17-04-2013, 03:56 PM
MOBILE TRAIN RADIO COMMUNICATION
[attachment=53121]
INTRODUCTION
Mobile Communications Principles
Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication. One for transmitting from the cell site, the forward link, and one frequency for the cell site to receive calls from the users, the reverse link.
Communication between mobile units can be either half-duplex or full-duplex. In case of half-duplex, transmit and receive communications between the mobile units are not at the same time, i.e. talking and listening can not be done at the same time. In case of full-duplex communication, transmit and receive communication is at the same time, i.e. one can talk and listen at the same time.
When communications between mobile units are within a cell, and if the same is half-duplex, then it shall require only one pair of frequency. If the same is full-duplex, then requirement of frequency pair shall be two.
When a mobile unit is communicating with a mobile unit outside the cell, then the requirement of frequency pair shall be one per cell for both half-duplex and full-duplex communication. Hence the system resources are utilized more if the mobile units communicate with each other in full-duplex mode.
Early Mobile Telephone System Architecture
Traditional mobile service was structured similar to television broadcasting. One very powerful transmitter located at the highest spot in an area would broadcast in a radius of up to fifty kilometers. The “cellular concepts” structure the mobile telephone network in a different way. Instead of using one powerful transmitter, many low-power transmitters were placed throughout a coverage area. For example, by dividing a metropolitan region into one hundred different areas (cells) with low-power transmitters using twelve conversations (channels) each, the system capacity theoretically could be increased from twelve conversations - or voice channels using one powerful transmitter- to twelve hundred conversations (channels) using one hundred low-power transmitters.
MPT1327 System
MPT1327 is an Open Standard for Analog trunked radio networks. The British Department of Trade and Industry (DTI) developed it in year 1988. In the course of the next twelve months of development continued and resulted in MPT1343 standards. A system based on MPT1327 generally comprises of several radio channels. At least one of these channels will have been defined as the CC (Control Channel) and all the other channels are TCs (Traffic Channel). Data messages between the mobiles and the networks are exchanged on the Control Channel at 1200 bits/sec using FSK (Frequency Shift Keying). Each subscriber in a trunked radio network has a unique call number. It consists of a prefix (3
digits), a fleet number (4 digits), and a subscriber number within the fleet (2 or 3 digits). After it has been entered the call number will be converted in the mobile to a 20-bit address. For the duration of the call a subscriber is exclusively allocated a traffic channel from the available trunk.
WESTERN RAILWAY SUBURBAN SYSTEM (CHURCHGATE TO VIRAR)
Western Railway has gone for a mobile communication system in its suburban section in Mumbai. This project is a part of the Train Management System, which is commissioned in the suburban section of Mumbai Division. Basic purpose of this communication system is to provide a continuous communication between the Motorman and the controller. The system consists of two base stations. One is installed at Mahalakshmi, and the other at Borivili each transmitting 50 watts of power. The Regional Node is installed at Mumbai Central. Mobile units are 25 watts full-duplex sets installed in the Motorman and Guard compartment of the 75 EMU rakes of the Suburban section of the Mumbai division. Together they cover the whole suburban section between Churcgate and Virar, a distance of 60 Kms. The system works on the principle of trunking, and is based on the MPT1327, MPT1343 protocols. M/s Tait New Zealand has supplied the System.
The System (T1540) Overview
The system consists of a number of radio sites, which are linked in groups to “Regional Nodes” (in the Western Railway System there are two radio sites, one at MX, and the other at BVI). Regional Nodes may be linked together to form a wide area network. Radio sites (base stations) are connected by fixed audio and data links (V.24 interface at 1200 bauds) in “Star Configuration around the Regional Node”.
In case of wide area network the interconnection between the Regional Nodes shall be with X.25/TCP IP (9600-baud link) for data, and by an audio network consisting of fixed link bearers for audio signals.
Conclusion
Mobile Communication today is a fast growing field. No one can deny its role in Modern Railway Operations. However there is a need of proper choice of technology looking into Railways' Operational needs. It is beyond doubt that incorporation of Mobile Communication into Railways will open new operational
avenues, there by reducing operational costs and increasing customer satisfaction by providing better services. This shall not only help in increasing productivity, but also help in increasing safety of operations. This is an age of communication. Indian Railways, which is a lifeline of the nation, is also geared up to take the requirements of the new millennium, which is knocking the door of this century.
