Spectrum management is the process of regulating the use of radio frequencies to promote efficient use and gain a net social benefit [1]. An efficient spectrum management has to address three main interrelated problems. First, the correct amount of spectrum needs to be allocated to certain uses or classes of uses. Second, it needs to assign usage rights to certain users or groups of users. Third, it needs to adjust established policies as technology and markets evolve over time.
The radio spectrum is considered in most countries as an exclusive property of the state (i.e. the radio spectrum is a national resource, much like water, land, gas and minerals). As such, there are different radio spectrum items that need to be nationally regulated (e.g. frequency allocation for various radio services, assignment of licence and radio frequencies to transmitting stations, type approval of equipment, fee collection, etc.). To this end, national regulatory authorities (NRAs) are commonly established within sovereign countries as the competent legal regulatory bodies for spectrum management and regulation. However, due to the very nature of radio spectrum (radio waves do not respect administrative borders), international agreements for regulating the use of radio frequencies are necessary to, among others, coordinate wireless communications with neighbours and other administrations. These international agreements typically combine both multilateral and bilateral dimensions. Therefore, effective spectrum management requires regulation at the national, regional and global levels.
The principles of regulating access to radio spectrum have remained essentially the same during the history of radio [2]. Spectrum blocks are first allocated, through international agreement, to services broadly defined (e.g. mobile service, broadcasting service, satellite service, radio astronomy service, etc.). This process is called allocation. Then, the next step is to assign frequencies and grant authorizations by NRAs to specific users or classes of users. In the end, authorizing the use of the spectrum is a national prerogative, subject to international obligations and, in some countries such as European Union (EU) member states, also subject to EU community law.
The remaining of this section provides an overview of the current key regulatory and legal instruments that govern the use of spectrum across the global, regional and national levels. The discussion on regional and national levels is primarily focused on the European context. The section is concluded with a discussion on the models and evolution of spectrum management practices in the quest for achieving a more efficient and flexible use of spectrum resources.
The international global regulatory framework is provided by the International Telecommunication Union (ITU), a specialized United Nations (UN) agency. Within the ITU, the ITU Radiocommunication Sector (ITU-R) plays the central role in the global management of the radio-frequency spectrum. ITU-R seeks to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services. The main priorities of the ITU’s regulation of radio spectrum are:
To do so, the most important ITU legal instrument is the Radio Regulations (RR) treaty [3], which is ratified by the ITU member states. The ITU RR is the global agreement on how the airwaves are defined, allocated and used without harmful interference between the various wireless services around the world. ITU RR are binding for the states, not for individuals or operators. The compliance with ITU RR therefore presupposes that each state will take the measures required (legislation, regulations, clauses in licences and authorizations) to implement domestically those obligations to other spectrum users (operators, administrations, individuals, etc.). As such, the ITU RR provide an international framework for effective spectrum management that is primarily structured by the need for global harmonization in various domains (satellite communication, maritime, civil aviation, scientific research, etc.), coexistence capability between different types of radio communication networks and physical properties of frequency bands. It has major implications for the industry in terms of economies of scale and therefore for the design of radio products.
The regulatory and policy functions of ITU-R are carried out through World and Regional Radiocommunication Conferences and Radiocommunication Assemblies. World Radiocommunication Conferences (WRCs) are regularly held every 4–5 years, and the decisions adopted are incorporated in the ITU RR. Ahead of the celebration of each WRC, there are many ITU-R study groups and working parties [4], with representatives providing support, research and background for ITU RR. Contributors to this work include representatives from state’s regulatory authorities as well as from regional spectrum management organizations that represent the common interests of a group of states. The last WRC was held in January–February 2012 (WRC-2012), and the next one is planned for November 2015 (WRC-2015).
The ITU RR (Article 5 of the RR) contains the so-called Table of Frequency Allocations (TFA) that allocates frequency bands for the purpose of their use by one or more terrestrial or space radiocommunication services or the radio astronomy service under specified conditions. A radiocommunication service is defined as the transmission, emission and/or reception of radio waves for specific telecommunication purposes. Terrestrial services and space services can themselves be subdivided in several different types of services (fixed, mobile, broadcasting, etc.). Each frequency band can be allocated with one or more radio services (typically two to four). Frequency bands are allocated to radiocommunication services on a primary or secondary basis. Stations of a secondary service shall not cause harmful interference to stations of primary services and cannot claim protection against harmful interference from stations of a primary service. In order to recognize certain regional differences that may be necessary in the frequency allocations, the ITU has split the world in three geographical regions (1, 2 and 3), so that the TFA is particularized for each region.
In addition to the frequency allocations to radio services, the ITU RR also contain administrative provisions on the registration (and protection) of specific frequency assignments as well as on the use of radio frequencies. The principle underpinning most of the provisions of ITU RR stipulates that any new assignment (i.e. any new authorization to operate a radio station) must be made in such a way as to avoid causing harmful interference to services rendered by stations using frequencies assigned in accordance with the agreed TFA and the other provisions of the ITU RR, the characteristics of which are recorded in the Master International Frequency Register (MIFR). In particular, a new assignment can only be recorded in the MIFR after completion of a procedure aimed at ensuring that it will not cause harmful interference to assignments made in accordance with the RR and previously recorded systems.
Regional spectrum management organizations also play a major role in the management of the radio spectrum resource. There are six main regional organizations in the world:
These organizations seek the harmonization and coordination of spectrum use in their regions. These organizations also represent within global forums, such as ITU-R WRCs, the interests of their member countries and their NRAs along with telecommunications providers and the regional industry. In particular, regional spectrum organizations have a WRC preparatory function: administrations in each region submit draft proposals to the regional spectrum organizations, the regional organization adopts common proposals before the WRC in accordance with their own procedures, and the regional proposals are submitted to the WRC on behalf of all of their members.
At the European level, the Electronic Communications Committee (ECC) within the CEPT brings together 48 countries to develop common policies and regulations in electronic communications and related applications for almost the entire geographical area of Europe. The prime objective of the ECC is to develop harmonized European regulations for the use of radio frequencies. Permanent negotiation on conditions of use of spectrum is critical over Europe as it enables adapting spectrum use conditions to industry requirements and national situations. The CEPT ECC takes an active role at the international level, preparing common European proposals to represent European interests in the ITU and other international organizations. In order to achieve these objectives, the CEPT ECC endorsed the principle of adopting a harmonized European Table of Frequency Allocations and Applications (known as European Common Allocation (ECA) and published within the European Communications Office Frequency Information System (ECO EFIS)) to establish a strategic framework for the utilization of the radio spectrum in Europe [5]. The CEPT ECC delivers ECC decisions (measures that NRAs are strongly urged to follow), ECC recommendations (measures that NRAs are encouraged to apply) and ECC reports (result of studies conducted by the ECC) [6]. The implementation of ECC decisions and ECC recommendations by CEPT member NRAs is made on a voluntary basis since CEPT deliverables are not obligatory legislative documents. However, they are normally implemented by many CEPT administrations [6].
Legal certainty on the availability of the identified spectrum for a given usage and under specified conditions is actually accomplished among the European countries that form part of the EU. The European Commission (EC), the executive body of the EU, is responsible to undertake the EU radio spectrum policy aimed to coordinate spectrum management approaches across the EU. This radio spectrum policy was launched by means of the Radio Spectrum Decision (676/2002/EC) [7] in year 2002. Two complementary bodies were set up following the Radio Spectrum Decision to facilitate consultation and to develop and support radio spectrum policy across the EU member states:
Therefore, harmonized conditions can be established on a European-wide basis either through an EC decision2 (which is mandatory for EU member states to implement) or by implementing the aforementioned CEPT ECC decisions or recommendations.3 Deviations from EC harmonization measures are possible but necessitates that the EU member states request derogation to be granted by the EC, expectedly for a limited duration. In addition, as a result of a recent update of the regulatory framework for electronic communications services (ECS), the EC is now allowed to submit legislative proposals to the European Parliament and Council for establishing multi-annual Radio Spectrum Policy Programmes (RSPP) [8]. The first RSPP, approved in 2012, created a comprehensive roadmap contributing to the internal market for wireless technologies and services, particularly in line with the Europe 2020 initiative and the Digital Agenda for Europe. The RSPP sets general principles and calls for concrete actions to meet the objectives of EU policies. Among the specific actions set out by the RSPP is making available sufficient harmonized spectrum for the development of the internal market for wireless safety services and civil protection. In the wider field of telecommunications regulation, the EU has also established a harmonized regulatory framework for rights of use in the context of electronic communications networks and services (ECN&S) [9]. The ECN&S regulation also establishes some provisions in relation with the management of radio frequencies for ECS. Among them, regulation mandates that member states shall ensure that spectrum allocation used for ECS and issuing general authorizations or individual rights of use of such radio frequencies by competent national authorities are based on objective, transparent, non-discriminatory and proportionate criteria.
Complementing the work of CEPT ECC and EC, the European Telecommunications Standards Institute (ETSI), an industry-led organization, also plays an important role in the European regulatory environment for radio equipment and spectrum. ETSI is officially recognized by the EU as a European Standards Organization. ETSI produces globally applicable standards for information and communications technologies (ICT), including fixed, mobile, radio, converged, broadcast and Internet technologies. In the context of spectrum regulation, among other things, ETSI has the faculty to develop the so-called system reference documents (SRDoc) that provide technical, legal and economic background on new radio systems under standardization. SRDoc are used to inform the ECC so that harmonization measures or other kind of actions might be started to support the new radio system or application.
At the national level, radio spectrum is managed by a designated competent government department or agency, which is commonly referred to as the NRA on spectrum matters. Examples of NRA are the Federal Communications Commission (FCC) in the United States, Ofcom in the United Kingdom and the Secretary of State for Telecommunications and Information Society in Spain.
Within the framework of action left by the observance of the regional and global agreements, NRAs must consider many factors, such as each country’s socio-economic benefit. Therefore, NRAs will typically consult with all interested parties and seek to release as much spectrum as possible to allow the country to benefit from global economies of scale, interoperability, interference minimization (including with neighbour countries), international roaming and alignment with regional and global agreements. Many trade-offs are likely to be faced by NRA decisions when assigning spectrum. An example would be the conjugation of the direct economic benefits arisen from the assignment of frequencies to commercial mobile communications compared with the less direct economic purposes that nevertheless benefit society in many indirect ways, such as the designation of spectrum for PPDR communications.
Figure 6.1 illustrates the general structure of the national legislation that is commonly in place in most countries to regulate the use of radio spectrum [10]. As depicted in the figure, the elaboration of a National Table of Frequency Allocations (NTFA) constitutes the first step and the basis of radio-frequency spectrum management, being the main instrument of the national legislation to govern the access to frequency bands. An NTFA primarily specifies the radio services authorized by an individual administration along the frequency bands (referred to as ‘allocations’) and the entities that might have access to these allocations (e.g. government use, private use). An NFTA can also include specific frequency assignments to individual users (e.g. reserved bands for the Ministry of Defence) or installations at particular locations (e.g. protection of specific facilities from potential radio interference). Moreover, an NTFA typically shows the internationally agreed spectrum allocations of the ITU RR.
In a second step, specific national frequency assignments allow the fine management of frequency bands in accordance with the rules set in NTFAs, particularly in bands shared by different type of users as well as to ensure the proper coexistence of the spectrum users in adjacent bands (e.g. channel bandwidths, guard bands, transmission power settings).
Finally, users have to be authorized to be able to transmit on specific frequencies (i.e. users are granted rights of use of the radio spectrum, which is property of the state). This is in accordance with Article 18 of the ITU RR that stipulates: ‘no transmitting station may be established or operated by a private person or by any enterprise without a license issued in an appropriate form and in conformity with the provisions of these Regulations by or on behalf of the government of the country to which the station in question is subject’. The term ‘licence’ is understood here in its broad acceptance, basically establishing that the use of spectrum must be explicitly permitted.
The way that authorization is performed differs between the two possible domains of use: ‘governmental’ and ‘non-governmental’.
‘Governmental’ use, or assimilated, covers various sectors (defence, civil aviation, maritime and waterways, public safety, meteorology, science, etc.). In this case, the rights of use are commonly limited to the rights described in the NTFA, and no additional legal acts are conducted to explicitly grant rights of use [11]. Access to spectrum resources by governmental users should be subject to regular review by the NRA.
In the case of ‘non-governmental’ uses of the spectrum, a public legal act issued by the NRA is necessary for the purpose of delivering spectrum usage rights to private entities or citizens. Under the EU regulatory framework, this legal act is referred to as ‘authorization’ (EU Authorization Directive [12]). On this basis, a legal differentiation is established between ‘individual authorization’ and ‘general authorization’ to reflect the obligation or not for the user to be granted individual rights of use before transmitting. For instance, radio applications that do not need individual frequency planning and coordination could be exempted from individual authorization and should be subject to a general authorization.
