Multi-band vs. Multi-mode
Cell Phones
Dual Band vs. Dual Mode
If
you
travel
a lot, you will probably want to look for
phones that offer multiple bands, multiple
modes or both. Let's take a look at each of
these options:
·
Multiple band
- A phone that has multiple-band capability
can
switch frequencies.
For example, a dual-band TDMA phone could
use TDMA services in either an 800-MHz or a
1900-MHz system. A quad-band
GSM phone
could use GSM service in the 850-MHz,
900-MHz, 1800-MHz or 1900-MHz band.
·
Multiple mode
- In cell phones, "mode" refers to the
type of transmission technology
used. So, a phone that supported AMPS and
TDMA could switch back and forth as needed.
It's important that one of the modes is AMPS
-- this gives you analog service if you are
in an area that doesn't have digital
support.
·
Multiple band/Multiple mode
- The best of both worlds allows you to
switch between frequency bands and
transmission modes as needed.
Changing bands or modes is done
automatically by phones that support these
options. Usually the phone will have a
default option
set, such as 1900-MHz TDMA, and will try to
connect at that frequency with that
technology first. If it supports dual bands,
it will switch to 800 MHz if it cannot
connect at 1900 MHz. And if the phone
supports more than one mode, it will try the
digital mode(s) first, then switch to
analog.
You can find both
dual-mode
and
tri-mode
phones. The term "tri-mode" can be
deceptive. It may mean that the phone
supports two digital technologies, such as
CDMA and TDMA, as well as analog. In that
case, it is a true tri-mode phone. But it
can also mean that it supports one digital
technology in two bands and also offers
analog support. A popular version of the
tri-mode type of phone for people who do a
lot of international traveling has GSM
service in the 900-MHz band for
Europe
and
Asia
and the 1900-MHz band for the United States,
in addition to the analog service.
Technically, this is a dual-mode phone, and
one of those modes (GSM) supports two bands.
In the next section, we'll take a look at 3G
mobile-phone technology.
Cellular vs. PCS
Personal Communications Services
(PCS) is a wireless phone
service very similar to cellular
phone service, but with an
emphasis on
personal
service and extended mobility.
The term "PCS" is often used in
place of "digital cellular," but
true PCS means that other
services like paging, caller ID
and e-mail are bundled into the
service.
While cellular was originally
created for use in cars, PCS was
designed from the ground up for
greater user mobility. PCS has
smaller cells
and therefore requires a
larger number of antennas
to cover a geographic area. PCS
phones use
frequencies between
1.85 and 1.99 GHz (1850 MHz to
1990 MHz).
Technically, cellular systems in
the United States operate in the
824-MHz to 894-MHz frequency
bands; PCS operates in the
1850-MHz to 1990-MHz
bands. And while it is based on
TDMA,
PCS has
200-kHz channel spacing
and
eight time slots
instead of the typical 30-kHz
channel spacing and three time
slots found in digital cellular. |
To read about any of the technologies click on the blue links
2G cell-phone networks
for transmitting information (we'll discuss
3G technologies in the 3G section):
·
Frequency division multiple access
(FDMA)
·
Time division multiple access
(TDMA)
·
Code division multiple access
(CDMA)
|