This article was originally published in the November 2001 issue of LINK magazine.
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Look between the front seats of almost any police car, and you'll see a computer terminal. A wireless one. Across North America, police officers have been moving wireless data for years—running license numbers, checking records, communicating with HQ.
They don't use any top-secret semi-military method to do it either. The terminals transfer data over the Internet, using cellular digital packet data (CDPD), a "wide-area wireless" network protocol. Other CDPD users include public utilities, couriers, and even banks (for ATMs without phone lines). However, CDPD's bandwidth is low: 9.6 kilobits per second (kbps), slower than an old 14.4 modem. Fine for police telemetry or e-mail, but not much else.
CDPD uses the same radio towers and channels as the analog cellular telephone network. But instead of working like a modem, which turns data into screechy sounds to be sent over the phone circuit, it piggybacks digital data packets between cellular voice calls—something like the way cable modems and ADSL share TV and telephone wires. Wireless phone companies started supporting CDPD in 1993, so it's widespread, and now you can buy PC Card modems to plug into your laptop or handheld. They let you connect to the Internet from almost anywhere you can use an analog cellular phone. But there is that pesky speed issue.
In the late 1990s, government regulators allowed cellular digital services, each one able to squeeze more calls into the same range of frequencies than their analog predecessors. That transition from first to second generation (1G to 2G) cellular made wireless service cheaper, and within a few years, even schoolchildren had mobile handsets. In the U.S.A. and Canada, the two major digital phone technologies are, somewhat obscurely, known as time division multiple access (TDMA) and code division multiple access (CDMA).
North America has a number of different TDMA standards, but elsewhere in the world, especially in Europe, the global system for mobile communications (GSM) version dominates. CDMA technology is owned by a single company, Qualcomm, which licenses it to carriers and phone manufacturers.
Data services didn't quite keep up with these radical changes in cellular technology, largely because the major customers for CDPD didn't find its slow speed a big problem, and because the infrastructure for adding data support to the new digital services was another expense carriers preferred to avoid.
So, until recently, computer users who wanted go-anywhere wireless Internet access over the digital cellular networks resorted to plugging modems into their mobile phones—at speeds not much better than CDPD's 9.6 kbps. Even more recently, a few carriers have made PC Card modems available that do the same thing without needing the phone.
Now, however, carriers have begun adding fully digital, Internet-based packet services to their digital voice networks, calling them 2.5G or 3G (two-and-a-half or third generation) services. Unfortunately, they have even more impenetrable names than before.
For TDMA and GSM networks, the emerging standard is known as general packet radio service (GPRS). Like CDPD, it offers an "always on" wireless Internet connection. Unlike CDPD, it supports speeds theoretically up to 171.2 kbps (closer to 44 kbps in reality) roughly comparable to fixed-wire ISDN, cable modems, and DSL. The equivalent for CDMA users is CDMA2000 (also known as 1xRTT) service, with a maximum data rate up to 144 kbps (again, in theory). GPRS is available in Europe, and begins to come on-stream in the U.S. and Canada around the beginning of 2002, as the wireless carriers upgrade radio towers and cellular infrastructure appropriately. 1xRTT is currently in testing, and will also become publicly available in 2002.
Future technologies have equally exotic names: EDGE (enhanced data rates for GSM evolution), up to 384 kbps, and UMTS (universal mobile telephone system), up to 2 Mbps. However, they and other 3G and 4G services are a few years off in North America.
The Ricochet network, run by Metricom, sometimes even exceeded its theoretical 128 kbps maximum. But the expense of setting up the totally separate Ricochet infrastructure in a number of U.S. cities drove Metricom into bankruptcy in late 2001, and the Ricochet network was shut down.
More grassroots are home and business users of the IEEE 802.11b wireless LAN standard (used by the D-Link Air line of products) who band together to create underground wireless networks totally separate from the cellular system, with current maximum speeds of 11 Mbps. These local wide-area networks may mount a serious challenge to cellular data providers, especially with faster networking coming soon.
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Page BBEdited on 19-Mar-04 (originally published November 2001)
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