Nokia Lte for Public Safety White Paper

7/25/2019 Nokia Lte for Public Safety White Paper

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LTE networks forpublic safety services

Public safety agencies and organizations have startedplanning to evolve their networks to LTE-based publicsafety solutions.

LTE supports a wide variety of services, from highbandwidth data services to real-time communicationservices all in a common IP based network.

Mission critical communication in demanding conditions, forexample 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 LTEpublic safety services, including standardization activitiesin 3GPP and highlight selected public safety requirementsthat aect LTE networks.

Nokia Networks

Nokia Networks white paper

LTE networks for public safety services


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Page 2 networks.nokia.com

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 safetymomentumThis paper provides some background and looks at issues of interestto parties considering implementing an LTE network for public safetyservices.

LTE is the most quickly adopted mobile technology so far, with over 300commercially launched networks globally. Current public safety networkssuch as TETRA or Project 25 (P25) support mission critical voicecommunication, but are limited to narrowband data. Mobile broadbandcan help emergency services signicantly, for example with live mobile

video, situation aware dispatching and remote diagnostics. In 2012 theUS government formed FirstNet and committed USD 7 billion to theventure. FirstNet was given responsibility for coordinating the use ofBand 14 (at 700 MHz), which was reserved for public safety in 2007 bythe local regulator. The TETRA and Critical Communications Association(TCCA) announced that LTE was the selected technology for missioncritical mobile broadband communications and public safety became thekey theme of 3GPP Release 12. Nokia took key rapporteurships in 3GPPto make the vision part of the standards.

Public safety use cases rely heavily on the existing E-UTRAN and EPScapabilities from 3GPP Release 8 onwards. There are even publicsafety specic requirements covered in the completed 3GPP releases.Highlights of public safety evolution in 3GPP are shown in Figure 1.


Figure 1. 3GPP Road to Public Safety

3GPP Rel-9

Location servicesand positioningsupport for LTE

MultimediaBroadcast /Multicast Service

E911 oremergency callingsupport

Enhanced HomeLTE base station:Cell On Wheels

Self-OrganizingNetworks (SONs)

3GPP Rel-8

Mobile dataconnections

Basic support forVoice over LTE(telephony)

Support for LTEBand 14

a rich set of QoS

priority and pre-emption features

Highly secureauthenticationand ciphering

3GPP Rel-10

Physical layerenhancements toincrease datathroughput(including LTE-Advanced features)

Relays for LTE, e.g.to allow a base

station mountedon a fre vehicle torelaycommunicationsfrom frefghters ina basement backto the network.

3GPP Rel-11

High power devicesfor Band 14 - 1.25Watts for publicsafety devicessignifcantlyimproving thecoverage of an LTEnetwork, beneftingpublic safety users

and reducingnetworkdeployment costs.

3GPP Rel-13

Mission CriticalPush-to-Talk

Enhancements toProximity-basedServices

Isolated E

MBMSEnhancements

-UTRANOperation forPublic Safety

3GPP work started -completion expected2016

-12

-based

-

3GPP Rel

GroupCommunicationSystem Enablersfor LTE

ProximityServices

3GPP work ongoingcompletion expected1Q2015


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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 includesnetwork infrastructure and related services such as network planning,implementation and optimization.

The main markets driving this growth are the US and the UK. FirstNetis expected to start main deployment in late 2016 in the US. In UK, theUK Home Oice has established a program with a target to build a newEmergency Service Network (ESN) that will provide mobile services forthe three emergency services (police, re and ambulance). Currently, it isestimated that the ESN will go live during 2016.

This provides signicant momentum for the LTE industry asgovernments start budgeting for next generation public safetynetworks.



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Spectrum and network deploymentoptionsA network dedicated to public safety can oer guaranteed spectrumand optimized security and resilience. This type of deployment modelexists in current narrowband public safety networks such as TETRA andProject 25. The same deployment model is a viable option for LTE publicsafety but is also the most expensive and reserves its own spectrumallocation, which cannot then be used for other purposes. Thereforepublic safety stakeholders are considering other models. Two key topicsto consider from the cost-eiciency 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 wasvery fragmented due to dierent frequency bands in dierent markets.However, this is no longer such an issue, as mobile devices increasinglyhave multi-band support for all major frequency bands used globally.LTE public safety networks can benet signicantly from the commercialLTE ecosystem if the same frequency bands are selected for publicsafety use.

