Nokia Lte For Public Safety White Paper [PDF]

Zitiervorschau

Nokia Networks

LTE networks for public safety services Public safety agencies and organizations have started planning to evolve their networks to LTE-based public safety solutions. LTE supports a wide variety of services, from high bandwidth data services to real-time communication services – all in a common IP based network. Mission critical communication in demanding conditions, for example after a natural disaster, sets strict requirements, which are not necessarily supported by regular commercial mobile networks. In this paper we present the technology evolution for LTE public safety services, including standardization activities in 3GPP and highlight selected public safety requirements that affect LTE networks.

Nokia Networks white paper LTE networks for public safety services

Contents Introduction - LTE public safety momentum

3

Spectrum and network deployment options

5

Group Communication

8

Proximity Services

10

Mission Critical Push to Talk

12

Prioritization of emergency responders

13

Security

16

Network resilience

18

Network coverage and capacity

20

Conclusions

22

References

23

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Introduction - LTE public safety momentum This paper provides some background and looks at issues of interest to parties considering implementing an LTE network for public safety services. LTE is the most quickly adopted mobile technology so far, with over 300 commercially launched networks globally. Current public safety networks such as TETRA or Project 25 (P25) support mission critical voice communication, but are limited to narrowband data. Mobile broadband can help emergency services significantly, for example with live mobile video, situation aware dispatching and remote diagnostics. In 2012 the US government formed FirstNet and committed USD 7 billion to the venture. FirstNet was given responsibility for coordinating the use of Band 14 (at 700 MHz), which was reserved for public safety in 2007 by the local regulator. The TETRA and Critical Communications Association (TCCA) announced that LTE was the selected technology for mission critical mobile broadband communications and public safety became the key theme of 3GPP Release 12. Nokia took key rapporteurships in 3GPP to make the vision part of the standards. Public safety use cases rely heavily on the existing E-UTRAN and EPS capabilities from 3GPP Release 8 onwards. There are even public safety specific requirements covered in the completed 3GPP releases. Highlights of public safety evolution in 3GPP are shown in Figure 1.

3GPP Rel-8

3GPP Rel-9

3GPP Rel-10

3GPP Rel-11

3GPP Rel-12

3GPP Rel-13

• Mobile data connections

• Location services and positioning support for LTE

• Physical layer enhancements to increase data throughput (including LTEAdvanced features)

• High power devices for Band 14 - 1.25 Watts for public safety devices significantly improving the coverage of an LTE network, benefiting public safety users and reducing network deployment costs.

• Group Communication System Enablers for LTE

• Mission Critical Push-to-Talk

• Basic support for Voice over LTE (telephony) • Support for LTE Band 14 • a rich set of QoS priority and preemption features • Highly secure authentication and ciphering

• Multimedia Broadcast / Multicast Service • E911 or emergency calling support • Enhanced Home LTE base station: “Cell On Wheels” • Self-Organizing Networks (SONs)

• Relays for LTE, e.g. to allow a base station mounted on a fire vehicle to relay communications from firefighters in a basement back to the network.

• Proximity-based Services

• Enhancements to Proximity-based Services • Isolated E-UTRAN Operation for Public Safety • MBMS Enhancements

3GPP work ongoing completion expected 1Q2015

3GPP work started completion expected 2016

Figure 1. 3GPP Road to Public Safety

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Nokia Networks estimates that the global market for LTE public safety networks will exceed 2 billion Euros in 2019. This estimate includes network infrastructure and related services such as network planning, implementation and optimization. The main markets driving this growth are the US and the UK. FirstNet is expected to start main deployment in late 2016 in the US. In UK, the UK Home Office has established a program with a target to build a new Emergency Service Network (ESN) that will provide mobile services for the three emergency services (police, fire and ambulance). Currently, it is estimated that the ESN will go live during 2016. This provides significant momentum for the LTE industry as governments start budgeting for next generation public safety networks.