The different mechanisms in use nowadays to grant (individual or general) authorizations for the use of spectrum can be classified under three main approaches, referred to as ‘licencing regimes’. These three main approaches are individual licencing (also denoted as ‘traditional licencing’), light licencing and licence exempt (also referred to as ‘unlicenced’). This classification, shown in Table 6.1, is established in CEPT ECC Report 132 [13] as a result of a review of the various terminologies used across the CEPT countries. The distinction between the three licencing regimes uses as a first-level differentiation factor the legal basis given under the EU regulatory framework for ECN&S (i.e. individual or general authorization). In this regard, while there is a clear association between ‘individual licence’ and ‘individual authorization’ as well as between ‘licence exempt’ and ‘general authorization’, a ‘light-licencing’ regime can be based on either an individual or a general authorization. In either of these two options, a light-licencing regime is characterized by the existence of an obligation for the spectrum user to register or notify its use to the NRA. This obligation is of administrative nature and necessitates, as a prerequisite for use, that the user contacts the NRA. Such provision remain in the field of ‘general authorization’ as long as they are only meant to allow controlling the deployment and use of the application so as to avoid harmful interferences on radio services, but not to restrict it. Conversely, this provision falls under the ‘individual authorization’ umbrella if associated with possible limitation of the number of users and specific requirements for coordination prior to use.
Table 6.1 Licensing regimes for the authorization of spectrum rights of use.
Individual licence(sometimes also referred to as ‘traditional licencing’) | Light licencing | Licence exempt(also referred to as ‘unlicenced’) | |
Based on individual authorization (individual rights of use are granted) | Based on individual authorization (individual rights of use are granted) | Based on general authorization (no individual rights of use are granted) | Based on general authorization (no individual rights of use are granted) |
Facilitates individual frequency planning and coordination | With limitations in the number of users | Obligation for registration and/or notification | No obligation for registration nor notification |
Traditional procedure for issuing licences | Facilitates individual frequency planning and coordination | No limitations in the number of users nor need for coordination | Intended for radio applications that do not require individual frequency planning or coordination |
Simplified procedure compared to traditional procedure for issuing licences | Intended for radio applications that do not require individual frequency planning or coordination |
It is worth noting that the licences that are issued as a result of a ‘light-licencing’ regime based on ‘individual authorizations’ are not different from ‘individual licences’ from a regulatory perspective. In both cases, the licences should contain technical conditions that are necessary and sufficient to avoid harmful interference to other systems and users. However, the process of issuing licences could vary significantly between the light-licencing and traditional licencing schemes. While in traditional licencing relatively complex administrative processes such as beauty contests or auctions could take place, licences under light-licencing regimes may basically involve the use of dedicated IT systems for automatic frequency planning and licence assignment. Also of note is that, as captured in Table 6.1, a licence-exempt regime is a general authorization regulatory regime where radio equipment operates under a well-defined set of regulator-imposed rules (e.g. constraints on maximum transmit power, spectral mask, duty cycle, etc.) and where no provision for registration and/or notification is required to the users of these devices.
Spectrum management should be designed and carried out with the main goal of ensuring the efficient use of spectrum. Efficient use implies that, given the state of technology, spectrum is channelled to its most productive uses. Importantly, efficient use has to be properly conjugated with the achievement of other non-market objectives such as national security, safety and equal access goals. As spectrum uses change over time, an efficient spectrum management regime also needs to minimize the transaction costs associated with these adjustments.
Historically, access to and use of radio spectrum has been highly regulated in order to prevent interference among users of adjacent frequencies or from neighbouring geographic areas, particularly for reasons of defence and security [2]. Fuelled by technological advances and the consolidation of liberalized regimes in the telecommunications market, there have been in the last years significant innovations in the theory of spectrum management along with gradual changes in practice of spectrum management and regulation. This gradual change follows a growing consensus that past and current regulatory practices originally intended to promote the public interest have in fact delayed, in some cases, the introduction and growth of a variety of beneficial technologies and services or increased the cost of the same through an artificial scarcity. In addition to these delays, the demand for spectrum has grown significantly, highlighting the need for efficient use of all available spectrum in order to avoid scarcity. Those factors are making policymakers and regulators worldwide focus on new spectrum regulation principles with an increasing emphasis on striking the best possible balance between the certainty required to ensure stable roll-out of services and flexibility (or light-handed regulation) leading to improvements in cost, services and the use of innovative technologies. In particular, a pioneering role in the introduction of many innovative spectrum management approaches should be credited to national authorities for radio-frequency management such as the FCC in the United States and Ofcom in the United Kingdom.
In practical terms, three main spectrum management models can be distinguished nowadays:
Governments have generally been cautious in determining which approach to use. The result, across the world, is a combination of spectrum management regimes that mainly incorporate legacy command and control regimes for government services, auctions and bidding for many commercial licences and licence-exempt uses for low-power devices. The three spectrum management models have unique advantages and disadvantages, and no single approach is superior on all counts. The optimal spectrum policy should determine the right mix of these methods rather than adopting one model [16].
The harmonization of spectrum for PPDR communications at the international level is recognized to offer many benefits. These include economic benefits (economies of scale in the manufacturing of equipment and more competitive market for equipment procurement), the facilitation in the development of compatible networks and services and the promotion of international interoperability of equipment for those agencies that require cross-border cooperation with other PPDR agencies and organizations (e.g. increased effective response to disaster relief).
Considering the above-mentioned benefits along with the growing telecommunication needs of PPDR agencies already anticipated in the late 1990s, the WRC-2000 resolved to invite ITU-R to study the identification of frequency bands that could be used on a global/regional basis by administrations intending to implement future advanced solutions for PPDR (ITU-R Resolution 645 [17]). In that context, the Agenda Item 1.3 (AI 1.3) was included in WRC-2003 to decide on which bands and to make regulatory provisions as necessary. Preparatory studies were carried out within ITU-R working groups that led to the delivery of Report ITU-R M-2033 [18], which constitutes a key reference in the context of PPDR communications. Report ITU-R M.2033 identified objectives, applications, general requirements, spectrum requirements and solutions to satisfy the operational needs of PPDR organizations. The report was notably based on the general assumption of a technology-neutral approach.
As a result of this previous work, ITU Resolution 646 was approved within AI 1.3 in WRC-2003. This resolution strongly recommends administrations to use regionally harmonized bands for PPDR to the maximum possible extent. The identified frequency bands/ranges, or parts thereof, to be considered by national administrations when undertaking their national planning are reproduced in Table 6.2. In the context of this resolution, the term ‘frequency range’ means a range of frequencies over which a radio equipment is envisaged to be capable of operating but limited to specific frequency band(s) according to national conditions and requirements (i.e. not all frequencies within an identified common frequency range are expected to be available within each country). Therefore, a solution based on regional frequency ranges enables administrations to benefit from harmonization while continuing to meet national planning requirements, which is important because the amount of spectrum needed for PPDR communications may differ significantly across countries. In any case, it’s worth noting that ITU Resolution 646 is just a recommendation, and as such, it does not preclude the use of the identified bands/frequencies by any other application within the services to which these bands/frequencies are allocated.
Table 6.2 Harmonized frequency bands/ranges established in ITU Resolution 646 (WRC-2003).
ITU-R region | Frequency bands/ranges |
Region 1 | 380–470 MHz as the frequency range within which the band 380–385/390–395 MHz is a preferred core harmonized band for permanent public protection activities within certain agreed countries of Region 1 |
Region 2 | 746–806 MHz, 806–869 MHz and 4940–4990 MHz (Venezuela has identified the band 380–400 MHz for public protection and disaster relief applications) |
Region 3 | 406.1–430 MHz, 440–470 MHz, 806–824/851–869 MHz, 4940–4990 MHz and 5850–5925 MHz (some countries in Region 3 have also identified the bands 380–400 and 746–806 MHz for PPDR applications) |
It is worth noting that the focus in WRC-2003 AI 1.3 was to identify harmonized bands for mission-critical (narrowband) voice and low-rate data services for PPDR agencies, though it recognized the trend towards the evolution of wideband and broadband data applications (broadband applications such as video were thought to be relevant only for hot spot coverage). From 2003 till date, the ITU has been continuously working on preparing reports and recommendations on PPDR communications. Indeed, AI 1.3 has been kept linked to the PPDR spectrum issue across the subsequent conferences WRC-2007 and WRC-2012, with new documents released but with no changes introduced to date to the frequency ranges initially identified in ITU Resolution 646. The main relevant resolutions and recommendations produced on this matter since WRC-2003 are captured in Table 6.3.
Table 6.3 Key reference documents from ITU-R since WRC-2003 with regard to PPDR spectrum harmonization.
Document | Brief description |
Report ITU-R M.2033, ‘Radiocommunication objectives and requirements for public protection and disaster relief’ (2003) | Radiocommunication objectives and requirements for public protection and disaster relief. This report was developed in preparation for WRC-03 Agenda Item 1.3. The document defines radiocommunication objectives and requirements for the implementation of future advanced PPDR solutions. The document also establishes reference terminology to precisely define and categorize public safety communications |
ITU-R Resolution 646, ‘Public protection and disaster relief’ (approved at WRC-2003 and revised in WRC-2012) | This resolution encourages administrations to consider a set of frequency bands/ranges when undertaking their national planning for the purposes of achieving regionally harmonized frequency bands/ranges for advanced PPDR solutions |
There is a review by WRC.12, though no changes in frequency ranges were introduced | |
ITU-R Resolution 647, ‘Spectrum management guidelines for emergency and disaster relief radiocommunication’ (approved at WRC-2007 and revised in WRC-2012) | This resolution encourages administrations to consider global and/or regional frequency bands/ranges for emergency and disaster relief when undertaking their national planning and to communicate this information to the Radiocommunication Bureau of the ITU. A database system has been established and is maintained by the Radiocommunication Bureau |
ITU-R Resolution 648, ‘Studies to support broadband public protection and disaster relief’ (WRC-2012) | This resolution invites ITU-R and administrations to study technical and operational issues relating to broadband PPDR and its further development and to develop recommendations, as required, on technical requirements for PPDR services and applications, the evolution of broadband PPDR through advances in technology and the needs of developing countries |
The resolution also resolves to invite WRC-15 to consider these studies on broadband PPDR and take appropriate action with regard to revision of Resolution 646 (Rev.WRC-12) | |
Recommendation ITU-R M.2015, ‘Frequency arrangements for public protection and disaster relief radiocommunication systems in UHF bands in accordance with Resolution 646 (Rev.WRC-12)’ (2012) | This recommendation provides guidance on frequency arrangements for public protection and disaster relief radiocommunications in certain regions in some of the bands below 1 GHz identified in Resolution 646 (Rev.WRC-12). Currently, the recommendation addresses arrangements in the ranges 380–470 MHz in certain countries in Region 1, 746–806 and 806–869 MHz in Region 2 and 806–824/851–869 MHz in some countries in Region 3 in accordance with resolutions ITU-R 53 and ITU-R 55 and WRC Resolutions 644 (Rev.WRC-07), 646 (Rev.WRC-12) and 647 (WRC-07) |
Recommendation ITU-R M.1637, ‘Global cross-border circulation of radiocommunication equipment in emergency and disaster relief situations’ (2003) | This recommendation addresses issues to be considered in order to facilitate the global circulation of radiocommunications equipment to be used in emergency and disaster relief situations |
ITU-R Recommendation M.1826 ‘Harmonized frequency channel plan for broadband public protection and disaster relief operations at 4940–4990 MHz in Regions 2 and 3’ (2007) | This recommendation addresses harmonized frequency channel plans in the band 4940–4990 MHz for broadband public protection and disaster relief radiocommunications in Regions 2 and 3. The recommendation provides two frequency channelling plans for national administrations to consider when allocating spectrum for use by users who are directly involved with PPDR |
ITU-R Recommendation M.2009, ‘Radio interface standards for use by public protection and disaster relief operations in some parts of the UHF band in accordance with Resolution 646 (WRC-03)’ (2012) | This recommendation identifies radio interface standards applicable for PPDR operations in some parts of the UHF band. The broadband standards included in this recommendation are capable of supporting users at broadband data rates, taking into account the ITU-R definitions of ‘wireless access’ and ‘broadband wireless access’ found in Recommendation ITU-R F.1399. This recommendation addresses the standards themselves and does not deal with the frequency arrangements for PPDR systems, for which a separate recommendation exists: Recommendation ITU-R M.2015 |
However, a key milestone is expected to be accomplished in WRC-2015 with regard to the identification of additional spectrum for mobile broadband PPDR use. In particular, WRC-2012 agreed to review and revise Resolution 646 for broadband PPDR under AI 1.3 in WRC-2015 so as to account for the new PPDR scenarios offered by the evolution of broadband technologies. To that end, Resolution 648 was approved in WRC-2012, inviting ITU-R to study technical and operational issues related to broadband PPDR and its further development and to develop recommendations, as required, on technical requirements for PPDR services and applications, the evolution of broadband PPDR through advances in technology and the needs of developing countries. Therefore, WRC-2015 AI 1.3 is anticipated to be instrumental in establishing new harmonized frequency bands for PPDR mobile broadband applications and the interoperability and economies of scale that will result. This is particularly relevant for Europe, which is consolidating a common position supporting the identification of new harmonized frequency band(s) (in addition to the 380–470-MHz band) for mobile broadband PPDR in Region 1, most likely within the range 694–862 MHz, while recognizing that it will be a national decision which band(s) is(are) selected for mobile broadband PPDR in each country.
