Higher running speeds, increasing traffic and ever more demanding passengers have been driving a revolution in railway communications. Tim Guest reports

Train communications have come a long way since 1913, when the first onboard wireless set, operated by Frederick Wally, relayed news bulletins about the Mexican revolution to passengers aboard a Pennsylvania-bound express. Today, complex rail networks, stringent safety requirements and user demands for bandwidth-hungry services mean that the railways have to combine a wide variety of communications solutions to meet all stakeholders’ needs.

Setting the scene

From train run number management, shunting yard operations and GPS-based vehicle location to passenger information, emergency service support and freight management, the complex world of train transport relies on a plethora of communications solutions to function safely and effectively.

Computer-aided dispatch (CAD), for example, combines both in-train radios and mobile data terminals to enable more detailed and clearer messages to be communicated between operational staff; automatic vehicle location (AVL) systems use onboard computer terminals and radio modems to derive location from the GPS satellite constellation and transmit this back to the command and control centre; and train control interface systems provide onboard passenger information and train status, which can be sent across the radio network to the control centre for analysis and management.

The range of applications on a rail network which require communications are many and the solutions which meet those needs are equally many and innovative.

In a typical rail operation, explained Stephen Northcott, senior solutions manager at Motorola Solutions, the variety of train-related communications solutions used by different interest groups, each having their own communications needs and requirements, enables scenarios such as the train driver being able to communicate outside the train with the main train controller as well as individual station controllers and depot maintenance staff. Inside the train, the driver will have a facility to communicate with passengers and onboard staff, as well as the likes of transport police who may be on or off the train.

Call priority

But with so many trains operating, he stressed that the central controller must allocate a strict priority system for calls, and individual trains/drivers must ‘request to speak’. Callers are held in a queue, if necessary, until existing calls complete, although station controllers can initiate communications if some form of co-ordination is required. 

Mark Skinner, Tetra sales manager at Motorola Solutions, emphasized a key factor: “There are a few controllers to many trains – and they need to stay in control, which is why a strict call request process has to be followed.”

He said that a train driver only really needs to speak to the line controller or the signal operator in the event of an incident. If held at a red signal for a period of time, he might request to speak in order to find out the reason for a delay, which he can then relay to the passengers. “The driver will generally take all his control from the control room and only talk to the main control or signal operator. If the train itself fails, he may also need to talk to the maintenance crew.”

For communications into the train, he said, there is typically a station-to-train communications link, essential for safety reasons. For example, if a train is pulling out from the station and platform staff see little Johnny with his school scarf caught in the door and running along the platform, trying to keep up with the ever-accelerating train, they can raise comms to the train driver before it leaves the platform.

Wireless LAN installations at the station, which are driver-only operated, are part of these safety solutions, sending video of what’s going on to consoles at the ends of platforms, to which the driver can react.

Overland with Wi-Fi 

While the main overland rail communications system, at least in Europe, is now GSM-R (see panel opposite), wireless LAN-type solutions are on the increase. With modems in the cab supporting a service at train speeds up to 100mph, these can provide wide-area coverage.

Skinner said: “Modems onboard pick up trackside signals and rebroadcast them throughout the train to provide onboard broadband connectivity for both staff and passengers. The faster the train goes, however, the greater the chance of losing data packets as a result of various effects, like fading. Handover becomes a challenge at high speeds.”

These views were echoed by Samuel Buttarelli, director for southern Europe sales at CommScope, a provider of on-board wireless systems. The main challenges in providing wireless/cellular/Wi-Fi aboard trains, he explained, are related to bringing the available mobile network signal along the trackside into the train carriages themselves. “Unfortunately, train structures, particularly the metallized windows of high-speed trains, can dramatically reduce wireless signal penetration into carriages”, he said.
(中国集群通信网 | 责任编辑：陈晓亮)