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Spectrum and network deployment options A network dedicated to public safety can offer guaranteed spectrum and optimized security and resilience. This type of deployment model exists in current narrowband public safety networks such as TETRA and Project 25. The same deployment model is a viable option for LTE public safety but is also the most expensive and reserves its own spectrum allocation, which cannot then be used for other purposes. Therefore public safety stakeholders are considering other models. Two key topics to consider from the cost-efficiency perspective are spectrum allocation and network infrastructure ownership. A spectrum allocation strategy should consider the device ecosystem, which has potentially high costs. Initially, the global LTE market was very fragmented due to different frequency bands in different markets. However, this is no longer such an issue, as mobile devices increasingly have multi-band support for all major frequency bands used globally. LTE public safety networks can benefit significantly from the commercial LTE ecosystem if the same frequency bands are selected for public safety use. Currently only regulators in the US and Canada have allocated band 14 for public safety and while this band is not currently allocated anywhere else, the result is a separate device ecosystem in North America. Other regulators tend to prefer bands that are already selected for commercial LTE networks such as band 20 (EU 800 MHz) and band 28 (APT 700 MHz). Even lower bands like band 31 (450 MHz) are considered in some countries, but then the problem arises of a compromised broadband performance due to a narrower available bandwidth, although it could present good opportunities for “voice only” services. The World Radiocommunication Conference 2015 has an agenda item on the harmonization of Public Safety spectrum but the outcome is likely to be a list of possible frequency bands (in ITU-R Res 646), which individual regulators could consider when deciding on the spectrum for Public Safety in their countries, as the topic is considered a national issue. Network infrastructure deployment depends on spectrum allocation. If dedicated spectrum is allocated, then a dedicated public safety network can be implemented. This is possible for example in the US, where FirstNet has a license for a nationwide public safety network. Economies of scale improve as more users are served by the network infrastructure and the spectrum and therefore network sharing can be considered to optimize the cost per user – also in the FirstNet case.

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Public safety services

Public safety services

Public safety services

Public safety services

AS AS, IMS, PCRF

VPN or Internet AS, IMS, PCRF

HSS

HSS S/PGW

MME

S/PGW

MME

HSS

P-GW SGW

MME

HSS

MME

Shared spectrum

Mobile operator Public safety over MBB

eNB

Shared spectrum

eNB

Shared spectrum

Mobile operator

Mobile operator

Hosted public safety

MVNO public safety

S/PGW

HSS

MME

AS, IMS, PCRF

S/PGW

S/PGW MME

eNB

AS, IMS, PCRF

eNB

Shared or dedicated spectrum

eNB

dedicated spectrum

Mobile operator RAN sharing for public safety

Private LTE for public safety

Figure 2. Examples of deployment options In the UK, the intention is to reduce costs by selecting existing mobile operators to offer LTE network services for LTE public safety users. This approach enables sharing a common LTE infrastructure for consumer, enterprise and public safety customers. The main cost in any mobile network is the radio access network and therefore the major saving is derived from the use of a common radio access network for both commercial and public safety services. This can be achieved using traditional and standardized sharing techniques, for example with the RAN sharing model or with an MVNO model (Mobile Virtual Network Operator). Network infrastructure and spectrum sharing can also be implemented so that the Mobile Network Operator (MNO) hosts public safety services in addition to the regular mobile services. When network sharing is used, LTE network features, planning and configuration must all take into account the requirements of public safety agencies. Public safety services can set tighter coverage, security and resilience requirements than is commonly planned in commercial networks. Furthermore, prioritization of public safety subscribers and services is critical in emergency situations. Public safety agencies have already noticed that existing commercial mobile broadband networks can be used to enhance emergency communication services. For example, mobile broadband services are available in areas without TETRA or P25 coverage. It is possible to find public safety applications that currently exist for commercial smartphones which allow public safety officers to communicate over existing mobile broadband networks. Thus, public safety services are implemented just like the Internet or so called over-the-top (OTT) services.

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Roaming is one more dimension in LTE public safety deployment that can be combined with the models depicted in Figure 2. Most especially, service resilience can be extended by using national roaming i.e. allowing public safety users to access services from any and all national LTE networks. This model can be further developed by allowing WiFi access to services, if no other terrestrial option is available. Satellite service is another alternative, for example in rural areas. The high level network architecture is similar in all deployment options. The network architecture depicted in Figure 3 includes key components of the LTE network and illustrates that different network elements and functions are located at different sites. The public safety application servers are highlighted and can be located in separate sites dedicated for public safety services and related interworking functions. Note that there are several options available and the decision on where different network functions are located and distributed in different sites will ultimately be for the authorized bodies and operators to agree. As an example, the public safety service provider (MVNO role) can be separated from the network provider (MNO role).

