The growing demand for data means evolution towards hybrid networks incorporating LTE, and eventually LTE-only networks. What does this mean for TETRA network planning? Vaughan O’Grady investigates
Network planners have to take a great many factors into account if their networks are to provide sufficient coverage
Although mission-critical features will soon be rolled out for LTE, TETRA isn’t going away in a hurry and neither is the need for access to radio spectrum, system architects and radio frequency (RF) planners, when building a new network or expanding an existing one.
While TETRA has relatively narrow RF carriers (25 kHz), and limited data capabilities, TETRA networks offer excellent coverage using fewer base stations than many other competing technologies. Also, voice capacity planning is less problematic: voice calls are often group or broadcast calls, and very efficient in their use of system resources. “The radio spectrum required by say an emergency services network using TETRA is tiny compared with a national 4G network,” says Adrian Dain, principal consultant with IT consultancy Mason Advisory.
Of course, depending on the country, you may be planning for a varied customer list. Alexander Heinz, chief information security officer at Hytera Mobilfunk GmbH, a supplier of PMR solutions and products, says: “Having implemented projects in all areas – from transportation, airports, industries and retail to public safety organisations – we know that each segment has its very special requirements.”
However, he adds: “Within all this, public safety is the most complex segment. Typically, several emergency services share the network and requirements on availability and security. In public safety networks we typically have to integrate with existing or new command and control infrastructure.”
As a cellular system, TETRA does offer challenges familiar to those who have worked with GSM, though frequency reuse is more problematic. “You have fewer channels to work with, so you have to be quite careful in your planning,” says Dain. That said, modern TETRA radios, mobiles and base stations are more sensitive than earlier versions, and able to work with lower received signal power levels. “That does help with radio planning to a certain extent,” says Dain.
Heinz adds: “The maximum level of interference is one of the factors determining reuse of frequencies and therefore the efficiency of frequency use. We have implemented a sophisticated way to activate capacity only in areas where capacity is needed with our capacity manager. This tool monitors and visualises the current state of the network utilisation and activates carriers where needed, considering reuse and maximum interference levels.”
Site acquisition has become more straightforward. The long-standing planning upside – that you need fewer sites than GSM or 3G – hasn’t changed. However, Vincent Seguy, responsible for radio network engineering with Airbus Defence and Space subsidiary Secure Land Communications, which develops, installs and maintains PMR platforms, network solutions and devices, points out that “site acquisition is really key for being competitive in a tender”. That means saving on acquisition costs and time by site-sharing. “Maybe 10 years ago we were used to designing networks based on greenfield sites. Today we are really focused on using existing sites and sharing with other operators.”
It certainly helps that TETRA base stations are getting smaller, simplifying site acquisition and making power needs less onerous. But mains electrical power is still a serious consideration. Dain notes: “Emergency services – and indeed utilities – generally want UPS [uninterruptible power supply] support at every base station, so as the base station electronics are miniaturised, the UPS system has become the bulkiest part. A number of emergency services require additional diesel back-up as well – so this adds to the space requirements.”
Terminals offer another, slightly unusual, challenge. Priit Roosipuu, head of network planning at Boftel Estonia OÜ, a service provider specialised in telecommunication networks services, asks: “Which type of terminals are used in a network? Is it in-car terminals with external antennas or handhelds? That’s the main issue on the planning side. Usually the [handheld] TETRA terminals are placed on a belt – you have a microphone on your shoulder. The loss of signal could be higher because this is not an ideal position. In a commercial network you usually take your mobile out and talk; you hold it in your hand and then it gets better coverage.”
Coverage planning in general is also a challenge, despite the fact that TETRA is much more efficient than its consumer counterparts. “Contractually, no vendor would commit to providing a 100 per cent signal coverage guarantee,” Dain says. “With a TETRA network you might have a contractual agreement to cover a target percentage of the land mass or so much of the population. You have to build the radio frequency plan around achieving those coverage objectives.”