Currently only regulators in the US and Canada have allocated band 14for public safety and while this band is not currently allocated anywhereelse, the result is a separate device ecosystem in North America. Otherregulators tend to prefer bands that are already selected for commercialLTE networks such as band 20 (EU 800 MHz) and band 28 (APT 700MHz). Even lower bands like band 31 (450 MHz) are considered in somecountries, but then the problem arises of a compromised broadbandperformance due to a narrower available bandwidth, although itcould present good opportunities for voice only services. The WorldRadiocommunication Conference 2015 has an agenda item on theharmonization of Public Safety spectrum but the outcome is likely to bea list of possible frequency bands (in ITU-R Res 646), which individualregulators 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. Ifdedicated spectrum is allocated, then a dedicated public safety networkcan be implemented. This is possible for example in the US, whereFirstNet has a license for a nationwide public safety network. Economiesof scale improve as more users are served by the network infrastructureand the spectrum and therefore network sharing can be considered tooptimize the cost per user also in the FirstNet case.



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In the UK, the intention is to reduce costs by selecting existing mobileoperators to oer LTE network services for LTE public safety users. Thisapproach enables sharing a common LTE infrastructure for consumer,enterprise and public safety customers. The main cost in any mobilenetwork is the radio access network and therefore the major savingis derived from the use of a common radio access network for bothcommercial and public safety services. This can be achieved usingtraditional and standardized sharing techniques, for example with theRAN sharing model or with an MVNO model (Mobile Virtual NetworkOperator). Network infrastructure and spectrum sharing can also beimplemented so that the Mobile Network Operator (MNO) hosts publicsafety services in addition to the regular mobile services.

When network sharing is used, LTE network features, planning andconguration must all take into account the requirements of publicsafety agencies. Public safety services can set tighter coverage, security

and resilience requirements than is commonly planned in commercialnetworks. Furthermore, prioritization of public safety subscribers andservices is critical in emergency situations.

Public safety agencies have already noticed that existing commercialmobile broadband networks can be used to enhance emergencycommunication services. For example, mobile broadband servicesare available in areas without TETRA or P25 coverage. It is possibleto nd public safety applications that currently exist for commercialsmartphones which allow public safety oicers to communicate overexisting mobile broadband networks. Thus, public safety services areimplemented just like the Internet or so called over-the-top (OTT)

services.


Public safety

services

Mobile operator Mobile operator

Public safetyover MBB

MVNOpublic safety

RAN sharing forpublic safety

Private LTE forpublic safety

Public safety

services

HSS

MME S/P-GW

eNB

VPN orInternet

AS

HSS

MME S-GW

eNB

AS,IMS,PCRF

P-GW

Public safety

services

Mobile operator

MME

S/P-GW

eNB

AS,IMS,PCRFHSS

MME S/P-GW

Public safety

services

eNB

AS,IMS,PCRFHSS

MME S/P-GW

Mobile operator

Hostedpublic safety

HSS

MME S/P-GW

eNB

AS,IMS,PCRF

Sharedspectrum

Sharedspectrum

Sharedspectrum

Shared ordedicatedspectrum

dedicatedspectrum

Figure 2. Examples of deployment options


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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. allowingpublic safety users to access services from any and all national LTEnetworks. This model can be further developed by allowing WiFi accessto services, if no other terrestrial option is available. Satellite service isanother 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 componentsof the LTE network and illustrates that dierent network elements andfunctions are located at dierent sites. The public safety applicationservers are highlighted and can be located in separate sites dedicated

for public safety services and related interworking functions. Note thatthere are several options available and the decision on where dierentnetwork functions are located and distributed in dierent sites willultimately be for the authorized bodies and operators to agree. As anexample, the public safety service provider (MVNO role) can be separatedfrom the network provider (MNO role).


CoresiteOSS, BSS

Cellsite

Cellsite

eNodeB

eNodeB

Management Charging

Coresite

PTT ,Group Comm

Livevideo sharing

Agency1

Control room / Dispatcher

Agency2


IP backhaulIP backbone

DNS

FW

Load Bal.

