Railway Automatic Train | Engineering Dissertations
The Dockland light Railway is one of Britain's great high-tech Automatic Train Control (ATC) system, now carrying over 60 million passengers. This highly developed train control system has expended more rapidly than any UK railways. DLR officially launched in 1987 to serve the existing Docklands population and helps to regenerate the Isle of Dogs area, with 11vehicles convoy and 15 stations. Since then the DLR network has extended to Bank, Beckton, Lewisham, London City Airport and King George V. It has 31 km of railway and 38 station with 94 vehicles [DLR Light News 2007]. DLR now carries more passenger than ever before, with additional increases in demand predicted over the coming years. The system's current 6o million passengers a year is expected to rise up to 80 million by 2009, when a further 55 cars will be added to the fleet [DLR Light News 2008].Passenger numbers will rise further when the DLR assumes a major role in transporting passengers to and from the London 2012 Olympic and Paralympics Games, serving five Olympic venues. [Olympic Delivery Authority (ODA)]
For twenty years, passengers travelling on DLR have been intrigued and puzzled by the unique trait of this network, the absence of train drivers. The entire railway operates as a driverless system, carrying more than 200,000 people across East London every weekday. As the trains appear to stop and start with its own harmony, the operation of the network managed and monitored 24 hour a day, 365 days a year, from the DLR Control Centre. For passenger safety, security and assistance there is a Passenger service Agent (PSA) on every DLR train.
The DLR is operated through a computerised Automatic control system. Control Room staff has access to a visual overview of the entire DLR network showing exactly where each train is along the railway at any given time. The benefit of operating a network in this way is incredible. As the system is controlled automatically it allows DLR to run many more trains. [DLR Light News 2007]
In the field of Automated Train Control System it is imperative to know all trains position on the system for swift and safe operation. On of the common train operating system was 'fixed block' system, where railway track are divided in to number of blocks. These blocks only allowed one train to occupy that block. Until that block is clear, it does not permit other train to get in to that part or track and big gap used to generated between two trains. To operate a numerous train service like DLR, the railway track has to be divided into many short blocks, requiring setting up and maintenance numerous number of signalling equipment, side track and head shunt. Previously DLR operating system was run by fixed-blocks system due to short rail way tracks, lack of side tracks and head shunts and more frequent service demand this system was later replaced by SELTRAC a Transmission-Based Automatic Train Control (TBAC) system based on the Moving Block Principle. SELTRAC is a registered trademark of Alcatel SEL. [Alcatel Canada Transport Automation]
The sole purpose of this comprehensive study is to go behind the scene of the infrastructure of the Docklands Light Railway operating system and how this transport service has harness the Advanced Train Control System technology to operate and transporting thousands of people around its network in a diversely populated city with great magnitude of fast growing economy.
2. Comprehensive Literature on Advanced Train Control System
(ATCS), Latest System Technology on Train Operation and
Top-Level Description of the Docklands Light Railway (DLR)
Automatic Train Control (ATC) System
The First International conference on Advanced Train Control, which was held in 1991 in Denver, suppliers from different countries of the world attended and demonstrated their technology, products and operating system. Burlington Northern (BN) in conjunction with Rockwell produced the first version of ATCS, known as ARES (Advanced Railroad Electronic System), where they developed satellite navigation system for locating trains on the system. They tested this ARES on BN's Iron Range lines in Northern Minnesota with the purpose to integrate trains information system with central commands and control functions. During year1987 to1993, Canadian National Railways (CN) and Canadian Pacific Rail (CP) made momentous improvements in the development and testing of ATCS. A key component in recuperating safety and productivity of train operations is ATCS technology; it provides better communication, more accurate information on train movement, train location, wayside interfaces and locomotive's condition. Railways are part of a technological rebellion where sophisticated communications equipment and computer systems are in use to control the movement of train. A main new expansion in train operation is data transmission, which help the train driver and the control centre staff to transmit information directly, by radio and on-board computer. [Edward Furman, 'Network Management for ATCS Communication System' 1991]
2.1 Current Technological Expansions
2.2 Advanced Train Control Systems (ATCS)
Bombardier in Europe, Railway Association of Canada (RAC) and American Association of Railroads (AAR) began to explore the viability of a radio-based control system that would get rid of human error in the field of train operations [RAC, AAR, 1984].This development was co funded equally by these companies and several other railway companies, suppliers and consultants from Europe, Canada and the U.S. The main purpose of the project was to develop a modular computer-based train control system that will provide safe and more proficient railway operation. ATCS is state-of-art technology, where it ensures a safe train operation service, train separation, train verifying, the safety and the reliability of all movement establishment issued to train and maintenance staff, and also monitoring all equipment status.[U.S Department of Transport, 'An Aid to positive Train Control', June, 1995]
The main goals of the ATC system are to provide:
Ability to implement a system with mechanism from different suppliers, which will reduce problems related to interconnecting and interfacing components from different manufacturers.
The ability for each railway to select the capabilities and character it needs to implement. interoperability.
System compatibility across the railway to ensure faultless operation and interoperability between different railways.
[Federal Rail road Administration, 1995]
The Advanced Train Control System's 5 major systems
i) Central Dispatch System (CDS): CDS manage the movement of trains all over the railway networks and ensure safe operation without train delays and it also provides automatic train tracking and monitoring, status and control of the train and the field system.
ii) The On-Board Locomotive System with two major sub-systems:
On-Board Computer (OBC): OBC provides automatic location tracking and automatic transmission of train movement via the data communication system.
On-Board Display Terminal (OBT): On-Board Display Terminal display and provides all the necessary information for example; actual train speed, speed limits and restrictions, train location, milepost, track geometry, type of authority, track work protection, and status of switches. The display of the information can be presented in text form or in graphical form depending on type of terminals.
iii) On-Board Work Vehicle System: The on-board terminal allows communication between track maintenance staff, central dispatch and vehicles operator via data communications system.
iv) Field System: Wayside Interface Units (WIU) are essential equipments in the field system, which provide monitoring and control of wayside devices for example; switches, interlocking, hot-bearing detector and train defect detectors.
v) Data Communication System: DCS gather the various information processing systems collectively and considerably reduce voice communications.
