CDMAONE / CDMA2000
a guide to the evolution of the CDMA system from cdmaOne through CDMA2000
1X to CDMA2000 1xEV-DO and CDMA2000 1xEV-DV
One of the major cell / mobile phone or cellular
telecommunications technologies today is the cdmaOne / CDMA2000 system. One of
its strengths is that it has focussed on being an evolutionary technology moving
from standards such as IS-95 (IS-95A and IS-95B) for cdmaOne through to
standards including IS-2000 and IS-856 for CDMA2000 1X, 1xEv, 1xEV-DO and
1xEV-DV. Currently the standard uses one standard channel under a system known
as 1X RTT, although for the future three channels (3X RTT) may be used).
In view of the fact that the CDMA2000 system has been
designed to be an evolutionary standard, it is relatively easy to introduce
upgrades to the system. This has made it particularly popular with operators
because the cost of upgrading to the new standards is much less, and they can
have users with a variety of types of phone on the same network. Thus users may
operate cdmaOne phones on the same network as CDMA2000 1X or CDMA2000 1xEV-DV
phones.
The story of how the system was developed is particularly
interesting, and it reveals much about the nature of the system as well as
telling its significant successes.
In the beginning .....
The idea for using the form of modulation known as direct
sequence spread spectrum (DSSS) for a multiple access system for mobile
telecommunications came from a California based company called Qualcomm in the
1980s. Previously DSSS had been mainly used for military or covert
communications systems as the transmissions were hard to detect, jam and
eavesdrop.
The system involved multiplying the required data with
another data stream with a much higher data rate. Known as a spreading code,
this widened the bandwidth required for the transmission, spreading it over a
wide frequency band. Only when the original spreading code was used in the
reconstruction of the data, would the original information be reconstituted. It
was reasoned that by having different spreading codes, a multiple access system
could be created for use in a mobile phone system.
In order to prove that the new system was viable a consortium
was set up and Qualcomm was joined by US network operators Nynex and Ameritech
to develop the first experimental code division multiple access (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 the new standard was published
as IS-95A in 1995 under the auspices of the Cellular Telecommunications Industry
Association (CTIA) and the Telecommunications Industry Association (TIA). As
part of the development of CDMA an organisation called the CDMA Development
Group (CDG) was formed from the founding network and manufacturers. Its purpose
is to promote CDMA and evolve the technology and standards, although today most
of the standards work is carried out by 3GPP2.
It then took a further three years before Hutchison Telecom
became the first organisation to launch a system. It is now widely deployed in
North America, and the Asia Pacific region, but there are also networks in South
America, Africa, and the Middle East as well as some in Eastern Europe.
System Basics
The CDMA system was totally unlike any system used before. In
the UK the original TACS system had used a channel spacing of 25 kHz and AMPS in
the US had used 30 kHz. The new GSM system used 200 kHz channels whilst the US -TDMA
standard kept compatibility with AMPS and was based around 30 kHz channels. CDMA,
IS-95A, used a 1.25 MHz bandwidth and this was much wider than anything that had
been used before. CDMA operates well with a wide bandwidth, but it was limited
to 1.25MHz to remain compatible with the spectrum allocations that were
available.
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Note on CDMA:
CDMA, Code Division Multiple Access, is a multiple
access scheme used by many 3G cellular technologies, and other forms of
wireless technology. It uses a process called Direct Sequence Spread
Spectrum where spreading codes are used to spread a signal out over a
given bandwidth and then reconstituting the data in the receiver by
using the same spreading code. By supplying different spreading codes to
different users, several users are able to utilises the same frequency
without mutual interference. |
There were other differences as well. CDMA mobiles did not
have SIM cards, although recently this has changed. Instead the subscriber data
has simply been stored in memory of the mobile with a method of over-the-air
programming of this data being available.
cdmaOne
The first offerings of CDMA under the guise of IS-95 catered
for voice as well as data up to a speed of 14.4 kbps. However with the market
moving towards data applications, the IS-95 specification was upgraded to IS-95B
to cater for the needs of operators. This new specification allowed packet
switched data transmission up to a speed of 64 kbps. IS-95B was first deployed
in September 1999 in Korea and has since been adopted by operators in Japan and
Peru.