MME S/P-GW

HSS, SPR

PCRF

IMS AS(e.g. VoLTE)

Interworking Tetra/P25core

Tetra/P25 BTS

MBMS-GW

Internet

BM-SC

Figure 3. Network architecture overview.


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Group CommunicationTo enable group communication services, 3GPP has introduced theconcept of the Group Communication Service application server, alsoknown as GCS AS [Reference TS 23.468] in Release 12. It provides ameans 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 explicitlyshown, the architecture allows the device to connect to GCS AS via IMS.

Public safety devices use the GC1 reference point to initiate, modify orterminate group communication sessions. The GC1 reference point willbe standardized as part of 3GPP Release 13. The GCS AS is the entitywhich makes the decision to use either unicast or broadcast mode for

sending traic (voice, video or data) to the public safety devices.


PCRF

BM-SC

S/P-GW GCS AS

Prioritylevel, session information

Bearerstatus info

MBMS bearermgmtGroup identity mgmt

Applicationcontrolinformation

Rx

SGi

MB2

GC1

Data relatedto GC1

Downlinktraffic(unicast)

Uplinktraffic

Downlinktraffic(broadcast)

Figure 4. Group Communication architecture.


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In unicast mode, the GCS AS uses the information from application

control signaling (GC1 reference point) to derive an appropriatepriority level, which it further communicates to Policy and ChargingRule Function (PCRF) over the Rx reference point, together with otherrelevant data (e.g. IP addresses, port numbers, codec). The PCRF usesthis information to create an EPS bearer with desired prioritizationvalues (such as public safety specic QCI value, ARP, pre-emptioncapability and pre-emption vulnerability).

In broadcast mode, the GCS AS uses eMBMS to deliver traic to thepublic safety devices. To establish an eMBMS bearer in a specicgeographical area, the GCS AS uses the MB2 reference point. TheeMBMS bearer can be pre-established, for example for mass events or

festivals, or it can be established in dynamically, for example when thenumber of users within an area has exceeded a certain threshold.

The Public Safety device is responsible for service continuity betweenunicast and broadcast modes. In other words, when the device and GCSAS detects that downlink media can also be delivered via MBMS, it canask the GCS AS to stop sending traic using the unicast bearer. Whenthe device detects that eMBMS coverage is becoming too weak, it asksGCS AS for unicast delivery in the downlink instead of eMBMS delivery.



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Proximity ServicesThe Public Safety solution needs to support communication betweenpublic safety users when the devices are in proximity and even if thenetwork is down or when the device is out of coverage. To enablethis, 3GPP is standardizing a feature called Proximity Services (ProSe)[Reference TS 23.303]. Proximity Services allows two devices tocommunicate directly, i.e. without the data path being routed via thenetwork infrastructure. The proximity range depends on the strengthof the radio signal and other radio conditions such as interference. Theactual range varies depending on the power level used for transmittingthe radio signal.

Public Safety is one of the ProSe use cases, while others includecommercial services such as friend nder. This ability to support directcommunication is a core requirement for public safety use cases. Inaddition, public safety devices should be able to communicate directlywith 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 withoutperforming a discovery procedure, as it is assumed that public safetypersonnel know each others whereabouts and can thus determinewhether the other person is reachable for direct communication or not.


Prose Discovery

How do I fnd otherProSe-enabled UEs in itsvicinity by using only the

capabilities of the two UEs withRel-12 E-UTRA technology

Prose CommunicationUser Equipment toNetwork Relay

DirectConnectivity

ConnectivityviaotherUE

Figure 5. High level Proximity functionality.


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The high-level ProSe feature set consists of:

ProSe discovery: allows a device to nd other devices in its vicinity byusing direct radio links or via the operator network. 3GPP Release 12supports discovery only when the device has network coverage.

ProSe Communication: allows a device to establish communicationbetween one or more ProSe enabled devices that are in directcommunication range. Communication is provided in a connectionlessmanner (no control plane involved).

Device to network relay: allows a device to act as a relay betweenE-UTRAN and devices not served by E-UTRAN (out of coveragedevices e.g. inside the building). This functionality is expected in 3GPP

Release 13.



