How critical to society is public transport? Consider what will happen in a major city if the public transit system stops. The roads will become gridlocked, commerce will slow, and the costs to society will be severe. Transit operators therefore need high-reliability communications to maintain service. They can also take advantage of broadband comms to enhance safety and customer experience.
Communications on metro systems are needed to maintain schedules, alert controllers to problems, and ensure the safety of passengers and trackside crews. In fact, for many metro operators, the trains are not permitted to move if the radio is not working. Buses and trams have similar needs for secure communication for efficient operation and to ensure safety.
Wireless technology is increasingly used to connect trains and trackside equipment for automatic monitoring of equipment and systems and to control movements and signals. As wireless broadband becomes available we can expect applications such as video to become widespread, increasing efficiency and safety for workers and passengers. Transportation in cities is seeing increased use of driverless trains – these require a secure communications solution to control the location and movement of the train.
Today, a number of solutions are used by transit operators for communications. Many favour TETRA because of its security, features and cost. It is in use in many European city metro and bus systems, and is being rolled out in Asia and North America. Voice remains the primary application for TETRA in metro systems. Train drivers can be sent and receive both routine and emergency messages over TETRA, even when the public mobile network is congested or down.
In special circumstances, a “stop, stop, stop” message can be sent by control to halt all trains. Drivers can report obstructions, disturbances in the train, track issues, or any other important information. Fixed onboard TETRA radios in the cab can be integrated with the intercom so the driver has just one microphone. TETRA can also transfer data from the onboard train management system over its Short Data Service (SDS) to applications in the control centre, allowing systems such as doors, air-conditioning, brakes and other important equipment to be monitored, thereby making it easier to schedule maintenance and identify where repairs are needed.
Guards and transport police carry portable radios to communicate with drivers or other colleagues. However, increasingly the driver is the only staff member on the train. In this case, when there are problems the passengers can use intercom positions throughout the train to talk to the driver, who can use fixed cameras to get a better view of what is happening and what needs to be done, and what to tell the controllers or emergency responders.
Public LTE is available in many countries and offers a stepping stone to a more customised LTE system for secure use in the future. Work on the enhancements for a public safety version of LTE is under way with the standards bodies and has been widely reported.
“I find that metro operators are keen on knowing about LTE, but they are conservative when it comes to deploying something new,” says Mark Skinner, Motorola Solutions’ lead on transportation solutions. Driverless trains are of interest to operators, given the constant drive to reduce operating costs, and they are keen to de-skill their workforce. “Driverless running is not a realistic option on older rolling stock but operators want to know about the possibilities available from broadband for when they update in the future. Broadband would enable controllers to monitor the view from the cab even on a fully automatic unit. Passengers can be concerned if they cannot see a driver if they are new to driverless units. So, if there is an automatic drive system there could still be an employee in the cab who is there to reassure passengers and maybe perform simple tasks such as opening and closing doors.”
Skinner points to another use for LTE. “Passenger information systems offer revenue opportunities, for example as a train approaches a station the location of restaurants and shops can be highlighted along with their daily offers.”
But will these transit operators use current public 4G/LTE services or insist on a private system? “In my experience, they like to have ownership of the communications to ensure safety and resilience. They have safety responsibilities to the public, which makes them cautious about their choice of technology and how it will be used. There also has to be spectrum available for a private LTE system even if the metro operator has the funding to build it. This will be problematic as organisations with deep pockets and a large public customer base will fight hard for it.”
Skinner has views on the longevity of TETRA in metro operations. “I believe TETRA will remain in service for a long time even after LTE is in use. It will provide the back-up in the event of any issues with LTE. I can even see it being available on driverless trains for when a member of staff has to travel for any reason and needs to contact the controller. Not everything needs LTE, applications can run over TETRA/SDS, such as alerts to maintenance staff from onboard sensors. In some of our installations the TETRA radio in the rear of the train is used for this purpose.”
Three metro systems highlight how LTE and Wi-Fi are being used together in metro operations.
Bilbao Metro, a pilot TETRA/LTE system
Amanda Esteban Sanchez is Teltronic’s lead on metro and train applications – she describes the TETRA/LTE pilot in Bilbao.
Bilbao metropolitan area in Northern Spain is a city of one million people – its metro system carries 88 million passengers a year across two lines, 41 stations and 45 kilometres. Esteban says “the deployment of a combined TETRA and LTE system for the Bilbao Metro system is an important pilot project to demonstrate how these systems will work together in a transport environment”. A series of use-cases have been implemented to validate the system and learn lessons that can be used in further developments and deployments.
The first use-case is to provide uplink transmission, real-time train-to-ground video surveillance from the train cab to a vehicle video management system in the control centre. “The controller can see what the driver sees, and can prompt the driver or alert other staff if a situation needs action.” The second use-case is the feeding of video to the driver from static cameras such as those in a station. “This gives the driver information on the platform before, during or after a stop. There’s also the uplink transmission of real-time user equipment to ground video surveillance, for example from a security officer’s camera on an LTE smartphone to the control centre. A suspicious passenger or vehicle could be watched while other officers are alerted and action planned and initiated.” Another use-case will be TETRA/LTE integration to provide full device interoperability for all services including voice.
Finally, there is TETRA + LTE integrated management through the Teltronic eNEBULA network management system. “This is a single network architecture for TETRA and LTE providing logical and physical network trees with all deployed equipment such as the EPC, eNodeB, MBS TETRA and CNC,” says Esteban. The unified fleet management system centralises management of radios, groups and subscribers independently of the technology of the devices. Currently, hundreds of TETRA terminals are in use. Service provisioning is provided per subscribers or group, as well as definition and configuration of QoS policies and priorities.