[George Achakji, March, 1992]
2.3 Data Communication System
Data Communications System is based on 5 levels of information dispensation:
i) Continental level: Continental level provides the functions that are obligatory for inter-railway operations. For example, transferring waybill.
ii) Railway level: Railway level provides the functions which are compulsory for train operations and also for non vital management of train operations.
iii) Regional level: Regional level provides operations across dispatch regions, from one dispatch centre to another.
iv) Dispatch level: Dispatch level is a central control function for train control. It can communicate with vital or non-vital information and it is also necessitate for this level to communicating of vital information to and from trains, track forces, switches, and other wayside equipments.
v) Wayside/mobile level: Wayside/mobile level provides both vital and non-vital processing of locomotive data, track units, and wayside devices; and communications information between trains, wayside and track forces.
[George Achakji, 'Advanced railroad Electronic system', January, 1991]
2.4 Advanced Railroad Electronics System (ARES)
The exertion on ARES began in 1984, when The Rockwell International and The Burlington Northern (BN) began to study new technologies that provide automatic identification of train speed and position. Initial tests conducted by The Rockwell International and they demonstrated that GPS could successfully track moving trains. ARES is an integrated command, control, communications, and information system which applies modern avionics technology to railway operations. Its design objectives were similar to those of ATCS, for example, safety and the efficiency of railway operations. In year of 1985, these two companies started to develop a prototype system to determine the production feasibility of this conception. In the year of 1987, Burlington Northern starts their expedition with 17 locomotives, 8 switchers with ARES hardware and GPS receivers, 50 WIU (wayside interface units), two high-rail trains with GPS system on the Mesabi Iron Range [230 mile test track] in Northern Minnesota. Their prototypes testing began in parallel with the existing control system in 1988 and lasted for four year and the company (BN) reported that good results were obtained. [George Achakji, Advance Railroad Electronic System' January 1991]
Advanced Railroad Electronics Systems are consists of the following integrated sub-systems: I) data management ii) rail operations control iii) locomotive analysis and reporting IV) on-board display v) energy management and VI) wayside interface. The ARES also has the capabilities for advanced traffic arrangement. The system provides direct dispatcher intervention in hazardous traffic situations, i.e., stopping the train by remote intervention [switch] which can be easily activated from the central dispatch office.
During the testing period [ARES] BN and Rockwell had some problem using GPS to achieve high accuracy of train position on parallel track. In an effort to correct the problem of parallel track, BN and Rockwell explored the possible use of real-time differential GPS in terminals and also used others methods to provide more accurate positioning inputs, for example, using transponders for trains approaching switches and sidings.
[George Achakji, 'Advanced railroad Electronic system, ARES', January, 1991]
2.5 Incremental Train Control System (ITCS)
On of the vital communications-based train control system is Incremental Train Control System (ITCS) where the system utilize digital data link between the wayside and on-board train location system and it also perform the requirement for traffic control functions. The ITCS provides enforcement of signal indications, speed limits, temporary speed restrictions, and advanced start of crossing signals. This system is developed by Harmon Industry for Amtrak in Michigan. [Peter Winter, ETCS system, 1995]
The Incremental Train Control System consists of 3 main sections:
i) The locomotive equipment: This locomotive equipment consists of On-Board Computer (OBC), display screen, GPS receiver and mobile communication package.
ii) The wayside equipment: This wayside equipment consists of Wayside Interface Units (WIU) and Wayside Interface Unit-servers (WIU-S) (WIU-S are the interface with the signal system), crossing signals and defect detectors.
iii) The communications network: This network consists of wayside local area networks (WLAN). This also use spread range radio, so it can link WIU with WIU-servers and radio frequency (RF) networks in the UHF range to link WIU-s with On-Board Computer.
Incremental Train Control System is supplemented by ATC or automatic train stop systems. During its normal train operation, the train driver are accountable for observing each signal feature and control the train accordingly the speed limits and restrictions and also stop the train where a stop is necessary. ITCS is responsible for monitoring the signal system and ensure that the train is properly controlled with the speed limits, speed restrictions, and stopping, not maintain these parameters in that case ITCS will automatically apply the breaks to stop the train.[Christian Tietze, 'ICE's On-Board Train Control and Diagnostics System', 1994]
Incremental Train Control System is also known as a distributed control system, not like the ATCS architecture which is a central control system. The On-Board Computer (OBC) store the data from signal indications, track curvature, speed limits, mileposts, speed restrictions, and the locations of all the devices which are needed to communicate with the train. The OBC is also works on the train status report with the help of wayside devices. If three status reports are missed, the OBC will automatically apply the train brakes.
The OBC monitors the location of the train with the help of GPS data and compared the track data base. After receiving a signal indicator it determines the appropriate speed of that track. The OBC also calculates a braking outline for the train and display the necessary information on the display screen. In the events of track crossing the OBC will calculate and issue a time to crossing (TTC) to the wayside interface units (WIU). The WIU will synchronize train start timer with the OBC and will confirm that start time.
If the train speed exceeds the initial speed, the OBC will calculate and issue a new TTC to the WIU. If the OBC still cannot receive any confirmation that the crossing timer has been began with the correct value, in that case it will demand that train speed to be reduced. In the event of private crossings, the OBC will observe the status and warning system through update messages from the Wayside Interface Units-Server (WIU-S). If the OBC does not receive a message indicating the warning sign is active, in that case train speed will be reduced. Most of the operation manual of ITCS is very close to a conventional ATC. [Christian Tietze, 'ICE's On-Board Train Control and Diagnostics System', 1994]
2.6 Positive Train Separation (PTS) System
The Positive Train Separation (PTS) System is a non-vital safety overlay system. PTS functions in combination with the active operation methods, signal and train control system. This PTS system was first designed for the Union Pacific/Burlington Northern Santa Fe (UP/BNSF) Railroads and state of Washington to Portland Oregon railroads. The PTS system is measured as an add-on system that enhances safety by protecting against all human errors.
PTS system is centrally controlled communications-based system, which takes control of movement ability and speed limits of the equipped trains. It is also translucent to the train driver as long as the train is operated according to its movement ability and speed requirement. It will become apparent if the train attempt to exceed its speed limit and movement authority, PTS will issue a warning sound alarm to the train driver and the brakes will be applied if the train driver does not brought the train under control immediately.