OSS, BSS

Management

Core site

Core site

HSS, SPR

PTT , Group Comm

Live video sharing

Interworking

Tetra/P25 core

Charging PCRF MME

Cell site

BM-SC

eNodeB

IMS

S/P-GW

MBMS-GW

DNS

FW

AS (e.g. VoLTE)

Load Bal.

Cell site

Agency 1

Control room / Dispatcher IP backhaul

IP backbone

Agency 2

eNodeB

Tetra/P25 BTS

Internet

Control room / Dispatcher

Figure 3. Network architecture overview.

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Group Communication To enable group communication services, 3GPP has introduced the concept of the Group Communication Service application server, also known as GCS AS [Reference TS 23.468] in Release 12. It provides a means for both one-to-one and one-to-many communication services. Figure 4 shows how the GCS AS is connected to the rest of the system, according to the 3GPP Rel-12 GCS architecture. Although not explicitly shown, the architecture allows the device to connect to GCS AS via IMS.

GC1

 Application control information

Rx

 Priority level, session information

PCRF

 Bearer status info SGi

 Downlink traffic (unicast)  Uplink traffic

S/P-GW

MB2 BM-SC

 Data related to GC1 GCS AS

MBMS bearer mgmt Group identity mgmt  Downlink traffic (broadcast)

Figure 4. Group Communication architecture. Public safety devices use the GC1 reference point to initiate, modify or terminate group communication sessions. The GC1 reference point will be standardized as part of 3GPP Release 13. The GCS AS is the entity which makes the decision to use either unicast or broadcast mode for sending traffic (voice, video or data) to the public safety devices.

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In unicast mode, the GCS AS uses the information from application control signaling (GC1 reference point) to derive an appropriate priority level, which it further communicates to Policy and Charging Rule Function (PCRF) over the Rx reference point, together with other relevant data (e.g. IP addresses, port numbers, codec). The PCRF uses this information to create an EPS bearer with desired prioritization values (such as public safety specific QCI value, ARP, pre-emption capability and pre-emption vulnerability). In broadcast mode, the GCS AS uses eMBMS to deliver traffic to the public safety devices. To establish an eMBMS bearer in a specific geographical area, the GCS AS uses the MB2 reference point. The eMBMS bearer can be pre-established, for example for mass events or festivals, or it can be established in dynamically, for example when the number of users within an area has exceeded a certain threshold. The Public Safety device is responsible for service continuity between unicast and broadcast modes. In other words, when the device and GCS AS detects that downlink media can also be delivered via MBMS, it can ask the GCS AS to stop sending traffic using the unicast bearer. When the device detects that eMBMS coverage is becoming too weak, it asks GCS AS for unicast delivery in the downlink instead of eMBMS delivery.

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Proximity Services The Public Safety solution needs to support communication between public safety users when the devices are in proximity and even if the network is down or when the device is out of coverage. To enable this, 3GPP is standardizing a feature called Proximity Services (ProSe) [Reference TS 23.303]. Proximity Services allows two devices to communicate directly, i.e. without the data path being routed via the network infrastructure. The proximity range depends on the strength of the radio signal and other radio conditions such as interference. The actual range varies depending on the power level used for transmitting the radio signal. Public Safety is one of the ProSe use cases, while others include commercial services such as friend finder. This ability to support direct communication is a core requirement for public safety use cases. In addition, public safety devices should be able to communicate directly with other devices, whether the device is served by E-UTRAN or not. These functionalities are enabled by ProSe in 3GPP Release 12. Public safety devices can initiate direct communication without performing a discovery procedure, as it is assumed that public safety personnel know each other’s whereabouts and can thus determine whether the other person is reachable for direct communication or not.

How do I find other ProSe-enabled UEs in its vicinity by using only the capabilities of the two UEs with Rel-12 E-UTRA technology

Direct Connectivity

Prose Discovery

Prose Communication

Connectivity via other UE User Equipment to Network Relay

Figure 5. High level Proximity functionality.

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The high-level ProSe feature set consists of: • ProSe discovery: allows a device to find other devices in its vicinity by using direct radio links or via the operator network. 3GPP Release 12 supports discovery only when the device has network coverage. • ProSe Communication: allows a device to establish communication between one or more ProSe enabled devices that are in direct communication range. Communication is provided in a connectionless manner (no control plane involved). • Device to network relay: allows a device to act as a relay between E-UTRAN and devices not served by E-UTRAN (out of coverage devices e.g. inside the building). This functionality is expected in 3GPP Release 13.