The preparatory work for WRC-2015 AI 1.3 at CEPT level [19] states that, in order to establish a family of cross-border functioning broadband PPDR networks, it is not required to designate identical bands for this purpose, but rather choose the suitable bands out of the (eventual) harmonized frequency range(s) and adopt a common technology. Hence, according to CEPT’s preparatory work, it may be more relevant to refer to ‘harmonized conditions’ rather than ‘harmonized frequencies’. For broadband PPDR communications, harmonized conditions can be established if (i) a tuning range can be identified and (ii) a technical standard such as LTE can be harmonized. On this basis, there is a proposal to replace the term ‘frequency range’ used in Resolution 646 (WRC-2012) with the term ‘tuning range’, defined as a range of frequencies in which radio equipment is envisaged to be capable of operating, which may be limited to specific parts of the relevant frequency band(s) according to national circumstances and requirements. In addition, when the broadband PPDR networks use a common technical standard (such as LTE), it is argued that the tuning range could also be specified as one or several band classes. Using these definitions of harmonized conditions and tuning ranges, it will be possible to offer full flexibility for administrations to decide on their dedicated PPDR spectrum to meet national needs and demands chosen within the tuning range. The technology will then provide full roaming and will be open for interoperability even if the PPDR spectrum is not strictly harmonized.
The need for spectrum suitable for the support of emerging broadband PPDR applications has been recognized for many years. This section first describes the different uses of spectrum needed across the different components of a PPDR communications delivery solution. Then, the methodologies commonly used for the computation of spectrum needs are explained. Finally, a number of estimates carried out by different organizations worldwide that quantify spectrum needs for mobile broadband PPDR applications are presented.
As outlined in Chapter 3 and further developed in Chapter 5, a multilayered communications approach is envisioned for future PPDR communications systems where complementary frequency bands and technologies can be used to deploy wide area (e.g. nationwide) coverage, with sufficient capacity to cater for routine, day-to-day communication requirements, together with the ability to extend coverage and capacity on an ad hoc basis to cope with challenging radio environments (e.g. tunnels, basements) or localized high-capacity demands. On this basis, spectrum needs related to different system components can be distinguished:
In general terms, the methodologies used to determine the amount of spectrum required are based on (i) the characterization of the traffic demand in a given area or per incident, (ii) the estimation of the number of cell sites covering the area of interest and of any other radio equipment brought into (e.g. ad hoc network) and (iii) the characterization of the underlying wireless technologies mainly in terms of achievable spectrum efficiencies. This generic approach is applicable to the different spectrum components identified in the previous subsection, though specific assumptions and considerations have to be introduced for each of them. In the case of the estimation of spectrum needs for terrestrial WAN, the following aspects are considered:
With all of the above elements, a coarse-grained estimation amount of spectrum can be straightforwardly derived. For example, in the case of data services, a common approach is just to compute the amount of spectrum (in Hz) needed in a single site/cell by dividing the estimated demand (in bit/s) by the achievable spectral efficiency (either average efficiency or efficiency at the cell edge). Once the spectrum needed in a single cell is estimated, the total amount of spectrum can be obtained from multiplying the single cell estimate by the applicable frequency reuse factor. A more fine-grained estimation, if necessary, can be pursued by considering more specifics on the network deployment and traffic distribution as well as other factors such as the possibility to use multicast/broadcast delivery for some applications or the introduction of weighting factors to capture the correlation between environments in coincident busy hours. These fine-grained computations may require the use of computational tools such as the ones used in the commercial domain for radio network planning and optimization. In any case, it is worth highlighting that the outcomes of any spectrum computation are usually very sensitive to the considered inputs and assumptions, so that spectrum estimations can differ considerably if no reference models are established.
A generic methodology for PPDR spectrum calculation based on the aforementioned principles is reported in ITU-R Report M.2033 [18]. The model describes how to address the characterization of four fundamental variables that determine the amount of spectrum required (i.e. demand for a given area, number of sites/cells covering the area, spectral efficiency of the technology providing the service and amount the technology is able to reuse frequencies). The model provides a spectrum calculation for each type of PPDR service, considering both voice calls and data services. The basic equation employed in the model is as follows:
This fundamental equation is applied for the various service categories in both the uplink and downlink paths. In calculating the total demand per cell, the ITU-R model factors in the total seconds of usage per user, the average users per cell and the bit rate for the application in question. Protocol overheads (e.g. channel coding) and service-grade parameters are considered in the computation of the traffic per cell (e.g. introduction of multiplicative factors to account for blocking probabilities). On the other hand, the net system capacity is directly a computation of the system spectral efficiency where factors such as frequency reuse, guard bands and the use of some resources for signalling channels are considered.
Despite some differences in the computation of the model’s inputs and in the applicability of the previously mentioned formula per incident and per cell or accounting for the overall system efficiency, the ITU-R spectrum model calculator has been considered as the baseline approach in several other studies that provide estimations for broadband PPDR spectrum (e.g. CEPT ECC Report 199 [20], US NPSTC [21], Canada DRDC CSS [22]). As an example to illustrate the applicability of this type of methodology, the computation of spectrum needs for day-to-day operations scenarios is briefly explained in the following as addressed in ECC Report 199. The proposed methodology used for such scenarios consists of the following five steps:
With regard to the computation of the traffic demand, this methodology follows an incident-based approach where traffic is summed over several separate incidents and background traffic is then added. The outputs of each step are summarized in Table 6.4.
Table 6.4 Example of the computation of spectrum needs for day-to-day operations scenarios as addressed in ECC Report 199.
Methodology | Description |
Steps 1 and 2 |
Characterization of the traffic demand in the following type of incidentsa and for background traffic:
|
Step 3 |
LTE technology has been chosen as the reference technology. Based on parameters from 3GPP performance specifications for LTE Release 10 and on the selection of the reference modulation for the communication link (i.e. modulation and coding scheme that would be available at cell edge), the following cell ranges are estimated for different frequency bands to achieve an uplink spectrum efficiency of 0.31 bit/s/Hz under different areas (Urban, Rural, Open):
|
Step 4 |
The number of incident per cell is computed taking into account the population within a cell and the number of PPDR incidents per population. The population in a cell is given by the size of the cell multiplied by the density of population. The number of incidents in the cell is then given by the size of population multiplied by the rate of incidents per population. Multipliers applied to allow for uneven distribution by time of day and geographic location. Based on statistics for the number of incidents occurring simultaneously across Germany at busiest times estimated from publicly available data, the following estimations are considered:
|
It is considered that number of incidents does not vary across urban, suburban and open cells due to differences in population density that counterbalances the differences in cell sizes | |
Step 5 |
The estimate of the total spectrum takes care of the location of incidents within the cell. In particular, it is assumed that one incident is located at cell edge, and the rest of traffic is evenly distributed on the cell coverage. Focusing on the uplink case, spectrum efficiency is considered to be 0.31 bit/s/Hz at cell edge, and two values are considered for the average spectrum efficiency across the whole cell: 0.64 (pessimistic) and 1.49 (optimistic). Based on these considerations together with the total traffic requirements from Steps 1 and 2, uplink spectrum requirements result in the following ranges:
|
a Additional details on the estimates of the throughput requirements for the mobile broadband data applications in use in these scenarios are provided in Chapter 2.
In addition to the earlier incident-based methodology, CEPT Report 199 also provides spectrum estimations based on a slightly different methodology that does not treat traffic separately from several incidents. This alternative methodology is based on the use of the Law Enforcement Working Party (LEWP)/ETSI Matrix described in Chapter 2. In particular, individual incidents and background traffic are combined together into the peak load in the busy hour in normal conditions and in emergency conditions. This is considered through a detailed characterization of the data requirements per application addressed within the LEWP/ETSI Matrix. Then, for each application, it is decided whether the application is ‘incident-centric’ or a background application spread out across the cell. This distinction is made to be able to consider either average or incident-specific spectrum efficiencies to be accounted for each application. In some way, this approach can be thought as a bottom-up approach where the estimated traffic from each individual user application and the number of users of that application are considered in creating the load. This is in contrast to the approach followed in the incident-based methodology to account for the background traffic load, which is completely separate from the incidents’ traffic load and estimated mainly based on the characteristics of the likely applications used in routine activities.
Methodologies such as the ones described previously can also be applied to some extent to the computation of the other spectrum components identified in Section 6.3.1. As a particular case, the basic methodology proposed in Ref. [18] has also been used to estimate the minimum bandwidth requirement for broadband disaster relief (BBDR) applications in localized areas using spectrum in the 5-GHz band [26]. However, the specifics of the localized area as well as the diversity of uses for that spectrum may prevent the ability to firmly determine specific spectrum needs. For example, in the case of spectrum for localized and ad hoc deployments, the applications can range from point-to-point, line-of-sight, broadband links with very high spectral efficiency to local area networking achieving much lower spectral efficiencies (e.g. Institute of Electrical and Electronics Engineers (IEEE) 802.11 type deployments with non-light-of-sight connectivity). The net spectral efficiency will then depend on the individual mix of applications. In addition, frequency reuse may also be highly variable. For example, if a region uses a given spectrum band for airborne operations on multiple assets, nearly the entire band can be exhausted by this application because of the difficulty in reusing frequencies.
Numerous studies have substantiated the spectrum needs for mobile broadband PPDR applications in different countries and regions across the world [20–26]. The main outcomes from a number of studies are summarized in Table 6.5.
Table 6.5 Studies addressing the assessment of spectrum needs for PPDR communications.
Study | Spectrum requirements |
CEPT ECC Report 199, ‘User Requirements and Spectrum Needs for Future European Broadband PPDR Systems (Wide Area Networks)’, May 2013 | The amount of spectrum for future European broadband PPDR wide area networks (WAN) is estimated in the range of 2 × 10 MHz |
The report also concludes that there could be additional spectrum requirements on a national basis to cater for DMO, AGA, ad hoc networks and voice communications over the WAN | |
ETSI SRDoc TR 102 628, ‘Additional Spectrum Requirements for Future Public Safety and Security (PSS) Wireless Communication Systems in the UHF Frequency Range’ |
The ETSI report establishes the following requirements:
|
The report proposes the spectrum to be allocated below 1 GHz, narrowband/wideband within the tuning range of existing allocations and a separate band for broadband | |
A revision of the document is underway in ETSI to include more detailed calculations to justify the requirements and to update the document to reflect the changes in the external environment since publication of the initial version of the SRDoc in 2010 | |
WIK Consulting and Aegis Systems, ‘PPDR Spectrum Harmonization in Germany, Europe and Globally’, December 2010 | Minimum spectrum requirements below 1 GHz for Germany are estimated to be 15 MHz (uplink) and 10 MHz (downlink) |
The spectrum already identified for public safety use in the 5150–5250-MHz band, augmented if possible with spectrum from the largely unused 1452–1479.5-MHz band (currently intended for T-DAB use), should be adequate to address capacity ‘hot spots’ arising from major events or incidents in Germany | |
A minimum of 15 MHz (unpaired) somewhere between 1 and 5 GHz is estimated to be required on a harmonized European basis to support AGA video links, with a further Germany-specific 7.5 MHz potentially required. Coordination with the military could be considered | |
Wireless backhaul requirements for the WAN can be met from existing microwave fixed link bands, possibly augmented by satellite in remote areas | |
NPSTC, ‘Public Safety Communications Report: “Public Safety Communications Assessment 2012–2022, Technology, Operations, and Spectrum Roadmap” ’, Final Report, June 5, 2012 | Estimates are provided for four disaster scenarios (a hurricane, a chemical plant explosion, a major wild land fire and a toxic gas leak)a |
The lowest demand is estimated at 6 MHz (downlink) and 7.5 MHz (uplink), representing a total of 15 MHz in case of paired allocations | |
The highest demand is estimated at 8.9 MHz (downlink) and 13.8 MHz (uplink), representing a total of 26.7 MHz in case of paired allocations | |
The report states that 20-MHz allocation (of 10 MHz (uplink) and 10 MHz (downlink)) for the highest demanding incident would be nearly 4 MHz insufficient on the uplink | |
Defence R&D Canada – Centre for Security Science (DRDC CSS), ‘700 MHz Spectrum Requirements for Canadian Public Safety Interoperable Mobile Broadband Data Communications’, February 2011 |
The key conclusions that are derived from this study are:
|
a Additional details on these scenarios are provided in Chapter 2.
There are many other similar studies addressed to compute the spectrum requirements. A study released in June 2013 considered eight Asian countries, namely, Australia, China, Indonesia, Malaysia, New Zealand, Singapore, South Korea and Thailand. The study supports that a minimum of 10 MHz for broadband PPDR is required on the basis of the opportunity cost argument [27]. In a separate study, China estimated between 30 and 40 MHz of spectrum required for broadband. The United Arab Emirates’ telecommunications regulatory authority (TRA) also conducted a PPDR spectrum study that concluded that PPDR use could in theory be supported in as little as 2 × 5 MHz of spectrum and that an allowance of 2 × 10 MHz would enable reasonable future growth [28].