[Ted Giros, 'Amtrak Tests Cab Signalling, July 1996]
The PTS system consists of 3 following segments:
I) The server: This segment confirm the enforceable movement authority and speed limit, train's identification, destination for each train under the PTS control and digitally transmit this information with the help of communication network to the locomotive segment of each equipped train. It also monitors all train movements to prevent conflict.
ii) Locomotive: This segment is consists of an On-Board Computer (OBC) and a location determination System (LDS), a mobile radio and a display unit, where train staff can receive textual information. The OBC calculates and constantly updates information about authority limits and speed limits and applies breaks if the authority limits are exceeded. It also calculates the distance required to stop the train.
iii) The Communication Segment: Communication segment gather and transmit all information with high reliability between the server and locomotive during the train operations.
[Railway Age, May 1997]
2.6.1 Positive Train Control (PTC) System
PTS is also a centrally controlled communications-based system. Its software is written in conformance with ATCS stipulation. The purpose of the PTC design is the removal of wayside block signal systems and the management train movements, for example; speed enforcement, enforcement of limits of the authority, protection of maintenance-of-way employees and work vehicles and also monitoring of highway-rail grade crossing.[W Moore Ede, 'Communications-Based Train Control, May 1997]
The Positive Train Control system has 3 main sections:
I) Office Equipment: The office equipments are consists of Computer-Aided Dispatching System (CAD), PTC Interface Computer (IC) and a protocol converter to interface with CAD, IC and data communication system.
ii) The Data Communications System: This system is consists of 3 interconnected networks: a) Ground Network b) Radio Frequency link Network c) User Network
- The ground network is consist of cluster controller(CC), base communications package(BCP), message processing nodes, microwave channels, telephone circuits, fibre-optic links and modem to connect the nodes.
- The Radio Frequency (RF) link is consists of base, mobile radio and radio communication channels.
- The User Network is consists of all application software within each field device.
iii) The Field Equipments: The field equipment is consists of mobile communication packages (MCPS), locomotives and wayside interface units (WIU). During an emergency brake application in normal routing operations, the system automatically transmits an emergency message that will invalidate the limits of authority of the other trains in the surrounding area. The PTC system carries out safety critical data through digital data communication system between Interface Computer (IC) and it self for the train locations, trains preset time and devices for highway-rail grade crossing. In PTC the higher priority data message is an emergency message which occurs due to train's emergency brake application. The PTC system has designed in such a way where failure of an emergency data message will not create any unsafe condition. [Railway Age, Washington may 1997]
PTC also uses transponders in the following critical areas: a) during approaching to PTC-equipped territory, b) during the entrance of PTC territory and c) during approach to a controlled point within PTC territory. This transponder provides exact train location and routing determination. When an equipped train passes the transponders to move towards PTC-equipped territory, the system initialize the On-Board Computer (OBC) and set the tachometer to zero for location determination. The equipped train does not enter in to the PTC territory if the OBC cannot be initialized. [R Lindsey, 'Communication- Based train Management', May 1997]
2.7 European Train Control System (ETCS)
The European Union (EU) has adapted a railway network system to overcome the major problems in the field of technical operating system, multiplicity of signalling and train control systems. In 1991 nine foremost European railway companies of the signalling industry reached an agreement with EU to develop a new train control system, which is now known as European train Control System (ETCS). ETCS has the ability to perform in combination with all the existing tracks and wayside equipment under the train protection and train control systems. [R. Ford, 1996]
The ETCS is designed to congregate wide series of operational requirements. The capability of ETCS are provided in three levels
a) Level 1: The new ETCS interfaces can meet the terms with the existing system. ETCS can also provide a basic Automatic Train Protection (ATP) capability combination with the conventional wayside signals.
B) Level 2: This level has the option of speed data display for automatic train speed control. New Cab signalling system is also been added up to ATP capability. But still the train's can be driven by wayside signals equipment and it can also determine the train location with help of tracks fixed equipments and track circuits.
c) Level 3: Train location and train integrity detection can be utilize with the help of transponders on the track (same as in ATCS). This system eliminates the need of track circuits and other detection techniques. In this level, the system incessantly provides an update of train location and also transmits the signalling information to all trains to ensure a safe separation. Level 3 ETCS is also capable of moving block signalling to maximize line capacity. One of the main goals behind the ETCS design is to develop common display units which can be easily understood by the all drivers across the boundaries of different European countries. The ETCS operates frequency range in 900 MHZ using data radio transmission called Euradio. This Euradio transmit encoded data in digital form with vital safety signalling standards. Each operational train does constant radio contact with a central computer. This central computer is responsible for controlling the trains movement and safe separation. [R.Ford, Railway Technology International, 1996]
2.7.1 Train a Grande Vitesse (TGV) Train Control System
TGV (train grande vitesse) is French high-speed train, which has no wayside signals. SNCF (French National Railways) has determined that for a safe train operation track side signals, cab signalling system and on- board equipment with reliable advance information (road status) are vital to the operator. These requirements led to the development of an ATC system. There are two generations of ATC systems are in use on the TGV network system. Both these systems are significant for continuous link between the train and the track. [George Achakji, 'TGV System Development', 1992]
TVM 300 is the first generation TVM. This TVM uses wired logic and has the following performance levels: at speed of 270 km/h with 5 min headway on the SE Line (in 1981) and at speed of 300 km/h with 4 min headway on the Atlantic Line (in 1989). [George Achakji, 'TGV System Development', 1992]
TVM 430 is the second generation TVM This TVM is a fully-digitized system and it also design to companionable with all versions ground equipment. The TVM 430 is designed to have the following performance levels: at speed of 320 km/h with 3 min headway on the North Line and a mixed traffic with 2.5 min headway in the Channel Link which connects Paris -London-Brussels operation route. The TVM 430 based on a real-time, fault-tolerant architecture. To establish the safety requirements and all other techniques are based either on the intrinsic features of certain components, or on hardware or functional dismissal. [George Achakji, 'TGV System Development', 1992]
The TGV has an on-board data transmission network called TORNAD. It has the facility to communicate between 18 computers (single-unit) and 36 multi-unit computers. The TORNAD has the following main functions: controlling, monitoring, and regulating of equipment; and carrying out the information exchanges for operation and maintenance. [George Achakji, 'TGV System Development', 1992]
TGV has built with an automatic braking system. It stops the train when the driver exceeds the speed limit. During operation period, the brakes are monitored in the region of once a minute, and their status is indicated to the train driver's OBC screen. If the train driver exceeds the maximum speed limit which is permitted by the system, than the automatic train stop system instigate an emergency braking action [George Achakji, 'TGV System Development', 1992]
2.7.2 Advanced Control System
Advance control system for train communication is an incorporated command, control and communication system. It is also known as ASTREE system. It was developed by the SociÃ©tÃ© National des Chemins de Fer (SNCF), for train operations and for the railway network management. The ASTREE system offers computerized real-time control of train movement, with the help of radio telephone communication between a central control and onboard microprocessors. This system provides train position and location modification, ground-train transmission (known as data and voice transmission), switch control, monitoring and interlocking, automatic vehicle identification, train consist acquisition, and train integrity checking.
