Spectrum for Public Safety LTE
Legacy PPDR (Public Protection and Disaster Relief) systems have limited mobile data support and therefore authorities globally plan evolution towards next generation public safety (PS) communications with mobile broadband capability. LTE is the choice for the first globally common technology for public safety i.e. current TETRA, Tetrapol and P25 systems will be gradually migrated to LTE [TCCA, APCO]. Although few countries have already started projects to deploy LTE based mission critical communication systems, it will take quite some time before significant number of governments will invest in new LTE based systems. For example Germany has just been finalizing its nationwide TETRA network in end of 2015 [BOSnet], so it is hard to expect any German federal government budget for a new network deployment in near or mid term.
Legacy PPDR systems have been deployed on dedicated spectrum. For example TETRA is often running on 400 MHz frequency range. Public safety organizations expect reliable communication in their daily operations as well as in special mass events [TCCA analysis], and dedicated spectrum certainly improves the network and service accessibility. However allocating dedicated spectrum for broadband communication below 1 GHz is not straightforward due to limited spectrum resources. Dedicated spectrum allocation for PPDR has also a price, because it cannot be used for commercial communication. This should be also considered because use of mobile broadband data increases continuously and number of commercial mobile subscriptions is significantly larger than for example TETRA users. In Germany, there are around 500 000 TETRA users while the number of commercial mobile subscriptions is over 110 million. Therefore some authorities consider also alternative approaches to share spectrum and LTE radio access between public safety and commercial users.
Public safety spectrum decision examples
South Korea selected traditional model and allocated dedicated spectrum for nationwide LTE public safety network [Korea spectrum]. 2 x 10 MHz FDD spectrum was allocated from band 28 (700 MHz). It is important to note that band 28 is becoming common commercial LTE band globally and it has already a good device ecosystem. A completely new nationwide LTE network for public safety will be deployed and operated by mobile operators. The first phase was won by Korea Telecom (KT) and SK Telecom (SKT) [Korea PS LTE]. The objective is to have nationwide coverage by end of 2017.
US has also allocated dedicated spectrum for LTE public safety. The allocation was the whole band 14 (700 MHz), which is 2 x 10 MHz FDD band. Congress has authorized an independent authority, FirstNet, to build and operate nationwide public safety broadband network [FirstNet]. Although the main focus is on dedicated network with own spectrum the architecture is also supporting LTE access via partner mobile operators [FirstNet Acrhitecture]. This is the so called hybrid model, which includes typically dedicated coverage in urban areas while the rural coverage cost can be reduced by sharing radio access with mobile operators. Band 14 is North America specific spectrum for public safety. Therefore it cannot use products from existing commercial LTE ecosystem: However the market is large enough to attract device and network infrastructure vendors to develop products for band 14. Official bidding process will start in January 2016
UK has selected completely different approach. There is no dedicated spectrum allocation for LTE based PPDR system. Instead UK Home Office decided to select a mobile operator, who provides LTE access for public safety users [UK Emergency Services Network]. There will be a dedicated core network, which includes communication applications and subscriptions for public safety users. However radio access is based on commercial spectrum that EE has and PS users access services via same LTE carries and base stations as commercial users access their LTE services. This means that PS users in UK can use existing commercial devices although also special ruggedized device will be required. Anyway the first ruggedized devices can be developed based on chipsets that support existing commercial LTE bands. UK Home Office has selected the winners and public safety LTE services should be available in 2017.
France is an example with dedicated PPDR spectrum, but still different to Korea or US cases. France allocated 2 x 3 MHz from band 28 and 2 x 5 MHz below band 28 [France 700]. The 5 MHz FDD slice was not even standard LTE band when France made the decision. It will be inside a new band 68, which will be standardized in 3GPP release 13 by March 2016. The total bandwidth is less than in US & Korea, and furthermore it is composed of two relative narrow slices for broadband communication. France has one more challenge with the new band 68. So far no other country has selected it although there is strong interest for band 68 at least in Middle East. If band 68 remains PPDR specific and only couple of countries select it, the availability and cost of devices may be a problem. The France PPDR spectrum is one of harmonization options identified for CEPT countries [ECC Report 218]. Also WRC15 concluded to encourage administrations to consider parts of the frequency range 694-894 MHz for PPDR applications [WRC15]. However these PPDR spectrum harmonization recommendations do not limit national regulators. It remains to be seen, how the ecosystem evolves for band 68 PPDR systems.
Public safety LTE technology aspects
When authorities make PPDR spectrum plans, there are also certain technology consideration at least with current standards and ongoing 3GPP work items.
Public safety users often work in extreme locations, which are also challenging for mobile network coverage. While there are technical base station solution, which can improve some 2 - 3 dB the uplink coverage (LTE coverage is uplink limited), the UE output power could also help, but currently 3GPP specifications support high power UEs (Class 1, 31 dBm) only in band 14. Operation on any other band is now limited to Class 3 (23 dBm) devices [3GPP TS 36.101].
Public safety users expect also that communication is possible out of terrestrial mobile network coverage. Typical solution is direct mode operation, which means that mobile devices support direct group communication when no network infra is available. 3GPP has also taken this into account and specified initially in 3GPP release 12 proximity services (ProSe) including LTE direct communication for public safety UEs. Although the technology is exactly what public safety users expect to have, there are spectrum limitations. Release 12 specifications support direct communication only on bands 3 (1800 MHz), 7 (2600 MHz), 14 (700 MHz), 20 (800 MHz), 26 (850 MHz) and 28 (700 MHz) with 10 MHz channel bandwidth and on band 31 (450 MHz) with 5 MHz channel bandwidth. There are no ProSe spectrum enhancements planned for 3GPP release 13. So LTE direct communication is not yet supported on any LTE band or any LTE channel bandwidth.
One more thing is that dedicated PPDR spectrum will never be very wide. Currently 2 x 10 MHz FDD spectrum has been allocated for PPDR in some countries. This means with 2x2 MIMO max 75 Mbps peak rate performance in excellent radio conditions. This is already now far from commercial products, which support 3 carrier components up to total 60 MHz bandwidth and 450 Mbps peak rate. So dedicated PPDR spectrum only will not allow public safety applications to benefit from the latest mobile broadband technology performance.
Based on the early adopters and their plans for LTE based public safety, there is no joint global approach for managing spectrum for public safety communications. Only common things are LTE technology and preference for spectrum below 1 GHz.
So far dedicated spectrum is typical decision, but there is no globally harmonized spectrum. Because first responders need ruggedized special devices, there is risk that devices can be market specific with low volumes and therefore expensive.
UK made a bold decision to provide PS services over commercial LTE access. Maybe UK is an example particularly for smaller countries, which want to deploy cost efficient solution for small number of public safety users. Technically there are no major problems to prioritize first responders over other users in all network load conditions.
UK and Korea decided to provide services over LTE spectrum, which is also widely used in commercial networks. The clear benefit is better chipset and device ecosystem, which hopefully reduces device prices even if special ruggedized variants are needed.
France decision to select fragmented PPDR spectrum, which is not yet fully standard, has certainly challenges to become attractive for network infrastructure, chipset and device vendors. If other major European countries follow the same spectrum plan, then there is an opportunity for wider harmonization and better ecosystem. Anyway the France PPDR allocation is not optimal for future public safety applications that expect high broadband performance.
3GPP public safety features that are frequency specific need further work in order to enable public safety LTE with wider range of bands and channel bandwidths. So far for example Korea, US and UK are pretty fine at least with opportunity to use LTE direct communication. But high power UEs can be available only for band 14 markets based on 3GPP release 13 specifications.