Summing up, despite the differences across some of these estimates, reserving a minimum of 2 × 10 MHz for mobile broadband PPDR is becoming the prevailing option, though not excluding additional country allocations to meet specific needs.
While national administrations do consider the harmonized frequency bands/ranges, or parts thereof, established in ITU Resolution 646 (WRC-2003) for the assignment of spectrum for PPDR communications within their jurisdictions, not all PPDR spectrum assignments fit within the ITU harmonized ranges. Indeed, due to the specific country needs and particular organization of the PPDR sector, the total amount of spectrum assigned to PPDR and the adopted frequency ranges differs significantly between countries. A description of the current PPDR spectrum availability is provided in the following, focusing on existing assignments as well as on the candidate bands under consideration in some regions for the delivery of mobile broadband PPDR communications.
At the European level, the band 380–385/390–395 MHz is in widespread use for permanent narrowband6 PPDR systems (mostly TETRA and TETRAPOL national and regional networks). Indeed, this 5 + 5-MHz block is the only harmonized band at the European level for narrowband systems, as established in ECC Decision (08)05 [29] and reflected in ITU Resolution 646 as the preferred core harmonized band within the tuning range of 380–470 MHz. Certain channels within this band have also been identified at the European level for DMO and AGA purposes to protect the land mobile infrastructure and to ease cross-border operation (provisions established in decisions ERC/DEC/(01)19 and ECC/DEC/(06)05).
ECC Decision (08)05 also establishes that sufficient amount of spectrum shall be made available for wideband7 digital PPDR radio applications within the available parts of the frequency range 380–470 MHz. However, the reality is that these frequencies are being heavily used by non-PPDR applications (e.g. civil PMR systems) in most European countries, preventing the designation of additional spectrum for the use of wideband PPDR systems [23].
In addition to the frequency designations for narrowband and wideband PPDR systems, ECC Recommendation (08)04 [30] establishes that administrations should make available at least 50 MHz of spectrum for digital BBDR radio applications. In particular, two possible frequency bands are identified: 5150–5250 MHz (preferred option) and 4940–4990 MHz. Such amount of spectrum is expected to allow PPDR agencies to implement on-scene broadband wireless networks (e.g. ‘hot spot’ access points in localized areas, temporary incident command centres erected at an incident scene) as well as deploy temporary point-to-point radio links. Nevertheless, the implementation of this ECC recommendation so far is quite limited across European countries (according to Ref. [31], only one third of CEPT countries have actually implemented it).
It is worth noting that many European countries also have national frequency designations for PPDR in the VHF frequency range, which are not harmonized throughout Europe. Moreover, some countries have already reserved spectrum specifically for AGA use (e.g. the United Kingdom has aggregated approximately 42 MHz between 3.1 and 3.4 GHz for digital video from airborne vehicles; Germany has allocated spectrum for that purpose in the 2.3-GHz band). However, at the moment, there is no European harmonized frequency band to support this type of applications.
A summary of the main bands with PPDR spectrum designations across European countries is given in Table 6.6.
Table 6.6 Main bands available across European countries for PPDR communications.
Frequency band (MHz) | Availablebandwidth (MHz) | Comments |
68–87.5 | — | Many European countries have national frequency designations for PPDR in the VHF frequency range. However, these are not harmonized allocations across Europe |
146–174 | — | |
380–385/390–395 | 10 | Extensively used for the operation of current PPDR narrowband wide area networks (TETRA and TETRAPOL). This is indeed the only actual European harmonized band |
385–390/395–399.9 | 10 | These bands form part of the tuning range identified in ECC Decision (08)05 for potential PPDR use, including wideband services (e.g. TEDS), across Europe. However, in many countries, these frequencies are mostly used for non-PPDR applications (e.g. civil PMR systems) |
410–430 | 20 | |
450–470 | 20 | |
5150–5250(alternatively 4940–4990) | 50 | Designated for local and temporary use through an ECC recommendation. Not actually implemented in most countries |
It is remarkable that no spectrum designations exist as of today in Europe for the deployment of WAN for mobile broadband PPDR services. Recognizing the need to provide the PPDR community with mobile broadband services and the benefits associated with European-wide harmonization of spectrum use for PPDR, the identification of new suitable spectrum bands for mobile broadband PPDR is on the agenda of the European institutions. Importantly, the RSPP approved in 2012 [8] adopted the following commitment in its Article 8.3:
The [European] Commission shall, in cooperation with the Member States, seek to ensure that sufficient spectrum is made available under harmonised conditions to support the development of safety services and the free circulation of related devices as well as the development of innovative interoperable solutions for public safety and protection, civil protection and disaster relief.
This commitment arrived after a series of efforts and initiatives fostered at different levels across the EU. In fact, back in 2009, the Justice and Home Affairs (JHA) Council of the EU approved a recommendation (Recommendation 10141/09, commonly referred to as the COMIX recommendation [33]) on improving radio communication between operational units in border areas. The COMIX recommendation concluded that law enforcement and public safety radio communication systems will need to support and to be able to exchange high-speed mobile data information beyond the capabilities of current networks, and a common standard operating in a harmonized frequency band will make this possible. Consequently, the COMIX recommendation suggested that CEPT/ECC should be tasked to study the possibility of obtaining sufficient additional frequency allocation below 1 GHz for the development of future law enforcement and public safety networks. Accordingly, the LEWP supporting the JHA Council activities established a Radio Communication Expert Group (RCEG) to work on relevant radio and spectrum matters, which asked CEPT/ECC to take into account the PPDR needs for a mission-critical broadband solution and for this purpose to designate harmonized frequencies [34].
It is worth noting that the current approach towards the harmonization of the broadband PPDR sector in Europe is not targeting a common frequency designation across Europe. Instead, a number of deployment options and spectrum bands for the delivery of broadband PPDR services in Europe are intended to be recognized [32]. In this way, national administrations could opt for the most suitable option or combination of options according to its particular national circumstances. At the end, this approach is believed to provide for the minimum harmonization needed to facilitate adequate interoperability and contribute to maximizing the benefits from the economies of scale for the delivered PPDR solutions.
The gross of the work towards the specification of this harmonized mobile PPDR communications framework in Europe is currently being conducted within the Frequency Management Project Team 49 (FM PT 49) at the CEPT/ECC level. This work is being addressed in cooperation with ETSI and other key organizations such as the RCEG/LEWP. It is expected that FM PT 49 work will eventually culminate in a CEPT/ECC deliverable by 2016 defining the harmonized framework for PPDR communications in Europe. More details on the expected deliverables and the roadmap established by FM PT 49 are given in Section 3.4.2.
Concerning the spectrum bands under consideration for this harmonized European PPDR framework, two candidate spectrum ranges have been identified within FM PT 49: 400 MHz (410–430 and 450–470 MHz) and 700 MHz (IMT-band, 694–790 MHz). The selection of the most suitable spectrum band for mobile broadband PPDR needs to assess and balance many different aspects such as:
Some main considerations in this regard concerning the two identified candidate spectrum ranges are given in Table 6.7. As previously mentioned, it is important to stress that the provisioning of broadband PPDR in Europe is not intended to be restricted to the use of 400- or 700-MHz spectrum. Instead, it is envisioned that PPDR capability can be enhanced by allowing mobile broadband PPDR services to be delivered across different bands (both below and above 1 GHz) and networks (both dedicated and commercial). Therefore, it is central that manufacturers produce multiple band integrated chipsets, including the designated PPDR ranges, using a common technology for PPDR user terminals ideally on a global or regional basis. In fact, leading chipmakers in the mobile industry have nowadays solutions that support access to over 12 spectrum bands, many of them under 1 GHz [39].
Table 6.7 Candidate bands considered in the harmonization of mobile broadband PPDR solutions across European countries.
Frequency band | Comments |
410–430 and 450–470 MHz | This band shows very good propagation characteristics, potentially reducing the number of sites needed to provide the necessary coverage (rural areas) |
This band would also allow benefiting from infrastructure from narrowband PPDR networks deployed in the 380–400-MHz band and facilitate a progressive implementation of LTE systems (e.g. in gradual steps of 1.4, 3, 5 MHz) which may end up in reusing at longer term the 380–385-MHz band (and duplex) for high data rates services by carrier aggregation of different sub-bands | |
However, this band is not considered to be a stand-alone solution for the full 2 × 10-MHz need for BB PPDR due to its limited availability in some European countries as well as the high cost that re-planning of this band might have (in addition to current uses, this band is also being considered as a suitable band to support M2M communications such as smart metering and smart grid in some European countries). For this reason, the deployment of a PPDR broadband solution in this band is mainly regarded as a complement to another solution (e.g. a 700-MHz solution or a roaming agreement with a commercial LTE operator) | |
Mobile broadband PPDR in this band could be realized as a 2 × 5-MHz LTE solution in the frequency range 410–430 and/or 450–470 MHz. Compatibility studies are being addressed at CEPT based on LTE technology (3GPP Release 12) with channel bandwidths of 1.4, 3 and 5 MHz. Results of these studies are expected to form part of ECC Report 218, to be released by mid-2015. Indeed, 3GPP has already added support for the use of LTE in the band 452.5–457.5 MHz paired with 462.5–467.5 MHz, which is specified as Band 31 and commonly known as LTE 450 MHz. Furthermore, the 450 MHz Alliance, an industry-based organization representing interests of 450 MHz spectrum stakeholders, is also pushing for the development of the LTE 450 MHz ecosystem. In this regard, first LTE 450 network deployments in the commercial domain have already been announced in 2014 [35] | |
694–790 MHz | This band is supported as the main candidate spectrum option for mobile broadband PPDR across Europe. Many countries see an opportunity for a national decision within this range for BB PPDR services, either as a dedicated network, a commercial solution or a combined (hybrid) solution |
The 700-MHz band in Europe is expected to be dedicated to wireless broadband by 2020 (±2 years) [38]. The band is currently occupied by terrestrial TV broadcasters and wireless microphones. This band repurposing is known as the second digital dividend (the first was the repurposing of the 800-MHz band) | |
The harmonized technical conditions for the use of the 700-MHz band (694–790 MHz) for wireless broadband in the EU have been already detailed in CEPT Report 53, in response to a European Commission Mandate. The CEPT Report 53 sets out the channelling arrangement based on a paired 2 × 30-MHz scheme (703–733/758–788 MHz) and a flexible approach to accommodate up to four blocks of 5 MHz for supplementary downlink (SDL) in the 738–758-MHz part of the duplex gap. This channelling arrangement of the 700-MHz band is well aligned with the Asia-Pacific Telecommunity (APT) 700 band plan, which is adopted by most countries across the Asia-Pacific and Latin America regions. The APT700 segmentation is based on two overlapping duplexers of 30 + 30 MHz, in which the lower duplexer band fits perfectly in the European scheme. Hence, a possible decision by national administrations could be the use of one or a number of blocks within this 2 × 30-MHz pairing for PPDR purposes | |
In addition, the channelling structure under consideration in CEPT also provides special arrangements that could be used as national options for PPDR usage (and/or other possible applications such as PMSE and M2M), as illustrated in Figure 6.2. One of these special arrangements for PPDR is to use the guard bands (i.e. 698–703- and 788–791-MHz blocks, paired with some spectrum within the duplex gap of the paired 2 × 30-MHz block in 733–758 MHz). In particular:
|
|
Another special arrangement is to use the 25-MHz duplex gap of the 2 × 30-MHz paired scheme to support a 10 + 10-MHz allocation for PPDR between 733 and 758, with an internal gap of (only) 5 MHz, even though this option faces important technical difficulties associated with the duplexer design for a 5-MHz duplex gap if the terminal has to cover the whole frequency range [36, 37] | |
On the plus side of using special arrangements for PPDR is that it could increase the chances for PPDR allocations without directly competing for spectrum with commercial operators. On the downside, a dedicated sub-band would create a niche market for PPDR, with possible negative effects on economies of scale and interoperability. In addition, PPDR adjacent to the 700-MHz band leaves less protection for broadcast networks. Compatibility and sharing studies for broadband PPDR systems considering these special arrangement options are currently being addressed in CEPT ECC. Results of these studies are expected to form part of ECC Report 218 |
In addition to the harmonization of spectrum suitable for the deployment of wide area mobile broadband PPDR networks, CEPT is also conducting studies that may end up with the allocation of additional harmonized spectrum for other PPDR-specific uses [40]. In particular, ECC is developing CEPT Report 52 in response to a recent EC mandate to undertake studies on the harmonized technical conditions for the 1900–1920 and 2010–2025 MHz frequency bands (unpaired terrestrial 2-GHz bands) in the EU. The aim of the report is to assess and identify alternative uses of the underused unpaired terrestrial 2-GHz bands other than for the provision of mobile broadband services through terrestrial cellular networks, as well as the development of relevant least restrictive technical conditions for spectrum use. Potential harmonized uses of this band consider BB PPDR ad hoc communications (e.g. local video links) including, for some countries, PPDR broadband AGA applications (e.g. video links between terrestrial units and helicopters). In addition, spectrum at the 5-GHz frequency range (i.e. 4940–4990 MHz) identified for BBDR radio applications in ECC/REC/(08)04 may be subject to further harmonization activities within CEPT.
