Bringing a paradigm shift in Communication Systems for Railways

Technology Evolution

Over the course of time, there has been a huge transformation in telecommunication technology, and the impact has also become evident in railway networks. Optical fibres are an ideal transmission medium for railway communication due to the availability of ROW. Having started out with narrow band communications decades ago when optical fibres made their appearance, the railways have been quick to adopt SDH. Due to the reserved bandwidth of TDM technologies and the accompanying benefit of guaranteed delivery, most mission-critical applications including the railways prefer to use SDH and its enhancements. The precision and scalability of SDH comes from the use of a precise clocking system defined in ITU-T G.811. The SDH interfaces are shown in Table 1.

A parallel development has been the ubiquitous growth of Ethernet as a common platform for packet-based communication. A growing number of systems are now integrated within the network to facilitate streamlined flow of information. So, in addition to SCADA for signalling and traction control, CCTV, VoIP and other enabling systems specific to railways are being integrated into the communication network. Railways have adopted next-generation SDH to transport these Ethernet services, thus broadening the range of applications and simplifying the network by providing a common layer-2 protocol for all services, while at the same time retaining the bandwidth assurance of TDM.

More recently, the number of options in telecom equipment based on the OTN standard (ITU-T G.709) has been increasing, as also those of Carrier Ethernet technologies such as PBB-TE (IEEE 802.1Qay) and MPLS-TP. The key to making Ethernet services as resilient as established transport networks is the use of a control plane for monitoring and managing the services across the network, as shown in Figure 3. Packet Optical Transport retains the carrier grade characteristics of TDM while providing the flexibility of packet transport. At the same time, DWDM provides tremendous bandwidth scalability and has been deployed in shared/leased networks with huge capacity demands. For packet transport, Gigabit Ethernet (802.3z) and 10G Ethernet (802.3ae) interfaces are now readily available. Thus, a plethora of technology options have opened up and it remains to be seen which of these emerging platforms arises as the preferred platform for railways. Considering the need to integrate with the huge base of legacy systems, it will most likely be a hybrid platform that supports both TDM and packet transport at some level. As on date, NG-SDH remains the technology of choice due to the mission-critical nature and rigorous criteria required for any new technology to qualify into railway networks.

Future of Railway Communications

With the emergence of long distance broadband wireless, there will be a complete transformation in the way the railways function. A high-speed two way communication link with the moving train would take rail traffic operations and management to the next level. For instance, drivers would be able to view the location of all trains on their route in real-time on a dashboard in front of them. They would then no longer depend exclusively on the signalling system, thus virtually eliminating the chance of collision between trains. Figure 4 shows the many possibilities for realising direct communication from train to trackside, train to station and train to control room while in motion. The possibility of in-train two-way communication between the driver and passengers is also opened up through on-board wireline or wireless systems.

A typical solution would comprise in-station and in-yard Wi-Fi network, in-train Wi-Fi network for passenger access, in-train wireless and wire-line dedicated networks for operational, safety and security applications. Connectivity between trains and the central locations would work through a trackside wireless network, and can also be interfaced with the HSPA networks of cellular operators where available.

Other applications would be a dedicated failsafe communication line between the driver and guard, real -time on-board passenger information and announcement systems and surveillance on the train with either real-time or offline streaming of footage to CCTV servers depending on the bandwidth.

While most of these technologies are conceivable today, the initial deployment of these concepts would happen in metro transit systems. It will be quite a challenge to implement all of them in high-speed moving trains on long-distance routes where installing the backhaul infrastructure would need significant investments. Another consideration is that many of the newer telecom technologies which have been designed for service provider networks would have to be made utility-grade since they would operate under extremely harsh conditions of vibration, dust and heat, with the high availability and other performance requirements for critical applications. However, by identifying the end-applications of highest priority, careful technology selection and a rigorous qualification process, these concepts can be converted to reality. These technological advances in telecommunication systems have set the stage to bring about a paradigm shift in railway travel and operations, and revolutionise the experience for both passengers and the railway operators alike.

Upendra H Manyam

Head, Emerging Technologies

Commtel Networks

(Upendra H Manyam oversees adoption of new technologies in telecommunication and sensing systems at Commtel Networks. He has extensive experience in systems design and product development in the areas of telecommunication equipment, optical fibers and related systems and holds 14 US Patents in this field. He received a Ph.D. in Fiber Optic Materials from Rutgers University).