Despite back-up generators the uncaring elements can knock sites down and serious incidents can occur in places where fixed infrastructure would be too costly to install. Sam Fenwick takes a look at the use of mobile base stations to address these issues
A scene from Exercise Unified Response, Europe's largest disaster training exercise © London Fire Brigade
A building has collapsed onto a London Underground station, causing more than 1,000 casualties. They are terrified, shocked and in need of medical attention.
This was the scenario the UK’s emergency services tackled during Exercise Unified Response, Europe’s largest ever disaster response training exercise. No effort had been spared to ensure realism and this included the construction and demolition of a replica Tube station.
The exercise, held between 29 February and 3 March, allowed the UK’s emergency services to practise working together on a large scale. It even had an international input from teams hailing from Hungary, Italy and Cyprus.
All of this required secure and reliable communications. Two-way radio coverage was provided by Airwave, the operator of the UK’s public safety TETRA network, using a mobile base station.
Image: © London Fire Brigade
Airwave is contracted by the Home Office to hold seven emergency response vehicles (which it owns and operates), each of them equipped with 1,040 metres of leaky feeder cable. “They were designed after 7/7 to provide service into the Underground in the event of a catastrophe. We have a contract to get the first two out in really quick time and then a staggered response time for the deployment of the rest,” says Nigel Hardaker, head of network operations at Airwave.
The company also keeps a fleet of five site recovery vehicles equipped with autopan VSAT, a 10-metre hydraulic mast, and self-contained generators that can run off the vehicle’s fuel tank or mains power. These are typically used to provide coverage at sites during large scale power outages, planned works, or when a site’s microwave link is damaged and weather conditions make it unsafe for an engineer to climb the mast to repair it.
Hardaker says one issue to consider is that of set-up time. “They generally take an hour’s set-up time post-driving... That’s because you have to make sure you give it the right sort of radio parameters such as neighbouring and RF-type information to make sure it integrates properly into the network. If you get these things wrong, you put the wrong frequencies in for example, then you can cause more damage than you were trying to recover from,” Hardaker explains.
To ensure that deployment goes as smoothly as possible Airwave plans which frequencies its mobile base stations will use in advance and where they will be situated, when possible.
It also sets them up in areas where it has good reason to believe a gap in coverage may occur. Hardaker gives a recent example: “During storms Eva and Frank a bridge in Tadcaster collapsed. On either side of that bridge there was a telecoms cable that traversed the bridge. While the cable remained intact we knew that if it did fail we would potentially see an impact to our service in Worksop and Skipton.
“So we deployed a mobile base station to both locations, just in case anything happened. We set them up and disabled them remotely and we’d have been able to turn them on within five minutes or so if that cable did collapse on the bridge.”
Mobile base stations are just one of the examples in Airwave’s service continuity toolkit. “All of our engineers have personal-issue generators, so if we have a straightforward power outage onsite rather than rolling out a mobile base station the easiest thing to do is for the engineer to deploy their personal-issue generator,” Hardaker adds. “They each have a 2kW generator which will run a three-base radio site on a single gas bottle for 11 hours.”
“Major public safety incidents – especially where a communications site has been destroyed – do occur, but more commonly it will be the remoteness of the location that demands a coverage extension,” says Steve Valentine, senior director ASTRO & TETRA infrastructure product management at Motorola Solutions. “This is not unusual when dealing with forest fires or accidents such as aircraft crashes.”
Motorola Solutions also sees regular non-incident deployment for temporary work sites established in remote regions. Examples include pipeline laying or open cast mining operations where the site is likely to move semi-regularly.
“It is not uncommon for transportable TETRA systems to be procured to manage a construction phase before evolving into a plant’s formal communications system,” Valentine adds.
Valentine notes that a simple means of increasing resiliency is by connecting two small base stations together. While mobile base stations come in a variety of sizes he says that one of the most popular solutions Motorola Solutions delivers is a custom 4x4 vehicle installation for quick deployment as a coverage or capacity enhancer to an existing TETRA network in case of an incident.
This can involve equipping the vehicle with a MTS2; a small, deployable base station with fan-free cooling capability making it ‘ideal’ for use in rural or inaccessible sites where maintenance can be expensive and difficult. The full solution could incorporate a pair of base radios to enhance capacity, a TETRA repeater and a VSAT backhaul. The vehicle can then be deployed as either a standalone repeater for existing TETRA coverage in areas of RF shadow, or as an entirely new TETRA site to radiate on no coverage zones or as replacement for an out-of-service site.