ASTREE system does not put any strong command for safety requested from the communications mechanism because in this system every train is equipped with location and communication capability equipment. During the train operation the train's location can be adjust with passive microwave tags (same as the ATCS track transponders, SNCF has new identification tags, capability to read train speed at 400km/h) through an on-board interrogator and the train constantly knows its own position and speed limit according to authority restrictions.
[George Achakji, 'High-Speed Train, TGV system Development, March 1992].
2.7.3 German InterCity Express (ICE) System
The German InterCity Express (ICE) System is one of the state of-art train operation system set with locomotive at each train coaches. This system implements a sophisticated integrated data transmission system network, which imposes with traction control and also interacts with the each coaches control system. ICE System network uses fibre-optic cable to transmit data for train's diagnostic systems, real-time processing, and block maintenance and also for on-board passenger information and amusement. Using of fibre-optic is the best method for train-bus communication, because it is technically more effective and much more economical. [Christian Tietze, 'ICEs Onboard Train Control and Diagnostics System, 1994]
ICE's electronic control and supervision devices are divided into 4 subsystem levels:
I) Train operation level: Train engineers inputs resolute command during train operation from Automatic Train Control (ATC) wayside and Automatic Train Protection ATP) devices.
ii) Train control level: This level handles trains automatic driving and braking and traction effort with the help of closed-loop control.
iii) Vehicle control level: The vehicle control level has resulting redundancy for the train bus fibre-optic interface and the train control, for example, power car (locomotive) and the train coach. Central diagnosis device on the locomotive called the David monitors and stores all functions and malfunctions. It also checks trains equipment at the beginning of operation. The train controller unit on the trailer coaches called the Zeus. Zeus controls diagnosis and co-ordinates functions for each car. After receiving data from the train levels, it distributes this information to the subsystem level.
iii) Subsystem level: The subsystem level includes propulsion control, brake control, auxiliary control, door control, and air conditioning control devices of the train.
[Christian Tietze, 'ICEs Onboard Train Control and Diagnostics System, 1994]
2.8 Intermittent Cab Signalling (ICS)
Cab signalling technology has been available and in use for many years. In 1979 it was first established on the Swedish State Railway (SJ - X2000) for high-speed train operations. Its function has been proven both in European and North American railways. In the recent years, supplementary developments were undertaken by various railway companies. In U.S.A, Amtrak has tested an intermittent cab signalling system for the future advanced civil speed enforcement system (ACSES). In their signalling design, the system can operates independently and it can also be integrated with existing train control systems. It has the capabilities for enforcement of train speed limits and the automatic stop command by applying the train's breaking system (calculates and compares by trains on-board computer). This system also uses separate passive radio frequency transponders to provide the required data to a passing train. [Ted Giras, 'Amtrak Tests Cab Signalling', July 1996]
2.9 Docklands Light Railway (DLR) System Overview
The Dockland light Railway (DLR) system outline is shown in Figure 1-1. The system comprises existing connection from Bank (BAN) to Canary Wharf (CAW), Tower Gateway (TOG), Stratford (STR) and Lewisham (LEW), Beckton (BEC), as well as a new line to the King George V (KGV) station. This automated system consists of approximately 27 km of double track, except between station Bowchurch (BOC) and Stratford, where section of single track exist. There are two manual deports, which are located at Poplar (POP) and Beckton (BEC).Alcatel Canada provided SELTRAC system, a transmission based signalling system for DLR.
Conventional signalling follows the 'fixed block' principle, where tracks are divided into section (blocks) of a prearranged length. A train is only authorized to carry on into a block when that block and the next are clear of traffic. To achieve the closer headway and system flexibility demanded by urban transit, shorter and more numerous blocks are needed in affixed block system.
An adaptation of the system known as SELTRAC was developed and implemented by SELC. The technology was expanded to permit fully driverless operation in high capacity (i.e. passenger) application for the cities of Vancouver, Toronto and Detroit for Light rapid transit systems. Over the years these systems have demonstrated high availability and superior operating flexibility. SELTRAC has provided several operation modes including fully automatic known as Automatic train Operation Function (driverless) and Automatic Train Protection function (ATP) Manual.
SELTRAC is based on the moving block principle, in which the safe separation behind the proceeding train is dynamically calculated based on the actual operating speeds, breaking curves and locations of the trains on guide way. This dynamic method allows shorter headways to be achieved without impinging on safety principles.
With the SELTRAC system, all DLR Automatic Train Operation (ATO), Automatic Train Protection (ATP), and Automatic Train Supervision (ATS) function are performed with a minimum of wayside hardware. Checked-redundant centralised computers are in continues cyclic two-way communication with vehicle-borne, checked-redundant microprocessor control component.
DLR major departure from conventional signalling is the centralisation of route and block interlocking. This function permits central operators to implement immediate, VITAL and supervised go-slow-zones, closed track sections or even emergency braking of a train. These VITAL actions, by the central operator, are not available in conventional system.
Conventional signalling systems utilise fixed parameters based on train performance expectations, particularly with respect to maximum train speed, maximum weight and minimum guaranteed braking capabilities.
Changes in vehicle capacities are not readily or economically accommodate with fixed block systems, as track circuit and signal instillations would have to be physically reconstructed.
A transmission-based moving block system can accommodate changes in vehicle capabilities by modifying software parameters and guide way list.
Development of such advanced controlled system can only be accomplished effetely if the system architecture and train control concepts are formed around computers and modern solid state technologies.
Among the many advantages of the SELTRAC control system are the capabilities to:
- Reduce headways
- Provide control of the complete velocity profile
- Enforce VITAL supervision of temporary speed restriction
- Provide bi-directional operation without additional way side hardware
- Provide way side monitoring of vehicle systems
- Provide continuous train identification for routing
- System-wide 'train hold at station' feature
- Schedule adjustment and related ATS functions
- Minimum turn back times
- Accurate station stopping without any additional station equipment
- Full bidirectional operational capabilities, including direction reversal capabilities at all stopping points
2.9.1 ATP functions on SELTRAC. System
Automatic Train Protection Functions
- Continuous positive presents detection of all train through out the system.