Roosipuu adds: “TETRA also supports direct mode operation and this will extend the coverage. If you get one police car in a place this will act like a repeater. With commercial networks you always need to go through the switching centre or the network operation centre to get the connection up and running. But in TETRA you can just reach for the first base station and then come back to the user.”
Small TETRA networks do exist and Airbus cites a growing TUI (transport, utilities and industry) market but, as far as the enterprises’ requirements are concerned, there is unlikely to be much planning complexity.
Whether a network is big or small, indoor coverage is still an issue. Dain says: “The 380-400 MHz band is good at penetrating buildings and for propagating around urban areas.” TETRA also has features to extend its reach; for example, an ambulance parked on the street can be used as a direct mode gateway for paramedics calling from a patient’s location inside nearby buildings; but otherwise, as Roosipuu says: “Especially in Finland we see more TETRA indoor solutions coming up.”
He continues: “Hospitals get indoor coverage with a dedicated network such as a distributed antenna system, which is usually combined with a commercial wireless network like 3G or 4G. Usually they are in the same network. TETRA gets a better signal, but what happens quite commonly is that TETRA doesn’t get base stations; TETRA gets repeaters. Because capacity is not the big issue with TETRA – most users make group calls.”
Hytera’s Heinz adds: “We have smart solutions, which deliver coverage for existing networks using a standalone base station, but also use a conventional repeater system to get radio coverage into the buildings.”
While the full range of small cells available for indoor coverage for commercial cellular networks is not matched by TETRA, a number of indoor base stations do exist. They include The ACCESSNET-T IP DIB-500 R4.1, the TetraFlex range of indoor base stations from DAMM, and units from Sepura, Motorola and others that operate in both indoor and outdoor environments. A recent arrival is the Airbus pico base station – TB3hp (for high power) – which is seen as mainly having indoor applications. It is, says Seguy, “well suited for building coverage, tunnel coverage and temporary coverage”.
Coverage is also one of the considerations driving redundancy planning: a much more urgent issue for the mission-critical or emergency networks TETRA often serves. As Seguy says: “We have redundancy on the backbone first: we define several paths to each base station. We have dual redundant switches. We have [redundant] coverage – a lot of overlapped areas. Redundancy is everywhere.”
Hytera’s Heinz explains: “Redundancy in all levels of a network architecture basically gives the network operator time to repair components. This is especially the case for switching centres. We recommend having them physically separated.” He adds: “Our base stations support transceiver, controller and power supply redundancy.”
Seguy adds: “The DRP – disaster recovery plan – is mandatory. We need to design and plan the network for DRP. We also have to cope with hardening, firewalling – all those activities related to performance, security, resilience. This makes the network planning more complex.”
Resilience also means cost, of course. “It’s always a trade-off between the technical solution and the cost that has to be taken at the network planning stage to make sure that we are competitive enough,” Seguy says.
Mission-critical users often require UPS support and diesel generators for their base stations, adding to on-site space requirements
Can technology advances or processing power help the planning process? Heinz notes: “Radio planning is still a complex topic as it has many dependencies like hardware constraints, available spectrum and capacity demands.” However, planning tools have become more sophisticated. “Compared with the beginning of TETRA, we now offer sophisticated measurement tools and devices which can be used to optimise the network.”
The ongoing transition to IP has also helped. Hytera has been delivering TETRA systems based on completely IP-based technology since 2009. “Our move from a PCM-based switching core to a fully IP-based switching dramatically reduced the complexity of hardware set-up and made our system very flexible for changes in the configuration,” says Heinz. Virtualisation is another key development. “With the virtualisation of servers we can even be independent of server hardware and can completely separate the installation of hardware from the deployment of software.” Seguy agrees: “Virtualisation is on its way,” he says and, referring to planning tools: “The enormous processing power now available is instrumental in making these advances possible.”
