Many of my readers would be aware that UK is probably the first country to have decided to move its emergency services network from an existing TETRA network to a commercial LTE network operated by EE.
While some people have hailed this as a very bold move in the right direction, there is no shortage of critics. Around 300,000 emergency services users will share the same infrastructure used by over 30 million general users.
The following is from an article in Wireless Magazine:
Steve Whatson, deputy director Delivery, Emergency Services Mobile Communications Programme (ESMCP) – the organisation within the UK Home Office procuring ESN – assured delegates that ESN will match the existing dedicated Airwave emergency services communication network in terms of coverage for roads, outdoor hand portable devices and marine coverage. Air to ground (A2G) will extend its reach from 6,000ft to 12,000ft.
Whatson also pointed out that coverage is not one single piece, but will comprise a number of different elements, which all need to mesh into one seamless network run by the ESN Lot 3 Mobile Services (main 4G network) provider – EE.
This includes: EE’s main commercial 4G network; Extended Area Services (hard-to-reach areas of the UK where new passive sites are to be built under a separate contract and then equipped with EE base stations); air-to-ground; London Underground; Crossrail; marine coverage (to 12 nautical miles); and special coverage solutions.
EE is currently rolling out new 4G sites – it will eventually have some 19,500 sites – and is upgrading others with 800MHz spectrum, which propagates over longer distances and is better at penetrating buildings than its other 4G spectrum holdings. Crucially for ESN, it is also switching on a Voice over LTE (VoLTE) capability, starting with the UK’s main cities.
Mission critical networks must be always available and have levels of resilience far in excess of commercial networks. Speaking exclusively to Wireless in early May, Tom Bennett, group director Technology Services, Architecture & Devices at EE, said: ‘We already achieve a very high availability level, but what the Home Office was asking for effectively was about a 0.3% increase against our existing commercial availability levels.
‘Now for every 0.1% increase in availability there is a significant investment because you are at the extreme top end of the curve where it is harder and harder to make a noticeable difference.’
There are very specific requirements for coverage and availability of the ESN network for the UK road system. Bennett says: ‘Mobile is based on a probability of service. No more than 1% of any constabulary’s roads are allowed to be below 75% availability, and on major roads it is 96% availability. A coverage gap in this context is no more than 1km.’
The current Airwave network has approximately 4,000 sites, many with back-up generators on site with fuel for seven days of autonomous running if the main power is cut, along with a range of resilient backhaul solutions.
Bennett says that out of EE’s 18,500 sites it has about the same number of unique coverage sites (ie. no overlapping coverage) – around 4,000. ‘As part of our investment programme, those unique coverage sites will need a significant investment in the causes of unavailability – ie. resilient backhaul and back-up batteries.’
He explains that EE has undertaken a lot of analysis of what causes outages on its network, and it has combined that data with the Home Office’s data on where the natural disasters in the UK have occurred over the past 10 years.
From this, EE is able to make a reasonable assessment of which sites are likely to be out of action due to flooding or other disasters for more than three or four days. ‘For those sites – and it is less than 4,000 – you need generators too, because you may not be able to physically access the sites for some days,’ says Bennett.
For obvious reasons, the unique coverage sites are mostly in rural areas. But as Bennett points out, the majority of cases where the emergency services are involved is where people are – suburban and urban areas.
‘In these areas EE has overlapping coverage from multiple sites to meet the capacity requirements, so if a site goes down, in the majority of cases we have compensation coverage. A device can often see up to five tower sites in London, for example,’ he says.
Having adequate backhaul capacity – and resilient backhaul at that – is vital in any network. Bennett says EE is installing extra backhaul, largely microwave and fibre, but other solutions will also be used including satellite and LTE relay from base station to base station – daisy chaining. On 9 May 2016, EE announced a deal with satellite provider Avanti to provide satellite backhaul in some areas of the UK.
Additional coverage and resilience will be offered by RRVs (rapid response vehicles), which EE already has in its commercial network today, for example, to provide extra capacity in Ascot during the racing season.
‘We would use similar, although not exactly the same technology for disaster recovery and site/service recovery, but with all the backhaul solutions,’ says Bennett. ‘Let’s say we planned some maintenance or upgrade work that involved taking the base station out for a while.
‘We’d talk to the chief inspector before the work commences. If he says, there’s no chance of doing that tonight, we can put the RRV there, and provided we maintain coverage, we can carry out the work. RRVs are a very good tool for doing a lot of things.’
At the British APCO event, Mansoor Hanif, director of Radio Access Networks at EE said it was looking at the possibility of using ‘airmasts’ to provide additional coverage. Meshed small cells, network in a box and repeater solutions are becoming available for these ‘airmasts’, which will provide coverage from balloons, or UAVs – tethered drones with power cables and optical fibre connected to them.
Feel free to let me know if you believe this will work or not and why.