LTE networks for public safety services
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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 Page 2 networks.nokia.com
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 • Location services • Physical layer • High power devices • Group • Mission Critical
connections and positioning enhancements to for Band 14 - 1.25 Communication Push-to-Talk
• Basic support for support for LTE increase data Watts for public System Enablers
• Enhancements to
Voice over LTE throughput safety devices for LTE
• Multimedia Proximity-based
(telephony) (including LTE- significantly
Broadcast / • Proximity-based Services
Advanced features) improving the
• Support for LTE Multicast Service Services
coverage of an LTE • Isolated E-UTRAN
Band 14 • Relays for LTE, e.g.
• E911 or network, benefiting Operation for
• a rich set of QoS to allow a base
emergency calling public safety users Public Safety
priority and pre- station mounted
support and reducing
emption features on a fire vehicle to • MBMS
network
• Enhanced Home relay Enhancements
• Highly secure deployment costs.
LTE base station: communications
authentication
and ciphering “Cell On Wheels” from firefighters in
a basement back 3GPP work ongoing - 3GPP work started -
• Self-Organizing to the network. completion expected completion expected
Networks (SONs) 1Q2015 2016
Figure 1. 3GPP Road to Public Safety
Page 3 networks.nokia.comNokia 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. Page 4 networks.nokia.com
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. Page 5 networks.nokia.com
Public safety Public safety Public safety Public safety
services services services services
AS
AS, AS, AS,
VPN or IMS, IMS, IMS,
Internet PCRF HSS PCRF HSS PCRF
AS,
HSS HSS IMS, HSS P-GW
PCRF MME S/P- MME S/P-
GW GW
MME S/P- MME S/P- MME S- S/P-
GW GW GW GW
MME
Shared or
eNB Shared eNB Shared eNB Shared eNB dedicated eNB dedicated
spectrum spectrum spectrum spectrum spectrum
Mobile operator Mobile operator Mobile operator Mobile operator
Public safety Hosted MVNO RAN sharing for Private LTE for
over MBB public safety public safety public safety 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.
Page 6 networks.nokia.comRoaming 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 Core site HSS, SPR Core site
PTT , Live
Group Comm video sharing
Management Charging
PCRF
MME S/P-GW IMS AS
Cell site (e.g. VoLTE)
Interworking Tetra/P25
core
BM-SC MBMS-GW DNS FW Load Bal. Agency 1
eNodeB
Cell site
Control room / Dispatcher
IP backbone
IP backhaul Agency 2
eNodeB
Internet Control room / Dispatcher
Tetra/P25 BTS
Figure 3. Network architecture overview.
Page 7 networks.nokia.comGroup 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
PCRF
Rx Priority level, session information
Bearer status info
SGi Data related to GC1
Downlink traffic (unicast)
S/P-GW GCS AS
Uplink traffic
MBMS bearer mgmt
MB2 Group identity mgmt
Downlink traffic (broadcast)
BM-SC
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.
Page 8 networks.nokia.comIn 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. Page 9 networks.nokia.com
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 Connectivity via
other UE
User Equipment to
Prose Discovery Prose Communication
Network Relay
Figure 5. High level Proximity functionality.
Page 10 networks.nokia.comThe 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. Page 11 networks.nokia.com
Mission Critical Push to Talk
Mission Critical Push to Talk (MCPTT) provides one-to-one and one-to-
many 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 multi-
unicasting 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 RTP packets
UL/DL unicast DL broadcast
eNodeB
BM-SC
eMBMS
eNodeB
Figure 6. Mission Critical Push to Talk.
Page 12 networks.nokia.comPrioritization 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
PCRF
emergency responders (ARP)
MME
3. Emergency calls and multimedia priority AC 14 X P/S-GW
services (MPS) calls get end-to-end eNB
priority treatment.
• High priority bearer with
X pre-emption capability (ARP).
4. User plane traffic is prioritized and AC 0-9
• Traffic prioritization matching
service requirements (QCI)
scheduled according to QoS parameters
(QCI, GBR/MBR, NBR).
Figure 7. User and bearer prioritization tools.
Page 13 networks.nokia.comOperators 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 pre- emption. 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 “non- GBR” 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]. Page 14 networks.nokia.com
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 Option 2 – Dedicated bearer for mission critical QoS
PCRF can trigger QoS HSS/SPR PCRF can trigger setup of HSS/SPR
modification of default bearer dedicated bearer
AC 0-9 PCRF Mission AC 0-9 PCRF Mission
critical critical
service service
P-GW P-GW
MME MME
eNB eNB
AC 14 Public safety AC 14 Public safety
APN Non-mission APN Non-mission
AC 14 critical AC 14
critical
services services
Public safety user Dynamic modification of Public safety user Dedicated bearer for
in emergency default bearer impacts in emergency mission critical service
mission. on all service flows mission. flows
Figure 8. QoS options for mission critical service flows.
Page 15 networks.nokia.comSecurity 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. Page 16 networks.nokia.com
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. Page 17 networks.nokia.com
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 Connectivity & routing
• Redundant HW units • Resilient IP network design with
(e.g. fans, power, blades) fast re-routing
• Redundancy options (N+, 2N) • Interface protection
• Session continuity in switchover • IPsec backup & emergency bypass
• Redundant Diameter routing
Inter-node resilience & pooling Management & automation
• MME pooling with S1-flex • Outage detection
• P/S-GW load balancing • Automatic re-configuration
• CSCF load balancing • Self-healing
• AS pooling
• Redundant timing master
Geo-redundancy Cloudification
• OSS, registers and core • Elastic scalability for
elements in geographically virtual network functions
distributed sites • Automatic load balancing and
• 3-site database replication resource allocation
Figure 9. High-availability and resilience on multiple levels.
Page 18 networks.nokia.comIt 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. Page 19 networks.nokia.com
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 networks.nokia.com
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 networks.nokia.com
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 Prioritized broadband data
LTE
Pre-standard 3GPP Rel-13
PTT MCPTT
Pre-standard 3GPP Rel-13
interworking interworking
TETRA
or Mission critical communication
P25
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.
Page 22 networks.nokia.comReferences
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
Page 23 networks.nokia.comNokia is a registered trademark of Nokia Corporation. Other product and company names mentioned herein may be trademarks or trade names of their
respective owners.
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