What is the main difference between GSM & CDMA?
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Answer Posted / john
GSM (Global System for Mobile Communications)..............
GSM is the “branded” term referring to a particular use of
TDMA (Time-Division Multiple Access) technology. GSM is the
dominant technology used around the globe and is available
in more than 100 countries. It is the standard for
communication for most of Asia and Europe. GSM operates on
four separate frequencies: You’ll find the 900MHz and
1,800MHz bands in Europe and Asia and the 850MHz and
1,900MHz (sometimes referred to as 1.9GHz) bands in North
America and Latin America. GSM allows for eight
simultaneous calls on the same radio frequency and
uses “narrowband” TDMA, the technology that enables digital
transmissions between a mobile phone and a base station.
With TDMA the frequency band is divided into multiple
channels which are then stacked together into a single
stream, hence the term narrowband. This technology allows
several callers to share the same channel at the same time.
2. CDMA (Code Division Multiple
Access).............................. CDMA takes an
entirely different approach from GSM/TDMA. CDMA spreads
data out over the channel after the channel is digitized.
Multiple calls can then be overlaid on top of one another
across the entire channel, with each assigned its
own “sequence code” to keep the signal distinct. CDMA
offers more efficient use of an analog transmission because
it allows greater frequency reuse, as well as increasing
battery life, improving the rate of dropped calls, and
offering far greater security than GSM/TDMA. For this
reason CDMA has strong support from experts who favor
widespread development of CDMA networks across the globe.
Currently, you will find CDMA mostly in the United States,
Canada, and North and South Korea. (As an interesting
aside, CDMA was actually invented for the military during
World War II for field communications.)
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