008). Technical Considerations Regarding Harmonisation Options for the Digital Dividend (CEPT Report 24). Retrieved from /http://www.erodocdb.dk/docs/doc98/ofcial/pdf/CEPTRep024.pdfS.

CEPT. (2011). SE43 Cognitive Radio Systems White Spaces (470790 MHz). Retrieved from /http://cept.org/ecc/groups/ecc/wg-se/se-43S.Daily Wireless (2011). White Space Test in UK. Retrieved from /http://www.dailywireless.org/2011/06/27/white-space-test-in-uk/S, last visited 19

August, 2011.Darpa X. G. (2012). Next Generation Communications Program. Retrieved from /http://www.sharedspectrum.com/resources/darpa-next-generation-

communications-program/S.Delaere, S. (2010). Service discovery: CPC or database?. Proceedings of the 11th Annual International Symposium on Advanced Radio Technologies

ISART2010 held in Boulder, Colorado, 2730 July 2010.EC, M. (2009). Directive 2009/140/EC of the European Parliament and of the Council of 25 November 2009 amending directives 2002/21/EC on a common

regulatory framework for electronic communications networks and services, 2002/19/EC on access to, and interconnection of, electroniccommunications networks and associated facilities, and 2002/20/EC on the authorisation of electronic communications networks and services.Ofcial Journal, 337, 00370069.

ECC. (2002). Refarming and Secondary Trading in a Changing Radiocommunications World (ECC Report 16). Messonlonghi, September 2002.ECC. (2011). Technical and Operational Requirements for the Possible Operation of Cognitive Radio Systems in the White Spaces of the Frequency Band

470-790 MHz (ECC Report 159). Retrieved from /http://www.erodocdb.dk/docs/doc98/ofcial/Pdf/ECCRep159.pdfS, last visited August 2011.ETSI (2009). Recongurable radio systems (RRS) (ETSI TR 102 802 v.0.1.2). Cognitive Radio System Concept (Draft). Retrieved from /http://www.etsi.org/

website/technologies/RRS.aspxS.European Commission. (2011). Radio Spectrum, a Vital Resource in a Wireless World. Retrieved from /http://ec.europa.eu/information_society/policy/

ecomm/radio_spectrum/index_en.htmS, last visited 21 July 2011.FCC, M. (1998). Part 18 Industrial Scientic and Medical Equipment. Federal Communications Commission Retrieved from /http://www.tscm.com/

FCC47CFRpart18.pdfS.FCC, M. (2011). Unlicensed Pperation in the TV Broadcast Bands, Additional Spectrum for Unlicensed Devices Below 900 MHz and in the 3 GHz Band (DA 11-131).

Federal Communications Commission Retrieved from /http://www.fcc.gov/document/unlicensed-operation-tv-broadcast-bands-additional-spectrum-unlicensed-devices-below-900-mhS.

Gonc-alves, V., & Pollin, S. (2011). The value of sensing for TV white spaces. Proceedings of the IEEE Symposia on New Frontiers in Dynamic SpectrumAccess Networks (DYSPAN) held in Aachen, 36 May 2011 (pp. 231241). Retrieved from /http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5936212S.

Hateld, D. N. (2003). Spectrummanagement reform and the notion of the spectrum commons. South African Journal on Information and Communication, 4, 112.Haykin, S. (2005). Cognitive radio: brain-empowered wireless communications. IEEE Journal on Selected Areas in Communications, 23(2), 201220

Retrieved from /http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1391031S.Hinchman, W. R. (1969). Use and management of electrospace: a new concept of radio resource. Proceedings of the IEEE International Conference on

Communications held in Boulder, 911 June 1969.Holland, O., Cordier, P., Muck, M., Mazet, L., Klock, C., & Renk, T. (2008). Spectrum Power Measurements in 2 G and 3 G Cellular Phone Bands During the

2006 Football World Cup in Germany. E2RII, Karlsruhe. Retrieved from //http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4221543SS.Hooli, K., Petschinger, S., Sun, W., Thilakawardana, S., Tierno, A., & Tolli, A. (2004). Winner Spectrum Aspects: Methods for Efcient Sharing, Flexible

Spectrum use and Coexistence. IST-2003-507581 WINNER D6.1. Retrieved from /http://www.ist-winner.org/DeliverableDocuments/D6.1v1.1.pdfS.

IEEE (2009c). IEEE standard for architectural building blocks enabling networkdevice distributed decision making for optimized radio resource usage inheterogeneous wireless access networks (IEEE Std 1900.4). IEEE Standard Coordination Committee 41 on Dynamic Spectrum Access Networks.Retrieved from /http://standards.ieee.org/ndstds/standard/1900.4a-2011.htmlS.

Industry Canada (2011). Study of Market-Based Exclusive Spectrum Rights. Retrieved from /http://www.ic.gc.caS.Islam, M. H., Koh, C. L., Oh, S. W., Xianming, Q., Lai, Y. Y., Cavin, W.,et al. (2008). Spectrum survey in Singapore: Occupancy measurements and analyses.

Proceedings of the 3rd International Conference on Cognitive Radio Oriented Wireless Networks and Communications held in Singpore, 1517 May2008 (pp. 17). Retrieved from /http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4562457S.