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Mission Critical Push to Talk Mission Critical Push to Talk (MCPTT) provides one-to-one and one-tomany voice communication services. The idea is simple. Users select the individuals or groups they wish to talk to and then press the “talk key” to start talking. The session is connected in real time. Push to talk sessions are one-way communication (also known as ‘half-duplex’): while one person speaks, the others only listen. Turns to speak are requested by pressing the “talk key” and are granted on a call prioritization basis, for example a dispatcher has a higher priority than other users. The push to talk service for group communication is based on multiunicasting and broadcasting. Each sending device sends packet data traffic to a dedicated mission critical push to talk application server and the server then copies the traffic to all the recipients (see Figure 6). 3GPP is in the process of standardizing MCPTT in Release 13 [Reference TS 22.179] - here the MCPTT application server is assumed to be part of the GCS application server. Note that GCS is a generic function for voice, video and data, but as the name implies, MCPTT is a voice communication service.

IMS

MCPTT AS

Control room / Dispatcher • Group management • Group member

GCS AS SIP

RTP packets UL/DL unicast

RTP packets DL broadcast

eNodeB BM-SC

eMBMS eNodeB

Figure 6. Mission Critical Push to Talk.

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Prioritization of emergency responders Regardless of the actual public safety network deployment model, public safety subscribers must have priority access to the network. Commercial mobile networks are dimensioned to serve typical busy hour traffic, but the networks do not necessarily have capacity for extreme cases. Therefore, subscribers may experience problems accessing mobile services during mass events, for example in sports stadiums. In overload conditions, the network signaling plane gets overloaded on the radio interface due to frequently repeated connection attempts by potentially thousands of smartphones in a single cell. Similar problems could also occur in a large scale accident or disaster, as hundreds or thousands of people attempt to make emergency calls and use mobile services at the same time. When moving emergency services into commercial mobile networks there must be a solution to limit the amount of connection attempts as well as allow priority access for high priority users, including emergency responders. This is solved with existing access class prioritization and the possibility to invoke access class barring. Barring of low priority users can prevent the signaling attempts and therefore effectively give adequate radio resources to high priority users.

1. In case of high load, access class barring can be activated for AC 0 – 9 users. HSS/SPR

2. Admission control and pre-emption can be used for prioritizing EPS bearers of emergency responders (ARP) 3. Emergency calls and multimedia priority services (MPS) calls get end-to-end priority treatment. 4. User plane traffic is prioritized and scheduled according to QoS parameters (QCI, GBR/MBR, NBR).

PCRF

AC 14

X X AC 0-9

MME P/S-GW

eNB • High priority bearer with pre-emption capability (ARP). • Traffic prioritization matching service requirements (QCI)

Figure 7. User and bearer prioritization tools.

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Operators can use access class barring and extended access barring capabilities as an overload control tool to reduce the load generated by regular users in normal operations. This mechanism can be automated so that access class barring activates if certain load thresholds are exceeded. Access class barring is commonly supported in LTE radio access and a key new requirement is that network operators open an interface for public safety authorities to quickly trigger emergency access class barring in selected locations. Access Class (AC) must be managed on a subscription level so that emergency responders get a USIM with AC 14, whilst regular users are distributed to access classes 0 – 9. Access classes 12 and 13 are also relevant in general public safety as they are meant for security services and public utilities respectively. It should be noted that barring regular users in LTE still leaves 2G and 3G accesses open for them. The next level of prioritization occurs in admission control and preemption. Public safety users and services can be prioritized on an LTE bearer level. Allocation and retention priority (ARP) defines a priority level (1 – 15), pre-emption capability and pre-emption vulnerability. Emergency responders must have higher priority for LTE data bearers than other subscribers. Furthermore, pre-emption parameters must allow public safety users and services to pre-empt other data bearers if network resources are limited. Access and service prioritization for emergency calls is a normal regulator requirement for mobile networks. Furthermore, a new capability called multimedia priority service (MPS) has uses in an emergency situation. MPS enables end-to-end prioritization for a call, important if an emergency officer must reach a regular subscriber. This means that with the MPS service, the terminating leg to the regular user is also prioritized in admission control and pre-emption. The last level of prioritization is managed in the user plane. Data bearers have a different QoS class, defined by the QoS class identifier (QCI) parameter. QCI defines delay and packet loss targets for the connection as well as whether the bearer is “guaranteed bit rate” (GBR) or a “nonGBR” connection. GBR bearers have additional parameters for the actual guaranteed bit rates in uplink and downlink directions. In addition to the existing standard QCIs (from 1 to 9), 3GPP has specified special GBR and non-GBR QCIs for public safety group communication (QCIs 65, 66, 69 and 70) [Reference TS 23.203].