- Safe train separation governs by the worst case safe stopping distance and safety distance.
- Point deadlocking to prevent the point elements from unlocking or moving while a train is approaching or is in a point area.
- An aligning locking routes supervising for train travel at all merging and diverging route locations.
- Limiting the speed of trains according to safe operating and civil speed limits.
- Supervising proper train travel direction throughout the systems.
2.9.2 ATO Functions on SELTRAC System
Automatic Train Operation Functions
- Regulation of train speed within imposed by the ATP subsystem and to provide passenger ride quality as established by operating policy.
- Control train movement with regard to speed, acceleration, deceleration, and jerk.
2.9.3 ATS Functions on SELTRAC System
Automatic Train supervision Function
- Train departure, destination assignments and identification assignment.
- Train routing functions.
- Modification of the system operations parameters in response to system delays and Control Room commands.
- Control of communications subsystem, displays and interfaces to assist the Control Room Staff.
- Collection and analysis of data for management reports.
- Station platform information display (PID) control
- Station platform announce
2.10 Moving Block System
Operation of the SELTRAC system in DLR is based on having the safe distance of separation continuously using actual train speed; location and braking profile (Figure 1-2). In addition a SAFETY ZONE is added to the calculate braking distance. The high resolution of the position detection system allows a following train to safely close up to a point of safe braking distance from the last verified position of the rear car of a preceding train. In many applications a significant reduction in headway, relative to fixed block system, is possible since the train need not be stopped at a braking distance calculate for the highest speed, worst braking, heaviest loaded train.
The SAFETY ZONE is a fixed distance between the confirmed position of the rear of the preceding train and the commanded stopping point of the following train. This distance is selected to allow for a series of worst-case events to occur and still ensure that safe separation is maintained. This distance is typically about 50 meters.
VITAL supervision is implemented by providing the Vehicle On-Board Control (VOBC) system information on the maximum allowable train speed and the current safe stopping point. The communication is updated cyclically to ensure that continuous updates are available to the train. The VOBC continuously calculates the point at which braking must commence for 'this' train at its prevailing speed and braking rate, to meet the current safe stopping point.
The train safety operates within the envelope defined by:
- The maximum allowable speed
- The target point
- The braking curve
- Present track grade
3.1.1 Timetables, Schedules, Train Orders, and Manual Block System (MBS)
The beginning days of railways, trains were operated by timetables, schedules, train orders and train separation was achieved by time parting. With the help of electric telegraph trains location used to establish and also to control the trains order and system traffics. When traffic used to increased, tracks used to divide in to blocks and train parting was made by space intervals using the manual block system (MBS). Those areas are referred as non-signalled areas or dark areas. [Furman Edwards, Network Management for ATCS communication system 1991]
3.1.2 Computer-Aided Manual Block Systems (CMBS/CAMBS)
Railway Industry's have urbanised CMBS and CAMBS with the support of computer in order help dispatchers in managing railway traffic and issuing train movement in to dark areas. Canadian Pacific (CP) Rail and Canadian National Railways (CN) Rail were among the first companies to expand and use the CMBS and CAMBS, correspondingly. To get rid of human errors, these computers were programmed to replace the dispatcher's train scheduling and also to help the dispatcher in verifying train movement and clearance .This CMBS system was introduced in middle of 1985 by CP Rail and it was extensively implemented and speedily stretched. The system provides a computer check for all train movement authorities and gets rid of human error at the dispatcher stage. [Canadian Pacific Rail, 1984]
3.1.3 Occupancy Control System (OCS)
The Occupancy Control System (OCS) is a computerised program which is very similar to the CMBS and CAMBS. All train movements is supervised by the Rail Traffic Controller (RTC) who can issues train clearances, track occupancy permits (TOP), general bulletin order (GBO), and instructions. By using this OCS, Rail Traffic Controller are able to protect all conflicting train in the system. [Janet L Darnell, ATCS Network Management, 1993]
3.2 Signalled Areas
3.2.1 Block Signal and Automatic Block Signal (ABS) System
As block signalling systems began in 1830s, the railway industries urbanized and tried a variety of electrical and mechanical systems. Near the beginning, systems were designed to permit one train at a time to pass into a block and hold back that block, so that no other train would be allowed into that block unless the first train left that block. Afterwards systems added a permissive feature allowing trains to follow one another into the same block. In the early hour's designs, interlocking system did not comply with switches and signals. The switches and signals were changed by a switchman using hand levers. This sort of methods required considerable physical strength and had no protection against the train which has inadvertently left that block. The block signal system was improved with the creation of the Absolute Permissive Block (APB) signalling and the advance of track circuits that allowed trains to operate in either direction on single track with full signal protection for both following and opposing movements. Many different actions of track circuits are in use now days (uncoded and coded with DC or AC track circuits); but their basic functioning principles are similar. A track circuit is fundamentally an insulated section of the track. When the train make an entry to that section of track, the train shunts the circuit by closing the loop through its wheels/rail contact. [GRS, 'Elements of Railway Signalling' June 1979]
3.2.2 Wayside Signal, Cab Signal and Centralized Traffic Control (CTC) System
In the last many years, Centralized Traffic Control (CTC) systems have been extensively used. These systems rely on track circuits for train detection and a set of codes sent through the rail and through wayside signals, or train borne cab signals, to provide train operators with signal indications and information's on the status of the track ahead. Later, these systems were measured safe to operate and moderately useful techniques for train control. The disadvantage of using this system is, it only offers limited functions and require fixed blocks (fixed segmentation of track) rather than flexible or moving block. In a fixed block, tracks are divided into prearranged distances between block lengths and wayside signals. Due to safety reasons, the block lengths are recognized by maximum stopping distance. From the safety point of view, the efficiency of conventional track circuits system is not good enough to provide full train control because its efficiency depends on the decree of the track circuits. For installation and maintenance conventional system can cost more. [Asrar Sheikh, 'An Evaluation for ATCS', 1998]
3.3 Communications-Based Train Control (CBTC) System
