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TETRA Communications over LTE
By Susan Layne and Thierry Sens, Strategic Industries, Alcatel-Lucent
TETRA (Terrestrial Trunked Radio) communication standard is widely used and deployed by Government, Transport and Public Safety agencies. This is mainly due to the numerous advantages TETRA provides compared to other radio systems, such as the quality of voice, the number of communication features (trunking, priority/preemption, encryption, recording, etc.) and its multi-vendor interoperability capabilities. TETRA is a perfect solution for operational voice communications. However, with the need to always improve the quality of response and the efficiency of operations, Private Mobile Radio (PMR) network users are willing to use broadband technologies. TETRA technologies cannot meet those new requirements.
LTE (Long Term Evolution), also known as 4G is the perfect technology for building the next-generation of broadband public safety networks, delivering applications such as video-based situational awareness that more difficult with TETRA. LTE offers high throughput (up to 170 Mbps) and low latency (10 ms), making it compatible with any mission-critical application.
However, replacing TETRA with LTE is not a short term option, for many reasons. First of all, LTE does not yet support the voice communication features of TETRA and second, we cannot rip out and replace the huge TETRA installed base in one day.
Alcatel-Lucent demonstrated at TETRA World Congress a very interesting compromise: TETRA communications over an LTE network. A PMR user with a TETRA client application running on an LTE rugged terminal, can communicate with other TETRA users over an LTE network, while using all of the TETRA services. This option opens the way to TETRA/LTE hybrid solutions combining the best of the two technologies to provide broadband overlay services to existing TETRA networks.
Cassidian and Alcatel-Lucent recently announced a joint development agreement under which the two companies will provide an innovative mobile broadband solution for emergency response and security communications systems operating in the 400 MHz spectrum band.
Using LTE technology, the joint Alcatel-Lucent and Cassidian offering will support broadband data services such as mobile video security, location-based video services and smart vehicle integration of devices and applications to complement the current voice and data systems.
This will ease the adoption of LTE (no need for public safety agencies to buy expensive LTE frequencies from government) for using a hybrid LTE/TETRA solution (or LTE as an overlay of an existing TETRA network) and this also opens a better path for a later smooth migration from TETRA to LTE.
With the hybrid TETRA/LTE solution, this enables new applications and services that will change the way emergency responses are delivered.
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very interesting for our LTE E2E Demonstration especially for markets where LTE-overlay is the best solution.
Very interesting, i heard that TETRA over Wimax and now tetra over LTE. what is tetra over LTE, use both TETRA and LTE feature on only one Terminal or TETRA terminal for voice and connect to LTE terminal for tranfer data ?
good idea for this!
c’est interssant de voir toutes ces évolutions de TETRA pour satisfaire à nos besoins. il serait interessant que l’on puisse aussi téléconduire les postes de distribution HTA/BT à travers le réseau TETRA/LTE.
Answer to the question of Mr Tsungu:
The Alcatel-Lucent Tetra over LTE demo consists of one and only one terminal for both voice and data, connected to the LTE broadband data network. On this single terminal, there is a TETRA software client (from the supplier Rohill) communicating with other TETRA terminals, over the LTE network. LTE acts as the transport network for Voice (TETRA) and data.
..and the security & reliability comparison of LTE vs. TETRA is what? I have noticed that no one usually speaks of this. However these are perhaps the most critical points…
Any information on the functional performance of the LTE terminal equipped with TETRA software client.
Sorry for the late replies! Here are answers from our Strategic Industries team:
@dwr: Although LTE is a commercial off the shelf technology, it includes advanced feature to provide a high level of security and reliability. Indeed, LTE is a carrier grade IP based system. For instance, every base stations can be connected to multiple core nodes using different transmission paths, ensuring that the service is resilient to core node or transmission line failure . Then, professional grade reliability can be achieved with a more stringent network design in line with the requirements. Additional E2E security can also be provided by strong E2E IP encryption that can easily be integrated over the LTE IP transmission layer.
@Hugo: The performance of the LTE terminal equipped with a TETRA software client mainly depends on the E2E performance of the LTE network. An LTE network provides broadband transmission of several Mbps and very low and controlled latency (down to 10 ms). This does not affect the performance of the TETRA software on the LTE terminals.
Hello,
Can you advise how the Tetra over LTE handset behaved in relation to Talk Group participation, were the calls point to point or was the heandset still able to subscribe to Tetra Talkgroups?, was any atempt made to subject the handset to DGNA commands? was Tetra status tried at all and was it successful? did the handset application include any GPS features that were able to generate AVLS over the LTE bearer that were then correctly interpreted by a host in the Tetra network? is the handset/Tetra App able to generate an emergency call over the LTE bearer that is recognised by the TETRA network?
