Broadband solution leverages unused broadcast spectrum
With the continued emphasis on homeland security, law-enforcement agencies nationwide are eager to take advantage of wireless data applications that would allow them to transmit photos of criminal suspects, building floor plans and blueprints, and surveillance video. The challenge to transmitting such rich media, of course, is that these are huge files that would choke most public-safety networks today.
Mesh networks and Flash OFDM-based systems have shown promise for opening the bottleneck, but both are still in a nascent stage. And there’s the matter of cost. Even in an era when federal grant money is available for system upgrades, many–if not most–municipalities today would find it difficult to find the resources to deploy a robust high-speed data network. Consequently, these are likely longer-term solutions.
Harris Corp.’s Broadcast Communications Division thinks it has hit upon a solution that is feasible in the near term. John Delay, director of strategic management, told me recently that the division would roll out at IWCE 2005 in Las Vegas a platform that uses vacant commercial broadcast spectrum. According to Delay, broadcasters have plenty of room in their pipes to transmit first-responder data traffic, and there is nothing in the FCC’s rules to prevent them from doing so.
“A local broadcast station could easily give up a couple of megabytes of its pipe,” Delay said. “Stations are given enough RF spectrum to broadcast a real-time stream of 19.8 megabytes per second of data. There is only one FCC regulation, and that is to broadcast one standard-definition video channel, which takes about four megabytes per second. It’s up to the station to decide how to use the rest of that spectrum.”
High-definition signals require about 14 megabytes, but Delay said compression technologies are evolving rapidly, so there should still be plenty of capacity in the pipe available to public safety as broadcasters transition to HDTV from analog. “Even 5 megabytes would be a daunting amount compared to what public safety has available today,” Delay said. “The typical public responder has about 19 kilobytes available to them.”
Here’s how the solution works, in a nutshell: A police officer would use the in-vehicle computer to tap into a database via Harris’s data broadcast architecture — something Delay described as a big software router platform — which establishes the necessary interfaces. Once the officer selects a file, Harris’s networking application maps the IP traffic into MPEG2 packets for transport, and then multiplexes the packets into the outbound broadcast stream.
“We do this in a secure way, so that the public viewer does not see that data,” Delay said.
After the officer’s in-vehicle computer receives the signal, the packets are extracted down to the IP stack, which enables them to be downloaded to the computer’s hard drive for viewing.
According to Delay, Harris’s solution compares favorably to peer-to-peer (i.e., mesh) networks in terms of packet loss, latency and jitter.
“Let’s say you wanted to send 100 megabyte video files to 50 police cars over a standard IP network, which is what a mesh network is,” he said. “You’re going to choke it to death. … Moving voice around in those networks is no big deal. Moving data around also is okay. But start moving video around in those networks. Move large files across large distances, and things get complicated really fast. That’s primarily why there aren’t a lot of people moving video over IP.”
An added benefit of the Harris system, according to Delay, is that there is very little infrastructure cost for public safety, because the traffic rides over the already-built broadcast pipe. The only cost, for vehicles that already have a computer on board, would be the insertion of a PCMCIA card equipped with an ATSB receiver antenna into the computer. (Delay estimated that cost at $100-$150 per vehicle.) Some vehicles might also need to mount an external antenna. Though public-safety agencies would have to pay a fee to broadcasters for transmitting the signal, Harris is banking on broadcasters keeping the fees manageable to curry favor with elected officials. Delay said federal grant money also could defray at least some of those fees.
It’s an interesting thought. But given how slowly federal homeland security funding flows to the local level and the convoluted nature of the application process, it also could be a pipe dream.
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