Dain adds: “I’ve seen radio planners working on laptops at airports on their way to meetings. In the early days you had to run those tools on substantial computer workstations that would keep crunching numbers through the night.”
It isn’t all good news for planners. IP backbone networks do make transmission planning easier but, as TETRA turns to IP, says Seguy, “we have to deal with redundancy, integration of third-party systems, RF acceptance testing. Drive test has become more difficult to address. We have to integrate a lot of subsystems also due to the IP and the growing demand for data and capacity.” Meanwhile, the installed base has to think about migrating networks from time-division multiplexing (TDM) to IP, product renewal and so on.
On the up side, many customers understand IP. Also, plenty of equipment – such as transmission, servers and IP routing – is almost ‘off the shelf’ these days. However, customers or consultants who understand IP may be inclined to draft a more demanding request for proposal (RFP).
An increasing number of data applications are available too, but they are already adding complexity to planning. As Seguy points out: “The applications are getting more and more demanding in terms of capacity.” He cites command and control applications, text messages, automatic vehicle location and LBS, among others. Heinz says: “Our TETRA system today supports single slot and multi-slot packet data as well as TEDS for high-speed data. The demand for data depends on the application scenario. We recently successfully tested the use of TETRA data services to transfer ETCS [European Train Control System – a signalling, control and train protection system standard-based train control data for a railway]. These kind of applications are very demanding as the loss of a data connection leads to an immediate emergency brake action. In this sense, the growing data demand comes from the fact that our system is able to support certain new segments.”
TETRA data services are undoubtedly an important development. Realistically, however, TETRA cannot compete with LTE as far as bandwidth is concerned, which is why most experts see a hybrid TETRA/LTE network as part of the eventual evolution to a broadband data service. This may bring new challenges to network planning, although not only tools but examples of actual network updates are available or on their way, notably through Airbus Defence and Space’s work to modernise the VIRVE network in Finland that supports public safety and security services and armed forces. Airbus now offers the Tactilon Suite broadband solution for hybrid networks, which it claims allows secure broadband capacities to be added to existing PMR networks.
This is an area where solutions are already being offered
by a few manufacturers. As we reported in May, Sepura launched its hybrid TETRA and LTE eNEBULA infrastructure solution at CCW 2016 in Amsterdam. Meanwhile, Teltronic claims that, with its eNEBULA platform, it “offers first-responders the possibility to access solutions based on TETRA market profitability, as well as establishing a clear path towards LTE services”. Planners – and operators – will no doubt be expecting the number of supporting technologies and manufacturers to expand as the market for hybrid networks grows.
For network planners the road ahead probably depends as much on the region as on the technology. Seguy explains: “I would say the European countries, perhaps except for the UK, will have a hybrid model based on the TETRA/PMR legacy plus a Mobile Virtual Network Operator (MVNO) approach. Plus, in parallel, a legacy system maybe for the next at least 20 years. But in some parts of the world they will go directly to dedicated broadband or a mix of TETRA plus a dedicated broadband approach. It really depends on the region.”
The transition to broadband will take time, as Seguy has suggested, so TETRA networks will still be planned and rolled out. Processing power, IP, off-the-shelf equipment and more are making this easier, along with the lessons learned from past roll-outs. As Heinz says: “Over the past years we have gained comprehensive know-how in how to set up TETRA networks – which is a big benefit for new customers.” But data and how to plan networks around it are going to be challenges in the coming years, albeit challenges that are already being managed.
Some situations, however, may defeat even the best planners and software. How, for instance, do you ensure you have accurate digital maps for the sort of uncontrolled urban expansion prevalent in some parts of the world? Seguy says: “If you have not updated your digital maps you could be in a very bad situation. For example, urban areas are increasing rapidly in some countries, like in the Middle East. We could commit on coverage which was initially in a desert area – and by the time we go to perform the coverage acceptance, something has been built.”
Even the most impressive technology can sometimes be defeated by human unpredictability.