Esteban has passed on the following feedback from the trial. “The Bilbao Metro is happy with the pilot and it has met their expectations. They would be delighted to deploy a similar system across the complete metro system. This will depend on the availability of frequencies.” Spain has reserved part of the 450MHz (5+5MHz) frequency band for LTE broadband services and is planning to have this cleared from January 2018. “Police and security forces will use this spectrum, but it is not known if transport operators will be permitted to use it.”
Toronto Transit Commission
Toronto Transit Commission (TTC) is rolling out a TETRA system from Sepura across its metro, tram and bus fleet. Milan Vignjevic is the project manager, communications engineering at TTC charged with managing the deployment of TETRA on the metro trains. “Just now the transit system is in the transition from analogue to TETRA for radio communication. This is going slowly as TTC do not have additional UHF frequencies available for TETRA, and so we are re-using the analogue radio frequencies made available by the co-ordinated transfer of analogue radio users to the TETRA,” he says.
A contract was awarded last year to provide a CAD/AVL solution replacing a custom analogue voice system on 2,000 buses and trams. Vignjevic adds: “We are in a prototype phase, testing an LTE radio in a combined housing with the TETRA unit. Adding bus and tram groups to the TETRA system will require additional capacity, so we have installed two additional base stations and additional radios on existing base stations.”
Vignjevic describes the objectives of the TETRA/LTE system. “Having both TETRA and LTE gives us a communication back-up even if one communications system is down. TETRA provides the voice link for the driver and also a narrowband data link. Vehicle location is provided to the control room over TETRA to manage schedules and deal with problems.”
Regarding the LTE system, Vignjevic states: “The vehicles are fitted with an onboard computer to monitor essential functions such as the condition of brakes and other critical systems. This vehicle diagnostic information is uploaded over LTE if there is a problem. Other vehicle driving information such as fuel consumption, speed and stops is also recorded.
“LTE can also be used to download large chunks of data; the onboard computer can be updated with fresh route information such as special journeys or excursions. A Wi-Fi system is used in the back in the depot to upload vehicle data and recorded video.” The integration of the broadband radio systems is provided as part of the CAD/AVL contract.
Vignjevic says that “ambience listening on the TETRA radio is enabled for both buses and trams. If an emergency button is pressed, the radio will remain listening but without giving any active indication to anyone in the cab”. Controlling and uploading real-time video in this situation is a feature that can be added later; video from several cameras on the vehicles is currently recorded and stored for playback if needed.
TTC has no plan to provide a public Wi-Fi service on the buses and trams. Vignjevic says “passengers generally have access to the public 3G/4G systems”. LTE will be used to link to a display on the vehicle, providing real-time information for disabled passengers, advertising, news and travel information.
The deployment of TETRA on the metro system is advanced, and is providing improved voice and data quality. Vignjevic plans for the metro deployment to be completed by March 2018. TETRA radio service is being provided above and below ground, including tunnels. As well as voice, TETRA uploads information from the event logger on the train which monitors onboard systems such as brakes; this goes in real time to the control centre maintenance teams, who can plan for repairs or maintenance.
BAI Canada provides TTC with LTE and Wi-Fi services in stations above and below ground. Vignjevic says: “As the LTE system does not include tunnels, the TETRA system remains the only regular and emergency communications system for the metro train drivers and the train monitoring systems. The distributed antenna system (DAS) used by TETRA is not available for LTE, and a private LTE system is not seen as being cost-effective at this time.” He adds that non-public secure Wi-Fi is installed and used in the stations; this is a key enabler for one-person train operation; cameras at up to six locations in the station are linked to the driver who can ensure that passengers are safely on the train before leaving. The driver can also watch as the train leaves to check that no passengers are caught in doors. The Wi-Fi system can also upload previously recorded video from trains anywhere on the line.
Zhengzhou Metro
Zhengzhou Metro is one of the first metro operators in China to deploy a dedicated LTE network. This is used for data, signal transmission and passenger information system transmission, such as broadcasting TV programmes in the passenger rail cars. The system (supplied by Huawei) also supports station indication, station and perimeter CCTV and information collection for training. In future, it will consider moving to an integrated communications platform. The metro does not use its Airbus supplied TETRA network for transmitting signal system information, but rather uses a redundant LTE system for signal system transmission. Redundancy means that there are two base stations in each station’s equipment room; one is the operating unit and the other is a back-up.
Zhengzhou Metro has integrated the LTE network with a system that monitors all the trains’ electrical and mechanical systems. The metro has just started researching the potential use of the ‘Internet of Trains’ to improve operations.
In summary
TETRA remains a safe and cost-effective choice for metro train communications. It offers security, resilience, voice and data comms, group and direct modes, and a host of other features. It is an open standard that enables users to choose between competing manufacturers to get a cost-effective solution. Public LTE is becoming widespread and can be used for non-safety-critical communications and to develop applications and experience in broadband service in metro operations.
Public LTE has its limitations: it may be limited in coverage underground and can become congested in emergencies, which is the time it would be most needed for the metro operator. A safety-critical LTE system would be the ultimate solution for metro use, but relies on the adoption of standards and the availability of funding and frequencies. Therefore the deployment of mission-critical LTE will be a process of evolution rather than revolution, varying widely between locations.
It is worth noting the use of Wi-Fi in specific locations such as stations or depots as demonstrated in Toronto – Wi-Fi is enabling savings in manpower and improvements in safety, and may be a useful stepping stone to the use of mission-critical LTE along the entire metro line.