In the United States, PPDR agencies can licence spectrum in seven separate frequency bands where the FCC has allocated spectrum for public safety use over the years [21]. Those bands, together with indications on the amount of spectrum available in each and its uses, are listed in Table 6.8. As shown in the table, there are several bands in use for narrowband voice and low-speed data systems. Each voice band has unique propagation characteristics, and each band is good or bad for different types of systems. The 30–50-MHz band is primarily used in some statewide systems to provide mobile coverage of highways. The VHF band is a good band for rural areas, while the 450- and 700/800-MHz bands are used in urban and suburban areas where good portable coverage is needed. The 700/800-MHz bands are best suited for trunking systems and increasingly are being used for large regional and statewide systems to provide improved communications and interoperability across multiple agencies and jurisdictions. Although not shown in the table, some PPDR entities in the United States currently utilize systems in some geographic areas in the 470–512-MHz band, known as the T-Band. However, the US Congress mandated in 2012 that public safety agencies with T-Band systems vacate the spectrum by 2021.
Table 6.8 Spectrum available in the United States for PS communications.
Frequency band (MHz) | Available bandwidth(MHz, approximate) | Comments |
25–50 | 6.3 | Used for narrowband services |
150–174 | 3.6 | Used for narrowband services |
220–222 | 0.1 | Used for narrowband services |
450–470 | 3.7 | Used for narrowband services |
809–815/854–860 | 3.5 | Used for narrowband services |
806–809/851–854 | 6 | Used for narrowband services |
758–768/788–798 | 20 | Wide area broadband |
768–769/798–799 | 2 | Guard |
769–775/799–805 | 12 | Used for narrowband services |
4940–4990 | 50 | Short-range broadband and point-to-point links |
With regard to mobile broadband PPDR, the frequencies that have been allocated in the United States are those in the range 758–768/788–798 MHz. Indeed, this is the spectrum assigned to FirstNet for the deployment of the nationwide public safety network. It is also worth noting that the Spectrum Act passed in 2012 also allows a flexible use of broadband in the 700-MHz narrowband spectrum (769–775 and 799–805 MHz), but any move to do so would first need to consider the potential for interference between broadband and narrowband systems.
In addition, the 4.9-GHz band is available in the United States for short-range broadband data and point-to-point data links. The FCC reallocated this band (4.94–4.99 GHz, 50 MHz of spectrum) from federal government use in 2002 and adopted rules designating the band for public safety services in 2003. The band can be used for any terrestrial-based radio transmission including data, voice and video. All multipoint and temporary (<1 year) point-to-point links are primary users of the band. Permanent point-to-point links are secondary users and require separate site licences. The FCC has implemented a geographic licencing scheme for mobile applications. A licence grants a PPDR agency authorization to use all 50 MHz of spectrum within its legal jurisdiction whether that jurisdiction is a state, town, city or county. Licencees must share the spectrum and coordinate frequency use. However, the overall operation can be made very reliable because the general public is prohibited from using the band. This band is currently under review by the FCC to promote greater use of the band, including opening up a part of the band for commercial applications and finding ways to complement the nationwide interoperable LTE public safety broadband network currently in development [41].
The United States was the first country to allocate broadband PPDR spectrum in the 700-MHz band. Initially, 5 + 5-MHz spectrum was allocated, though early in 2012 the US Congress passed a law consolidating an additional 5 + 5 MHz (the so-called D-Block) that sat contiguous to the initial allocation. The channelling arrangement for the 700-MHz band in United States is illustrated in Figure 6.3. Canada is following a similar allocation.
For the deployment of LTE equipment in the US band plan, the 3GPP has designated four operating bands: 12, 13, 14 and 17 (Band 17 is a subset of Band 12). The spectrum already assigned for mobile broadband falls within Band 14 (758–768 and 788–798).
In the Asia-Pacific region, the 806–824-MHz segment is widely used for the provision of narrowband communications in support of PPDR applications. This allocation is harmonized through ITU Resolution 646.
The 800-MHz band is also considered by some countries (e.g. Australia, Singapore) for the designation of new spectrum for mobile broadband PPDR, while other national administrations consider the 700-MHz band (South Korea, Mexico, United Arab Emirates) [42]. In the case of Australia, the NRA (ACMA) is undertaking a number of initiatives to improve spectrum provisions for public safety. The most important are:
The channelling arrangements for the 700 and 800 MHz are illustrated in Figure 6.4, showing some of the considered allocations for mobile broadband PPDR.
The segmentation of the 700 MHz follows the harmonized APT band plan, commonly known as APT700 band plan. This band plan has been standardized by the 3GPP into two operating bands: Band 28 for FDD operation and Band 44 for TDD operation. The FDD option (Band 28) has attracted the most support from the industry so far. Indeed, many countries have already allocated, committed to or recommend allocating APT700 FDD (Band 28) spectrum for LTE deployments. It is worth noting that the APT700 band plan is not compatible with the 700-MHz arrangement adopted in the United States, since both rely on different channel bandwidths and channel locations within the 700-MHz band.
In a further boost to the dominance of the 700-MHz band for PPDR LTE systems, it was recently announced that Brazilian public safety, national defence and critical infrastructure services will be allocated spectrum in this band. Significantly, in a departure from the common South American practice of adopting the US spectrum planning arrangements, the announcement stated that the APT 700-MHz band (Band 28) would be used [43]. In a related effort, the CITEL recommended to its member states across North, Central and South America that PPDR broadband spectrum allocations should be made along the 700-MHz band, considering either the APT 700-MHz band (Band 28) or the US band (Band 14).
The case of assigning a minimum amount of dedicated spectrum to support the delivery of wide area mobile broadband PPDR services is gaining momentum in many countries.8 As discussed in the previous section, some national administrations have already designated spectrum blocks of 10 + 10 or 5 + 5 MHz in the 700- or 800-MHz bands for mobile broadband PPDR use. This amount of dedicated spectrum is estimated to be enough to satisfy PPDR needs for mission-critical communications in most operational scenarios, as concluded in some of the studies presented in Table 6.5. However, it is also recognized in some of those studies that this amount of spectrum might fall short to satisfy the capacity requirements in a major incident. Indeed, estimations by ECC PT49 [20] and NPSTC [21] show some worst case scenarios where more than 10 + 10 MHz of spectrum would be required. Nevertheless, it is also acknowledged that it would be highly inefficient to dimension PPDR spectrum provisions around what might be a once-in-a-generation event, likely resulting in a very low utilization of a significant portion of the dedicated spectrum during most of the time.
In this context, the introduction of spectrum sharing approaches between PPDR and other services in some specific bands could be instrumental to have the required degree of flexibility that would allow PPDR to use substantially more spectrum at times of stress while ensuring the utilization of this spectrum for other uses at times of day-to-day PPDR activity. Spectrum sharing refers here to the application of technical methods and operational procedures to permit multiple users to coexist in the same region of spectrum [44]. The use of spectrum sharing for PPDR use constitutes a plausible approach to complement a dedicated assignment with additional spectrum that could be required to handle an exceptional demand or just for the deployment of particular PPDR applications in a more efficient manner at specific times and locations. Likewise, the introduction of spectrum sharing could become a facilitator for administrations to designate a larger amount of spectrum for PPDR use (e.g. 20 + 20 MHz instead of 10 + 10 MHz) under the basis that (a portion of) this spectrum can be effectively shared with others when not actually in use by PPDR applications [45].
The consideration of a spectrum sharing framework for PPDR needs to evaluate two main central requirements: availability (i.e. guarantees that the sufficient amount of spectrum will be available when and where it is needed) and responsiveness (i.e. how fast the spectrum is ready for PPDR use since the need arises). Depending on the level of fulfilment of these requirements, a particular spectrum sharing solution can be considered suitable to support mission-critical applications or just intended to provision additional capacity for non-mission-critical applications.
The possibility to rely on a higher spectrum amount on a temporary basis with respect to that used in day-to-day conditions is captured in ITU-R Resolution 646, ‘Public Protection and Disaster Relief’, from WRC-2012, where it is recognized that ‘the amount of spectrum needed for public protection on a daily basis can differ significantly between countries, that certain amounts of spectrum are already in use in various countries for narrow-band applications, and that in response to a disaster, access to additional spectrum on a temporary basis may be required’. Furthermore, there are several ongoing initiatives at regulatory and standardization level that envision the applicability of spectrum sharing techniques for PPDR communications to some extent:
The next subsection develops some fundamental concepts and provides a categorization of spectrum sharing models for PPDR communications together with a discussion on the suitability of each model. On this basis, the subsequent subsections further develop two possible solution frameworks for PPDR spectrum sharing: one based on applicability of the Licenced Shared Access (LSA) regime and another exploiting secondary access to TV white spaces (TVWS) for PPDR use.
Spectrum sharing may be achieved by numerous methods such as coordinating time usage, geographic separation, frequency separation, directive antennas and so on. In the past, the employment of spectrum sharing mechanisms has typically been on a static, pre-planned basis. For example, the simplest means of spectrum sharing is the operation of systems in the same frequency band but in different geographical areas. Nevertheless, spectrum sharing can be more complex and allow sharing frequencies in the same geographical area. For instance, cognitive radio (CR) technologies (e.g. geo-location databases (GLDBs), spectrum sensing) can be utilized to adapt, in a dynamic and flexibly manner, the spectrum used by PPDR communications equipment considering the presence and activity of other users of the shared band.
A general classification (not specific to PPDR) of spectrum sharing models is based on two defining features [49]:
Based on these two above-mentioned features and on the types of licencing regimes and spectrum management models discussed in Section 6.1, three categories of spectrum sharing models for PPDR use can be distinguished [50]:
The feasibility of each sharing model for PPDR communications primarily depends on the type of users involved in the sharing framework, which may involve users across the commercial, military and PPDR domains. The adoption of a given sharing model may require changes to the organizational structures and relationships among these users. In some cases, these changes are just an extension of existing agreements (e.g. joint procedures for disaster management between military and public safety entities in large natural disasters). In other cases, new agreements (e.g. sharing rules or conditions among users) must be put in place. Moreover, the amount of changes required in the existing infrastructures managed by these different communities is another important aspect to consider. Any proposed sharing model should minimize the changes to the existing infrastructures.
The adoption of a sharing model is also dependent on the development of suitable technologies and regulatory frameworks. Different sharing models may require more or less complex modifications to existing standards and undertake different technical challenges. In some cases, the technical requirements for specific functions (e.g. spectrum sensing case of models built upon CR technologies) may be difficult to implement with existing technological capabilities (e.g. computing/processing power). Furthermore, international and national spectrum regulations must be modified to permit the deployment of some of the sharing models.
Based on earlier observations, Tables 6.9, 6.10 and 6.11 describe the principles, applicability and some examples for the three identified categories of spectrum sharing models. The tables also provide a discussion on the suitability of each model considering organizational and operational aspects of the involved users as well as relevant technical and regulatory initiatives that can contribute to pave the way towards their adoption.
Table 6.9 Models based on the dynamic transfer or coordination of individual spectrum rights of use.
Sharing principles | Individual rights of use are dynamically transferred or coordinated between users by means of, for example, spectrum leasing procedures or technical mechanisms that guarantee that there is only a single user authorized to use the spectrum at a given time and location. Prioritization and pre-emption principles can be considered in the transfer or coordination to give preferential access to some users |
Applicability | Spectrum bands where access authorization relies on holding individual spectrum rights of use. This includes traditional licences as well as LSA licencesa |
Illustrative examples | Temporary transfer of spectrum usage rights from non-PPDR to PPDR users. PPDR users involved in an incident response or in a major planned event (e.g. Olympics games) could request, for example, military authorities or other private holders to lease part of its spectrum for PPDR use |
Temporary transfer of the spectrum usage rights from PPDR to non-PPDR users. In this case, when there is no emergency situation and part of spectrum designated for PPDR is not being used, spectrum usage rights could be leased to other users such as telecom operators. This leasing could be interruptible under strict guarantees when required by the PPDR spectrum licencee | |
Suitability considerations | Transfer of exclusive spectrum rights of use is already regulated in many countries [51–53]. Current spectrum transfer procedures can take some days, which is suitable for long-planned events (e.g. G20 summit or Olympic games). Operation at lower timescales needs further regulatory and technical developments (i.e. new technical capabilities are needed for executing the transfer in the order of 30 min/1 h, which is the timescale for the initial response to an emergency crisis) |
The advantage of this solution is that spectrum availability is guaranteed with exclusive spectrum usage rights for all the duration of the lease. Therefore, if a framework is defined and deployed to guarantee also the timeliness of the provision of the spectrum, this is a feasible model even for mission-critical PPDR applications. Its realization needs cognitive or (at least) tuneable radios that can be configured to operate in different spectral bands | |
Initial deployment could be restricted to spectrum transfers among PPDR users, including the possibility to create spectrum pools contributed by multiple licencees for mutual use [54]. Extension to other governmental and/or commercial marketplace users could be addressed in a subsequent stage | |
Newly allocated bands could explicitly be designated by regulatory authority for spectrum sharing through dynamic transfer of rights of use. Assignment of spectrum usage rights could be managed through a centralized mechanism in the form of spectrum coordination server or spectrum broker [55]. A new spectrum regulatory model such as LSA can facilitate this approach | |
Dynamic transfer of exclusive rights of use can be applied between military domain and PPDR organizations, but it will require new regulatory frameworks and new procedural interfaces between the correspondent control centres [56] |
a Licenced Shared Access (LSA) is a new spectrum regulatory approach that facilitates the introduction of new users in a frequency band while maintaining incumbent services that may exhibit low or localized utilization in the band. The new users hold LSA licences that grant individual spectrum usage rights subject to some utilization conditions that account for the existence of incumbent users. More details on LSA are covered in Section 6.5.2.
