When we hear about real-time surveillance, it's often associated with fixed cameras around a facility, monitored in a basement room by on-duty security officers. But what about getting real-time video off of moving vehicles that are moving at upwards of 50 miles per hour?
That's the challenge that the Mumbai, India, metro transit system faced as it has been developing a modern addition to its existing train/subway transit lines. The transit administrators wanted to have real-time video from inside the train cars themselves routed back to a command center for live security monitoring.
That need for real-time video in a mobile environment presented the obvious limitation that such a system couldn't be hard-wired. The Mumbai metro decision makers worked with global systems integrator Thales Portugal to develop a wireless video system network that could stream the live video from the trains over a 40-mile segment of track. The project started with over a year of research and planning work that involved a comprehensive site assessment and a wireless site assessment (the process requires examining the area for problems with wireless interference and conducting signal propagation range studies). In the end, after examining a number of vendors and putting some of the vendors through two rounds of live tests, Thales settled on equipment from Silicon Valley wireless technology firm Firetide, whose systems have been popular for connecting remote video surveillance cameras and providing campus-wide mesh communications infrastructure.
The technology testing process took roughly six months to ensure that Mumbai was purchasing appropriate technology. Thales Portugal's CEO Joao Araujo said that part of the reason for the lengthy, involved testing is that the project required "high speed bandwidth and reliable performance" in what he termed a "harsh network environment."
The Mumbai metro system will span 40 miles of track, and in Phase 1, Firetide's Ksenia Coffman said that Thales is beginning to install Firetide wireless radio communicators every 500 meters along the track. Those communicators pick up video signals from inside the trains themselves, which have Firetide's radios (a.k.a. nodes) installed the vehicles. According to Coffman, Mumbai will be using dual-radio devices; one radio in each unit is designed to transfer the video data from the cameras on the trains, while the other radio inside each transceiver is handling the communications processes that allows video to be handed off to the track nodes as a train moves down the track. The fixed nodes along the track are connected via a fiber-optic backbone that allows the video to be routed back to the command center. Besides the downlink of video, the system will also support an uplink design which will allow text-based messages to be sent in real-time to monitors mounted inside the train's cars.
"The key to this project," explains Coffman, "is the self-healing nature at high speeds." She added that Firetide has a special routing protocol and node management system that helps enable this type of design. As the train moves in range of one radio, it switches the video data transfer to that node from the previous node on its track; it is constantly patching into the different nodes based on which has the best signal strength. The design is said to allow for zero packet loss while handing off the video data, and it supports a number of data encryption options, including AES, WEP, WPA2 and IP layer data encapsulation. The nodes offer 10 mbps connection speeds.
Coffman says this type of real-time mobile video surveillance project has been done just once before – in Seoul, South Korea, for that city's subway system. A similar network design was deployed to allow for the video hand-offs as the trains glided down the rail paths. "It's a trend we're seeing in transit applications where they want real-time visibility in trains and in the stations," Coffman added. "They want video off moving transit vehicles in real-time."