Regards
Hello – here’s a reply from one of our expert, Jérôme Brouet:
The TETRA over LTE demo showed at TWC2011 included the capability for the LTE terminal to subscribe to multiple TETRA Talkgroups and to transmit SDS (Short Data Service). The communication to the LTE terminal was using unicast communications over the LTE network; future evolutions of LTE will include the capability to use multicast communication over the LTE air interface to optimise the bandwidth usage in case of large talk-groups.
Linking of GPS information to an ALV system was not showcased during the event, but indeed this can be easily done and has already been demonstrated at other events.
More advanced features, like DGNA, Emergency call were not supported in the demonstration and are already part of further enhancements. Indeed, since LTE is a smart IP pipe offering excellent performances in terms of throughput and latency coupled with a comprehensive framework to support guaranteed and differentiated QoS, this technology is well suited to smoothly support the most demanding applications. Thanks for your interest in our offering, the Alcatel-Lucent team remains at your disposal for further discussion.
Does this implementation of Group call via LTE scale to an arbitrary number of LTE handsets engaged in the call? If we assume tens or hundreds of LTE handsets, does this provide the required immediacy of transmission, and does it include some form of PTT arbitration? If so, is this arbitration handled in the network, or do the LTE terminals have to deal with it (eg similar to Tetra Direct Mode Operation arbitration)? I am trying to understand if this is an interesting demonstration, or a realistic operational feature for emergency/security services.
Hello, I would like to know : the presented solution consists of a LTE network, and on the top of that you implement a TETRA functionality as some kind of ‘overlay network’ – right ? Would it be possible to adopt such kind of solution if you have an existing TETRA network ? What would the necessary changes be ?
Yes the LTE is deployed first as an overlay network, and therefore is compatible with an existing TETRA network. A migration from TETRA to LTE would be the facilitated if the LTE solution used is the LTE 400 MHz solution like the one announced by Alcatel-Lucent/Cassidian called EVERCOR.
Thank you very much for your helpfull response, Stephane !
If I understand correctly, then the main point is that LTE is
at 400 MHz…in that way the LTE network can be established in parallel to the existing TETRA network…where TETRA is covering the voice services and LTE the broadband data services..? Furthermore LTE and TETRA has to interwork in such a way that it appears as an integrated system to the users, right ? (I guess you will have seperate radio terminals for LTE ?) best regards, Volkmar
Yes see this video of Evercor: http://www.youtube.com/watch?v=CDuEMS1N_UY
Hi,
several questions today’
1. Spectrum So it appears that dedicated 400Mhz spectrum is required (or refarming of some of the 400Mhz already assigned for Tetra in many countries). Typically how much spectrum would be asigned to LTE and how much to Tetra, if refarming there must be a trade off here in terms of voice channel capacity availability for native tetra users (those without LTE devices) unless the allocation of bandwidth to both is in some way dynamically assigned.
2. Security – it would appear unlikely that those clients who have a valid security concern would permit LTE devices (not running TEA) to connect to the netwoka, how are Alcatel Lucent and Cassidain addressing this concern 3. ECO System – economies of scale – Whilst I recognise that 400Mhz has it’s attractions (already assinged for PS in many places, range and penetration) it seems like an awfully limited eco system to support reasonably priced dLTE devices running the app, is there not a concern that similar apps could soon be developed for LTE devices running in the more prolific LTE bands,alhtough that spectrum will not be dedicated to Public Safety users?
Regards
Les
Hi Les
here a reply from one of our Public Safety expert:
1. Spectrum – Indeed deploying LTE at 400 MHz may involve refarming of part of the 380 – 470 MHz spectrum. In the 400 MHz tuning range, LTE can accomodate deployments with frequency blocks of 2×1.4 MHz, 2×3 MHz, 2×5 MHz. Some countries have started this process and have been able to identify 2×5 MHz for broadband wireless systems. This leaves enough space to continue narrowband PMR operations in the short/mid term. And as time will go by, additional spectrum will be freed for LTE in this band while moving users from narrowband to broadband networks.
2. Security – LTE per se is a secure system. It features mutual authentication between terminals and infrastructure (i.e. a non trusted terminal cannot connect to a trusted infrastructure and a trusted terminal cannot connect to a non trusted infrastructure). It also includes sophisticated encryption algorithm over the air for both traffic and control messages. If specific encryption is required, end-to-end encryption can be easily implemented on top of the LTE layer.
3. Ecosystem – 400 MHz is indeed a smaller market compared to commercial bands. However, the public safety market is attractive and the 400 MHz market goes much beyond this one since it also includes other mission and business critical users (Defense, Transportation, Utililties) and also some commercial networks in the 450 MHz band.
Best regards
1. The main limiting factor within LTE is the availability of radio channel on the air interface. In LTE, it is very common to experience busy cell and therefore the TETRA user will be able to initiate the call. How do you tackle this issue? Do you have any mechanism other than setting priority on Establishment Cause (EB) bit?
