In the summer of 2006, Phoenix police were looking for two serial criminals who were terrorizing the city. One criminal was suspected of up to 38 drive-by shootings, and the other was suspected of a series of sexual assaults and murders. As part of the investigation into the crime spree, Phoenix Police received emergency funding for a video surveillance system to cover a five-square-mile area.
Police turned to the Avrio Group, Salisbury , Md. The Avrio Group responded by deploying a system of 30 remote cameras with video transmission over a wireless mesh network. Using the city's fiber network, the video is backhauled to a central command center. The command center uses video management software from OnSSI , Suffern , N.Y. , to display the cameras on multiple, large plasma displays.
Detective Chris Jenson with the Phoenix Police Department is thrilled with the performance and mobility of the system. According to Jenson the system was deployed in less than three weeks and individual cameras and mesh nodes can be relocated as needed for other investigations.
This mobility was accomplished by deploying Avrio's self-contained Rapid Deployment Pole Cam system. The Pole Cam includes a network camera; Firetide radio node and power supply in a NEMA rated enclosure.
Mark Jules, President of Business Development, Avrio , said Phoenix joined a rapidly growing list of municipalities, airports and seaports that have deployed wireless video.
The primary advantage of wireless outdoors is to avoid expensive and labor-intensive trenching, digging and cabling.
A wireless infrastructure can also extend the range of a data network. While Category 5 Ethernet is limited to lengths of 100 meters, traditional wireless mesh can extend to lengths greater than 500 meters between nodes.
Another advantage is mobility. Both cameras and the client workstations that receive the streamed video feeds have a degree of mobility.
Wireless Spectrum for Public Safety
Wireless networks are typically deployed using 802.11 (Wi-Fi) standards for radio transmission and reception. 802.11 works over the license-free 2.4GHz (802.11b/g) and 5.0GHz band (802.11a).
The unlicensed 2.4/5.0 GHz spectrum may not be well-suited for public safety applications like fire, police and emergency medical services. It can be congested by countless private and commercial Wi-Fi hotspots operating in the area.
To address these issues, the FCC reserved the 4.9GHz spectrum for public safety agencies to conduct surveillance and emergency data transfers. Law enforcement and public safety entities can license this spectrum.
What is a Mesh Network?
A wireless mesh network is a series of interconnected nodes or transponders that route data from point to point until the destination is reached. Data can be routed around broken or slow nodes to eliminate single points of failure. Mesh nodes connect to each other dynamically to provide a multi-hop network that can be extended over a large area.
Many wireless video applications are built on a wireless mesh infrastructure using 802.11 radio nodes operating at 4.9GHz. Although most mesh products use 802.11, the similarity stops there. The node routing protocols are proprietary such that one vendor's mesh mode will not interoperate with another. (The IEEE is working on a mesh standard 802.11s that is expected to be ratified sometime next year.)
Challenges with Video on Mesh Networks
Mesh networks are not without challenges, particularly when implementing video. As the mesh grows larger, bandwidth decreases and latency increases. As a general rule, bandwidth can be reduced by up to 50% at each hop or move to another node. The net effect of requiring more than a couple node hops is to decrease bandwidth to a level that supports only a few video frames per second and introduces latencies that make pan-tilt-zoom control a struggle.