The other side of the story
For America’s police departments, wireless video surveillance quickly is becoming a weapon of choice for many reasons. Foremost among them is that wireless digital video cameras are easy to deploy: Just plug them into power and they start broadcasting almost instantly.
“Our crews can set up and connect wireless video cameras in a matter of minutes,” said Fred Capper, deputy chief of the Lakewood (N.J.) Police Department. The department has installed a PacketHop-enabled surveillance system “that allows us to send live surveillance video back to our command post in real-time,” Capper said.
Also, today’s wireless video cameras are connected to IP encoders/transmitters. They send out signals that, once received, travel easily over wired and wireless TCP/IP networks to dispatch centers and police command headquarters. The IP-encoded video that these systems transmit also can be received by patrol cars. For officers on their way to a site that’s under video surveillance, the footage provides accurate, up-to-the-second intelligence on who’s there and the level of resistance that they might offer.
“We use the Sting [Surveillance Systems] DVR and camera system for our undercover recording and LEA [Law Enforcement Associates] micro-cameras and transmitters for remote recording,” said Scott Sullivan, a detective with the Addison (Ill.) Police Department. “These units are so portable that they can be discreetly located almost anywhere, or even be worn on an undercover officer.”
Wireless surveillance systems typically consist of small digital video cameras, IP encoders/transmitters, and RF receivers that port the data into TCP/IP networks for distribution to designated police monitors.
The actual setup varies from vendor to vendor. For instance, the Axis Communications surveillance system used by the Dallas Police Department’s narcotics division is built upon weatherproof, hardened plastic cases, each of which contains an Axis video camera and a Junxion Box IP encoder/3G cellular broadband transmitter.
“These cases are easily mounted on lampposts or walls by police officers disguised as utility workers,” said Fredrik Nilsson, general manager for Axis North America. “All they have to do is ensure that the equipment is linked to a local power source (usually available at such locations), that the camera is pointing at the target, and that the unit itself is being picked up via a local 3G cellular network.”
In Lakewood, the PacketHop system is deployed to create a mesh network. Each camera transmitter can link to any other transmitter, creating a redundant, multi-path network for signals to get to their destinations.
“A typical Wi-Fi network provides 30 to 54 megabits per second of bandwidth; full-motion video of 30 frames per second at 320 by 240 pixels resolution and true color requires 1.8 megabits of bandwidth,” said John Leddy, PacketHop’s vice president of marketing. “Although PacketHop can work on a range of bands, we prefer to use the 4.9 GHz band that has been reserved for first responders, and can successfully send and receive signals up to a range of 3000 feet. For non-public-safety applications, 5 GHz is the preferred frequency.”
For vendors and installers, wireless video surveillance is a promising new market. However, it comes with some limits, both RF- and IP-related. On the RF side, there’s always the issue of which spectrum to use. Wi-Fi offers extreme data throughput, but it has a severely limited range of 300 feet or less. Interference can be a serious problem, as well, especially in the crowded 2.4 GHz band.
Using commercial cellular networks can eliminate range problems, as coverage is virtually ubiquitous in America, but the data rates are far lower. For instance, cutting-edge 3G EDGE networks operate at 384 kb/s. That speed is enough for full-motion video, but at a lower picture size and resolution than other transmission technologies.
“My advice is to deploy broadband transmitters in 4.9 GHz,” Capper said. “4.9 GHz provides good coverage, high data throughput and relative freedom from interference.”
For those who choose to use 4.9 GHz or the other microwave bands, Mike Butler suggests they do their homework first. As project manager for BearCom, which helped the Dallas police set up their wireless surveillance system, Butler learned that “microwave doesn’t follow the same laws as VHF, UHF or 800 MHz transmission. In particular, microwave is line-of-sight unless you know the right tricks. As well, microwave requires minimum signal levels to connect successfully.”
Even with these challenges, IP is where things “really get complicated,” Butler said. The main challenge is data capacity.
“You really have to figure out just how much data the cameras will be sending first, so that the network can be built to accommodate it,” he said. “If you don’t provide enough capacity — if you undersupply — the video signals can get choked. This means that you can lose some or even all of the video feeds, which is the last thing police want during a surveillance operation.”
Mesh networks provide more signal paths and overall redundancy compared with conventional hub-and-spoke networks, where one central receiving station handles all incoming feeds. However, even in mesh networks, “you have to plan your capacity very accurately,” Butler said. “If you load too many cameras on a mesh network, you can ‘bust’ it. Again, the result can be lost video feeds.”
Butler added one last piece of advice: “When it comes to wireless surveillance networks, one size does not fit all,” he said. “Instead, I use the analogy of a golf bag to explain how you need to pick the right RF/IP strategy to suit every individual circumstance. You use a wood for teeing off, and a 7-iron to get onto the approach.
“In the same vein, if you opt for the unlicensed 5.8 GHz band for wireless video surveillance, you get lots of range but risk interference from other users. If you are close enough, you can use 60 GHz. It provides great data throughput but has distance limits that you have to think about.”
That’s not all. At the receiving end, IP signals need to be sent into a router management switch that can output streamed video, so that multiple users can tap into it at the same time, according to Butler.
If there’s a moral to this complex tale, it is that “you have to know a lot about RF and a lot about IP to do these deployments successfully,” he said.
