ZyXEL Communications 2864 Series, User Manual, Page: 149 / 267

14–1
Chapter 14
CELLULAR MODE OPERATION
The ZyXEL 2864 series models are equipped with a special communication mode -
cellular mode - which enables the modem to perform reliable high speed data trans-
missions over cellular phone links. Although most ZyXEL modems can provide the
cellular mode, the U-1496P portable modem is specially designed for mobile use. It
is portable in size and capable of using DC12V car battery power. An optional
power cable that plugs into the cigarette lighter can be used with the modem. The
ZyXEL cellular modes are called the ZyCellular mode for the ZyXEL series mo-
dems.
This chapter explains the cellular mode usage and gives background information on
cellular data communications.
Cellular Phone Systems
We are refering here exclusively to the analog cellular phone system. It is called
AMPS (Advanced Mobile Phone Service) in North America. The cellular phone
system got its name by dividing its covered area into many small cells. Each cell has
a cell site radio station maintaining a radio link with every cellular phone that is in
use in the cell. If a cellular phone moves out of one cell's boundary and goes into
another cell, it will be instructed to switch its radio link to the new cell using a new
frequency channel. This is called cell hand-off.
By limiting the radio transmission power in each cell's radio communication, it will
not interfere with a distant cell's radio communication using the same frequency.
Frequency reuse is the principle of cellular phone systems used to increase the
number of radio channels available.
Cellular Impairments
A common problem in cellular communication is cell hand-off. In the process of
cell hand-off, the radio link, hence the modem carrier, will be interrupted for 0.2
second to 1.2 seconds. A normal modem will respond with retrain which takes
about 10 seconds, or may even hang up.