FEATURED ARTICLES Latest Developments for Safe and Reliable Railways New CBTC System for Smart Operation The adoption of CBTC systems that use radio communications for train control has been encouraged by railway systems around the world in recent years, enabling more eff icient operation than conventional signalling systems as well as significant maintenance sav- ings and reductions in the amount of equipment needed. Hitachi has received an order from the SDC in Singapore to upgrade the signalling system for the Sentosa Monorail to CBTC, to supply additional rolling stock, and to install a voice radio communication system. This article provides an overview of the CBTC system and describes the work leading up to its installation. Kenta Nakashima Toru Yanagida Kenichi Fujii Shintaro Oki Sungin Lim 1. Introduction 2. Project Overview Communication-based train control (CBTC) is a 2. 1 signalling system that uses communication between Project Overview onboard and trackside equipment for train opera- Th e Sentosa Express is a monorail operated by tion and control. CBTC has been widely adopted in SDC that runs from the Singapore mainland south recent years on monorails, commuter trains, metros, to Sentosa Island (four stations and a total route and other urban railway services. In October 2014, of 2.1 km). Hitachi won a full turnkey contract to Hitachi, Ltd. won an order for a CBTC system and deliver the rolling stock, signalling system, electri- additional trainset from the Sentosa Development cal distribution system, traffi c management system, Corporation (SDC) in Singapore. Th is article provides points, and other key equipment and systems for the an overview of the Sentosa Express and describes the monorail in 2007. Issues subsequently arose, however, features of Hitachi’s CBTC system. with crowded cars and stations due to the growth 66. in passenger numbers following the opening of new (3) Voice radio communication system developments in 2010 that included a casino and For emergencies, the previous system included a Universal Studios Singapore*. With the Singaporean facility whereby passengers could use the emergency government expressing a strong desire to see matters communication equipment provided in each passen- improve, Hitachi set about resolving the problems by ger car to talk to the driver in the cab. In the case of upgrading the signalling system to increase capac- the new CBTC system, however, because it is driver- ity. Hitachi installed a CBTC system to replace the less, a voice radio communication system was installed previous signalling system and supplied an additional to allow passengers to talk to staff at the control center. (CBTC-compatible) trainset and a voice radio com- Furthermore, the installation used the same interfaces munication system for communications between pas- as the previous radio system to enable reuse of the fre- sengers and the operation control center (OCC). quencies and the antennas, cables, and other equipment from the existing wireless data communication system. 2. 2 Overview of Subsystems 3. Features of a CBTC System (1) Signalling systems Th e new CBTC system uses driverless automatic train operation (ATO). Under ATO control, the train 3. 1 departs, accelerates, runs, decelerates, and brakes in Standards Compliance and Other Features accordance with a set “diagram” (schedule), and the Th e previous signalling system was based on the use system also handles station stopping points, train door of fi xed blocks, an approach that has long been used opening and closing, and cab switchover. on existing railways. Th e fi xed-block method only (2) Onboard systems permits one train at a time between stations, such that As the project required continued operation using a train cannot depart its station until the preceding the previous system during the changeover to the new train has departed the next station down the line. Th e system, all existing onboard systems remained in use. distance of these track blocks imposes a bottleneck Th is required the new CBTC system to use the same on operations, preventing trains from running more interfaces as the previous onboard systems. closely together and limiting how much the headway * Universal Studios Singapore is a trademark of Universal Studios. (gap between trains) can be reduced. Figure 1 — Conceptual Diagram of CBTC The diagram shows the flow of information Subsystem Information flow Functions during train control by the CBTC system. Train location Trackside LMA information information Train tracking signalling Train headway control system Route (interlock) control Radio Information route system Onboard train location Onboard Control pattern detection Control pattern system calculation LMA Speed control CBTC: communication-based train control LMA: limit of movement authority Hitachi Review Vol. 67, No. 7 830–831 67. In contrast, a CBTC system is defi ned in the IEEE and tacho-generator to calculate its own location 1474 international standard with location determina- and transmits