Application Note
 

Secure Train-to-Ground Wireless Communications for Enhanced Passenger Security on Light Rail Transits

  
 
Introduction
Light Rail Transit (LRT) is a form of urban rail public transportation with low speed and low capacity. LTR falls between streetcars and the heavier rail/metro system. Uncompromising train safety and highly available connectivity are a first priority for LRT systems. With the mobile nature of the application, the LRT system increasingly relies on wireless LAN networks in support of in-train surveillance and train-to-ground data transfer, which are important aspects of fully-automated driverless LRT systems. With WLAN technology, station operators can access real time information between trains and stations to immediately handle unexpected events, such as the status of arriving and departing trains. In response to the severe rail conditions, communication networks must meet or exceed the high standards of industry-proven ruggedness, vibration resistance, network redundancy, and EMI immunity.
 
Application Requirements
  • Real time train-to-ground connection for improved real time response
  • Reliable inter-carriage data transmission
  • Real time video streaming for security surveillance of passenger carriages
  • A high degree of network availability and reliability
  • Reliable operation under severe rail conditions
 
System Description

Wireless LANs are being increasingly deployed as communication networks between carriages and train-to-ground links due to the clear advantages of lower installation and maintenance costs, due to the fact that fewer cables means that maintenance personnel spend less time replacing damaged cables. Industrial grade wireless LANs in particular need to meet higher standards of network reliability to withstand the harsh rail environments. 

Wireless LANs provide both inter-carriage and train-to-ground links. For this application, the train consists of six carriages, with each carriages required to set up an IP surveillance camera that can be connected to the wireless network via an Ethernet port. Moxa's AWK-3121 and AWK-5222 are used to provide Wi-Fi within the trains. The AWK-3121, which is a single RF device, is installed in the first and last carriages as a client to access the IP cameras. The AWK-5222, which has a dual RF design and is installed in the middle four carriages, can be configured for AP-client connection mode. In this mode, RF1 can be used to provide the inter-carriage link or an AP, whereas RF2 can be used as a client to access the IP cameras. One path operates at IEEE 802.11b 2.4 GHz, and the other path uses IEEE802.11a 5 GHz, to better avoid RF interference. This kind of dual-frequency device is a great way to get around the interference inherent in a train station's complex RF environment.

In order to maintain a connection between the train and ground as the train approaches a station, the fourth carriage has an additional AWK-3121 used as a client that is linked via an Ethernet port on the AWK-5222. The AWK-6222 with outdoor dual RF design is installed to act as an AP outside the station. This access point is rugged enough for outdoor use and satisfies compliances for both a railway rolling stock apparatus and shock and vibration (EN50155/50121). Together with Moxa's unique 100 ms Turbo Roaming feature, this architecture ensures seamless train-to-ground data communications under mobile outdoor conditions.

Moxa Solutions

   Recommended Products
  • IEEE 802.11a/b/g access point and access client in one device suitable for inter-carriage and train-to-ground links
  • Operates at 2.4 GHz and 5 GHz
  • High availability and WLAN redundancy with two RF modules
  • 100 ms roaming for seamless wireless connection
  • Multiple SSID support for separate user groups
  • Robust metal housing with anti-vibration M12 connector
  • Compact for space-saving rail mounting
  • EN50155/50121-4 certified
    		•   
    AWK-6222 AP outside the station
     
    IEEE 802.11a/b/g Outdoor Dual RF AP/Bridge/Client
  • Fully redundant: Dual RF, Ethernet redundancy and redundant power inputs
  • 100 ms roaming for seamless handover
  • IP68 rated for outdoor use
  • -40 to 75°C operating temperature
  • EN50155/50121-4 and e/E mark certified
    		•
     
    AWK-5222 Client for in-carriage data access
     
    IEEE 802.11a/b/g Indoor Dual RF AP/Bridge/Client
     
    AWK-3121 Client for in-carriage video data access
     
    IEEE 802.11a/b/g Indoor Single RF AP/Bridge/Client
     
     
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