1.FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 154ACCEPTED FROM OPEN CALLLTE: The Technology Driver for Future Public Safety Communications Ramon Ferrs and Oriol Sallent, Universitat Politcnica de Catalunya Gianmarco Baldini and Leonardo Goratti, Joint Research Center European CommissionABSTRACTThe views expressed are those of the authors and cannot be regarded as stating an official position of the European Commission.154INTRODUCTIONWireless communications technologies play an essential role to support the Public Protection and Disaster Relief (PPDR) operational needs. The current Private/Professional Mobile Radio (PMR) technologies used for PPDR communications offer a rich set of voice-centric services but have very limited data transmission capabilities, which are unable to handle the increasing PPDR community demand for a wider range of data-centric services. Though some efforts have been devoted to upgrade PMR technologies with better data transfer capabilities, the progression towards an enhanced mobile broadband PMR standardized solution still lags behind the achievements made in the commercial wireless industry, which recently culminated in LongTerm Evolution (LTE) technology. Because of this contrasting progress, the adoption of commercial mainstream LTE technology to satisfy the PPDR communitys data communication needs is gaining momentum and offers significant opportunities to create and exploit the synergies between the commercial and PPDR domains, which have remained almost entirely separate to date. In this context, this paper first discusses the suitability of LTE and related technologies for mobile broadband PPDR service provisioning. Next, it presents the argument that the most plausible future scenarios to deliver the increasingly data-intensive applications demanded by the PPDR agencies are expected to rely on the use of both dedicated and commercial LTE-based mobile networks. From this basis, the paper proposes a system architecture solution for PPDR service provisioning that enables PPDR service access through dedicated and commercial networks in a secure and interoperable manner and ensures proper allocation of the networks capacity to PPDR applications through the dynamic management of prioritization policies. In addition, the spectrumrelated issues that are central to the proposed PPDR service provisioning solution are addressed, and a solution based on the joint exploitation of dedicated and shared spectra is proposed.In Europe, many countries have deployed dedicated radio networks for PPDR communications based on Private/Professional Mobile Radio (PMR) technologies, such as TETRA and TETRAPOL. While these technologies offer a rich set of voice-centric services (e.g., group call with Push-to-Talk (PTT) features), they provide a very limited range of data services. Though some efforts have been devoted to upgrade the PMR standards with wideband data capabilities, the progression towards an enhanced mobile broadband PMR standardized solution lags behind the achievements of the commercial wireless industry. The technological advances in the commercial domain have led to top-of-the-line radio technologies. The state of the art is Long-Term Evolution (LTE) mobile broadband technology, which is currently positioned to become a prevalent technology in most future commercial mobile networks. In this context, the adoption of commercial mainstream LTE technology to deliver the increasingly dataintensive applications demanded by PPDR agencies is gaining strong momentum among the PPDR community [1, 2]. Establishing common technical standards for the PPDR and commercial domains offers significant opportunities for creating and exploiting the synergies between these two domains. A harmonized market for PPDR broadband devices and the infrastructure equipment can maximize the economies of scale. Some studies have anticipated that the components that add the highest customization costs in the devices (i.e., operating system, baseband chipset, and radio frequency chipset) can be 100 percent leveraged [3]. Furthermore, grounded on the use of common technical standards, a synergic operation of dedicated PPDR networks and commercial mobile networks can be pursued to overcome the lack of capacity, interoperability, and broadband data rates that commonly arise in emergency scenarios. This article proposes a solution framework for the provision of PPDR services that considers the involvement of both dedicated and commercial LTE-based mobile networks and allows0163-6804/13/$25.00 2013 IEEEIEEE Communications Magazine October 2013

2. FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 155External IP networks (Internet, corporate networks, operator services) Application serversIMSRx PCRFHSSP-GW Gx S5/S8S6a MMELTE has been designed to provide a high-rate, very-low-latency IP connectivity service between User Equipment (UE) and external IP networks, referred to as Packet Data Networks (PDNs). This IP connectivity service can be utilized by almost any application relying on IP communication, enabling a large number of services to be provided over LTE networks. An LTE network consists of two main parts [4]: the radio access network, known as Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), and the Evolved Packet Core (EPC). E-UTRAN is mainly responsible for radio transmission functions, while the session and mobility management functions are handled by the EPC. E-UTRAN consists of base stations called evolved NodeBs (eNBs) that implement the whole radio protocol stack. The EPC comprises a Mobility Management Entity (MME), which handles the control functions (e.g., location management), a Serving Gateway (S-GW), which anchors user traffic from/to the E-UTRAN into the EPC, and a PDN Gateway (P-GW), which provides the IP connectivity to the external IP networks. The operation of the EPC is assisted by the Home Subscriber Server (HSS), a central database that contains, among other things, user subscription-related information. The LTE IP connectivity service is realized through the establishment of Evolved Packet System (EPS) bearer services between the UE and P-GW. The EPS bearer represents the level of granularity for the quality of service (QoS) control. IP-based service control platforms, such as the IP Multimedia Subsystem (IMS) also part of the 3rd Generation Partnership Project (3GPP) specifications, can be used in addition to this QoS-aware LTE connectivity service to support advanced multimedia services. 3GPP has also specified a Policy and Charging Control (PCC) system, which provides the operators with advanced tools for service-aware QoS and charging control. The PCC architecture, through the Policy and Charging Rules Function (PCRF) entity, enables the control of the EPS bearers (e.g., QoS settings) for both IMS and non-IMS services. Figure 1 illustrates the LTE network components and main interfaces among these components, as well as the concept of the EPS bearer service.IEEE Communications Magazine October 2013S1-MME E-UTRANLTE AS A TECHNOLOGY ENABLER PPDR BROADBAND SERVICESFORS11S-GW S1-ULTE networkeNBX2 eNBCell UuEPC bearer(s) for IP packet transferCxEPCthe PPDR users to have a tight control of the service provisioning and network resources. To this end, we first discuss the suitability of LTE technology for PPDR service provisioning. We then describe a plausible system view for future PPDR networks based on the coexistence of dedicated and commercial infrastructures. From this basis, we develop the proposed system architecture and address the radio-spectrumrelated issues that are central to the proposed solution. Finally, a discussion on current outstanding initiatives concerning the use of LTE for PPDR is provided, leaving our main conclusions for later.UEFigure 1. Basic architecture of an LTE network.PROVISIONING OF PPDR SERVICES OVER LTE A diverse range of data, imaging, and multimedia applications is currently in demand within the PPDR community. The demand is being driven by changes in working practices, requiring access to a far wider range of multimedia sources (textual, images, and video). Some examples of mobile data applications being demanded are video on location, mobile office applications and online database enquiry [5]. Most of the new in-demand PPDR services are data-centric services that can be implemented in client and server applications residing on terminals and network servers. This type of services only requires IP connectivity between clients and servers so they can be made readily available through the basic IP connectivity service provided by LTE. In addition to LTE, standardized commercial technologies, such as IMS and a number of service enablers specified by the Open Mobile Alliance (OMA), can also be leveraged for the realization of IP-based multimedia services tailored to PPDR users. There are IMS-based solutions, such as Voice over LTE (VoLTE) and OMA Push-to-Talk over Cellular (PoC), which can be adopted for the implementation of enriched PMR-like services over LTE capable of one-to-many, voice/video/data communication with PTT capabilities. In the longer term, the support of PMRlike services over LTE is crucial for facilitating the convergence of legacy PMR services and emerging data-intensive/multimedia PPDR services over the same infrastructure.PRIORITIZATION OF PPDR SERVICES OVER LTE The capability to ensure that important connections/calls are always established is essential for mission-critical PPDR communications. Preferential treatment for access to and utilization of155 3. FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 156PPDR domainCommercial domain PPDR service platforms control roomsLegacy PMR network (e.g. TETRA, TETRAPOL, P25)LTE dedicated PS network(s)LTE and legacy 3G commercial network(s)Access to PPDR services from commercial networksPMR/LTE multimode terminalsGroup communications across networksFigure 2. System view of the future PPDR networks. LTE network resources can be supported as a realization of the Multimedia Priority Service (MPS) specified by 3GPP. MPS is a subscription-based service that creates the ability to deliver and complete high-priority sessions in times of network congestion. A set of priority levels shall be defined and granted to authorized MPS subscribers. These MPS levels