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Calling All Cars

To see the cop radio of the future, all you have to do is look in a San Diego Police Department patrol car.

November 01, 2003  |  by Jo'el Roth

If the test of the new integrated system is successful, San Diego PD plans to slowly upgrade its entire fleet, car by car, over the next two years.

The new system will eventually allow officers out in the field to immediately view color images, such as mug shots and fingerprints. They will also be able to work on their laptop computers outside of their cars and then connect them back into the cars as needed.


Looking inside the interiors of the cars with the upgraded comm systems, you won't notice much of the new equipment. The new computers and display screens are the only parts of the San Diego PD's technology upgrade that can be actually seen. And in some ways, they are the least critical.

The backbone of the new San Diego PD wireless communications is the latest evolution of cellular transmission systems that carry the voice and data messages. The department is currently on a digital cellular system, and will eventually change to a newer version of a digital cellular system, or protocol.

Officer Backrog remembers the days before digital communications systems. "Twenty-five years ago, when I started, it was just a radio. When I received a call, I would write down the information on a notepad that we always kept in the car on the seat next to us."

The older two-way radios operated on the UHF, or Ultra High Frequency band, in the 450MHz range. A radio-sized console at the dashboard was connected to the main transmitter unit, which was roughly the size of a three-ring binder and was installed in the trunk. When an officer spoke into the microphone, the signal was sent from the car's transmitter, through the antenna, over the airwaves, to a repeater unit that was located on the roof of a tall office building, or at the top of a hill just outside of town. The repeaters would then receive and re-amplify, or repeat, the radio signal and send it to the system's base station at headquarters.

This system worked very well for the time, but it had its limits. For example, radio transmissions were often affected by the location of the sender, depending on the power of the car transmitter and the range of the repeater stations.

"We had handheld walkie-talkies, too," recalls Backrog. "But sometimes there weren't enough to go around. In that case, if we had to communicate after we left the vehicle, we would toss the microphone out the window, and talk loud."


In contrast, the San Diego PD is now connected via a digital cellular system that operates on Cellular Digital Data Packet (CDPD) protocol. (See "Cellular Protocols" on page 46 for explanation). The new system will gradually change from CDPD to GPRS, or GSM Packet Radio Service that features packet-switching technology for high-speed data transfer.

While the change in digital transmission will not be obvious to the SDPD's officers as they talk on the radio, the different technology offers several advantages. Shawn Wells of Peak Wireless points out that the GPRS System moves up to a different frequency band, and more data can be sent through the networks. And Glenn Antonelli, product manager for Sierra Wireless, explains that the conversion process will be relatively easy. "We have made the new MP modem half the size of the old one, but we have designed it to fit in the same foot space of the old unit. We use the same mounting bolts and the old connectors."

The proof is in the performance, and Powell's group must look at whether the technology can be easily used, and evaluate the physical ergonomics of each device. For example, does it take three clicks of a mouse to bring up the right screen, or can the officer just click once to get the information that's needed? Afterall, even the highest data transfer rate is irrelevant if the system is hard to use.

Jo'el Roth is a freelance technology writer who works in the San Diego area. She has been writing for Police for more than a decade.

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