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It should be noted that public safety users are not necessarily, by default, prioritized to the highest level. The default subscription priority for a default bearer can be higher than regular subscribers’ priority, but additionally, public safety users handling emergency incidents should be prioritized over other public safety users. Therefore, public safety responders and control room officers can indicate emergency priority for specific communication sessions. One option for higher admission priority and scheduling priority during mission critical sessions is to dynamically modify the QoS of the default bearer. The drawback here is that all service flows are affected, including any lower priority activities such as potential background data transfers. A preferred option is to differentiate mission critical sessions with dedicated bearers as shown in Option 2 in the figure below. Establishment and release of dedicated bearers requires the use of PCRF with a Rx reference point to the application control function. Option 1 – Default bearer modification PCRF can trigger QoS modification of default bearer

Option 2 – Dedicated bearer for mission critical QoS

HSS/SPR

PCRF can trigger setup of dedicated bearer

PCRF

AC 0-9

MME

AC 0-9

Mission critical service

MME

Mission critical service

P-GW

eNB

AC 14 AC 14

Public safety user in emergency mission.

PCRF

P-GW

eNB

HSS/SPR

Public safety APN

Non-mission critical services

AC 14

Dynamic modification of default bearer impacts on all service flows

AC 14

Public safety user in emergency mission.

Public safety APN

Non-mission critical services

Dedicated bearer for mission critical service flows

Figure 8. QoS options for mission critical service flows.

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Security Security is already important in the commercial mobile network. The network infrastructure and related IT infrastructure, such as the management system, must be protected, for example against illegal access, viruses, malware and denial-of-service attacks. Therefore, there must be controlled access authorization to management tools. Software updates and maintenance must also be secure. The network must be protected with firewalls and intrusion detection systems. Security requirements for a public safety network may be more stringent than in a normal mobile network. This also includes physical security, not only in the data centers and core sites, but also in all distributed sites, especially base station sites. Physical security also requires tight control of personnel with access rights to different sites. Authorized access to network services and adequate confidentiality for subscribers is well standardized by 3GPP. Authentication and authorization are based on secure USIM based methods. Furthermore, signaling and user plane traffic are ciphered over the air interface. The LTE network specification does not require user plane traffic encryption in the backhaul and transmission networks, but this is possible with optional IP security based solutions and is highly recommended when using third party transport providers. Most especially, the control and management plane traffic must be protected, as a potential attacker could in some locations have relatively easy access to the physical connections of the transmission links at base station sites. User identity management and related user priority level and service access rights require special attention in public safety communities. Typically, many of the devices used are shared. Thus, the user identity and user profile cannot be based on a common USIM inside the device. If the USIM is kept inside the mobile device and used for network access authentication and authorization, another method is needed for actual user authentication and setup of the access profile (for example QoS). Alternatively, public safety users could have individual USIM cards, but to make it easy to change devices a Bluetooth based remote SIM access could be considered.

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Additional security is needed in the application layer. Public safety services must have their own user authentication and authorization, which is managed by the public safety service provider. Public safety communication content is highly sensitive and therefore confidentiality in public safety communication must be based on end-to-end security in the application layer. This guarantees confidentiality without any specific dependency on the security solutions implemented in the network for the user plane traffic. The same end-to-end security approach is also used, for example, in current TETRA networks. Due to the sensitive communication content, the public safety application servers and content storage devices must be located at highly secure sites. Public safety networks must also support traffic separation using VPN technologies. If the same network is used by a public safety user and other regular subscribers, public safety traffic must be separated, for example using VPN solutions commonly used for enterprises. Furthermore, different public safety agencies should be separated from each other with controlled interconnection interfaces between agencies.