are then used to select the QoS parameters of the EPS bearer(s) that will enforce the desired preferential treatment, including pre-emption. The decision making on the appropriate setting of an EPS bearers QoS parameters (e.g., QoS Class Identifier (QCI), Allocation and Retention (ARP) and Guaranteed Bit Rate (GBR)) is handled by the PCRF entity according to the network operator policy. The inputs for the PCRF decisions can consist of subscription-related information (e.g., MPS priority level) as well as dynamic session information provided to the PCRF by application servers and/or IMS platforms involved in the user session signaling (e.g., the interface Rx shown in Fig. 1). In addition to QoS settings, the MPS priority level is also used to grant the MPS subscriber with one or more of the special access class categories used in E-UTRAN to prevent an overload of the radio interface control channels by restricting access attempts from some users.SYSTEM VIEW OF FUTURE PPDR NETWORKS There is a wide consensus among PPDR organizations regarding the need of dedicated Public Safety Networks (PSNs) for mission-critical communications because commercial Public Mobile Networks (PMNs) are not considered able to provide the required degree of service availability, reliability, and security. Nevertheless, the significant investment required to rollout dedicated PSNs may not be considered convenient or even affordable for some public administrations. Hence, while some countries can deploy new dedicated PSNs with nationwide coverage, others may decide to cover only some critical areas156with dedicated infrastructures or to rely exclusively on PMNs. Even when dedicated PSNs can be rolled out, the unpredictable nature of the time, place, and scale of an incident renders it virtually impossible to ensure that the first responders will have proper support from the PSNs during the emergency (e.g., due to lack of coverage, capacity, or damaged infrastructure). In this context, significant opportunities for creating and exploiting synergies between PMNs and PSNs arise. Synergies can produce a number of benefits, including increased aggregate capacity, improved resiliency and enhanced radio coverage. Consequently, the use of PMNs is anticipated to be a cornerstone for the provisioning of emerging data-intensive/multimedia PPDR services, yet the level of dependability on dedicated and/or commercial networks and their use can be quite varied across countries and regions. The introduction of LTE for PPDR is expected to complement, not replace, the existing legacy PMR networks (e.g., TETRA/TETRAPOL/Project 25 (P25)/Analog PMR), which will continue to be the standards for mission critical voice service for at least the next 10 years. Therefore, interworking services with legacy systems and the adoption of PMR/LTE multimode UE will also be fundamental to PPDR users. Figure 2 depicts such a system view of the future PPDR networks and illustrates the cases where access to specific PPDR services (e.g., communications with control rooms and access to PPDR service platforms) is achieved while attached to a commercial network, group call communications are established among PPDR users connected through the different networks, and the service continuity between networks is provided through multimode PMR/LTE terminals.FUTURE PPDR SERVICE PROVISIONING: SYSTEM ARCHITECTURE Our system view of future PPDR network scenarios with coexisting dedicated LTE-based PSNs and PMNs raises a number of technical challenges. In particular, the PPDR service provisioning solutions shall encompass capabilities to: Enable PPDR service access through PSNs and PMNs in a secure and interoperable manner Ensure a proper allocation of the network capacity to PPDR users according to the established prioritization policies Though several approaches are possible, a solution allowing PPDR users to have a tight control of the mentioned capabilities is proposed. The core infrastructure of this solution (depicted in Fig. 3) consists of IMS functions, application servers, and a given set of 3GPP network components (i.e., HSS, PCRF, and P-GW), all interconnected by means of a private IP network. This core infrastructure will be used to provide PPDR services to the users in the field equipped with LTE-enabled PPDR terminals through a number of dedicated LTE-based PSNs and/orIEEE Communications Magazine October 2013 4. FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 157Control room systems Dispatch position(s)Priority access management applicationS6d Service management applicationUser management applicationMMES8S-GWCommercial LTEbased PMN(s) S1-MME S1-UeNBThere is a wide consensus among PPDR organizations regarding the need of dedicated PublicAPI interfaces LTE Uu Core infrastructure RxPCRFNetworks and terminals management interfacesNetwork management system (NMS)AF IMS functionsPPDR terminal USIMSpSPRApplication clientsHSSRxLegacy PSC radio interface LTE Uu*AF Application serversPrivate IP networkGxmunications because commercial Public Mobile Networks are not considered able to provide thePCEFS6aMMEP-GW GW functionsSafety Networks for mission-critical