Often IS-95 A and B versions are marketed under the brand
name cdmaOne. This is a registered trademark of the CDMA Development Group.
CDMA2000 1X
cdmaOne had been very successful and was introduced into many
countries, but with operators seeing revenue from voice services levelling off,
the pressure to migrate to 3G technologies where data speeds were higher and
revenue growth could be maintained. As a result of this the IS-2000 standard was
developed to enable the higher 3G data rates to be provided.
Within IS-2000 a number of further developments were
included. It was envisaged that with many more areas moving towards 3G standards
and the old AMPS systems being made obsolete it would be possible to have
systems operating on a wider bandwidth. As a result of this the new standards
allowed for systems that would use the single channel bandwidth (1X or 1X RTT)
and also ones that would use three times the bandwidth (3X). Currently all work
is focussed on the 1X systems, with the idea for the 3X (or 3X RTT) systems to
be used some time in the future.
CDMA2000 1X can double the voice capacity of cdmaOne networks
and delivers peak packet data speeds of 307 kbps in mobile environments although
today's commercial CDMA2000 1X networks (phase 1) support a peak data rate of
153.6 kbps. CDMA2000 1X has been designated a 3G standard and it is now widely
deployed.
Evolution
CDMA2000 1X is the basic 3G standard, in fact some people
only consider it a 2.75G system, and it is being developed beyond this. In what
is termed CDMA2000 1xEv, there are further developments to bring it in line with
the UMTS or Wideband CDMA system that is being deployed in Western Europe and
many other areas.
The first of these known as CDMA2000 1xEV-DO (EVolution Data
Only) is something of a sideline from the main evolutionary development of the
standard. It is defined under IS-856 rather than IS-2000, and is as the name
indicates is only carries data, but at speeds up to 2.4Mbps in the forward
direction and the same as 1X in the reverse direction.
The forward channel forms a dedicated variable-rate, packet
data channel with signalling and control time multiplexed into it. The channel
is itself time-divided and allocated to each user on a demand and opportunity
driven basis. A data only format was adopted so that the system could be
optimised for data applications, and if voice is required then a dual mode phone
using separate 1X channel for the voice call is required. In fact the "phones"
used for data only applications are referred to as Access Terminals or ATs.
The first commercial CDMA2000 1xEV-DO network was deployed by
SK Telecom (Korea) in January 2002. Now operators in Brazil Ecuador, Indonesia,
Jamaica, Puerto Rico, Taiwan and the USA to mention but a few have all launched
networks and more are to follow.
Data and voice
The next logical evolution of the system is to incorporate
both data and voice into the standard. This is exactly what CDMA2000 1xEV-DV
achieves. This is catered for under Release C of the IS-2000 standard. And is
effectively 1X with additional high speed data channels. In this way it is able
to provide complete backward compatibility with both CDMA2000 1X and cdmaOne. In
addition to this the migration requires comparatively few upgrades to a 1X
system and as such it is a very attractive option for network operators. Further
developments are available under Release D of the IS-2000 standard. This
provides for 3.1 Mbps data in both directions as well as many other upgrades.
Summary
The first CDMA networks in the form of IS-95 / cdmaOne were
the first deployments of CDMA technology, the technology that is being used for
all 3G cell phone systems. This formed the basis for a unique evolutionary
system as CDMA2000. CDMA2000 is a well established 3G technology, and it is
particularly successful in the USA, and Asia Pacific regions as well as having a
significant presence in many other parts of the world. It was able to offer 3G
services well before W-CDMA became established, and it is now continuing to
build on this success.
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