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Mission Critical Push to TalkMission Critical Push to Talk (MCPTT) provides one-to-one and one-to-many voice communication services. The idea is simple. Users select theindividuals or groups they wish to talk to and then press the talk key tostart talking. The session is connected in real time. Push to talk sessionsare one-way communication (also known as half-duplex): while oneperson speaks, the others only listen. Turns to speak are requested bypressing the talk key and are granted on a call prioritization basis, forexample a dispatcher has a higher priority than other users.

The push to talk service for group communication is based on multi-unicasting and broadcasting. Each sending device sends packet datatraic to a dedicated mission critical push to talk application server andthe server then copies the traic to all the recipients (see Figure 6).3GPP is in the process of standardizing MCPTT in Release 13 [ReferenceTS 22.179] - here the MCPTT application server is assumed to bepart of the GCS application server. Note that GCS is a generic functionfor voice, video and data, but as the name implies, MCPTT is a voicecommunication service.


BM-SC

GCS AS

MCPTT AS

eNodeB


Group management Group member

eNodeB

SIP

IMS

RTP packetsUL/DL unicast

RTP packetsDL broadcast

eMBMS

Figure 6. Mission Critical Push to Talk.


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Prioritization of emergency respondersRegardless of the actual public safety network deployment model, publicsafety subscribers must have priority access to the network. Commercialmobile networks are dimensioned to serve typical busy hour traic,but the networks do not necessarily have capacity for extreme cases.Therefore, subscribers may experience problems accessing mobileservices during mass events, for example in sports stadiums. In overloadconditions, the network signaling plane gets overloaded on the radiointerface due to frequently repeated connection attempts by potentiallythousands of smartphones in a single cell. Similar problems could alsooccur in a large scale accident or disaster, as hundreds or thousands of

people attempt to make emergency calls and use mobile services at thesame time. When moving emergency services into commercial mobilenetworks there must be a solution to limit the amount of connectionattempts as well as allow priority access for high priority users, includingemergency responders. This is solved with existing access classprioritization and the possibility to invoke access class barring. Barringof low priority users can prevent the signaling attempts and thereforeeectively give adequate radio resources to high priority users.


eNB

MME

P/S-GW

PCRF

HSS/SPR

AC 0-9

AC 14

1. In case of high load, access class barringcan be activated for AC 0 9 users.

2. Admission control and pre-emption canbe used for prioritizing EPS bearers ofemergency responders (ARP)

High priority bearer withpre-emption capability (ARP).

Traffic prioritization matching

service requirements (QCI)

3. Emergency calls and multimedia priorityservices (MPS) calls get end-to-endpriority treatment.

4. User plane traffic is prioritized and

scheduled according to QoS parameters(QCI, GBR/MBR, NBR).

X

X

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 byregular users in normal operations. This mechanism can be automatedso that access class barring activates if certain load thresholds areexceeded. Access class barring is commonly supported in LTE radioaccess and a key new requirement is that network operators open aninterface for public safety authorities to quickly trigger emergencyaccess class barring in selected locations. Access Class (AC) must bemanaged on a subscription level so that emergency responders get aUSIM with AC 14, whilst regular users are distributed to access classes0 9. Access classes 12 and 13 are also relevant in general public safetyas they are meant for security services and public utilities respectively.It should be noted that barring regular users in LTE still leaves 2G and 3Gaccesses open for them.

The next level of prioritization occurs in admission control and pre-emption. Public safety users and services can be prioritized on an LTEbearer level. Allocation and retention priority (ARP) denes a prioritylevel (1 15), pre-emption capability and pre-emption vulnerability.Emergency responders must have higher priority for LTE data bearersthan other subscribers. Furthermore, pre-emption parameters mustallow public safety users and services to pre-empt other data bearers ifnetwork resources are limited.

Access and service prioritization for emergency calls is a normal

regulator requirement for mobile networks. Furthermore, a newcapability called multimedia priority service (MPS) has uses in anemergency situation. MPS enables end-to-end prioritization for a call,important if an emergency oicer must reach a regular subscriber. Thismeans that with the MPS service, the terminating leg to the regular useris also prioritized in admission control and pre-emption.

