What is the main difference between GSM & CDMA?
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Answer Posted / kapil
In cellular service there are two main competing network
technologies: Global System for Mobile Communications (GSM)
and Code Division Multiple Access (CDMA). Cellular carriers
including Sprint PCS, Cingular Wireless, Verizon and
T-Mobile use one or the other. Understanding the difference
between GSM and CDMA will allow you to choose a carrier that
uses the preferable network technology for your needs.
The GSM Association is an international organization founded
in 1987, dedicated to providing, developing, and overseeing
the worldwide wireless standard of GSM. CDMA, a proprietary
standard designed by Qualcomm in the United States, has been
the dominant network standard for North America and parts of
Asia. However, GSM networks continue to make inroads in the
United States, as CDMA networks make progress in other parts
of the world. There are camps on both sides that firmly
believe either GSM or CDMA architecture is superior to the
other. That said, to the non-invested consumer who simply
wants bottom line information to make a choice, the
following considerations may be helpful.
Coverage: The most important factor is getting service in
the areas you will be using your phone. Upon viewing
competitors' coverage maps you may discover that only GSM or
CDMA carriers offer cellular service in your area. If so,
there is no decision to be made, but most people will find
that they do have a choice.
Data Transfer Speed: With the advent of cellular phones
doing double and triple duty as streaming video devices,
podcast receivers and email devices, speed is important to
those who use the phone for more than making calls. CDMA has
been traditionally faster than GSM, though both technologies
continue to rapidly leapfrog along this path. Both boast
"3G" standards, or 3rd generation technologies.
EVDO, also known as CDMA2000, is CDMA's answer to the need
for speed with a downstream rate of about 2 megabits per
second, though some reports suggest real world speeds are
closer to 300-700 kilobits per second (kbps). This is
comparable to basic DSL. As of fall 2005, EVDO is in the
process of being deployed. It is not available everywhere
and requires a phone that is CDMA2000 ready.
GSM's answer is EDGE (Enhanced Data Rates for GSM
Evolution), which boasts data rates of up to 384 kbps with
real world speeds reported closer to 70-140 kbps. With added
technologies still in the works that include UMTS (Universal
Mobile Telephone Standard) and HSDPA (High Speed Downlink
Packet Access), speeds reportedly increase to about 275—380
kbps. This technology is also known as W-CDMA, but is
incompatible with CDMA networks. An EDGE-ready phone is
required.
In the case of EVDO, theoretical high traffic can degrade
speed and performance, while the EDGE network is more
susceptible to interference. Both require being within close
range of a cell to get the best speeds, while performance
decreases with distance.
Subscriber Identity Module (SIM) cards: In the United States
only GSM phones use SIM cards. The removable SIM card allows
phones to be instantly activated, interchanged, swapped out
and upgraded, all without carrier intervention. The SIM
itself is tied to the network, rather than the actual phone.
Phones that are card-enabled can be used with any GSM carrier.
The CDMA equivalent, a R-UIM card, is only available in
parts of Asia but remains on the horizon for the U.S.
market. CDMA carriers in the U.S. require proprietary
handsets that are linked to one carrier only and are not
card-enabled. To upgrade a CDMA phone, the carrier must
deactivate the old phone then activate the new one. The old
phone becomes useless.
Roaming: For the most part, both networks have fairly
concentrated coverage in major cities and along major
highways. GSM carriers, however, have roaming contracts with
other GSM carriers, allowing wider coverage of more rural
areas, generally speaking, often without roaming charges to
the customer. CDMA networks may not cover rural areas as
well as GSM carriers, and though they may contract with GSM
cells for roaming in more rural areas, the charge to the
customer will generally be significantly higher.
International Roaming: If you need to make calls to other
countries, a GSM carrier can offer international roaming, as
GSM networks dominate the world market. If you travel to
other countries you can even use your GSM cell phone abroad,
providing it is a quad-band phone (850/900/1800/1900 MHz).
By purchasing a SIM card with minutes and a local number in
the country you are visiting, you can make calls against the
card to save yourself international roaming charges from
your carrier back home. CDMA phones that are not
card-enabled do not have this capability, however there are
several countries that use CDMA networks. Check with your
CDMA provider for your specific requirements.
According CDG.org, CDMA networks support over 270 million
subscribers worldwide, while GSM.org tallies up their score
at over 1 billion. As CDMA phones become R-UIM enabled and
roaming contracts between networks improve, integration of
the standards might eventually make differences all but
transparent to the consumer.
The chief GSM carriers in the United States are Cingular
Wireless, recently merged with AT&T Wireless, and T-Mobile
USA. Major CDMA carriers are Sprint PCS, Verizon and Virgin
Mobile. There are also several smaller cellular companies on
both networks.
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