Current system of signalling and train control system are known as Communications-Based Train Control (CBTC) Systems, where Advanced Train Control Systems (ATCS) and Commands Control and Communications Systems (CCCS) are included. These systems are mainly designed as vital systems planned to replace conventional systems for example CTC, ABS, wayside signal, CMBS etc. Other new systems are known as Positive Train Control (PTC), where Positive Train Separation (PTS) and Incremental Train Control Systems (ITCS) are included. As of many, one of the primary differences between the system used in conventional train control systems and the newly developed CBTC systems is that in conventional system train can only manoeuvre in fixed blocks, whereas with the CBTC systems, a train can manoeuvres in flexible blocks or moving blocks, which is a more proficient. The modern communications-based signal system is based on data communication over a range of paths (including radio) to congregate information for train location and system assimilation. The new systems is able to classify the variability or flexibility of the moving block systems based on real time train speed, the geometry of the train, and the direction of movement as well as safe braking distance. In the frequent changing moving block process, the geometrical distance in between one to other trains no longer plays any part on the length of blocks and it can be abridged to the desired braking distance with a pre-satisfied safety margin. Small trains can carry on more frequently and the waiting time can be reduced significantly. CBTC systems are more capable over existing systems and are designed for the modern railway operating atmosphere. [Vikram Rana, Anup Ghosh, W Barry Johnson, 'Distributed Safety-Critical System for Real-time Train Control', 1995]
3.3.1 Data Communication
Data communication system has lots of advantages over traditional radio telephone communication. Train operator and track workers can communicate with the control centre in less time, without delay and with great precision and efficiency. These possessions of data communications on train staff and track workers were investigated by the Federal Railroad administration. [Federal Railroad Administration, 1996]
3.4 Case Study: DLR Automatic Train Control (ATC) System
Docklands light Railway's Automatic Train Control System is an Alcatel SELTRAC Train Control System. The main purpose of this case study to introduce and classify with the concepts and feature of the SELTRAC Train Control System and its sub-system. Upon completing this case study we will be able to the following:
a) Understanding the main DLR SELTRAC operating principle
b) Identify the major SELTRAC sub-system and their function
c) Describe overall system configuration
DLR Automatic Train Control System Main Components
- SENNET Management Centre (SMC)
- Vehicle Control Centre (VCC)
- Vehicle On Board Controller (VOBC)
3.4.2 SELTRAC Management Centre (SMC)
The SMC is a Local Area Network (LAN) based distributed processor control system developed specifically for control room environment. This architecture provides the flexibility necessary to configure site-specific systems with unique workstation, system interface, and operational requirements such as is required by the DLR.
The SMC is the backbone of the DLR SELTRAC ATC system and provides the following Automatic train Supervision (ATS) function:
- CRS Interface
- Train Tracking
- Train Routing Control / Assignment
- Schedule performance Monitoring
- Schedule regulation
- Data logging
- Passenger Information Display Interface
- Platform announcement System Interface
- Management Information
- System Status Display
- Health Status Monitoring
3.4.3 Vehicle Control Centre (VCC)
The hearts of SELTRAC ATP system are three VCC control regions with coverage arrears as shown Figure 1-3. Each VCC region is designed to operate with and enforce a maximum of 30 three car AUTO/ATP Manual mode trains within its boundaries.
The VCC is responsible for providing the ATP functions required for the safe automatic operation of the DLR line. Specifically, the VCC provides these Automatic Train protection (ATP) functions:
- Train Detection
- Train Separation
- Train length Supervision
- Unscheduled Door Opening supervision (in conjunction with the VOBC)
- Maximum speed limit and
- Route interlocking (in conjunction with the station Controller system)
All ATC requests from SMC which relate to automatic train movement and route interlocking are processed by the VCC prior to implementation, in order to guarantee that no unsafe situation arises as a result of these requests.
3.4.4 Vehicle On Board Controller (VOBC)
The VOBC system provides the interface between the ATC system and the vehicle. The VOBC is primarily responsible for implementing the vehicle ATP function. The VOBC also provides the Automatic Train Operation (ATO) functions of the system. Specifically, the following ATO functions are provided by the VOBC, within the constraints imposed by the Automatic Train Protection (ATP) functions:
Stopping Point Control
Door Release Control
The VOBC also provides Train Health Monitoring along with the following Automatic train Protection (ATP) system functions:
The Train Captain interface to the ATC system is provided through the Door Header Panel, or the Emergency Driving Position (EDP) panel, which are connected to the VOBC system.
3.4.5 Station Controller System (SCS)
Point control for route interlocking is performed by the Station Controller system. The Station Controller system implements VITAL commands received for the VCC and returns VITAL status of points, axle counter blocks wayside emergency stop push buttons to the VCC. Axle counter blocks are provided over all main line tracks and in all point and crossing areas. During normal operations, it is possible to have more than one train in a block between points with safe train separation. Blocks in the points and the crossing areas provide dead locking of points.
Indicators are driven from the point status (independent of interlocking equipment) at all point locations.
3.5 Operating Concept
The operating concept for the DLR system is based upon a fully automatic main line system. During normal operations, each train is staffed by a Train Captain, whose primary responsibility are to provide passenger interface and to initiate the door close sequence prior to the train departing station. The SELTRAC system is capable of supporting 270 vehicles. During peak periods, 33 trains comprised of a mix of 1, 2 and 3 vehicle trains can provide the initial level of service.
Modes of Train Operation
The DLR system is designed to normally operate in an automatic mode of operation. However, four modes of operation are supported by the system. These are:
Automatic Mode (AUTO)
ATP Manual Mode
Emergency Shunt Mode, and
All Panels Off (APO)
The Train Captain, using a mode select master switch located on the Emergency Driving Position (EDP) panel, performs mode selection between Auto, ATP Manual, APO and Emergency Shunt. Any changes in operating mode of vehicles communicating with ATC system are detected by the VCC and logged by the SMC, with mode changes to Emergency Shunt Mode alarmed on the SMC.
3.5.2 Automatic Mode (AUTO)
Normally daily system operation is performed with all trains in AUTO mode. Full ATO and ATP functions are provided during AUTO mode operations. The Train Captain placing the mode select switches in the AUTO position and depressing the AUTO button on the Emergency Driving Position (EDP) panel requests the AUTO mode. The AUTO mode can be entered directly from the ATP Manual mode without Control Room Supervisor action. This mode change can be performed at any time, provided the train is stationary, with the thrust lever in brake position. All mode changes Emergency Shunt to Auto require the train to be stationary, and must be authorized by the Control Room Supervisor entering a Train Activate command to the VCC system.