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Network resilience Network resilience is based on high-availability and redundancy solutions on multiple layers. Most resilience features needed in public safety networks are commonly available from LTE manufacturers. However, commercial LTE networks may not implement resilience fully to fulfill all public safety requirements. Most network elements have high-availability designs, for example, to recover from hardware failures. Pooling of elements and load balancing between core elements improves system reliability and guarantees network service availability, even if a single node fails. Centralized functions like management systems and core network elements are usually located in at least two geographically separated locations, in order to survive possible complete site failure. Connectivity between sites and network elements supports resilience against link and node failures. Backup connections and nodes can generally be designed into the IP transport network, and specifically for IPSec tunnels, timing synchronization, management connections and signaling (e.g. Diameter routing).

High available nodes • Redundant HW units (e.g. fans, power, blades) • Redundancy options (N+, 2N) • Session continuity in switchover

Connectivity & routing • Resilient IP network design with fast re-routing • Interface protection • IPsec backup & emergency bypass • Redundant Diameter routing

Inter-node resilience & pooling • MME pooling with S1-flex • P/S-GW load balancing • CSCF load balancing • AS pooling • Redundant timing master

Management & automation • Outage detection • Automatic re-configuration • Self-healing

Geo-redundancy • OSS, registers and core elements in geographically distributed sites • 3-site database replication

Cloudification • Elastic scalability for virtual network functions • Automatic load balancing and resource allocation

Figure 9. High-availability and resilience on multiple levels.

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It is not always straightforward to detect certain failures, such as performance degradation in cells, but advanced management and Self Organizing Network (SON) automation tools can detect events like cell outages and activate automatic self-healing. The network must also be prepared for power outages and solutions such as battery backup and generators are common in current commercial networks. There is one more topical technology that is not driven by resilience requirements, but can further enhance system availability. This is the transfer of network function to a “cloud”, enabling elastic scalability and automatic load balancing. Resilience in LTE public safety networks can be further enhanced from typical commercial LTE networks. Public safety networks can have dedicated core network elements for public safety services (HSS, EPC, IMS, ASs), which simplifies the dimensioning and enables management of peak load at a lower level for better performance and more reliable operation. Natural disasters can destroy base station sites and network connections and therefore rapidly deployable cells are important for disaster recovery [See Network coverage and capacity]. Future features also enable local communication when network coverage is missing or the backhaul connection is disabled. For example, as mentioned previously, 3GPP proximity services will introduce direct device-to-device communication. 3GPP is also expected in Release 13 to support isolated E-UTRAN operation for public safety [Reference TS 22.346]. This means the eNodeB site can continue offering network services locally, even if backhaul connection to core network sites is lost. One further consideration for network connectivity resilience is based on the Internet service model, i.e. enabling access independent public safety services. Such a model would allow authorized access to public safety services via any broadband capable IP access. Public safety users could have subscriptions that allow connection to the LTE access of all national mobile operators. As a backup option, WiFi or satellite access could be used when other services are not available.

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Network coverage and capacity Service coverage for public safety users is critical and previous TETRA solutions, operating in low frequency spectrum, offered coverage almost everywhere. It is a critical requirement when moving to commercial LTE networks that this coverage is maintained and if possible, enhanced. Public safety networks must provide very high national geographic coverage - not only high population coverage. Furthermore, public safety users may have to work in various indoor locations where commercial mobile services are not currently available. The most basic approach, for a simple and cost efficient coverage is to use lower frequency bands. In the case of broadband LTE this typically means bands in 700 MHz and 800 MHz ranges. Even lower bands like 450 MHz are considered, but this typically results in a compromised broadband performance due to a narrower available bandwidth. The deployment of macro network coverage uses well known optimizations employed in commercial LTE networks. Cell range is normally uplink limited because of the low transmission power allowed in mobile devices. Wide area coverage of high transmission power and the receiver sensitivity of eNodeBs can be optimized with a number of techniques, such as 4-way receiver diversity, higher-order sectorization and TTI (transmission time interval) bundling. Cell range can be extended in the uplink by specifying high power mobile devices (power class 1, 31 dBm) also for other than existing band 14 (in other bands only class 3 devices, 23 dBm, specified). Indoor coverage can be optimized with different indoor solutions such as distributed antenna systems (DAS) and low power indoor cells, also known as ‘small cells’. Small cells can be used for filling indoor white spots. However, specialized in-building solutions will not solve all indoor coverage issues except in selected buildings. Capacity is an additional aspect that must be taken into account in network dimensioning. Although the number of public safety users is significantly lower than regular subscribers in any commercial mobile network, the number of simultaneously active public safety users can be very high, especially in a relatively small area when a major incident occurs. Such situations are more likely to happen in dense urban areas and therefore the network planning in urban areas should follow the same principles as in commercial networks, i.e. a denser site grid and smaller cells in urban locations. Capacity requirements in public safety networks can make high demands on the network design due to new public safety video applications. If for example there is a need for multiple HD quality video streams in cell edge radio conditions, then 10 + 10 MHz FDD spectrum would be far from adequate and therefore more carrier bandwidth is needed. Regardless of how well the network is designed and implemented, there will always be emergency incidents in locations without existing network coverage (outdoors or indoors). Additionally, public safety network Page 20

