Wireless Video Surveillance and Monitoring System for Buses
Background
As digital information has become an important part of daily lives, buses and other moving vehicles have gradually introduced wireless digital transmission technology into their applications. HangZhou, one of the most ancient cities in China, is now also one of the most advanced. The HangZhou's WLAN 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 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.
 
Application Requirements
 
Digital data transmission from moving vehicles to wireless APs is difficult for a variety of reasons:
 
The batteries of the vehicles are only able to provide a 12 VDC power source and the voltage can fluctuate considerably. At times, the voltage becomes so low that it is scarcely enough to keep the wireless device functional. It is essential that wireless devices support 12 VDC and at the same time be tolerable to low voltage.
The speed of buses can be very fast and since they do not slow down for the access points, wireless clients must support millisecond-level handoffs.
Since the wireless antennas are positioned outside of the buses, they need to be small enough as not to be damaged when the buses enter carwash tunnels. The 3 dBi antenna is a top choice, but due to the unique compact size of the 3 dBi antenna, its transmission strength can be limited when sending signals while in motion; however, boosting the power of the wireless client to 200 MW will solve this problem.
Vibrations on buses can be severe, so wireless clients must be shock resistant.
Wireless clients need to be fanless and be at least IP30 rated to prevent dust and small particles from damaging the devices.
To facilitate easy maintenance and management, it is essential that the wireless devices used in this project come with software to locate, monitor, and troubleshoot them.
 
System Diagram
 
 
Benefits
Moxa's AWK-3121 is the best choice for the project since the AWK-3121 meets or exceeds the requirements:
 
The AWK-3121 supports a wide range of 12 to 48 VDC power inputs and can tolerate intense voltage fluctuations, even as low as 10 VDC.
When used in pairs, the AWK-3121's can deliver millisecond-level roaming time.
The AWK-3121 is EN50155 certified, which means it is very stable and can withstand the intense vibrations inherent in railway applications.
The AWK-3121 is IP30 rated to prevent dust and particles from getting into the devices.
Moxa provides a management suite that gives users the freedom and flexibility to monitor, manage, and configure wireless devices with ease.
 
 
Recommended Products
AWK-3121 Series
Industrial-strength IEEE
802.11a/b/g wireless
AP/bridge/client
IEEE 802.11a/b/g compliant
Powerful security with WPA/WPA2 packet filters
Redundant 24 VDC power inputs or PoE
2 digital inputs and 1 relay output for monitoring and warnings
RS-232 console/web-based management
STP/RSTP support to prevent network looping and to increase reliability
-40 to 75°C operating temperature range (for -T models)
DIN-Rail or wall mountable
 
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