Telebit Dials Up Mobile Future with New Cellular Modem
 
Microbytes Daily News Service
Copyright (c) 1989, McGraw-Hill, Inc.
With its eye on the "mobile office of the future," Telebit Corp.
announced Firday a high-speed modem specifically designed to send
and receive data using the cellular telephone network. The
CellBlazer modem, which attaches by a jack to a standard cellular
phone, is rated at transmission speeds of up to 16,800 bits per
second and accommodates the special problems of cellular
transmission, Telebit said.
 
Don R. Gibson, vice president of marketing for Telebit, described
the CellBlazer as one component in an emerging "mobile office" of
the future. The fast growth of both cellular phones and laptop/
portable computers has led naturally to cellular modems, which
will in turn foster new applications for remote data
communication, he said. For example, with a cellular modem, field
insurance inspectors won't even need to find a phone booth to
file claim reports and receive settlement authorizations.
 
The CellBlazer modem, available now in both internal and external
configurations, achieves very high transmission rates by using
the same patented technology in Telebit's TrailBlazer modems, the
company said. The internal CellBlazer ($1295) is a full-size
8-bit (XT bus) card that Telebit says will fit in some laptops
from each of the leading manufacturers. The external model is
$1495.
 
Cellular data transmission presents several difficulties not
found with land-based phone lines, Telebit said. The bandwidth
allotted to data is smaller, ranging from 300 Hz to 3 KHz (versus
3 Hz to 3.4 KHz for land lines), and signal quality is subject to
distortion, interference, and fadeouts, which increases the need
for good error-correction functions. Additionally, cellular
transmissions experience "handoffs" when responsibility for the
call is switched from one cellular station to another; these cell
site handoffs can cut transmission for up to 1.2 seconds, which
would be disastrous for data communication without proper
protection.
 
The CellBlazer's multicarrier modulation and PEP error correction
are well-suited to handle these problems, Telebit claims. Because
the packets are split across many carriers, the data rate on any
given frequency is quite low, which helps overcome delay distor-
tion, signal fading, and impulse noise.
 
The modem runs tests on the line and determines which frequencies
are the most and least distorted, according to Telebit. The
transmission scheme is then adjusted to send more packets on the
clearer frequencies and fewer or none on the bad ones. Telebit
claims that these provisions permit the CellBlazer to establish,
maintain, and optimize connections on lines that ordinary modems
could not. Many V.32 modems, for example, drop from 9600 to 4800
bps when they encounter poor line quality; Telebit's PEP drops
speed in 100-bps increments to sustain the highest possible rate
for a given connection.
 
Under good conditions, the CellBlazer can communicate over
cellular lines at up to 10,000 bps, Telebit said. The modem can
also be used for regular land-line transmission at up to 19,200.
At a demonstration in New York, however, the CellBlazer was able
to send at only 6500 bps, which Telebit executives attributed to
poor cellular quality in the Big Apple.
 
Contact: Telebit, 1345 Shorebird Way, Mountain View, CA
94043-1329; (415) 969-3800 or (800) 835-3248.
 
                              --- Andy Reinhardt
 
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