Table 6.10 Models based on primary–secondary sharing.
Sharing principles |
Secondary access is allowed in an opportunistic manner in a band where there is a primary user that holds the spectrum rights of use. Secondary access is opportunistic (i.e. time and location availability of the spectrum are dependent on the actual activity of the primary user that can be dynamic) and in a non-interference basis (i.e. the primary user shall not be affected by secondary transmissions). Two possible variants are distinguished:
|
Applicability | Spectrum bands where there is an (primary) owner of spectrum rights of use and the NRA decides to authorize secondary access (e.g. TV UHF bands in the United States and United Kingdom) |
Illustrative examples | Secondary access allowed to PPDR users in non-PPDR bands. For example, communication devices such as ad hoc communications systems brought in the incident area by PPDR agencies could use, for example, a military band on a restricted geographical basis [57]. Coordination mechanism between military and PPDR agencies could be established |
Secondary access is allowed in PPDR bands. For example, a PS network operator may advertise that part of spectrum is not being used and so make this spectrum available for secondary access. Secondary users can be restricted to other PPDR applications or be open to non-PPDR services like critical infrastructure agencies (e.g. energy and other utilities) or even commercial use | |
Suitability considerations | Solutions for PPDR spectrum sharing may benefit from proposals and achievements within the TV white space domain, based at present on the usage of a geo-location database [58] |
If PPDR is primary use, it is a feasible model even for mission-critical PPDR applications. Indeed, secondary access to (primary) PPDR spectrum is not precluded by ETSI in Ref. [23] under a strict pre-emptive regime to ensure the performance of PPDR communications. Using PPDR spectrum for commercial use with preferential access given to PPDR in case of emergencies was also considered by FCC in an intent to promote the deployment of a joint-use network employing both PS and commercial spectrum (i.e. D-Block) [59] | |
If PPDR is secondary use, it can provide an opportunistic additional capacity to alleviate congestion problems for mission-critical applications as well as facilitate the deployment of non-mission-critical applications. PPDR secondary access to (primary) military spectrum is a possible approach, considering that military organizations possess considerable regions of spectrum that may not be used in the location of the incident. A three-level sharing scheme, where military is the primary user, PPDR is a second-tier primary user and commercial networks are the secondary users, is discussed in Ref. [23] | |
Sharing between military users and PPDR users can be done on the space dimension or the time dimension as described in Ref. [57]. In the space dimension, PPDR users can use the spectrum in an opportunistic way if the spectrum is used by the military only in specific areas (e.g. military compounds). In the time dimension, spectrum can be shared as in the case of radar [60]. For example, low-power systems could potentially share with radar if the radar sweep can be detected and the transmission of the device timed to avoid interference. This solution would require a close coordination or reliable technical solutions to ensure that the military radio communication services are not impacted by harmful interference. A potential challenge is the lack of network interfaces between military networks and PPDR networks due to security reasons | |
Coordination models can offer more QoS guarantees at the cost of added complexity. Coordination can be addressed at the communications system level (e.g. beacon signals broadcasted by PPDR networks to enable/disable secondary access) or at the organizational and procedural level (e.g. extension of existing procedures for coordinated disaster management in the case of military–PPDR spectrum sharing) | |
Coexistence models are necessary in cases that coordination fails or is not possible (e.g. geo-location databases not reachable). CR technology is particularly relevant in these cases |
Table 6.11 Models based on a collective use of spectrum.
Sharing principles | Multiple users are authorized to use the band as a result of either a general authorization regime (e.g. licence-exempt band with no limitations in the number of users) or a light-licencing regime (e.g. limits on the number of authorizations might be in place) |
Two variants:
|
|
Applicability | Spectrum bands where collective usage rights are in place instead of individual (exclusive) usage rights |
Illustrative examples | Shared access in a spectrum band designated only for PPDR use. For example, all registered and explicitly authorized PPDR agencies might use this band to set up fast deployable equipment (e.g. wireless access points, point-to-point links). Coordination for, for example, channel assignment could be carried out through a common protocol supported by all authorized devices. The development of such a common protocol is facilitated by the restriction of this band to PPDR applications |
Shared access in a general purpose licence-exempt band such as the 2.4- or 5-GHz ISM bands. The use of this band can bring additional capacity in the incident area for local area communications, yet no preferential access or coordination mechanisms will be available for PPDR users to control the interference from any other legitimate user of the band (e.g. personal devices or private/public wireless access networks) | |
Suitability considerations | Application-specific bands for PPDR communications are already available in the United States (4.9-GHz band) and in some European countries (broadband disaster relief [BBDR] band in the 5-GHz frequency range), especially to implement on-scene broadband wireless networks. Authorized users are responsible for interference prevention, mitigation and resolution coordination among them |
The establishment of frequency planning coordination processes would be also a plausible option to share these bands with other non-PPDR users such as utilities or transportation. This approach has been recently proposed by the National Public Safety Telecommunications Council (NPSTC) with regard to allowing access to 4.9-GHz spectrum to critical infrastructure industries, including the energy sector, on a shared, co-primary basis with public safety | |
Coordination can be also based on technical mechanisms (e.g. use of technologies such as IEEE 802.11y that could allow frequency coordinators to have dynamic control over channel access in a PPDR shared band) | |
Shared spectrum can be used for mission-critical PPDR applications if suitable coordination mechanisms such as those referred above are in place | |
Coexistence approaches (e.g. using existing general purpose licence-exempt bands such as ISM bands at 2.4 and 5 GHz) cannot offer QoS guarantees for mission-critical PPDR. However, as proven by the massive adoption of Wi-Fi devices, the reality is that achieving some additional capacity with good perceived QoS in these bands is not so unlikely. This fact can be even more evident in the utilization of those bands in non-residential areas (e.g. crisis incident in rural areas) |
LSA is a new spectrum regulatory approach that facilitates the introduction of new users in a frequency band while maintaining incumbent services that may exhibit low or localized utilization in the band. LSA fits under an individual licencing regime, so that LSA licences are to be granted to the new users. LSA aims to ensure a certain level of guarantee in terms of spectrum access and protection against harmful interference for both the incumbent(s) and LSA licencees, thus allowing them to provide a predictable quality of service (QoS) (i.e. each user would have exclusive individual access to a portion of spectrum at a given location and time). Therefore, LSA excludes concepts such as ‘opportunistic spectrum access’, ‘secondary use’ or ‘secondary service’ where the new user has no protection from primary user(s). Remarkably, LSA applies only when the incumbent user(s) and the LSA licencees are of different nature (e.g. governmental vs. commercial users) and operate different types of applications, being subject to different regulatory constraints. Hence, an LSA sharing framework is expected to have limited impact – likely no impact – on the market regulation policy objectives since incumbent and LSA licencees belong to two different vertical markets. From the incumbent’s perspective, LSA could be an alternative to spectrum refarming processes that might be too costly to be implemented, not possible in a reasonable timeframe or simply not desirable.
The LSA10 framework was proposed by the EC’s RSPG in 2011 [61]. The RSPG Opinion on LSA [62] approved in November 2013 provides the following definition:
A regulatory approach aiming to facilitate the introduction of radiocommunication systems operated by a limited number of licensees under an individual licensing regime in a frequency band already assigned or expected to be assigned to one or more incumbent users. Under the Licensed Shared Access (LSA) approach, the additional users are authorised to use the spectrum (or part of the spectrum) in accordance with sharing rules included in their rights of use of spectrum, thereby allowing all the authorised users, including incumbents, to provide a certain Quality of Service (QoS).
It is worth noting that the LSA concept embraces the so-called Authorised Shared Access (ASA) concept, which was firstly proposed by an industry consortium (involving Qualcomm and Nokia) to provide shared access to IMT spectrum under a licensing regime in order to offer services with a certain quality of service [63]. In particular, it could be said that both LSA and ASA concepts are equivalent excepting the fact that ASA was proposed in the context of IMT bands, while the LSA concept has been defined with a broader scope of applicability, not limited to IMT bands. Therefore, the terms LSA and ASA terms are often used interchangeably, and even sometimes some documents use the notation ‘LSA/ASA’ model [64].
A report on LSA (ECC Report 205 [10]) was released by CEPT ECC in February 2014. ECC Report 205 establishes the scope and components of the LSA regulatory approach and provides detailed considerations towards the potential implementation of LSA in the 2300–2400-MHz (‘2.3-GHz’) frequency band in the EU to provide access to additional spectrum for mobile broadband services (referred to them as mobile/fixed communications networks (MFCN)). In this regard, technical harmonized conditions for this band to support wireless broadband ECS are being developed by CEPT in response to a mandate by the EC [65]. In particular, ECC Report 55 [66] and related ECC Decision 14(02) [67] set out the technical conditions to allow coexistence between wireless broadband applications in the 2.3-GHz band and to ensure coexistence with the services and applications above 2400 MHz (e.g. Wi-Fi networks). The ECC Report 55 also contains guidelines on the additional conditions to be applied, on a case-by-case basis, for coexistence between wireless broadband and services below 2.3 GHz. This band is rather different from others where similar initiatives have been applied, because of a range of important incumbent services in limited but specific parts of Europe. In this context, the ECC intends to develop further guidelines to aid administrations in developing an appropriate sharing framework for coexistence between communications networks and incumbent services and applications at the national level (e.g. see [68]).
In parallel, and in close cooperation with regulatory efforts, the ETSI technical committee on RRS is addressing the standardization of an LSA technical framework. In this regard, an SRDoc proposing the adoption of LSA usage in 2.3–2.4 GHz was issued in 2013 [69], and LSA system requirements were released in October 2014 [70]. Work is currently ongoing towards the specification of a system architecture and high-level procedures (to be reported in ETSI TS 103 235 [71]).
A description of the regulatory and technical frameworks of the LSA model is provided in the next two subsections. Then, the use of a potential applicability of the LSA framework for PPDR communications is discussed.
The central piece for the implementation of LSA is the establishment of the so-called sharing framework to define the spectrum that can be made available for alternative usage under an LSA model.
The sharing framework can be understood as a set of sharing rules or sharing conditions, which have to be established under the responsibility of the NRA. In particular, the sharing framework has:
The definition of an effective sharing framework requires the involvement of all relevant stakeholders (illustrated in Figure 6.5):
The Administration/NRA should identify the relevant parties to be involved in the development of the sharing framework. After this, a dialogue between Administration/NRA, incumbent(s) and prospective LSA licencees should be initiated, with the aim of determining the terms of the sharing framework:
Then, in accordance with the established sharing framework, the Administration/NRA would set the authorization process with a view to delivering, in a fair, transparent and non-discriminatory manner, individual rights of use of spectrum to LSA licencees. LSA does not prejudge the modalities of the authorization process to be set by NRA taking into account national circumstances and market demand (e.g. traditional licencing, light licencing with individual authorization). Granting LSA individual rights of use can also be associated with a number of obligations, as commonly done in traditional (exclusive rights of use) licences.
Depending on the dynamic nature of the spectrum use by the incumbent(s), the LSA licencee may need to be provided (e.g. through a database) with information on the area(s)/time of availability of the spectrum. If this information remains constant over time, it can be provided when the LSA licencee applies for its LSA authorization. Should the incumbent needs to have access to (a part of) the band used by the LSA licencee in accordance with the conditions defined in its LSA authorization, the LSA licencee has to be informed by agreed means and has to modify its use.
The concept of ‘sharing framework’ associated with LSA should not be mixed with a conventional sharing arrangement that is applied for, for example, fixed services such as microwave links or PMR-like services. In such cases, there is no ‘incumbent’ having priority or exclusive spectrum access across a territory, and new systems are typically introduced on a first-come/first-served basis by applying appropriate coordination measures (e.g. geographic frequency separation measures).
ETSI is standardizing a technical framework for the implementation of an ‘LSA system’ in the context of enabling access for MFCNs to the 2.3-GHz band. As such, an ‘LSA system’ comprises one or more incumbents, one or more MFCNs (LSA licencees) and the means to enable the coordination between the incumbents and the LSA licencees, such that the latter may deploy their networks without harmful interference.
