Seamless WLAN Communications for Video Surveillance on Buses
As digital information has become an important part of daily life, wireless digital transmission technology has gradually been introduced for bus and other moving vehicle applications. Hangzhou, one of the most ancient cities in China with a population of around 8.7 million residents (1,214/km2 population density) is now also one of the most advanced. Hangzhou’s WLAN, covering an area of more than 16,000 square-kilometers, has made it possible to transmit digital data in and out of moving buses. One of the many wireless applications in Hangzhou is its bus video surveillance system. China’s transportation authority sought to enhance the security of its public transportation, and the plan was to install video surveillance systems on the buses to record images for security measures. As each bus passes a wireless AP (strategically positioned at traffic lights and other locations), the recorded video is uploaded in real-time. However, installing a real-time video surveillance system aboard a large fleet of buses that can be remotely monitored by the traffic control center presented certain challenges.
• Fast roaming to provide wireless real-time information updates.
• Wireless devices must accept unstable 12 VDC onboard power supply, which can fluctuate considerably.
• Wireless devices must be able to fit into the existing wireless network setup by the pre-established wayside APs.
Since an existing network of wireless access points was already strategically installed on traffic lights and overhead signs throughout the city, the bus company wanted to contain costs by not installing additional access points. The highly versatile AWK-3121 802.11a/b/g wireless client devices provided the perfect solution by integrating seamlessly with the existing access points.
First, security cameras and video servers were installed inside each of the buses. Then, in order to transmit real-time video to the traffic control center, Moxa configured the AWK-3121 as wireless clients on each of the buses. With Moxa’s Turbo Roaming, the AWK-3121’s roaming time between the access points can be as fast as 100 ms even when deployed aboard the fast-moving vehicles.
Due to the fact that bus batteries can only provide 12 VDC of power, which fluctuates considerably, the AWK-3121 was also selected due to its ability to support a wide range of power inputs from 12 to 48 VDC, as well as tolerate voltage fluctuations as low as 10 VDC. The AWK-3121 is also EN 50155 certified to withstand the intense vibrations found in railway applications that are comparable to, or even more severe than, those encountered by buses. What’s more, the AWK-3121’s IP30-rated housing provides protection from dust and particles. Finally, Moxa also provided the bus company with a central management suite to easily monitor,manage, and configure all network devices from the traffic control center.
• Moxa’s Turbo Roaming enables non-stop streaming of video surveillance data, and allows police and OCC personnel to monitor the conditions on board the buses in real time.
• Moxa’s wireless products support a wide range of 12 to 48 VDC power inputs and can tolerate intense voltage fluctuations, even as low as 10 VDC, so they are compatible with the buses’ onboard power supplies and do not require additional power converters.
• The AWK-3121 includes a tailor-made adjustable transmission power service. It boosts the power of the AWK-3121 so that it can operate with the limitations of the existing network, resolves issues related to transmission strength, and also extends wireless coverage.
See More Real World Applications
Moxa’s comprehensive line of WLAN and cellular solutions have been successfully implemented in various mission-critical industrial applications, including transportation, factory automation, smart grid, and heavy industry. For more information, please click on the icon to download the Industrial WLAN success stories.