com-S-GWS1-MMErequired degree ofS1-Uservice availability,S5 eNB Dedicated LTE-based PSNreliability, and security.Interfaces to legacy PSNs BS Legacy PSN (e.g. TETRA, TETRAPOL networks)Figure 3. System architecture to support access to commercial networks on a priority basis with service interoperability across PSNs and PMNs. commercial PMNs interconnected by means of standardized 3GPP interfaces (e.g., S5/S8 for data transfer and S6a/S6d for signaling transfer [4]). The LTE interface of PPDR terminals may have added functionality when connected to LTE PPDR broadband technology while being backward compatible with commercial LTE access. This core infrastructure will also be interconnected through Application Programming Interfaces (APIs) to Control Rooms Systems (CRSs) used for tactical and operational management. CRSs can include dispatch applications to communicate with users in the field as well as control and monitoring applications to address the administrative and operational issues of the provided PPDR services. The operation of this core infrastructure, along with the dedicated PSNs, will be managed by a PSN operator through a Network Management System (NMS). Further details on the required capabilities for PPDR service access and prioritization management are provided in the next section.ACCESS TO PPDR SERVICES FROM PSNS AND PMNS Access to an LTE network is controlled through the management of the subscription information (e.g., IMSI, security keys, and service profile) handled by the Universal Subscriber Module Identity (USIM) module on the terminal side and by the central HSS database on the network side. Maintaining control over such PPDR subscription information is essential to the tactical and operational PPDR managers because it allows PPDR users to completely manage the user provisioning process (e.g.,IEEE Communications Magazine October 2013activation/removal of subscribers) and to establish the required subscriber capabilities (e.g., subscriber service profiles). Therefore, as depicted in Fig. 3, the envisioned solution considers that PPDR users will deploy their own HSS as part of the core infrastructure and issue and control their own USIM cards. This solution would be a natural choice in the case that PPDR users can afford to deploy dedicated LTE-based PSNs. The dedicated networks will have their own Public Land Mobile Network Identifiers (PLMN IDs) and PPDR users, or a governmental agency or private PS specialized service provider on their behalf, would serve as full Mobile Network Operators (MNOs). If no dedicated PSNs are rolled out, the proposed solution can be viewed as a possible realization of the Mobile Virtual Network Operator (MVNO) model in which the MVNO has its own PLMN ID but relies exclusively on the network capacity provided by the commercial MNOs. This solution allows PPDR users to get access through a number of commercial MNOs without changing its PPDR users USIM cards. The realization of this solution requires both roaming agreements to be established among PPDR users and commercial operators and the deployment of the associated a signaling interfaces to support the roaming service between the PPDR core infrastructure facilities and participating commercial PMNs (i.e., S6d interface [4]). Control and administration of the PPDR subscribers data will be realized through specific User Management Applications integrated within the CRS. The proposed solution also considers that the PPDR core infrastructure integrates its own dedicated P-GW so that the IP connectivity service157 5. FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 158Although the inherent spectrum flexibility of the LTE standard is a technological facilitator, the political, regulatory, and economical facets will have greater influence on the final solutions to be adopted.can be autonomously managed (e.g., private IP address allocation). This approach also facilitates seamless mobility across PSNs and PMNs with the P-GW serving as a mobility anchor point for PPDR traffic. Hosting the P-GW within the PPDR core infrastructure requires the deployment of an additional interface (i.e., S8 interface [4]) with the commercial networks, which shall support access through external PGWs (i.e., a home-routed roaming configuration [4]). End-to-end security can be further improved by deploying PPDR-customized Mobile Virtual Private Network (VPN) solutions between the terminals and PPDR core infrastructure. Enabled by IP connectivity through the PPDR P-GW, the delivery of PPDR services will rely on the IMS service control functionalities, a number of server applications and a number of related client applications installed in the PPDR terminals. Dynamic management of the provided service capabilities will be possible through specific Service Management Applications within CRS so that PPDR users in the control rooms can adjust PPDR service provisioning to specific operational needs (e.g., creation of groups) or to address unexpected events during the emergency crisis. Solutions for the terminals client applications downloading and installation can also be considered for PPDR terminal programming and customization (e.g., the likes of popular applications stores in the commercial domain), along with other post-manufacturing terminal configuration performed via Mobile Device Management (MDM) software solutions (e.g., OMA Device Management).PRIORITIZATION MANAGEMENT The solution depicted in Fig. 3 is a possible realization of the MPS in which a PCRF functionality is allocated within the PPDR core infrastructure. In addition to the PCRF entity, the proposed implementation also considers the following 3GPP functional entities: an Application Function (AF) located within IMS and the application servers, which is needed for the dynamic invocation of MPS and transferring dynamic session information to PCRF (e.g., the requested media types and session/application priority extracted from IMS signaling); the Service Profile Repository (SPR), which contains the subscriber-related information (e.g., users MPS priority level and allowed services) and can be integrated within the HSS; and the Policy and Charging Enforcement Function (PCEF), which is located at the P-GW and is used to enforce the policy decisions in the user data plane (e.g., rate control). This solution enables operational and tactical PPDR managers in the control rooms to have direct control on the priority policies applied to the PPDR traffic. Therefore, through Priority Access Management Applications in CRS, PPDR managers would be able to configure the information and rules used by the PCRF of the PPDR core infrastructure for QoS decision making. Thus, PPDR users will be able to dynamically enforce the desired priority access policies that may consider not only the relative priority of a particular user based on their agency affiliation but also the situational context of158applications (e.g., mission critical) or type of emergency. The deployment of this solution through commercial PMNs requires policies and related QoS parameters used for prioritization management to be harmonized and agreed upon by both the commercial operators and PPDR users. Limits on the maximum capacity allocated for proper PPDR and commercial traffic sharing shall be determined as well. The establishment of a welldefined, validated policy framework for prioritization management is essential to avoid uncertainties in network congestion situations and to eventually increase their trust in the operation of prioritization. All of these aspects must be considered in the formulation of the roaming and service level agreements to be established among PPDR users and commercial operators [6].FUTURE PPDR SERVICE PROVISIONING: SPECTRUM MANAGEMENT Clearly, the deployment of future dedicated LTE-based PSNs raises the issue of identifying the spectrum band(s) and spectrum management model(s) on which these networks will be deployed and operated. Although the inherent spectrum flexibility of the LTE standard is a technological facilitator, the political, regulatory, and economical facets will have greater influence on the final solutions to be adopted. The allocation of a dedicated, exclusive-use spectrum has been the traditional approach to support PPDR communications and is the preferred option of the PPDR community. Nevertheless, dedicated spectrum is not well matched to the dynamics of PPDR spectrum needs, which show a high fluctuation between the amount of spectrum needed in major incidents/events and that used for daily routine tasks. Therefore, driven by the growing competition for spectrum and the requirement that the spectrum be used more efficiently, innovative spectrum sharing solutions are needed for PPDR communications to have instant and reliable access to sufficient spectrum while simultaneously improving the overall spectrum utilization [7]. In this context, our envisioned approach for wide-area coverage in future PPDR network scenarios (depicted in Fig. 4) consists of a hybrid solution based on the joint exploitation of two categories of spectrum for PPDR: dedicated and shared spectrum. The dedicated spectrum is for exclusive use by PPDR and shall be sufficient to satisfy PPDR needs for mission-critical communications in most operational scenarios. Investment in dedicated PSNs is believed to be fully contingent upon the allocation of some amount of dedicated spectrum below 1 GHz. In the United States (US), a total of 10+10 MHz spectrum in the 700 MHz band has been already designated. In Europe, a need in the range of 10+10 MHz [8] has been initially identified and spectrum regulatory authorities have started the process of finding a proper spectrum allocation. As discussed inIEEE Communications Magazine October 2013 6. FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 159The FirstNet boardA. Dedicated PPDR spectrumexclusive usehas already noted that building a dedicated standaloneEU second dividendnetwork would be infeasible from a 960 MHzIMT, GSM-R 862 MHz 870 MHz790 MHzCivilian PMR 694 MHzCurrent narrowband PPDR allocationTV broadcast 470 MHzCivilian PMR 380 MHz225 MHzMilitarycost standpoint, so partnerships with network operators will be essential to leverage theB. Shared PPDR spectrumexisting networkFigure 4. Dedicated and shared spectrum for PPDR communications