The last level of prioritization is managed in the user plane. Data bearershave a dierent QoS class, dened by the QoS class identier (QCI)parameter. QCI denes delay and packet loss targets for the connectionas well as whether the bearer is guaranteed bit rate (GBR) or a non-GBR connection. GBR bearers have additional parameters for the actual

guaranteed bit rates in uplink and downlink directions. In addition to theexisting standard QCIs (from 1 to 9), 3GPP has specied special GBR andnon-GBR QCIs for public safety group communication (QCIs 65, 66, 69and 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 priorityfor a default bearer can be higher than regular subscribers priority, butadditionally, public safety users handling emergency incidents shouldbe prioritized over other public safety users. Therefore, public safetyresponders and control room oicers can indicate emergency priorityfor specic communication sessions. One option for higher admissionpriority and scheduling priority during mission critical sessions is todynamically modify the QoS of the default bearer. The drawback here isthat all service ows are aected, including any lower priority activitiessuch as potential background data transfers. A preferred option is todierentiate mission critical sessions with dedicated bearers as shownin Option 2 in the gure below. Establishment and release of dedicatedbearers requires the use of PCRF with a Rx reference point to theapplication control function.


Option 2 Dedicated bearer for mission critical QoSOption 1 Default bearer modifcation

eNB

MMEP-GW

PCRF

HSS/SPR

AC 0-9

AC 14

Mission

criticalservice

Non-missioncritical

services

AC 14

eNB

MME P-GW

PCRF

HSS/SPR

Mission

criticalservice

Non-missioncritical

services

Public safety userin emergencymission.

Dynamic modifcation ofdefault bearer impactson all service ows

Public safetyAPN

PCRF can trigger QoSmodifcation of default bearer

Public safety userin emergencymission.

PCRF can trigger setup ofdedicated bearer

Public safetyAPN

Dedicated bearer formission critical serviceows

AC 0-9

AC 14

AC 14

Figure 8. QoS options for mission critical service ows.


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SecuritySecurity is already important in the commercial mobile network.The network infrastructure and related IT infrastructure, such as themanagement system, must be protected, for example against illegalaccess, viruses, malware and denial-of-service attacks. Therefore, theremust be controlled access authorization to management tools. Softwareupdates and maintenance must also be secure. The network mustbe protected with rewalls and intrusion detection systems. Securityrequirements for a public safety network may be more stringent thanin a normal mobile network. This also includes physical security, notonly in the data centers and core sites, but also in all distributed sites,

especially base station sites. Physical security also requires tight controlof personnel with access rights to dierent sites.

Authorized access to network services and adequate condentialityfor subscribers is well standardized by 3GPP. Authentication andauthorization are based on secure USIM based methods. Furthermore,signaling and user plane traic are ciphered over the air interface. TheLTE network specication does not require user plane traic encryptionin the backhaul and transmission networks, but this is possible withoptional IP security based solutions and is highly recommended whenusing third party transport providers. Most especially, the control andmanagement plane traic must be protected, as a potential attacker

could in some locations have relatively easy access to the physicalconnections of the transmission links at base station sites.

User identity management and related user priority level and serviceaccess rights require special attention in public safety communities.Typically, many of the devices used are shared. Thus, the user identityand user prole cannot be based on a common USIM inside the device.If the USIM is kept inside the mobile device and used for network accessauthentication and authorization, another method is needed for actualuser authentication and setup of the access prole (for example QoS).Alternatively, public safety users could have individual USIM cards, butto 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 safetycommunication content is highly sensitive and therefore condentialityin public safety communication must be based on end-to-end security inthe application layer. This guarantees condentiality without any specicdependency on the security solutions implemented in the network forthe user plane traic. The same end-to-end security approach is alsoused, for example, in current TETRA networks. Due to the sensitivecommunication content, the public safety application servers andcontent storage devices must be located at highly secure sites.

Public safety networks must also support traic separation using VPN

technologies. If the same network is used by a public safety user andother regular subscribers, public safety traic must be separated,for example using VPN solutions commonly used for enterprises.Furthermore, dierent public safety agencies should be separated fromeach other with controlled interconnection interfaces between agencies.



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Network resilienceNetwork resilience is based on high-availability and redundancysolutions on multiple layers. Most resilience features needed in publicsafety networks are commonly available from LTE manufacturers.However, commercial LTE networks may not implement resiliencefully to fulll all public safety requirements. Most network elementshave high-availability designs, for example, to recover from hardwarefailures. Pooling of elements and load balancing between core elementsimproves system reliability and guarantees network service availability,even if a single node fails.