The LSA system is designed considering that sharing may in general be dynamic (i.e. the requirements of the incumbent may be such that some portions of the spectrum are not permanently available to the LSA licencee in any given location). In this regard, the set of practical details for sharing a given LSA spectrum resource is referred to as ‘sharing arrangement’, which may be subject to change but should always remain consistent with the ‘sharing framework’ defined by the Administration/NRA. For instance, a particular spectrum sharing arrangement between an incumbent and an LSA licencee may include constraints on the potential variations of resource availability to, for example, facilitate the implementation and operability of the sharing system. Examples of such constraints are:
On this basis, the proposed LSA system architecture at the time of writing (work is still in progress) is shown in Figure 6.6. It consists of two functional entities:
Three reference points are defined:
An illustrative scenario implementing this LSA system architecture is shown in Figure 6.7. The scenario considers the case of an MNO who holds two (traditional) licences to operate some amount of spectrum (referred to as licenced band/carrier A and licenced band/carrier B) over the entire coverage area where its network is deployed. In addition, it is considered that the MNO also holds an LSA licence to use some additional spectrum that is only available in a smaller restricted area due to the presence of incumbents in the rest of the network coverage (referred to as LSA licenced band/carrier C). In this situation, the MNO is responsible for ensuring that only the appropriate base stations (i.e. those out of the grey area depicted in Figure 6.7) can actually operate in the LSA spectrum, either using this spectrum in a stand-alone manner or combining its use with the other licenced bands if carrier aggregation capabilities are in place. To this end, an LC would form part of, or interact with, the network management system (NMS) of the MNO. The LC will receive information on LSA spectrum resource availability over the LSA1 interface from the LR that governs the access to this band. On this basis, the NMS then would translate the information on spectrum availability obtained by the LC into the appropriate radio resource management commands to the base stations in the operator’s network. Hence, a user terminal located in the area where the LSA band is available can have access to either of the licenced bands and the LSA bandusi or to all of them if it has the appropriate carrier aggregation capabilities. A user terminal located in the area where the LSA band is not available can only use the licenced bands.
From MNO’s point of view, LSA introduces a variability in the amount of spectrum that can be utilized for its normal operation, and in principle, the mechanisms required to utilize the LSA band are similar to the inter-RAT or inter-band load balancing means that already exist in the NMS and are widely deployed in today’s cellular systems. Hence, using the LSA spectrum will require the following steps:
Vacating the LSA spectrum will require the following steps:
Some considerations on the potential applicability of an LSA framework to support PPDR communications were addressed within the European research Project HELP [72]. In this project, a functional architecture in line with the LSA reference model described in the previous section was proposed for the dynamic coordination of some amount of spectrum between a PPDR operator and other users in a manner that predictable QoS was ensured for all sharers. Project HELP pointed out two candidate bands where the applicability of this model would deserve special consideration: the 700 MHz, where mobile broadband services are to become co-primary services in Europe after WRC-2015, and the 225–380-MHz band, used for military applications in NATO countries. In the first case, an LSA model could be adopted involving a PPDR network operator, who would have the role of the incumbent, and a commercial MNO, who would be granted the LSA licence. In the second case, the LSA model would involve the military authorities, who would act as the incumbent, and a PPDR network operator, now in the role of the LSA licencee.
Similarly, a study by a consultancy firm requested by the TCCA on the matter of the need for PPDR broadband spectrum in the bands below 1 GHz in Europe [45] argued that consideration should be given to the shared use of spectrum for PPDR and commercial LTE based on a sort of LSA model,11 on the basis that the case for a minimum of 10 + 10 MHz of dedicated PPDR was already taken for granted. In particular, the study identified the following approaches for allocating and assigning spectrum so as to permit varying degrees of flexibility between PPDR use and commercial use by an MNO:
More recently, a use case entitled ‘Licensed Shared Access for Supplemental BB PPDR’ has been included within ETSI TR 103 217 [73], which reports on a feasibility study12 that explores the potential areas of synergies between commercial, civil security and military domains in the medium/long term (5–15 years) in response to the EC mandate for RRS (M/512). This use case proposes to apply LSA for providing supplemental data broadband connection to existing narrowband PPDR. In particular, the use case states that administrations may consider introducing BB PPDR application as primary user into a newly refarm frequency band but permit spectrum resources to be shared based on LSA with commercial systems such as mobile broadband. The document recognizes that PPDR operations that are by nature largely unexpected would be an important drawback for commercial systems as it means uncertainty access to spectrum resources, additional risk and complexities associated with spectrum sharing and could make investment by commercial systems less certain compared to the case of exclusive spectrum. However, the document ascertains that this drawback should be balanced with the fact that PPDR operations are geographically localized and limited in time, which may result in a few percent of resource spectrum unavailability for commercial systems at the scale of a country with national coverage.
In the light of the previous text, the sharing case based on LSA between PPDR and commercial operators could actually represent an efficient approach worthy of further investigation to permit varying degrees of flexibility for PPDR BB spectrum use. Technology is not seen as an impediment for this kind of approach. Nonetheless, the definition of the ‘sharing framework’ becomes the central question to be answered, setting up crystal clear sharing rules along with the mission-critical levels that would trigger spectrum resource pre-emptions. Doing so, an LSA framework may provide adequate guarantee in terms of spectrum access at a regional or national scale to commercial LSA licencees in order to incentivize and secure investments in network and equipment.
A white space can be defined as ‘a part of the spectrum, which is available for a radiocommunication application (service, system) at a given time in a given geographical area on a non-interfering/non-protected basis with regard to other services with a higher priority on a national basis’ [74]. The concept of allowing additional transmissions in white spaces is a technique to improve spectrum utilization as well as to unlock some spectrum for new uses, provided that the risk of harmful interference to the existing licenced users of the spectrum can be appropriately managed. Most efforts currently underway related to the exploitation of white spaces are focused on the parts of the VHF and UHF frequency bands used for TV broadcasting (i.e. TVWS). The existence of a significant amount of unused parts of spectrum within these bands has been reported in some studies (e.g. see [75]). However, the actual availability of white space spectrum differs significantly among countries (depending on the relevance that terrestrial TV broadcasting service plays in front of other TV delivery platforms such as cable TV or satellite TV) as well as among areas within the same country (e.g. urban and rural areas).
The favourable propagation of radio waves in the VHF/UHF bands and their ability to penetrate deep inside buildings make this frequency range quite valuable. Indeed, many and diverse potential use cases for the exploitation of unused TVWS have been identified such as broadband Internet access in rural areas, wide area machine-to-machine communications, wireless backhauling, rapid deployed networks, in-home networking, etc. [76].
In this context, consideration should be given to the use of TVWS by PPDR equipment to leverage on the long-reaching and highly penetrative signal capabilities of this band, especially in hard-to-reach areas (e.g. tunnels, building basements) as well as in low or very low populated areas where an important part of this spectrum might remain underutilized.
In the regulatory domain, some of the world’s most influential regulators, including FCC in the United States, Ofcom in the United Kingdom and the European CEPT/ECC, Japanese Ministry of Internal Affairs and Communications (MIC) and Singapore’s Info-Communications Development Authority (IDA), are at the forefront of developing the rules for the use of TVWS [58]. In the standardization and industrial domains, the ETSI, IEEE, Internet Engineering Task Force (IETF) and ECMA International have also started several activities to shape future solutions for the so-called white space devices (WSD) or TV band devices (TVBD).
The regulatory and technical frameworks that set the playing field for the potential exploitation of TVWS by PPDR applications are described in the following two subsections. On this basis, a functional architecture of a technical solution for the control and use of TVWS in a LTE-based PPDR network is presented in the last subsection, together with the identification of some regulatory actions that would further contribute to increase the level of dependability that PPDR users could have on this kind of spectrum sharing solution.
A first regulation on the use of TVWS was released by the FCC in the United States in 2010 [77] and went officially into effect in early 2011. Since then, some corrections to the rules have been introduced [78], and the operation of TVBDs for commercial use is now a reality in the United States in the TV channels frequencies across the VHF and UHF bands [79].
In Europe, leading efforts are taking place in the United Kingdom towards the allowance of WSDs in the spectrum range between 470 and 790 MHz. While this spectrum is mainly used for digital terrestrial television (DTT), other services such as programme making and special event (PMSE) systems (e.g. use of wireless microphones, talkback systems and in-ear monitors in concerts, sport events and others) have also to be accounted as incumbents to be protected. Regulatory requirements have been already drafted by Ofcom [80], and white space technology is currently being piloted in the United Kingdom [81].
Furthermore, possible harmonization measures for the use of WSDs in the band 470–790 MHz across Europe are also under consideration within CEPT/ECC, which established the Frequency Management Project Team 53 (FM PT 53) in September 2012 [82] to study the potential use of TVWS in Europe. Among others goals, FM PT 53 is intended to provide a master set of the overall requirements for CEPT countries and develop, if appropriate, harmonized regulatory measures to complement the related standardization activities in ETSI with the aim of enabling the development and deployment of WSD while ensuring protection to incumbent services.13 Thus far, some technical studies have been performed within CEPT on the technical and operational requirements for the possible operation of (so-called) cognitive radio systems (CRS) in the frequency band 470–790 MHz (ECC Reports 159, 185 and 186 [74, 83, 84]). Based on these CEPT/ECC studies, ETSI produced a harmonized standard that went into effect in September 2014 [85]. The ETSI harmonized standard covers the essential requirements that must be met by WSDs to be conformant with the R&TTE Directive that regulates the placement of radio and telecommunications terminal equipment in the EU market.
Other countries that are moving forwards in the regulation of TVWS are Canada, Singapore and South Africa.
All these regulatory frameworks advocate for a licence-exempt regime for spectrum authorization where WSDs learn about the available WS channels that can be used at a given time and location from a GLDB. The main components of the regulatory framework enabling the operation of WSDs are depicted in Figure 6.8 and briefly described in the following.
The existing regulations consider both fixed and portable WSDs. Fixed WSDs are intended to be deployed at a fixed location with a fixed antenna height. Fixed WSDs typically must store their location, which can either be entered by a professional installer or self-determined using geo-location technologies. On the other hand, portable WSDs must be able to self-geo-locate whenever they move more than a specific distance (typically, it could be 50 m, which is related to the accuracy of the geo-location technology in use). The issues inherent with self-geo-location (e.g. latency, accuracy and time to fix) mean that the use cases for these devices tend to be more limited than those for fixed devices.
WSDs provide their location to a given GLDB, which returns information on the available frequencies and permitted transmission settings (e.g. a list of channels on which they may operate, maximum transmit power, etc.). This approach shifts the complexity of spectrum policy conformance out of the device and into the database. This approach also simplifies the adoption of policy changes, limiting updates to the GLDB, rather than numerous devices. It also opens the door for innovations in spectrum management that can incorporate a variety of parameters. In the current approaches, WSD queries typically provide device location, device information (e.g. type, serial number, certification ID, etc.), antenna height (for fixed) and additional identifying information (e.g. device owner). In the future, GLDB can include other parameters, such as user priority, signal type and power, spectrum supply and demand, payment or micro-auction bidding and more.
GLDBs are likely to be provided by third parties authorized or contracted by regulatory agencies. There is also the case that a regulatory agency decides to manage the GLDB on its own, much like an online licencing system. Regulatory agencies can opt to have single or multiple GLDB providers. Competition among multiple database providers can be beneficial to end users, as it is likely to drive innovation and give users greater choice. Regulatory agencies will collect the details of the incumbents’ usage (e.g. DTT, PMSE systems). Incumbent information can range from very detailed planning information gathered from the incumbent user (e.g. detailed planning of the DTT broadcast network) to the information gathered from the registration processes used to protect entities that are eligible to receive interference protection in TV spectrum (e.g. online registration of licenced wireless microphones to operate in a given location). This information can be delivered to the GLDB providers for them to conduct the calculations to apply protection criteria to these systems (e.g. computation of exclusion zones for specific TV channels and sometimes for the adjacent channel as well). Alternatively, a regulatory agency may decide to carry out the bulk of the calculations in-house and deliver to the database very specific information datasets such as the maximum equivalent isotropic radiated power (EIRP) values that a WSD can use at all locations for a combination of parameters. These two approaches are not exclusive and can be combined (e.g. a regulatory agency must decide to keep all the computations for the DTT service and task the GLDB providers with the computations concerning the protection of PMSE equipment). The protection criteria of the methodologies for the protection calculations are commonly established through regulatory proceedings allowing feedback from all stakeholders.
It is worth mentioning that spectrum sensing can also be used to determine the availability of unused channels, though today’s regulations mainly consider spectrum sensing as an optional feature that complements the mainstream geo-location approach. With spectrum sensing, WSDs would try to detect the presence of the protected incumbent services in each of the potentially available channels. Spectrum sensing essentially involves conducting a measurement within a candidate channel, to determine whether any protected service is present. Ideally, spectrum sensing could be used as a stand-alone technique to determine the usability or not of a given channel, not requiring any existing local infrastructure such as connection to a database. However, the fact that measurements are taken only at a given location and the low-power levels that some incumbent signals might have prevent the full reliance on spectrum sensing. The emergence of cooperative sensing, in which devices share their findings, may bring in the future the potential to improve sensing reliability and reinforce the role of the sensing approach into the overall solution [74].