in Europe.the next section, the two most propitious candidate bands in Europe are 400470 MHz and 694790 MHz. The shared spectrum represents an additional spectrum that is not exclusively assigned to PPDR but shared with other domains. This spectrum can provide additional capacity to better cope with a surge of PPDR traffic demand during an emergency situation. Two potential nonmutually exclusive, spectrum-shared components are envisioned for exploitation for PPDR: Secondary access to television (TV) white spaces (WSs) [9]. Good propagation conditions and the anticipated high availability of TV WS in low populated areas (e.g., rural areas) make this spectrum a valuable asset also for PPDR communications. Further regulatory/technical extensions could be conceived to increase the reliability of this spectrum for PPDR use (e.g., higher authorized maximum transmission power for PPDR equipment and/or support of priority access PPDR applications). Temporary licensed access to some shared bands, aligned to the concept of the Licensed Shared Access (LSA) model [10]. A LSA regime is intended to enable a dynamic use of shared spectrum with predictable QoS. In the context of a possible European Union (EU) second digital dividend in the 700 MHz band, this model can be introduced to share some amount of spectrum between the commercial and PPDR network operators. Furthermore, the military bands offer another challenging case in which the LSA concept might be conveniently exploited. The European Comission (EC) standardisation mandate (M/512) issued in November 2012 pursues the study of architectures and interfaces for the dynamic use of spectrum resources among commercial, civil security, and military applications for disaster relief. In addition to the proposed hybrid solution to support wide-area PPDR communications, additional spectrum above 1 GHz will also be used for local-area communications. In Europe, resolution ECC/REC/(08)04 for the implementationIEEE Communications Magazine October 2013infrastructures.of Broad Band Disaster Relief (BBDR) radio applications, issued by European Conference of Postal and Telecommunications Administrations (CEPT), recommends countries administrations make at least 50 MHz of spectrum available within two possible frequency bands: 5,150-5,250 MHz (the preferred option) and 4,940-4,990 MHz (which coincides with the band allocated in the US and some other countries). This amount of spectrum in 5 GHz can permit PPDR agencies to implement on-scene broadband wireless networks (e.g., permanent hot-spot devices in high-use areas or temporary incident command centers erected at an incident scene) and establish temporary fixed links.STATE OF PLAY Most leading operators, device, and infrastructure manufacturers support LTE as the mobile technology for the future. The first commercial LTE networks were launched in December 2009 and, as of January 2013, there are more than 100 LTE networks in service in over 60 countries, and many additional trials and deployments are underway. In the PPDR arena, as early as 2009, the National Public Safety Telecommunications Council (NPSTC) and other organizations in the US endorsed LTE as the technological standard for broadband PPDR communications. Some PPDR entities were given waivers by the US Federal Communications Commission (FCC) [1] along with federal stimulus grants to pursue the early deployment of statewide or regional LTE-based PSNs. Many of these networks were scheduled to begin operating in 2013, but the deployments were halted during 2012 to ensure the initiatives to get on track with the plans of the First Responder Network Authority (FirstNet), an independent authority within the National Telecommunications and Information Administration (NTIA) tasked with overseeing the development of a nationwide LTE-based PSN with a total of 10+10 MHz spectrum and $7 billion in funding. The FirstNet board has already noted that building a dedicated standalone network would be infeasible from a cost159 7. FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 160ASTRID, the Belgium national provider of mission critical communications through a nationwide TETRA network, has already unveiled its plans to become a MVNO and offer mobile data services to its PPDR users through the commercial 3G/LTE networks.160standpoint, so partnerships with network operators will be essential to leverage the existing network infrastructures [11]. In Europe, the LTE standard is also increasingly backed as the technology of choice for the evolution of current PMR networks [2]. Nevertheless, the main discussion is still centered on the allocation of European- harmonized spectrum for broadband PPDR, a task being primarily addressed through the CEPT Project Team FM49 started in September 2011. Below 1 GHz, the two main candidate bands under consideration are the 400-470 MHz band, which is widely used by two-way radio, and the 694790 MHz band, which is primarily used for TV broadcasting but expected to be allocated to the mobile service after 2015 on a co-primary basis. The allocation of some spectrum in the 400-470 MHz band is feasible in many countries, but there is