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cell sites may be just as vulnerable in natural disasters as commercial network sites and may be damaged. Therefore, public safety network operators should be prepared with rapidly deployable base station solutions. Deployable solutions should enable fast macro coverage to provide and recover network availability in both rural and urban locations. Rapidly deployable small cells may be required in difficult indoor locations such as mines and caves and can be further used for an instant capacity boost when required. Rapidly deployable small cells can be also pre-installed in emergency vehicles in order to automatically provide network coverage around the vehicles. Availability of radio communication is further guaranteed by providing direct device-to-device communication. In LTE this is enabled by 3GPP proximity services [See Device to Device Communication]. ProSe can partially solve network coverage white spot problems based on the ProSe device relay solution. Availability and reliability of service coverage can be improved using the resilience mechanisms mentioned in the Network resilience section, i.e. allowing service access via any national broadband capable network including HSPA and WiFi or via satellite access. Other techniques, such as Assured Shared Access coupled with MOCN (Multi-Operator Core Network) could be used to improve the economics of deep rural coverage and improve the service proposition by allowing all operators’ low frequency spectrum to be pooled in these locations. Typically 800 MHz is scarce and distributed amongst the operators of the country in question, limiting the peak rates to the selected partner operator. By pooling the spectrum, a much enhanced service is available and use of MOCN technology would allow all operators to provide service from this same eNodeB in a location where it was previously uneconomical to deploy. Using the catalyst of emergency services coverage to improve the mobile broadband offerings in rural locations can only improve the economics and personal well being of people living in these remote locations.

Figure 10. Rapidly deployable macro eNodeB on a trailer Page 21

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Conclusions Public safety networks provide communications for services like police, fire and ambulance. In this realm, the requirement is to develop systems that are highly robust and can address the specific communication needs of emergency services. This has fostered public safety standards – such as TETRA and P25 – that provide a set of features not supported in commercial cellular systems. TETRA and P25 networks are implemented in low frequency bands for better coverage, often using the 400 MHz band range. The main disadvantage of the current systems is very limited data connectivity. The supported data rate can be less than 10 kbps and even in the enhanced TETRA specification the data rate is around 150 kbps. For evolution of public safety networks over mobile broadband, LTE has been the technology of choice.

Best effort broadband data

LTE

TETRA or P25

Prioritized broadband data

Pre-standard PTT

3GPP Rel-13 MCPTT

Pre-standard interworking

3GPP Rel-13 interworking

Mission critical communication

Figure 11. Evolution to LTE based public safety services The evolution from current narrowband systems to LTE based public safety will take several years and will happen gradually. During the transition period, public safety agencies are expected to use existing TETRA and P25 systems in parallel with LTE based systems. The first and the simplest step is to rely on TETRA and P25 in mission critical voice and messaging, while LTE can offer enhanced data services, potentially with slightly lower reliability. Initially officers will use separate TETRA or P25 and LTE smart devices, but at some stage, device vendors may implement multimode devices supporting several technologies in the same device. In the distant future we assume that TETRA and P25 technologies will no longer be maintained and all public safety service requirements will be fulfilled by LTE networks. Service interworking will be crucial in the evolution to public safety solutions based on LTE alone.

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References TS 23.468 3GPP TS 23.468 Group Communication System Enablers for LTE (GCSE_LTE); Stage 2 TS 23.303

3GPP TS 23.303 Proximity-based services (ProSe); Stage 2

TS 23.203

3GPP TS 23.203 Policy and charging control architecture

TS 22.179 3GPP TS 22.179 Mission Critical Push to Talk (MCPTT); Stage 1 TS 22.346 3GPP TS 22.179 Isolated E-UTRAN operation for public safety; Stage 1

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