What is GSM:
Brief History Of CDMA:
CDMA
is based around a form of transmission known as Direct Sequence Spread
Spectrum. The CDMA history can be directly linked back to the 1940s when
this form of transmission was first envisaged. As electronics
technology improved, it started to be used for covert military
transmissions in view of the facts that the transmissions look like
noise, it is difficult to decipher without the knowledge of the right
codes, and furthermore it is difficult to jam.
With the revolution in cellular telecommunications that occurred in the 1980s a then little know company named Qualcomm working on DSSS transmissions started to look at this as the basis for a cellular telecommunications multiple access scheme - CDMA - code division multiple access.
The concept of CDMA had to proved in the field and accordingly Qualcomm was joined by US network operators Nynex and Ameritech to develop the first experimental CDMA system. Later the team was expanded as Motorola and AT&T (now Lucent) joined to bring their resources to speed development.
As a result this it was possible to start writing a specification for CDMA in 1990. With the support of the Cellular Telecommunications Industry Association (CTIA) and the Telecommunications Industry Association (TIA) a standards group was set up. This group then published the standard for the first CDMA system in the form of IS-95, resulting in the formal publication of IS-95-A in 1995.CDMA technology advantages
The use of CDMA offers several advantages and it is for this reason that CDMA technology has been adopted for many 3G cellular telecommunications systems.
Improvement in capacity: One of the chief claims for CDMA is that it gives significant improvements in network capacity. Original expectations for some of the proponents of CDMA technology were for some very significant improvements:
18 fold increase in capacity when compared to AMPS (1G technology used in USA)
6 fold increase in capacity when compared to US TDMA (2G technology used in USA) - similar increases were also claimed over GSM.
In reality the original expectations were not fulfilled although increases of a factor of about two were seen when compared to US TDMA and GSM. This in itself was a significant improvement.
Improvement in handover / handoff: Using CDMA it is possible for a terminal to communicate with two base stations at once. As a result, the old link only needs to be broken when the new one is firmly established. This provides significant improvements in terms of the reliability of handover / handoff from one base station to another.
GSM (Global System for Mobile communications) is an
open, digital cellular technology used for transmitting mobile voice and
data services. GSM differs from first generation wireless systems in
that it uses digital technology and Time Division Multiple Access (TDMA)
transmission methods. GSM is a circuit-switched system that divides
each 200kHz channel into eight 25kHz time-slots. GSM operates in the
900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the
US. The 850MHz band is also used for GSM and 3GSM in Australia, Canada
and many South American countries. GSM supports data transfer speeds of
up to 9.6 kbit/s, allowing the transmission of basic data services such
as SMS (Short Message Service). Another major benefit is its
international roaming capability, allowing users to access the same
services when travelling abroad as at home. This gives consumers
seamless and same number connectivity in more than 210 countries. GSM
satellite roaming has also extended service access to areas where
terrestrial coverage is not available.
Global
System for Mobile Communications. The first European digital standard,
developed to establish cellular compatibility throughout Europe. It's
success has spread to all parts of the world and over 80 GSM networks
are now operational. It operates at 900 MHz.
Brief History Of CDMA:
CDMA
is based around a form of transmission known as Direct Sequence Spread
Spectrum. The CDMA history can be directly linked back to the 1940s when
this form of transmission was first envisaged. As electronics
technology improved, it started to be used for covert military
transmissions in view of the facts that the transmissions look like
noise, it is difficult to decipher without the knowledge of the right
codes, and furthermore it is difficult to jam.
With
the revolution in cellular telecommunications that occurred in the
1980s a then little know company named Qualcomm working on DSSS
transmissions started to look at this as the basis for a cellular
telecommunications multiple access scheme - CDMA - code division
multiple access.
The
concept of CDMA had to proved in the field and accordingly Qualcomm was
joined by US network operators Nynex and Ameritech to develop the first
experimental CDMA system. Later the team was expanded as Motorola and
AT&T (now Lucent) joined to bring their resources to speed
development.
As
a result this it was possible to start writing a specification for CDMA
in 1990. With the support of the Cellular Telecommunications Industry
Association (CTIA) and the Telecommunications Industry Association (TIA)
a standards group was set up. This group then published the standard
for the first CDMA system in the form of IS-95, resulting in the formal
publication of IS-95-A in 1995.
With the revolution in cellular telecommunications that occurred in the 1980s a then little know company named Qualcomm working on DSSS transmissions started to look at this as the basis for a cellular telecommunications multiple access scheme - CDMA - code division multiple access.
The concept of CDMA had to proved in the field and accordingly Qualcomm was joined by US network operators Nynex and Ameritech to develop the first experimental CDMA system. Later the team was expanded as Motorola and AT&T (now Lucent) joined to bring their resources to speed development.
As a result this it was possible to start writing a specification for CDMA in 1990. With the support of the Cellular Telecommunications Industry Association (CTIA) and the Telecommunications Industry Association (TIA) a standards group was set up. This group then published the standard for the first CDMA system in the form of IS-95, resulting in the formal publication of IS-95-A in 1995.CDMA technology advantages
The use of CDMA offers several advantages and it is for this reason that CDMA technology has been adopted for many 3G cellular telecommunications systems.
Improvement in capacity: One of the chief claims for CDMA is that it gives significant improvements in network capacity. Original expectations for some of the proponents of CDMA technology were for some very significant improvements:
18 fold increase in capacity when compared to AMPS (1G technology used in USA)
6 fold increase in capacity when compared to US TDMA (2G technology used in USA) - similar increases were also claimed over GSM.
In reality the original expectations were not fulfilled although increases of a factor of about two were seen when compared to US TDMA and GSM. This in itself was a significant improvement.
Improvement in handover / handoff: Using CDMA it is possible for a terminal to communicate with two base stations at once. As a result, the old link only needs to be broken when the new one is firmly established. This provides significant improvements in terms of the reliability of handover / handoff from one base station to another.
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