The military’s long-term evolution
Several manufacturers are starting to offer mobile base stations that combine both TETRA and LTE to provide secure, reliable voice and broadband data. Examples include Teltronic’s TETRA + LTE Deployable Base Station, which it launched at last year’s Critical Communications World. It uses the company’s eNEBULA infrastructure. As a TETRA base station it features two carriers, or when working in dual mode it can deliver a TETRA carrier and an LTE eNodeB.
A similar approach is also being considered by the German armed forces (Bundeswehr) to bridge ‘the last mile’ i.e. providing every soldier with voice and data connectivity. It has been testing HochZeN (Hochmobile Zellulare Netze or Highly Mobile Cellular Networks) – a solution supplied by Airbus Defence and Space and Alcatel-Lucent (which has been acquired by Nokia). For stationary cells, and depending on distance and the height of the antenna, data rates of between 100 kbps and two Mbps and distances of up to 20 km were attained when LTE and TETRA were used in parallel.
Blackned, a German SME, is also working with the military, but rather than focusing on TETRA-LTE integration it provides an in-vehicle mobile LTE system and ultra mobile backpack system with mesh EPC and networking capabilities, as well as various uplink types including satellite backhaul. Timo Haas, Blackned’s managing director, says that part of the thinking behind it is that “the network needs to follow the mission, rather than the mission following the network”.
One of the important features often requested by military forces is a reduction in the size and visibility of external antennas and other communications equipment as it makes the vehicle in question a target. This is because enemies assume a vehicle with these is a command vehicle and therefore taking it out will reduce cohesion and morale. Haas adds this is also an issue for public safety users and is something that Blackned is working towards solving with its current military prototypes.
One of the key challenges for any mobile network operator looking to serve the public safety sector is how to provide sufficient coverage, particularly in rural and lightly populated areas in an economic way. Use of mesh-networked, mobile base stations could reduce public safety users’ need for fixed infrastructure.
“We had a conversation with the traditional vendors about this scenario and none of them fitted into it, so we started customising with companies such as Core Network Dynamics (CND), Fraunhofer Focus and others,” says Haas. “We will have a commercial release this year at Critical Comms World... There we will be presenting the backhaul mobility/ MESH EPC concept to the public safety community.
“We’re finalising the prototype – the lab phase should end mid-March and go into field tests. Right now we have a big test bed installation with four equipped cars and different RAN vendors. We’re raising partnerships with system integrators in France and all around to get that project handled,” he adds. Haas explains that Blackned has had to simplify CND’s software as it is a “full-blown” evolved packet core and as a consequence the system doesn’t have optimised coverage, “but we think the way to cope with that is just to equip more cars and make [the resulting mesh-4G-network] self-organising.”
Blackned is currently conducting some public safety demonstrations and trial system installation with various nations’ military and public safety institutions.
Blackned provides a backpack- mounted LTE system that can provide service for a minimum of four hours using batteries for up to 300 LTE users. it is looking to bring similar technology to the public safety in-vehicle market
Think before you buy
TETRA Today asks Valentine for some tips on how to go about procuring mobile base stations. He explains that a range of factors should be considered, such as how responsive does the solution need to be, and does it need to be deployed instantly or is a longer set-up time acceptable? There’s also the question of scale and whether the system will be used to provide in-fill coverage or act as a mobile command centre.
Valentine also notes that power is a critical consideration, “not only understanding the hours of service delivery needed, but whether a single or multiple power option is required [battery, generator, solar] or connection for direct grid access”.
He adds that customers need to have a clear understanding of their needs so that they chose an appropriately-designed solution. “While an off-the-shelf product may appear to fit needs, in our experience this is pretty rare and each solution will require some level of custom design or integration.”
Hardaker shares some lessons from Airwave’s early days: “When we started the contract we had four mobile base stations that were fairly large towable units; they had a mast, a base station and a generator, but no way of connecting back to our switch sites. We found that while they had a use, it was far more useful to have something that will provide connectivity back to your switch site and integrate fully into your network.”
He adds that Airwave has found that it’s better to use a vehicle-mounted solution rather than a tow-type equivalent, as the latter needs a bigger vehicle and the in-vehicle product allows for easier, one-man deployment.
In mission-critical situations “the worst thing you can do is have a disaster and a flat tyre,” says Hardaker. He explains that Airwave has a strict regime in place to maintain the equipment and “at the moment we anticipate that they’re going to last the length of the contract”.
“We purchase rather than lease in the majority of cases but we also have a maintenance agreement with the equipment providers,” he concludes.
General S. Patton famously said “fixed fortifications are a monument to the stupidity of man”. While that quote cannot be applied to fixed critical comms infrastructure there’s no doubt that mobility has its merits, particularly when public safety organisations find themselves reacting to unforeseen circumstances, be they a hole in coverage caused by equipment malfunction or an incident in a remote area where permanent base stations just aren’t economical.