While operating in the AUTO mode, the AUTO light on the EDP panel is illuminated, indicating that the train functions of acceleration, cruise speed, deceleration, stop and door release are controlled by the VOBC. The doors on the station platform side of the train are enabled automatically after the train has come to a complete stop and is correctly positioned in the station. An enabled door will open when a passenger activates the associated door open button. The Train Captain initiates door closure in AUTO mode.
Mode changes into AUTO mode are recognized by the VCC, and the SMC logs the event and changes the colour of the Train ID on the line overview screens.
3.5.3 Automatic Train Protection (ATP) Manual Mode
The ATP Manual Mode of operation provides full ATP functions while train operation is under control of the Train Captain. This mode is primarily used during failure management.
The Train Captain placing the mode select switch in the ATP manual position selects the ATP manual mode. While operating in the ATP manual mode, the ATP Manual light on the panel is illuminated. The ATP manual mode is entered directly from the AUTO mode without the Control Room Supervisor action. This mode change can be performed at any time.
All mode changes from Emergency Shunt to ATP Manual require the train to be stationary, and must be authorised by the train Control Supervisor by entering the Train Activate command on the VCC system. Mode changes into ATP Manual are recognised by the VCC. The SMC logs the event and changes the colour of the train ID on the line overview screens.
In ATP Manual Mode, the train functions of acceleration, coasting, deceleration and stop are under the direct manual control of the Train Captain and are supervised by the ATP system. Door Control (both release and closing) is performed by the Train Captain and can be initiated any time when the train is stationary at a platform, and the docked lamp is illuminated. After closing the doors, a departure will not occur unless the scheduled station departure time has arrived on a route is given by the Control Room Supervisor. This is indicated by the illumination of the 'ready to depart' light on the EDP panel. Station stopping points for ATP Manual trains will be identical to those of AUTO.
3.5.4 Emergency Shunt Mode
The Emergency Shunt Mode of operation provides full override of the ATO and ATP function of the train. The ATC system continues to provide protection to train operating in Emergency Shunt mode from trains operating in AUTO or ATP Manual. Emergency Shunt operating is always governed by strict operating procedures under verbal communication between the Control Room Supervisor and the Train Captain.
All the vehicles movement also authorised by the Control Room Supervisor. DLR operating speeds are restricted to 20 km/hr by the propulsion system during train operation. Emergency Shunt mode can be selected at any point at the track by placing the mode select switches in the Emergency Shunt option. Provided that, the thrust lever is in the braking position. Mode changes into Emergency Shunt are recognised by the VCC and the SMC. When the train gets an Emergency Shunt mode it sends an alarm to Control Room Supervisor.
3.5.5 All Panel Off Mode
A train enters All Panel Off mode when the Train captain selects the off position on the EDP without first going into automatic. The train cannot be moved either automatically or by the Train captain while in APO. The change to APO mode from ATP Manual is not logged by VCC until the time expires. This timer accepts 10 minutes to allow the Train Captain to select a mode on the panel at the other end of the vehicle without impact on operations. Once the APO mode is logged, any current reservations and routing assignments are cancelled by the VCC and CRS action will be required to reroute the train. The SMC logs the change to the APO and sends an alarm to the Control Room Supervisor.
3.6 New Control Centre (NCC) Amenities
The New Control Centre (NCC) at Poplar provides a facility to monitor all aspects of the DLR proceeds line. Deport operations room at the Poplar and Beckton has the ability to monitor trains via movements out of or into the reception roads between the manual deport and the automatic mainline track, as well as surrounding mainline movement.
3.6.1 SELNET Management Centre (SMC) Interface
The SMC system is organised as a series of workstation located in the NCC Control, equipment and simulation rooms. Each workstation comprised of a PC with a colour VDU display and a keyboard/trackball interface and provides specific control area tasks relating to the DLR operations. Workstations are provided in the NCC for:
Control Room Supervisors (4 PC)
Control room Assistants (2 PC)
Control Room Manager (1 PC)
Control Room Technician (1 PC) and
Poplar Depot (1 PC)
In addition of the overview screens available on all SMC workstations a line overview with an overview of the entire DLR system is provided in front of the Control Room Supervisor's Console.
Remote workstations connected via Modem's to the SMC are provided at:
West India Quay
Monument (LUL Control Room)
Poplar Booking-on Room
Island Gardens and
London City Airport
The assigned area of authority defines the functions available to SMC workstations. Prior to entering any commands, the operator must request an area of authority from the Control Room Manager. The Control Room Manager defines two Control Room Assistants (CRA) areas, by selecting which area's are to be assigned to CRA2. All other stations are assigned to CRA1 by default.
The Control Room Manager defines the two Control Room Supervisor's (CRS) areas, by selecting which interlocking areas are to be assigned to CRS2. By default, all others belong to CRS1. When an operator starts a shift, the appropriate area (CRS1, CRS2, CRA1, etc) is requested. The Control Room Managers workstation receives the request, which must be granted or denied.
3.6.2 Vehicle Control Centre (VCC) Interface
Each VCC interfaces with the Control Room Supervisor's via a dedicated terminal. These VCC terminals are accessible to both Control Room Supervisors. The terminal provides the Control Room Supervisor with ability to input commands directly to each of the VCC control in the DLR system. System massages originating from the VCC are displayed on this terminal. VCC commands relating to VITAL system functions are verified by the CRS.
The VCC keyboard also provides the Control Room Supervisors with ability to operate the DLR system in a non-scheduled fashion with trains on fixed line assignments, in the event of communications failure between the SMC and VCC system. This VCC controlled operation does not, however, provide ATS functions such as schedule monitoring, junction management, or any of the interfaces to platform or Control Room system.
3.6.3 Station Controller Interface
Normally the Station Controller system operates in an automatic fashion under the direct control of the VCC system. However, Emergency Point Control Selector switches are provided in order to allow the Control Room Supervisors to interface directly to the Station Controllers from the SMC to operate the main line point machines in case of total VCC failure. These switches are located near the two Control Room Supervisors position. When these switches are activated, the Station Controller provides the following information directly to the SMC:
- Point positions
- Block status
- Wayside (Station and Track side) emergency stop button status
- Station Controller alarms and massages
3.6.4 Passenger Information Display (PID) Controller Interface
The PID Controller interface is used for three purposes:
- To transform data to displayed on the Platform Display Unit
- To control the Point Heaters, and
- To transfer non-vital wayside alarm status to the Control Room
3.6.5 Supervisory Controlled and Data Acquisition System(SCADA)
There is a serial interface between the SMC and the SCADA system. The SCADA system will send massage to the SMC whenever there is a change in the state of power supply equipment or ventilation equipment. The SMC will log the complete status of all the SCADA inputs each and every single occurrence.