Based on the previous description, Table 6.12 outlines and contrast some of the main characteristics of the US and UK regulations.
Table 6.12 Main characteristics of the US and UK regulatory frameworks for the use of TV white spaces.
FCC regulation [77–79] | Ofcom draft regulation [80] | |
Types of TVWS devices | Fixed devices. Operate at fixed positions and obtain channel availability from databases |
Two main, non-exclusive, dimensions to classify devices:
|
Portable/mobile devices. The location of these devices might change. Two different subtypes:
|
||
Information provided to the GLDB | Unique device identifier | Unique device identifier |
Antenna geographical coordinates and their accuracy (50 m) | Antenna geographical coordinates and their accuracy (50 m) | |
Device type (fixed, Mode I, Mode II) | Technology identifier | |
Device’s antenna height above ground level (meters) | Fixed or portable/mobile nature | |
Contact information of the owner of the device and of the person responsible for the device’s operation | Lower and upper frequency boundaries and maximum EIRP spectral densities of in-block emissions | |
Indoor or outdoor nature (optional) | ||
Antennas’ characteristics (optional) | ||
Power limits | 4 W EIRP for fixed devices | Variable maximum transmit power per location. Power limits are specified in terms of maximum permitted EIRP spectral density (in units of dBm/0.2 MHz). The power limit is a function of the quality of the DTT coverage in the geographical area where the DTT receiver is located. Spatial resolution of the power values that is based on 100 × 100 m geographic pixels. The area of the United Kingdom is covered by over 20M pixels |
100-mW EIRP for personal/portable devices. This is further reduced to 40-mW EIRP in case of operation of these devices in channels adjacent to occupied TV bands channels | ||
50-mW EIRP for sensing-only devices | ||
Additional limits on power spectral density (PSD) are defined considering a uniform distribution of transmit power limits over the channel frequencies. Adjacent channel emission limits are also specified | Additional limits are to be set out in terms of through minimum adjacent channel leakage ratio (ACLR) settings | |
Specification of authorized frequency | A list of permitted TV channels | A list of lower and upper frequency boundaries (not restricted to TV channel boundaries) with a resolution of 100 kHz. Maximum permitted EIRP spectral density for each frequency boundary pair is indicated |
Authorization principle | Licence-exempt regime based on geo-location and database access for spectrum authorization | Licence-exempt regime based on geo-location and database access for spectrum authorization |
Spectrum sensing is not mandatory but optional feature | Spectrum sensing is not mandatory but optional feature | |
Sensing-only devices also permitted (these devices have additional approval requirements and lower power limits) | No provisions for sensing-only devices | |
Authorization validity and rechecking | Database must be checked at least once per day. If channel list cannot be refreshed, it times out next day at 11:59 p.m. | Time validity of parameters (in minutes) is to be provided by the database as part of the channel availability response |
Mode II device needs to check its location at least once every 60 s, except in powered-down modes. Rechecking database must be done if location changes by more than 50 m with respect to previous consultation | The database can send instruction for a WSD to cease transmission in 60 s (i.e. the so-called ‘kill-switch’ feature) | |
Mode I devices must either receive a special signal from the Mode II or fixed device that provided the list of available channels to verify that it is still in reception range of that device or contact a Mode II or fixed device at least once every 60 s to re-verify/re-establish channel availability | ||
Database awareness of the operation of WSDs | Fixed devices shall register their operation in the database | Registration is not mandated |
No provisions for any kind of reporting back to databases from WSDs once channel availability information has been provided | Requirement to have an acknowledgement of receipt of information from WSDs on used channels and EIRPs |
It is also important to note that TVWS operations face some challenges. For example, geo-locating portable WSDs is problematic when trying to support indoor operation or full mobility at high speed. Geo-location accuracy, latency and time-to-fix limitations may not easily support the requirement to re-query the GLDB whenever the device moves more than, for example, 50 m. In addition, the WSD out-of-band emission (OOBE) masks are more stringent than for most unlicenced devices in other bands in order to protect operation close to TV receivers. This OOBE limit has proven difficult to achieve at a cost point low enough to make WSDs further broadly attractive.
Moreover, regulatory uncertainty is also hindering the uptake of TVWS operations. For instance, in the United States, there is an ongoing incentive auction proceeding by the FCC in the 600-MHz band aimed to repack and repurpose some spectrum now used for TV stations and auction it off to mobile licenced services. This poses uncertainties on how much spectrum will be available for TVWS following that auction. Similarly, the future spectrum availability for TVWSD within the TV UHF band in Europe is also unclear [86, 87]. In this regard, co-primary allocations for mobile and broadcasting services between 694 and 790 MHz will be a fact for the EU after WRC-15, so that this band could be used for mobile services in some countries in the near future (around 2020, with some countries like Germany and France already planning the auctioning of this spectrum along 2015), importantly reducing the availability of TVWS. In addition to the 700-MHz band, the possible need and point in time for a further co-primary allocation for broadcasting and mobile services below 700 MHz, that is, 470–694 MHz, is also under discussion for the longer term (beyond 2030) in Europe [38]. However, no consensus has been reached in this case since the sustainability of the current European audiovisual model is highly dependent on the availability of this core spectrum.
In spite of these technological challenges and regulatory uncertainties, the capability of database-enabled devices to operate in vacant TV spectrum without causing interference is already proven (there are hundreds of registrations of database-controlled fixed TVBDs in the United States), paving also the way to apply this concept in other spectrum bands other than the TV bands.
Standards related to the use of TVWS are being addressed in multiple bodies, including the ETSI, IEEE, IETF and ECMA International. A summary of these standardization activities is provided in Table 6.13.
Table 6.13 Summary of standardization initiatives related to TVWS.
Organization | Standardization activities | Comments |
ETSI | TS 103 143, EN 303 144 | System architecture and protocols for the information exchange between different geo-location databases (GLDBs) |
TS 103 145, EN 303 387-1 | System architecture and high-level procedures for coordinated and uncoordinated use of TV white spaces | |
ETSI EN 301 598 | Harmonized EN covering the essential requirements of article 3.2 of the R&TTE Directive | |
IEEE | 802.11af | Specifying enabling technologies in TV white spaces for WLAN systems |
802.22 | IEEE 802.22 is a standard specifying WRAN communication systems operating in TV bands | |
802.15.4 | Specifying enabling technologies in TV white space for low-rate WPAN systems | |
802.19.1 | Coexistence framework for dissimilar systems in 802 standards | |
1900.X | Specifying enabling technologies in TV white space communications | |
ECMA | ECMA-392 | Specifies a medium access control (MAC) sub-layer and a physical (PHY) layer for cognitive wireless networks operating in TVWS bands |
IETF | PAWS | Extensible protocol to obtain available spectrum from a geospatial database by a device with geo-location capability |
Within the ETSI, standardization activities related to TVWS are mainly undertaken within the technical committee on RRS (ETSI TC RRS). In particular, TC RRS has developed the following elements:
Additionally, ETSI has produced the harmonized standard ETSI EN 301 598 [85] covering the essential requirements of the R&TTE Directive concerning the use of WSD in the in the 470–790-MHz band. It’s worth noting that this standard basically focuses on the uncoordinated case since requirements to facilitate coexistence between WSDs were not considered essential with respect to compliance with Article 3.2 of Directive 1999/5/EC. However, this point may be subject to further review in the future.
Within IEEE, a number of working groups in the IEEE 802 LAN/MAN standards committee [92] have also triggered multiple activities related to TVWS usage:
Still within the IEEE, the Dynamic Spectrum Access Networks (DySPAN) standards committee (IEEE DySPAN-SC) develops standards related to TVWS. The scope of the DySPAN-SC includes [96] dynamic spectrum access radio systems and networks with the focus on improved use of spectrum, new techniques and methods of dynamic spectrum access including the management of radio transmission interference and coordination of wireless technologies including network management and information sharing among networks deploying different wireless technologies. There are several working groups. The baseline IEEE 1900.1 standard that defines the terms and definitions in the field of dynamic spectrum access and related technologies and the IEEE 1900.4 standard that specifies the architectural building blocks to enable network-device distributed decision-making for optimized radio resource usage in heterogeneous wireless access networks are already published [97]. Further activities within IEEE DySPAN-SC are conducted by IEEE 1900.5 Working Group on ‘Policy Language and Policy Architectures for Managing Cognitive Radio for Dynamic Spectrum Access Applications’, IEEE 1900.6 Working Group on ‘Spectrum Sensing Interfaces and Data Structures for Dynamic Spectrum Access and other Advanced Radio Communication Systems’ and IEEE 1900.7 Working Group on ‘White Space Radio Working Group’, this latter aimed at specifying a radio interface for white space dynamic spectrum access radio systems supporting fixed and mobile operation.
Within ECMA International, an industry association dedicated to the standardization of ICT and consumer electronics (CE), the standard ECMA-392, ‘MAC and PHY for Operation in TV White Space’ [98], has also been produced (it was released as early as 2009 and later revised in 2012). ECMA-392 specifies a medium access control (MAC) sub-layer and a physical (PHY) layer for cognitive wireless networks operating in TVWS bands. The standard also specifies a multiplexing sub-layer to enable the coexistence of concurrently active higher layer protocols within a single device and a number of incumbent protection mechanisms which may be used to meet different regulatory authorities requirements, which themselves are outside of the scope of the standard.
Within the IETF, a Protocol to Access White Space (PAWS) databases to address interaction with the databases has been standardized [99]. This specification defines an extensible protocol that can be used to obtain available spectrum from a geospatial database by a device with geo-location capability. The work is based on the assumption that the database will be reachable via the Internet and that radio devices too will have some form of Internet connectivity, directly or indirectly. The protocol supports the following main functions:
Not all of the specified PAWS functions are necessarily mandated in a given regulatory framework. Some functions can be optional or just not used depending on the regulatory domain and database implementation. The IETF has reused existing protocols and data encoding formats where possible for the specification of PAWS. In particular, PAWS is based on the use of HTTP Secure (HTTPS) for information exchange between the WSD and the GLDS, and JSON-RPC request/response objects are used to encode the exchanged information elements.
The access to TVWS by PPDR users can bring additional spectrum for PPDR communications. The long-reaching and highly penetrative signal capabilities of this spectrum make it especially valuable in hard-to-reach areas (e.g. tunnels, building basements) as well as in low or very low populated areas where an important part of this spectrum might remain underutilized.
Based on the prevailing regulatory approach being adopted for the operation of WSDs (described in Section 6.5.3.1), the following challenges shall be considered for the potential exploitation of TVWS by PPDR applications:
A functional architecture for the exploitation of TVWS for PPDR was developed within the EU research Project HELP [72]. This functional architecture, reproduced in Figure 6.9, is intended to enable and control the use of TVWS spectrum in a PPDR network. LTE is assumed to be the technology in use. The solution encompasses the following functional components:
Regarding the communication interfaces depicted in Figure 6.9, interface (A) is used for GLDB access and could be based on the IETF PAWS protocol. Interface (B) forms part of the protocols used by the NMS to remotely access to network elements and manage them, thus leveraging/extending the protocols used for network management. Interfaces (C) and (D) are technology dependent (e.g. LTE interface adapted for use in TV bands, IEEE 802.11af interface) as they actually support the radio transmissions. Interface (E) is needed for the registration of entities that are eligible to receive interference protection in TV spectrum. Web-based interfaces can be a solution for this interface. Finally, interface (F) represents the Application Programming Interfaces (APIs) that are reachable in control room systems (CRS) to develop applications enabling tactical and operational PPDR managers to have control on the capacity and coverage of the network, including the use of TVWS spectrum (e.g. the use of TVWS within the network can be enabled or disabled from control room positions).
The implementation of this spectrum sharing solution requires that the configuration of LTE hardware installed in eNBs can be adjusted to operate in TV UHF bands. There are certain aspects that need to be considered for LTE to operate in TVWS:
Indeed, the implementation of this spectrum sharing solution could leverage the technological enhancements being targeted under 3GPP Release 13 for the operation of LTE in unlicenced spectrum [101], commonly referred to as LTE-U. These enhancements are expected to introduce a so-called Licenced-Assisted Aggregation (LAA) operation mode in LTE to aggregate a primary carrier (using licenced spectrum, to deliver critical information and guaranteed QoS) and a secondary carrier (using unlicenced spectrum, to opportunistically increase capacity and data rates). The secondary carrier operating in unlicenced spectrum could be configured either as downlink-only carrier or contain both uplink and downlink. While current work in LTE Release 13 is on the use of LTE in the 5-GHz band, the underlying principles and technologies could be directly extended to other unlicenced bands (e.g. 2.4 and 3.5 GHz, TVWS).
The opportunistic nature of the usage of the TVWS does not fit well with the deployment of services that require provisioning of QoS as there is uncertainty about the availability of spectrum resources and there is no protection from harmful interference from other WSDs. However, different measures could be considered by the regulatory authority to increase the degree of reliability and QoS guarantees on the exploitation of TVWS for PPDR: