Sending Security Video Through Thin Air
a&s International | Date:
The wireless technology market for security is growing at a double-digit rate, as systems become easier to user and more cost-effective. Beyond city surveillance, there are other surveillance applications where wireless networks show a lot of promise, including transportation/transit, utilities and remote industries.
Wireless technology is becoming more capable of handling burdensome video data that is needed for backhauling video surveillance. “A low-end HD camera today requires 3-Mbps TCP/IP throughput,” said Xu Zou, Senior Director for Outdoor Strategy and Technologies, Aruba Networks. “Some high-end HD cameras demand 50 Mbps and above useful throughput.” Most companies seem to adopt MIMO radios that allow for redundancy in the network. However, there is some debate and tension among different technologies.
For video installations of more than one camera, one of two topologies is often used: mesh or point-to-multipoint (P2MP).
Mesh is appealing because of its flexibility and its ability to get around barriers and line-of sight (LOS) issues. Mesh is able to create dedicated streams for each HD camera. “A best practice is to have a multiradio, multifrequency architecture so dedicated radios are used for each HD video stream, rather than one radio carrying multiple streams,” Zou said. Mesh can also create redundant paths if one path is not working. “Networks should always be designed with redundancy in mind.”
According to Zou, there are four issues that may cause degradation during wireless transmission, especially if multiple hops are involved: packet loss, packet reordering, delay and jitter. Given the multiple hops that may be necessary to backhaul video, some problems such as variable data rates and bandwidth spikes could arise for the video data. “H.264 is especially sensitive to packet loss and jitter with its high compression ratio, as each frame carries more video quality information,” Zou said. “If any frame is lost, reordered, delayed or experiences varied latency (jitter), the overall video quality is likely to degrade.”
Geoffrey Smith, VP of Business Development and Strategic Accounts, Proxim Wireless, argues that instead of mesh, it is better to use P2MP topologies so that data travels along a deterministic path, and radios work in a coordinated manner. “One master radio controls the access of all the other radios connected to it. A scheduled or poling mechanism controls all the communications among all the radios. It's like a traffic cop. The traffic cop controls traffic flow over a given wireless network, whereas wireless mesh works like stop signs. In rush hour, it will take you longer to get through stop signs than traffic lights.”
While P2MP might be more reliable, others argue that it might be less able to handle the high bandwidth generated by megapixel cameras. “Traditional P2MP wireless backhaul technology works well with traditional low-resolution cameras,” Zou said, “but a single radio-based P2MP architecture is unlikely to provide sufficient bandwidth for multiple HD cameras because of each camera's high-throughput requirements.”
Ensuring that radios connected to megapixel cameras are able to handle the data rates will go a long way in ensuring a P2MP deployment will work. “You need to understand the capacity required by each radio when planning a wireless network. For HD or megapixel, sometimes cameras require 10s of Mbps of throughput, and some 360-degree cameras require 20 Mbps of capacity. So you need to ensure your infrastructure can handle more than 100 Mbps of capacity to support multiple cameras in the same network,” Smith said. “P2MP MIMO radios can easily handle this capacity, supporting many megapixel cameras in a single network of distances exceeding several miles.”
Given that most of today's wireless offerings are proprietary products, the results of wireless deployments can vary from vendor to vendor. “Designing a camera wireless backhaul network could include disparate solutions such as mesh, point-to-point (P2P) and P2MP. For example, in challenging LOS locations, a mesh topology could be used to bring the video from the cameras to an aggregation point. The video can then be backhauled using P2P/ P2MP/fiber back to the storage or viewing location,” said Mrinalini Lakshminarayanan, Video Solutions Strategist, Motorola Solutions. “Most of the time, a combination of different solutions are used, including leveraging as much wired as possible. This is done based on specific location, interference, LOS and accessibility issues.”
Product Adopted:Network Cameras