Across the UK, Mobile Network Operators (MNOs) have delivered an extensive network of high-quality mobile voice and data services, meeting coverage targets set by the government. These targets have typically prioritised the provision of indoor coverage, so densely populated areas where signal is needed most are well serviced. However, this has also meant that transport corridors continue to experience network ‘not-spots’.

Covering rail passengers’ entire commute, as well as other journeys they might take, presents a range of unique challenges. Successfully resolving them depends on the use of sophisticated Radio Frequency (RF) engineering techniques.

Limiting connectivity losses

There are a range of elements to consider when delivering mobile connectivity for railways. First and foremost, the trackside is a highly regulated environment, and one which it’s been difficult for MNOs to gain access to. As a result, there are not enough cellular masts in range of trains to deliver high-quality consistent coverage to passengers. Moreover, the UK rail network features a high number of tunnels and deep cuttings, blocking signal and exacerbating this problem.

Train carriages and passengers themselves can present challenges too. Today’s trains travel extremely fast and the modern materials used to build them create a ‘Faraday Cage’ (a term used for structures that block external electronic signal), preventing wireless communications from reaching the carriage interior. Even train windows can block signal as they often contain metallic film inside the glass. Meanwhile, inside the train, a high density of surrounding passengers can have a similar effect, especially during rush hour

All these factors impact what’s known as the ‘link budget’, an accounting of all the gains and losses that occur between the transmitter and the receiver in a telecommunication system. Each unit of loss, whether it’s the distance between an antenna and a mobile device, or an obstruction blocking the signal, will affect the overall quality experienced by the end user. Mastery of the link budget is central to designing an excellent radio communications system.

Addressing attenuation

Balancing the link budget requires extensive RF planning expertise to ensure the correct coverage and capacity are effectively transmitted to passengers. Radio waves behave like light shining from a torch, moving from source to receiver. This means all sorts of variables need to be considered to ensure consistent performance. Let’s imagine a network is installed during the Winter and is delivering high-quality performance. Something as innocuous as trees coming into leaf in Spring can weaken signal if they sit between transmitters and the end user. This is the level of detail that’s required when conducting a detailed RF planning exercise.

With cellular base stations and antennas often hundreds of metres away from the track, it’s common for this signal loss, known as attenuation, to occur. Addressing it demands additional infrastructure. More antennas need to be installed closer to the trackside and connected to MNO equipment housed in remote Base Station Hotels (BSH) via optical fibre. Taking this approach minimises signal loss whilst also reducing the need for ongoing trackside access, as most installation and maintenance work can take place away from the track.

Track proximity isn’t the only factor when it comes to antenna placement. Ensuring the positioning is right is also critical for optimal network performance. They should be placed within clear sight of trains, at the right height and angle. Crucially, equipment must be in place within the train to receive the signal and distribute it throughout carriages. The overall planning process involved demands extensive use of modelling tools to accurately predict the resulting coverage and performance.

Managing customer experience

Once a network is in service, the optimisation phase can commence, allowing fine-tuning to enhance customer experience. The MNOs themselves have real-time monitoring capabilities and can apply software parameters to facilitate this – in some cases they can even remotely move and re-orientate antennas to minimize loss. Some organisations are also finding social media a useful performance-monitoring tool, as passengers can be relied on to provide quick user feedback if networks are not providing the quality of service they expect.

Getting it all to work

Among the public, mobile coverage and Wi-Fi are increasingly considered as the essential ‘4th utility’, like clean water, gas and electricity. Reliable service is now expected 24/7. This increasingly depends on in-depth planning, solving complex link budgets to provide the performance that customers deserve. And for railways, consistent connectivity directly impacts customer experience – if passengers are unable to use devices onboard, the perception on their entire journey can be tarnished.

The Department for Culture, Media and Sport (DCMS) recently advocated greater collaboration via a neutral host model for the delivery of next-generation communications, an approach that is particularly effective for connecting rail corridors. A single independent organisation with transport industry experience is best placed to manage relationships with the transport authorities responsible for these highly regulated environments. Further, allowing them to install and maintain shared network infrastructure means passengers can enjoy a seamless service whatever network they happen to be on.

With 5G on the horizon, it is vital operators work closely with telecommunications specialists and the public sector to connect transport corridors and realise the next stage of the mobile connectivity revolution.

By Andrew Conway Director of Engineering, BAI Communications UK