Centralized functions like management systems and core networkelements are usually located in at least two geographically separatedlocations, in order to survive possible complete site failure. Connectivitybetween sites and network elements supports resilience against link andnode failures. Backup connections and nodes can generally be designedinto the IP transport network, and specically for IPSec tunnels, timingsynchronization, management connections and signaling (e.g. Diameterrouting).


Connectivity & routing Resilient IP network design with

fast re-routing Interface protection IPsec backup & emergency bypass Redundant Diameter routing

Management & automation Outage detection Automatic re-confguration Self-healing

Cloudifcation Elastic scalability for

virtual network functions

Automatic load balancing andresource allocation

High available nodes Redundant HW units

(e.g. fans, power, blades) Redundancy options (N+, 2N) Session continuity in switchover

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

Geo-redundancy OSS, registers and core

elements in geographically

distributed sites 3-site database replication

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 SelfOrganizing Network (SON) automation tools can detect events like celloutages and activate automatic self-healing. The network must also beprepared for power outages and solutions such as battery backup andgenerators are common in current commercial networks. There is onemore topical technology that is not driven by resilience requirements,but can further enhance system availability. This is the transfer ofnetwork function to a cloud, enabling elastic scalability and automaticload balancing.

Resilience in LTE public safety networks can be further enhanced fromtypical commercial LTE networks. Public safety networks can have

dedicated core network elements for public safety services (HSS, EPC,IMS, ASs), which simplies the dimensioning and enables managementof peak load at a lower level for better performance and more reliableoperation.

Natural disasters can destroy base station sites and networkconnections and therefore rapidly deployable cells are important fordisaster recovery [See Network coverage and capacity].

Future features also enable local communication when network coverageis missing or the backhaul connection is disabled. For example, asmentioned previously, 3GPP proximity services will introduce direct

device-to-device communication. 3GPP is also expected in Release 13to support isolated E-UTRAN operation for public safety [ReferenceTS 22.346]. This means the eNodeB site can continue oering networkservices locally, even if backhaul connection to core network sites is lost.

One further consideration for network connectivity resilience is basedon the Internet service model, i.e. enabling access independent publicsafety services. Such a model would allow authorized access to publicsafety services via any broadband capable IP access. Public safety userscould have subscriptions that allow connection to the LTE access of allnational mobile operators. As a backup option, WiFi or satellite accesscould be used when other services are not available.



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Network coverage and capacityService coverage for public safety users is critical and previous TETRAsolutions, operating in low frequency spectrum, oered coverage almosteverywhere. It is a critical requirement when moving to commercial LTEnetworks that this coverage is maintained and if possible, enhanced.Public safety networks must provide very high national geographiccoverage - not only high population coverage. Furthermore, public safetyusers may have to work in various indoor locations where commercialmobile services are not currently available.

The most basic approach, for a simple and cost eicient coverage is touse lower frequency bands. In the case of broadband LTE this typicallymeans bands in 700 MHz and 800 MHz ranges. Even lower bands like450 MHz are considered, but this typically results in a compromisedbroadband performance due to a narrower available bandwidth.

The deployment of macro network coverage uses well known optimizationsemployed in commercial LTE networks. Cell range is normally uplink limitedbecause of the low transmission power allowed in mobile devices. Widearea coverage of high transmission power and the receiver sensitivity ofeNodeBs can be optimized with a number of techniques, such as 4-wayreceiver diversity, higher-order sectorization and TTI (transmission timeinterval) bundling. Cell range can be extended in the uplink by specifying

high power mobile devices (power class 1, 31 dBm) also for other thanexisting band 14 (in other bands only class 3 devices, 23 dBm, specied).

Indoor coverage can be optimized with dierent indoor solutions suchas distributed antenna systems (DAS) and low power indoor cells, alsoknown as small cells. Small cells can be used for lling indoor whitespots. However, specialized in-building solutions will not solve all indoorcoverage issues except in selected buildings.