[attachment=53121]
INTRODUCTION
Mobile Communications Principles
Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication. One for transmitting from the cell site, the forward link, and one frequency for the cell site to receive calls from the users, the reverse link.
Communication between mobile units can be either half-duplex or full-duplex. In case of half-duplex, transmit and receive communications between the mobile units are not at the same time, i.e. talking and listening can not be done at the same time. In case of full-duplex communication, transmit and receive communication is at the same time, i.e. one can talk and listen at the same time.
When communications between mobile units are within a cell, and if the same is half-duplex, then it shall require only one pair of frequency. If the same is full-duplex, then requirement of frequency pair shall be two.
When a mobile unit is communicating with a mobile unit outside the cell, then the requirement of frequency pair shall be one per cell for both half-duplex and full-duplex communication. Hence the system resources are utilized more if the mobile units communicate with each other in full-duplex mode.
Early Mobile Telephone System Architecture
Traditional mobile service was structured similar to television broadcasting. One very powerful transmitter located at the highest spot in an area would broadcast in a radius of up to fifty kilometers. The “cellular concepts” structure the mobile telephone network in a different way. Instead of using one powerful transmitter, many low-power transmitters were placed throughout a coverage area. For example, by dividing a metropolitan region into one hundred different areas (cells) with low-power transmitters using twelve conversations (channels) each, the system capacity theoretically could be increased from twelve conversations - or voice channels using one powerful transmitter- to twelve hundred conversations (channels) using one hundred low-power transmitters.
MPT1327 System
MPT1327 is an Open Standard for Analog trunked radio networks. The British Department of Trade and Industry (DTI) developed it in year 1988. In the course of the next twelve months of development continued and resulted in MPT1343 standards. A system based on MPT1327 generally comprises of several radio channels. At least one of these channels will have been defined as the CC (Control Channel) and all the other channels are TCs (Traffic Channel). Data messages between the mobiles and the networks are exchanged on the Control Channel at 1200 bits/sec using FSK (Frequency Shift Keying). Each subscriber in a trunked radio network has a unique call number. It consists of a prefix (3
digits), a fleet number (4 digits), and a subscriber number within the fleet (2 or 3 digits). After it has been entered the call number will be converted in the mobile to a 20-bit address. For the duration of the call a subscriber is exclusively allocated a traffic channel from the available trunk.
WESTERN RAILWAY SUBURBAN SYSTEM (CHURCHGATE TO VIRAR)
Western Railway has gone for a mobile communication system in its suburban section in Mumbai. This project is a part of the Train Management System, which is commissioned in the suburban section of Mumbai Division. Basic purpose of this communication system is to provide a continuous communication between the Motorman and the controller. The system consists of two base stations. One is installed at Mahalakshmi, and the other at Borivili each transmitting 50 watts of power. The Regional Node is installed at Mumbai Central. Mobile units are 25 watts full-duplex sets installed in the Motorman and Guard compartment of the 75 EMU rakes of the Suburban section of the Mumbai division. Together they cover the whole suburban section between Churcgate and Virar, a distance of 60 Kms. The system works on the principle of trunking, and is based on the MPT1327, MPT1343 protocols. M/s Tait New Zealand has supplied the System.
The System (T1540) Overview
The system consists of a number of radio sites, which are linked in groups to “Regional Nodes” (in the Western Railway System there are two radio sites, one at MX, and the other at BVI). Regional Nodes may be linked together to form a wide area network. Radio sites (base stations) are connected by fixed audio and data links (V.24 interface at 1200 bauds) in “Star Configuration around the Regional Node”.
In case of wide area network the interconnection between the Regional Nodes shall be with X.25/TCP IP (9600-baud link) for data, and by an audio network consisting of fixed link bearers for audio signals.
Conclusion
Mobile Communication today is a fast growing field. No one can deny its role in Modern Railway Operations. However there is a need of proper choice of technology looking into Railways' Operational needs. It is beyond doubt that incorporation of Mobile Communication into Railways will open new operational
avenues, there by reducing operational costs and increasing customer satisfaction by providing better services. This shall not only help in increasing productivity, but also help in increasing safety of operations. This is an age of communication. Indian Railways, which is a lifeline of the nation, is also geared up to take the requirements of the new millennium, which is knocking the door of this century.