3.6.6 Long Line Public Address System (PAS) Interface
There is a serial interfaces between the SMC and the Long Line Public Address System( PAS). The SMC will send an arrival massage to the PAS whenever a train on a line approaches a through-station. No arrival massage to be send to those station where the train is about to turn back in a Head Shunt, the SMC will send an 'out of service' massage to the PAS for that same station upon the arrival of the train at the station before the head shunt. The SMC will send a departure massage prior to the departing of a train from a terminus station (such as; STR, LEW, TOG, BAN, BEC, KGV, and CAW).
If a train arrives at a station where it will loose its current assignment due to an out of service command or a couple, uncoupled or exit transition, and out of service massage will be sent to the PAS.
3.7 Train Captain Facilities
The Train Captain's interface to the ATC system is provided through the Emergency Diving position (EDP) panel, the door header panel Local to each door and the wayside point indicators. These interfaces are described in the following sections.
3.7.1 Emergency Driving Position (EDP) Panel
Each vehicle is equipped with an EDP panel at each end and it provides the interface between the Train Captain and the ATC system during ATP Manual and Emergency Shunt operations.
3.7.2 Door Control Panel
Each door location is equipped with a door control panel. These panels provide the Train Captain with the ability to control the train doors from each door location. The following controls and indication are provided at each of these panel:
- INE Keyswitch
- Release other doors
- Close this door
- Close other doors
- Ready to Depart
- All Doors Closed
- Train Inhibit
3.7.3 Wayside Point Indicators
The Train Captain is provided with point station information through Wayside point indicators located at all point areas. These indictors display the current position of the point of the interlocking area. They do not indicate that the approaching train has been authorised to proceed along the indicator route.
3.7.4 Service Requirements
SELTRAC required operating a 2 minutes service over many sections of track under Dockland Light Railways performance obligation specifications. SELTRAC system is implementing with a System-wide headway capability of 90 seconds or less, subject to extend civil restrictions such as limiting traffic in the Bank Tunnel, Point clearance and turn back lines, etc.
In addition the control Room Assistant (CRA) may at any time close a station to AUTO/ATP Manual traffic. The ATC system will prevent a train from being routed to a station, which has been closed, except in the case where the CRS routes a train to a track section in the station platform area. In this case the train will stop at the assigned destination but the doors will not be enabled. Normally, the system is serving all station on a line. Special lines have been defined to implement certain non-stop services.
4 Research and Discovery
4.1 Compare and Contrast of Other Automatic Train Network
System around the World
4.2 Vancouver Sky Train - Fully Automated System
Vancouver Sky Train Transit System is one of the most primitive transit systems in the world. It is completely automated, computerized driverless system. Since 1986, this system has been in operation at Vancouver and British Colombia. Vancouver Sky Train system operates exclusively in a full automatic mode without any train driver. It is SELTRAC (from Alcatel Canada) Automatic Train Control system, which was formally developed by standard Elektic Lorenz AG (SEL) in Germany. Its operating system based on the moving block principle. It has designed to cope with high population density in swift mass transit system with the capacity to provide 60 sec operation headway at the speed up to 90 km/h.
Train system operations are moving block principle, where the system uses an inductive loop cable to make continuous two-way communication. Vancouver Sky Train system is based on 3 level of control:
Management Level: This level operates through System Management Centre (SMC). SMC is a central control capacity centre. It allows the dispatchers with the help of mini-computer to control of the entire systems. Dispatchers can monitor development of each train, regulate the schedules, in or out trains for service, trains propulsion, braking, control and communication system.
Operation Level: This level operates through the Vehicle Control Centre (VCC). Its responsibilities are to operate safe train separation and monitoring train position and velocity. It also monitors on train safe braking distances and control switches with interlocking. One VCC can keep on eye to another VCC. If one VCC fail then the other VCC automatically alert a maintenance alarm to the system.
Activation Level: This level operates through the Vehicle On -Board Control (V OBC). VOBC is a microprocessor unit based on every train. Its responsibilities to calculate trains speed and distance limits. It can apply train braking system in the event of over speed. [Alcatel, Canada]
4.3 New York City Transit (NYCT)
The NYCY is a Communication- Based Train Control (CBTC) system. This railway system is consists of 25 lines (unified) and about 722mile track with 6000 vehicle. Operating with CBTC system NYCT is facing some problem because of its interoperability between train and many lines.
4.4 Washington Metro
Washington Metro is an ATC system. ATC makes sure that all trains operate in the system according to signal indication. It has 3 main sub-systems:
Automatic Train Supervision (ATS)
Automatic Train Protection (ATP)
Automatic Train Operation (ATO)
These 3 sub-systems are synchronised with a dual computer at Central Control Centre to incorporate a real -time control system. ATP sub-system is responsible for locating trains position and speed limits. The ATO sub-system controls start-up and train acceleration, speed restriction and stopping train on right platform position. The ATS sub-system controls arrival and departure of train from different stations through automatic wayside equipment. Central control's main task is to monitor the entire system and it operation performance and change the operation plan to regulate traffic flow if it is necessary.
4.5 Lyon's Metro Automation
Lyons Metro system is fully automatic train control systems know as MAGGALY system. This system based on deformable block principle. This system can verify speed of each train, train position and control train braking system. During the train, operation if any train become as a fail train it can remove that train of the system and the system can locate any obstacle on the track. If the train move towards any obstacle, the system automatically puts emergency braking and cut off power supply of that track. MAGGALY system also provides high level consistency for anti-collision and trains total control
4.6 MÃ©tÃ©or Paris Metro
Paris metro system is an ATCS system with numerous sub-systems. Central Traffic Control operates the system with Automatic Train Operation (ATO) and Automatic Train Protection (ATP) system. The headway average of metro system is 85 sec.
4.7 Moscow Metro
Moscow Metro system based on Automatic Block Signal (ABS) and Communication-Based Train Control (CBTC) systems. Moscow system consists of 500 trains, 550 km of tunnels, and 262 km of track. The fundamental elements that metro system uses with one-person operation are, light signal, zone protection and track circuits. The system also uses extended range radio communication channel.
Compare and Comparison