no chance for a single harmonized band, as was achieved for the current 5+5 MHz allocation for narrowband PPDR communications. Alternatively, the 694-790 MHz band is a viable option to enable the necessary harmonization, but this option would require a second digital dividend and a new reallocation of TV broadcasters, which is not supported by some national administrations. A decision from PT FM49 is not expected before 2014, and the opinion of industry organizations, such as the TETRA and Critical Communications Association (TCCA), is that dedicated LTE-based PSNs using harmonized frequencies and standards can be eventually realized by approximately 2020. Given such a long-term perspective, the TCCA recognizes that commercial networks can be the solution to provide wide/broadband data capacity moving forward [12]. In this regard, ASTRID, the Belgium national provider of mission critical communications through a nationwide TETRA network, has already unveiled its plans to become a MVNO and offer mobile data services to its PPDR users through the commercial 3G/LTE networks. At a standardization level, cooperation has been established between 3GPP and other groups, such as ETSI Technical Committee (TC) TETRA, TCCA, and the US National Institute of Standards and Technology (NIST), to ensure a broad representation of the PPDR community and carry out the specification of the additional LTE features that will increase the suitability of the LTE technology for PPDR. In this regard, support for device-to-device communications and enhanced group communications over LTE was recently agreed upon as two strategic areas to be prioritized in LTE Release 12, scheduled for June 2014. In addition to PPDR, these two areas are also important to raise new business opportunities in the commercial and other professional sectors (e.g., transportation, utilities, and government). Device-to-device communications is being addressed by the Proximity-based Services (ProSe) Work Item (WI). ProSe capability is intended to satisfy the need for direct/talk-around communication among PPDR users in even the absence of network coverage. Proximity-based services are to be complemented with enhanced group communications withPTT features. The WI Group Communication System Enablers for LTE (GCSE_LTE) will establish the requirements as relevant to improve LTE for group communications and will define the functional split between the application and network layers. This work will determine whether new native LTE features have to be added to the standard to more efficiently support group communications. In addition to ProSe and GCSE_LTE features, the delivery of PMR-like services over LTE will also benefit from the enhancements being introduced for the VoLTE service, such as the bundling of transmission opportunities for terminals at cell edges to improve the uplink power budget. Furthermore, the specification of a high-power UE class is underway to further increase the coverage range of PPDR terminals.CONCLUDING REMARKS The adoption of LTE as the common technical standard for PPDR and commercial mobile broadband offers significant opportunities for creating and exploiting the synergies between both domains. After a discussion on the suitability of LTE to cope with the new demand of PPDR data-centric services, this article has proposed a system architecture that enables PPDR service access across a number of LTE-based dedicated and commercial networks and is conceived to allow the PPDR users to have a tight control of the service provisioning and network resources. The solution can be implemented through a MVNO model in the case that no dedicated LTE networks are deployed. The control of PPDR priority access policies to commercial networks is a cornerstone of the proposed solution. The article has also discussed spectrum-related issues that are central to planning investments in future PSNs and proposed a solution for the management of the PPDR spectrum based on the joint exploitation of both dedicated and shared spectra. Finally, main initiatives towards the introduction of LTE for PPDR in the US and Europe has been discussed, noting the technical work currently being undertaken within 3GPP to further increase the suitability of the LTE standard for PPDR and other professional sectors.ACKNOWLEDGEMENTS The research leading to these results received funding from the European Unions Seventh Framework Programme (FP7/2007-2013) under grant agreement n 261659. Part of this work has also been supported by the Spanish Research Council and FEDER funds under ARCO grant (ref. TEC2010-15198). The authors are grateful to the other members of the consortium, the User Advisory Board (UAB), and Operator Advisory Board (OAB) for their valuable support and contributions. Special thanks for their valuable comments and suggestions are given to R. Pisz (DataX), P. Hirst (British APCO), S. Delmas (Cassidian), E. Bovim (National Centre on Emergency Communication in Health), D. Clavero (Vodafone), P.D Lansard (Orange), C. Lluch (COIT), and D. Radis (BITE).IEEE Communications Magazine October 2013 8. FERRUS_LAYOUT_Layout 9/27/13 12:26 PM Page 