Capacity is an additional aspect that must be taken into account innetwork dimensioning. Although the number of public safety users issignicantly lower than regular subscribers in any commercial mobilenetwork, the number of simultaneously active public safety users can

be very high, especially in a relatively small area when a major incidentoccurs. Such situations are more likely to happen in dense urban areasand therefore the network planning in urban areas should follow thesame principles as in commercial networks, i.e. a denser site grid andsmaller cells in urban locations. Capacity requirements in public safetynetworks can make high demands on the network design due to newpublic safety video applications. If for example there is a need formultiple HD quality video streams in cell edge radio conditions, then10 + 10 MHz FDD spectrum would be far from adequate and thereforemore carrier bandwidth is needed.

Regardless of how well the network is designed and implemented, there

will always be emergency incidents in locations without existing networkcoverage (outdoors or indoors). Additionally, public safety network



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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 networkoperators should be prepared with rapidly deployable base stationsolutions. Deployable solutions should enable fast macro coverageto provide and recover network availability in both rural and urbanlocations. Rapidly deployable small cells may be required in diicultindoor locations such as mines and caves and can be further used foran instant capacity boost when required. Rapidly deployable small cellscan be also pre-installed in emergency vehicles in order to automaticallyprovide network coverage around the vehicles.

Availability of radio communication is further guaranteed by providingdirect device-to-device communication. In LTE this is enabled by 3GPP

proximity services [See Device to Device Communication]. ProSe canpartially solve network coverage white spot problems based on theProSe device relay solution.

Availability and reliability of service coverage can be improved using theresilience mechanisms mentioned in the Network resiliencesection,i.e. allowing service access via any national broadband capable networkincluding HSPA and WiFi or via satellite access. Other techniques, suchas Assured Shared Access coupled with MOCN (Multi-Operator CoreNetwork) could be used to improve the economics of deep rural coverageand improve the service proposition by allowing all operators lowfrequency 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 poolingthe spectrum, a much enhanced service is available and use of MOCNtechnology would allow all operators to provide service from this sameeNodeB in a location where it was previously uneconomical to deploy.Using the catalyst of emergency services coverage to improve the mobilebroadband oerings in rural locations can only improve the economicsand personal well being of people living in these remote locations.


Figure 10. Rapidly deployable macro eNodeB on a trailer


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ConclusionsPublic safety networks provide communications for services like police,re and ambulance. In this realm, the requirement is to develop systemsthat are highly robust and can address the specic communication needsof emergency services. This has fostered public safety standards suchas TETRA and P25 that provide a set of features not supported incommercial cellular systems. TETRA and P25 networks are implementedin low frequency bands for better coverage, often using the 400 MHzband range. The main disadvantage of the current systems is very limiteddata connectivity. The supported data rate can be less than 10 kbps andeven in the enhanced TETRA specication the data rate is around 150

kbps. For evolution of public safety networks over mobile broadband, LTEhas been the technology of choice.

The evolution from current narrowband systems to LTE based public

safety will take several years and will happen gradually. During thetransition period, public safety agencies are expected to use existingTETRA and P25 systems in parallel with LTE based systems. The rst andthe simplest step is to rely on TETRA and P25 in mission critical voiceand messaging, while LTE can oer enhanced data services, potentiallywith slightly lower reliability. Initially oicers will use separate TETRAor P25 and LTE smart devices, but at some stage, device vendors mayimplement multimode devices supporting several technologies in thesame device. In the distant future we assume that TETRA and P25technologies will no longer be maintained and all public safety servicerequirements will be fullled by LTE networks. Service interworking will

be crucial in the evolution to public safety solutions based on LTE alone.


TETRAorP25

LTE

Best effort broadband data Prioritized broadband data

Pre-standardPTT

3GPP Rel-13MCPTT

Mission critical communication

Pre-standard

interworking

3GPP Rel-13

interworking

Figure 11. Evolution to LTE based public safety services


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ReferencesTS 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 publicsafety; Stage 1



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Nokia is a registered trademark of Nokia Corporation. Other product and company names mentioned herein may be trademarks or trade names of theirrespective owners.

NokiaNokia Solutions and Networks OyP.O. Box 1FI-02022Finland

Visiting address:Karaportti 3,ESPOO,FinlandSwitchboard +358 71 400 4000

Product code C401-01129-WP-201411-1-EN

Nokia Solutions and Networks 2014

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