ITU (2009). Annex 21 to Working Party 5A Chairmans Report; Working Document Towards a Preliminary Draft New Report ITUR [LMS.CRS]; CognitiveRadio Systems in the Land Mobile Service. ITU Radiocommunication Study Groups. Retrieved from /http://www.itu.int/md/R07-WP5A-C-0305/enS.

Matheson, R., & Morris, A. C. (2011). The Technical Basis for Spectrum Rights: Policies to Enhance Market Efciency. Retrieved from /http://www.brookings.edu//media/Files/rc/papers/2011/0303_spectrum_rights_matheson_morris/ 0303_spectrum_rights_matheson_morris.pdfS, March 3,2011.

McHenry, M. A., Tenhula, P. A., McCloskey, D., Roberson, D. A., & Hood C. S. (2006). Chicago spectrum occupancy measurements & analysis and along-term studies proposal. Paper Presented at the 1st International Workshop on Technology and Policy for Accessing Spectrum. Retrieved from/http://www.wtapas.org/nal-papers/ChicagoSpectrum-McHenry-Session-I-1.pdfSS.

Microsoft White Space Research (2011). Microsoft Research Whiteservice. Retrieved from /http://whitespaces.msresearch.us/S, last visited 19 August,2011.

Milligan, G. W. (1980). An examination of the effect of six types of error pertubation on fteen clustering algorithms. Psychometrika, 45.Mitola, J. (2006). Cognitive Radio Architecture: The Engineering Foundations of Radio XML. USA: Wiley-Interscience.Mitola, J., & Maguire, G. Q. (1999). Cognitive radio: making software radios more personal. IEEE Personal Communications Magazine, 6, 1318.Neul (2011). Technology. Retrieved from /http://www.neul.com/technology.phpS.Ofcom. (2011). Implementing Geolocation: Summary of Consultation Responses and Next Steps. Retrieved from /http://stakeholders.ofcom.org.uk/

binaries/consultations/geolocation/statement/statement.pdfS.Quasar. (2010). Regulatory Feasibility Assessment (Deliverable D 1.2). Retrieved from /http://www.quasarspectrum.eu/downloads/public-deleverables.

htmlS.Renk, T., Blaschke, V., & Jondral, F. K. (2008). Time-dependent statistical analysis of measurements for the evaluation of vacant spectrum bands.

Proceedings of the International Union of Radio Science General Assembly held in Chicago, Illinois, 717 August 2008.RSPG (2010). On cognitive technologies. Radio Spectrum Policy Group, European Commission, January 25, 2010. Retrieved from /http://www.apwpt.org/

M. Barrie et al. / Telecommunications Policy 36 (2012) 546559 559downloads/rspg10-306_cognitive_techn_jan2010.pdfS.RSPG (2011). RSPG Opinion on Cognitive Technologies (RSPG10-348). Retrieved from /http://rspg.groups.eu.int/_documents/documents/meeting/

rspg24/rspg_10_348_ct_opinion_nal.pdfS, last visited on August 18, 2011.SENDORA (2008). Scenario descriptions and system requirements. EU Project 216076, Deliverable Reference Number D 2.1. Retrieved from /http://www.

sendora.eu/system/les/SENDORA(216076)_D2-1-v5-0.pdfS, last visited on August 18, 2011.Sokolowski, C., Petrova, M., de Baynast, A., & Mahonen, P.(2008). Cognitive radio testbed: exploiting limited feedback in tomorrows wireless

communication networks. Proceedings of the ICC Workshops 08. IEEE International Conference on Communications held in Beijing, 1923 May2008 (pp. 493498). Retrieved from /http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4531947S.

Spectrum Bridge (2011). Spectrum Bridge, Enabling Universal Spectrum Access. Retrieved from /http://www.spectrumbridge.comS, last visited 19August, 2011.

Weiss, M., & Altamaimi, M. (2011). The cost of knowing: an economic evaluation of context acquisition in DSA systems. Paper presented at the 40thResearch Conference on Communication, Information and Internet Policy held in Arlington, VA, USA. Retrieved from /http://d-scholarship.pitt.edu/6074/S.

Weiss, M., & Lehr, W. (2009). Market Based Approaches for Dynamic Spectrum Assignment. Retrieved from /http://d-scholarship.pitt.edu/2824S.Wellens, M., Wu, J., & Mahonen, P. (2007). Evaluation of spectrum occupancy in indoor and outdoor scenario in the context of cognitive radio. Paper

presented at the International Conference on Cognitive Radio Oriented Wireless Networks and Communications held in Orlando, FL, USA. Retrievedfrom /http://www.inets.rwth-aachen.de/leadmin/templates/images/PublicationPdfs/2007/SpectOcc.pdfS.

Aligning technology, business and regulatory scenarios for cognitive radioIntroductionEconomic scenarios for CRUnlicensed spectrumSpectrum poolSpectrum marketFlexible operator

Regulatory bottlenecks and requirements for CRUnlicensed spectrumSpectrum poolSpectrum marketFlexible operator

Technologies for enabling cognitive radioSpectrum sensingBeaconing/CPCGeolocation databaseWhich CR enabling technology?

ConclusionsAcknowledgmentReferences