161REFERENCESBIOGRAPHIES[1] Federal Communications Commission (FCC), Third Report and Order and Fourth Further Notice of Proposed Rulemaking In the matter of implementing a Nationwide, Broadband, Interoperable Public Safety Network in the 700 MHz Band, Document FCC 11-6, January 2011 [2] M. Nouri, Selection of A Broadband Technology for TETRA, Chairman of TC TETRA Working Group 4 (HighSpeed Data). Presentation available online at TETRA Association website, http://www.tetramou.com/Library/Documents/Files/Presentations/FutureVision2009Nouri.pdf. [3] The Public Safety Broadband Wireless Network: 21st Century Communications for First Responders, Public Safety Homeland Security Bureau, Federal Communications Commission, Mar. 2010. [4] M. Olsson et al., SAE and the Evolved Packet Core, Academic Press, 2009, ISBN 978-0-12-374826-3. [5] LEWP-RCEG (Radio Communication Expert Group of the Law Enforcement Working Party of the European Council), Draft PPDR Applications Catalogue, available at http://www.cept.org/Documents/fm49/4618/FM49(12)001_PPDR-applications-catalogue. [6] R. Hallahan and J. M. Peha, Policies for Public Safety Use of Commercial Wireless Networks, 38th Telecommun. Policy Research Conf., Oct. 2010. [7] R. Ferrus et al., Public Safety Communications: Enhancement Through Cognitive Radio and Spectrum Sharing Principles, IEEE Vehic. Tech. Mag., vol. 7, no. 2, June 2012, pp. 5461. [8] ETSI TR 102 628, Additional Spectrum Requirements for Future Public Safety and Security (PSS) Wireless Communication Systems in the UHF Frequency, Aug. 2010. [9] Federal Communications Commission (FCC), Third Memorandum Opinion and Order Unlicensed Operation in the TV Broadcast Bands, Document FCC 12-36, Apr. 2012. [10] CEPT ECC FM Project Team 53 on Reconfigurable Radio Systems (RRS) and Licensed Shared Access (LSA), Public website: http://www.cept.org/ecc/groups/ecc/wgfm/fm-53/page/terms-of-reference. [11] F. Craig Farrill, FirstNet Nationwide Network (FNN) Proposal, First Responders Network Authority, Presentation to the Board, Sept. 25, 2012, available at http://www.ntia.doc.gov/files/ntia/publications/firstnet_f nn_presentation_09-25-2012_final.pdf. [12] R. Davis, Developing The Business Case For Critical Communications Broadband, PMR Summit/Professional LTE 2012, Barcelona, Sept. 2012.R A M O N F E R R S (ramon.ferrus@upc.edu) received the Telecommunications Engineering and Ph.D. degrees from the Universitat Politcnica de Catalunya (UPC) in 1996 and 2000, respectively. He is currently an Associate Professor in the Department of Signal Theory and Communications at UPC. His research interests include network architectures, protocols, radio resource and spectrum management for wireless communications. He has participated in several research projects within the European Commission 6th and 7th Framework Programmes as well as in research and technology transfer projects for private companies. He is co-author of one book on mobile communications and over 60 papers published in peer reviewed international journals, magazines and conference proceedings.IEEE Communications Magazine October 2013ORIOL SALLENT (sallent@tsc.upc.edu) is Full Professor at the Universitat Politcnica de Catalunya. His research interests are in the field of mobile communication systems, especially radio resource and spectrum management for cognitive heterogeneous wireless networks. He has published more than 200 papers in international journals and conferences. He has participated in more than 20 research projects of the 5th, 6th and 7th Framework Programme of the European Commission and served as a consultant for a number of private companies.The adoption of LTE as the common technical standard for PPDR and commercial mobile broadband offers significant opportunities for creating and exploiting the synergies between both domains.G IANMARCO B ALDINI (gianmarco.baldini@jrc.ec.europa.eu) completed his degree in 1993 in Electronic Engineering from the University of Rome La Sapienza with specialization in Wireless Communications. He has worked as Senior Technical Architect and System Engineering Manager in Ericsson, Lucent Technologies, Hughes Network Systems and Selex Communications before joining the Joint Research Centre of the European Commission in 2007 as Scientific Officer. His current research activities focus on standardization of wireless communication technologies, security and privacy in Internet of Things. He has published more than 40 papers on wireless communications and security topics. LEONARDO GORATTI (leonardo.goratti@create-net.org) received his M.Sc. in Telecommunications engineering in 2002 from the University of Firenze. From 2003 until 2010, he worked at the Centre for Wireless Communications Oulu, Finland, where he obtained his Ph.D in 2011. Until February 2013 he worked with the European Joint Research Centre of Ispra, Italy. His research interests cover MAC protocols for wireless personal/body area sensor networks, UWB technology and mmWave communications. He is currently working on cognitive radio and spectrum sharing techniques for public safety communications and he recently joined the research centre CREATE-NET in Trento, Italy.161