this via its mobile station (MS) to the tion that is independent from track circuits, that uses trackside. Th e CTBC logical unit receives this train bidirectional train-to-trackside data communications location via the antennas installed on the track, the to ensure safety, and that has continuous train-to- base stations (BSs), the base station controller (BSC) trackside communications. Th e new CBTC system in the equipment room, and the CTBC’s local-area is based on the use of moving blocks, with train loca- network (LAN). Th e unit uses the received informa- tion determination and operational control being per- tion to generate train control information that is sent formed using a wireless system. back to the onboard ATC equipment via the same Onboard systems send train location information route. Th e train then operates in accordance with this to the trackside signalling system that then uses this information. information as a basis for sending control information to each train. Th e trains then use this control informa- 3. 3 tion received from the central system to determine Details of the Signalling System how far they are able to travel, what is known as the In the CBTC system, each train fi rst adjusts its loca- “limit of movement authority” (LMA) (see Figure 1). tion using the cumulative distance traveled and tran- Hitachi’s CBTC system complies with the IEEE sponder information. Taking into account its own 1474 international standard and has obtained reliability, distance traveled, speed, and direction, each train uses availability, maintainability, and safety (RAMS) cer- the CBTC wireless link to send its location to the tifi cation at safety integrity level (SIL) 4 (the highest trackside signalling system in real-time. Th is train level possible, indicating full compliance with interna- location information indicates the distance from a tional safety standards) from a European certifi cation transponder on the trackside. agency. Th is makes Hitachi the fi rst Japanese company Based on the received train location information, to obtain such certifi cation from a European agency(1). the trackside signalling system sends train control information (including LMAs) back to each train. 3. 2 Based on the train control information received from System Architecture the trackside signalling system, each train generates Figure 2 shows the architecture of the CBTC system. a speed control pattern in a real-time and fl exible Th e onboard automatic train control (ATC) equip- manner and operates in accordance with that pattern ment uses information from the transponder receiver (see Figure 1). Figure 2 — System Architecture The diagram shows the architecture of the CBTC system. CBTC Interlocking System logical unit equipment console Radio link Control of on-site equipment BSC IOM BS1 BS2 I/O relay rack Antenna Point, signal, and other external devices MS2 Onboard ATC unit MS1 Tacho-generator Transponder receiver LAN: local-area network IOM: input/output module BSC: base station controller BS: base station MS: mobile station ATC: automatic train control 68. FEATURED ARTICLES Figure 3 — Overview of WLAN and CBTC Radio Channels The diagram shows the WLAN and how CBTC uses the diff erent radio channels. WLAN 1611Three channels are used in a way 2712 that avoids radio 3813interference 22 MHz 5 MHz 123456789101112 13 Channel 2,412 2,417 2,422 2,427 2,432 2,437 2,442 2,447 2,452 2,457 2,462 2,467 2,472 Frequency (MHz) 2,400 MHz 83.5 MHz 2,483.5 MHz 123 456 78910111213141516 2,405 2,410 2,415 2,420 2,425 2,430 2,435 2,440 2,445 2,450 2,455 2,460 2,465 2,470 2,475 2,480 WLAN: wireless local-area network Th is makes it possible to keep the distance between (4) Zone-based frequency allocation trains as short as the circumstances allow, increasing Th is increases the number of non-overlapping the service capacity by shortening operating schedules channel combinations by reducing the bandwidth of and increasing the number of trains that can run at each channel compared to a conventional WLAN to the same time. make more channels available. 3. 4 Features of the CBTC Wireless System 4. Future Challenges and Responses Th e CBTC wireless system operates on the same 2.4- GHz frequency band as wireless local-area networks Th e construction of further attractions and other facil- (WLANs). WLANs normally use three non-overlap- ities is planned for Sentosa Island. Plans also include ping channels to avoid interference. extensions to provide access to these new facilities Hitachi’s CBTC wireless system adopts the follow- and the number of monorail passengers is expected ing four techniques to ensure reliable wireless com- to grow. munications (see Figure 3). Although the switch from a fi xed- to a moving- (1) Orthogonal frequency-division multiplexing block system that has accompanied the installation (OFDM) of the new CBTC system has allowed an increase Th is avoids interference by transmitting data over in the number of trains that can operate at the same multiple carrier frequencies.