Underground system gets it all together

A trunked radio system installed in Bangkok's underground railway enables the system to carry out maintenance, deal with emergencies, give train information to passengers and tell the control centre where the train is via induction loops laid in the tunnels. This converging of facilities has been brought about by TETRA ACCESSNET-T.

TETRA radio systems such as ACCESSNET-T implement an open ETSI standard and are known for their reliability throughout the world.

ACCESSNET-T systems are already being used in government authorities and organisations with security missions, oil and gas companies, railway companies, public transport and private network operators.

Secure communications facilities are also a basic prerequisite for trouble-free operation in underground trains.

Siemens TS thus had good reason to select ACCESSNET-T for its project in Bangkok.

The main criteria were reliability, ruggedness and flexibility.

Nineteen TETRA base stations cover the above- and underground lines, the railway premises (Figure 1) and the stops.

The project implements a wide variety of antenna types.

Special antennas were installed to cover the inner and outer areas and flat vehicle antennas were installed on the trains. Leaky feeders ensure secure communication within tunnels.

The central exchange controls all communications facilities (Figure 2). The base stations are coupled to the central exchange via E1 lines and an optical network.

The exchange has interfaces to the private telephone network (PABX), the voice recording system and the SCADA system.

The network management system and the control centre for trains are also directly coupled to the exchange.

The trains have two train-borne radio subsystems each.

SRP-2000 TETRA terminals from Sepura were selected as the radios for mobile use; SRM-1000 terminals, also from Sepura, were selected for use in the vehicle.

The control centre is the heart of the complete system. It manages and monitors all communications including rail traffic.

If necessary, it coordinates and controls unscheduled events. The multiposition TRD-500 dispatcher system with eight workstations was installed for this task.

It is connected to the central exchange via a LAN. Voice communications are handled via a voice-over-IP connection.

The full functionality of the PABX interface can be used via the control centre. TETRA subscribers can thus make phone or mobile phone calls to other communications networks.

Addressing is user-specific and based on train numbers, ie, staff members wanting to make a call use the corresponding train number as an address.

This number will then be displayed on the units and in the control centre. Received and sent status calls, text messages as well as individual or group calls will be processed in the centre.

A control centre monitoring mode is available as well as a data mailbox and a call memory. Priorities for individual subscribers can be assigned, if required.

Public transport applications are subject to particularly stringent security requirements.

The TETRA Voice Recorder R&S TVR-500 was installed to ensure continuous traceability of communications in the event of down time or emergencies.

The system records the 8 Kb data stream as a TETRA-code signal. This ensures much higher capacity than other voice recording systems on the market.

Service and maintenance work can be performed on the radio system with the network management system NMS-500. Every network element (exchange, base station) has its own network management server including database.

Operating data is exchanged via the lines of the network elements.

Different clients can be used for different tasks - one for subscriber management, another for network configuration and network optimisation and a third for error analysis.

The clients are connected to the server via a LAN and can be operated either locally or remotely, eg, in a central control office.

The clients are installed on commercial PCs as a central network management system in a technical office.

In addition to the four-storey underground stations and technical offices, underground train paths and tunnels are also covered.

Antennas tailored to the specific requirements of the coverage area as well as leaky feeders for tunnel coverage are coupled to the base stations.

To meet high security requirements also in this area, BICK Mobilfunk developed a leaky feeder monitoring facility which automatically signals cable breaks or ruptures to the control centre.

The trainborne radio subsystems TRS-500 (Figure 3) were developed to ensure communication with and inside the trains.

The terminals are connected to these trainborne radio subsystems. The trainborne radio subsystems transmit train maintenance and positioning data.

A maintenance system in the underground trains uses sensors to monitor the electronics, air pressure and temperature.

The system signals any data deviating from specified values to the maintenance control centre via the TETRA system.

The centre immediately takes appropriate actions and provides the maintenance staff with the required information.

This saves time and helps to avoid costly repairs. The trainborne radio subsystem transmits general information for passengers to the loudspeaker system of the train. In the event of emergency, emergency calls are transmitted to the centre via the TRS-500 systems.

Since GPS reception is not possible in a tunnel, a different procedure was selected. The train receives its positioning data when travelling over induction loops installed in the stations.

A positioning signal is transmitted to the control centre via ACCESSNET-T and displayed there.

Each network element has alarm sensors. An alarm is immediately triggered at high priority via ACCESSNET-T.

The SCADA interface is the preset address. This ensures that the alarm is sent to the SCADA system and can be processed in compliance with the required operating regulations.

Reprinted from 'News from Rohde & Schwarz'.