2. Do you need any modification on the SwMI side to accommodate the interconnection to the LTE EPC? If so, are there any standards already in place?
From our Public Safety expert:
1. LTE systems offer throughput of several Mbps to several 10s of Mbps per carrier per sector (depending on the signal bandwidth available). This throughput is shared dynamically with all users / applications in session in the cell. LTE system also implement comprehensive and sophisticated end-to-end quality of service mechanisms that ensure that each user / application is granted the appropriate resources end-to-end in line with their quality of service level. One of the parameters for ensuring quality of service is the priority level. This parameter is used in the event of a congestion of a cell to ensure that higher priority sessions will get access to required volume of resources by pre-empting if necessary resources from other less priority sessions.
2. The interconnection with the SwMI is today based on IP protocols and is proprietary. However, standardization is on the way to enable interoperable interworking between LTE and narrow-band LMR/PMR systems such as P25 or TETRA.
Interesting and well formulated article.
In my view TETRA can be perceived in two blocks: First TETRA is a four time-slot TDMA radio access technology borrowing most of the radio technology from GSM. The divider between TETRA and GSM is GSM has been developed to a mass market primarily of one-to-one communication. TETRA and the other hand was from the beginning designed to meet the needs of the PMR/LMR community therefore driving features as true multicast where several users share the same time slot during group calls thereby utilizing the radio interface/spectrum more efficient. GSM-R, a special flavor of GSM targeting users in the railway industry featured a set of features grouped under the label ASCI, among one shared time-slot multicast similar to TETRA’s.
The second block contains the PMR functions provided by TETRA: one-to-one calls, group-calls, text messaging, presence, emergency call, priority, ambient listening, etc.
By implementing TETRA over LTE all the features of the radio technology block is forsaken and replaced by the LTE (or LTE-A) capabilities and behaviors. Potentially this may be enhanced by introducing eMBMS to implement true multicast also to a TETRA over LTE solution.
From an end-user point of view having the implementation of the traditional TETRA/P25 PMR features available is good enough and the utilized access technology really does not play an important role as long as the PMR system requirements (capacity, latency, reliability, security, etc.) is meet.
My question is then, assuming my interpretation of TETRA over LTE is correct, what really remains of TETRA system in this new version if all is a new implementation of the old/traditional PMR features (and several new such as video services, blue-force tracking, etc.)?
My impression is we really talk about a completely new solution with only a portion of the functional requirements common with the original TETRA technology. Implementations like the EVERCOR and its co-siting of TETRA R1 and LTE enodeb will ease the migration and enable a nice graceful transition, but the bottom line is the two technologies are two completely separated systems bridged only by ISI or similar.
See below for a joint response to your comment.
Interesting ! Especially your suggestion ” My impression is we really talk about a completely new solution with only a portion of the functional requirements common with the original TETRA technology”. I tend to agree with that. If we would assume, that this is realistic, then I have the following questions :
(1) How much – if at all – of the existing infrastructure of the legacy Tetra network could be reused ?
I had lost my second question :
(2) in what time frame (3 – 5 – 8 years ?) could this become reality ?
To Volkmar and Mikael:
Adding an LTE layer other an existing TETRA (or other narrowband technology) has primarily an objective to bring broadband capabilities and expand applications offered to professional users. Such applications relate to the capability to exchange and share in real-time video, images, files and any other data that will enhance the operational effectiveness of the professional users and their safety. Now, when an LTE overlay is deployed, it is also possible to have the existing narrow-band PMR/LMR applications (group calls, messaging, individual calls…) transported over LTE and consequently have interworking between the LTE and narrowband system through a gateway (as highlighted in your post, one should split the overall systems into applications and radio layer; LTE being a flexible and IP QoS aware radio layer, it is indeed easy to transport any applications over LTE). So, the overall solution is new (LTE, new applications) but it also leverages existing applications and servers for existing narrowband PMR/LMR applications (plus in the Evercor solution it also leverages sites and sites equipments).
Regarding the timeframe, from a technology perspective, everything is available for deploying LTE as an overlay over narrowband LMR/PMR and interworking. For a complete migration to LTE, the timescale will depend on user requirements and LTE evolutions to support advanced mission critical communications. For instance, for public safety users, it is extremely important to have direct terminal to terminal communications when users are off-network coverage and massive group calls with several 100s of users for handling exceptional events. These features are not readily available yet, but the 3GPP standardization is working on those in the current release (3GGP Release 12, due by mid 2014) under to working items called ProSe (Proximity Services) and GCSE (Group Call System Enabler). So for the most demanding users, complete migration will be possible when these features will be available; for less demanding users, migration can start earlier.
For developing a Public Safety Network i would like to know the following:
Is tetra infrastructure (base Stations & other Network Components) compatible & upgradable to LTE Network??
What Components of a Public Safety Communication Network for TETRA are Compatible & upgradable with LTE? Please reply