Code Division Multiple Access (CDMA)
Code Division Multiple Access (CDMA) is a digital technique for sharing
the frequency spectrum. Multiple users are assigned radio resources using spread Spectrum techniques.
Although all users are transmitting in the same RF band, individual
users are separated from each other via the use of orthogonal codes. CDMA is based on proven Spread Spectrum communications
technology”
There are several CDMA
implementations that are currently deployed or under development. The first
commercial and most widely deployed CDMA implementation is cdmaOne.
CDMA is an
advance digital technology that can offer 7 to 10 times the capacity of analog
technologies and up to 6 times the capacity of digital technologies such as
TDMA. The speech quality provided by the CDMA systems is far superior to any other
digital technology particularly in difficult radio environments such as dense
urban areas and mountainous regions. It provides the most cost effective
solution for cellular operators.
CDMA Technology
is constantly evolving to offer customers new advanced services. The mobile
data speeds offered through CDMA phones are increasing and new voice codecs
provide speech quality close to wire line. Internet access is now available
through CDMA terminals. The CDMA systems and technology have been standardized under
Interim standard-95 (IS-95 A&B).
cdmaOne
The foundation of cdmaOne is the
TIA/EIA IS-95 standard. The term cdmaOne is intended to represent the
end-to-end wireless system and all of the necessary specifications that govern
its operation. cdmaOne technology provides a family of related services
including cellular, PCS, and fixed wireless (Wireless Local Loop). cdmaOneTM is a trademark of the CDMA
Development Group (CDG).
CDMA2000
CDMA2000 is an improvement on TIA/EIA
IS-95. It provides a significant improvement in voice capacity and expanded
data capability, and is backward-compatible with IS-95 handsets.
CDMA Evolution – From a Standards Perspective
To understand the evaluation of CDMA it is important to know how the
technology’s evolution will continue into the next decade, it is also important
to understand CDMA2000 from a standards perspective since there is a fair
amount of confusion about what is and is not 3G, and how 3G will evolve into
4G.
IS-95
The first CDMA standard for mobile networks is referred to as Interim
Standard 95A (IS- 95A), and is considered to be a 2G technology. The IS-95A standard was
completed in 1993 and served as a digital wireless technology that could
replace analog systems. IS-95B, which is an upgrade to IS-95A, was deployed in a few markets
including South Korea, Japan, and Peru.
What is Third Generation?
The International Telecommunications
Union–Radio Communications (ITU-R) began an effort to create a worldwide
wireless standard known as Third Generation or 3G.
Work began in earnest in the mid to
late 1990s under the name Future Public Land Mobile Telephony (FPLMTS). Later,
the effort was renamed to the more manageable International Mobile Telephony
for the Year 2000 (IMT-2000).
The impetus for this work was to increase voice capacity and to provide
for wireless data and Internet services.
Third
Generation Standards:
After considering several proposed
standards, the ITU approved three, all based on CDMA
CDMA2000/FDD-MC:
CDMA2000 is using Frequency Division
Duplexing Multicarrier (FDD-MC) mode. Here multicarrier implies N x 1.25 MHz
channels overlaid on N existing IS-95 carriers or deployed on unoccupied
spectrum. CDMA2000 includes:
CDMA2000 1X
1X is the technology that follows IS-95. The term 1X is an abbreviation
of 1xRTT (1x
Radio Transmission Technology), and a fallback to the period when 3xRTT
was being considered within the CDMA2000 community. In this case the “1” and
“3” refer to the number of 1.25MHz radio carriers that are combined together,
with the de facto number being 1. One common misconception is that 1X is not a
3G standard, with the moniker “2.5G” sometimes used by various entities when
referring to the standard. The ITU (International Telecommunications Union),
however, explicitly acknowledged 1X as a 3G technology in November 1999.
Interestingly, the ITU does not officially recognize terms such as “2.5G,”
“3.5G” and “4G,” as they are not well-defined terms within the body. Instead,
various organizations use these terms as marketing tools when trying to
segregate various advancements for a given technology. Examples include GPRS
(“2.5G”), HSDPA (“3.5G”) and WiMAX (“4G”).
Operators who have selected the CDMA2000 evolutionary path are now in the
process of deploying, or have already deployed, EV-DO (Evolution – Data
Optimized).
As the name suggests, EV-DO is a data centric technology that allows
operators to take advantage of the performance characteristics of the
technology to offer advanced data services. Like 1X, EV-DO is an ITU-recognized
3G technology, with the standard (cdma2000 High Rate Packet Data Air Interface,
IS-856) approved in August 2001. As discussed in this paper, the combination of
an EV-DO and 1X service is very compelling for operators that want to maximize
voice capacity in their networks while still being able to deliver advanced
revenue-generating data services.
CDMA2000
1xEV-DV:
With the recent decision by Sprint Nextel to
deploy EV-DO, work within the standards body on 1xEV-DV (Evolution – Data and
Voice) has ceased and is instead focused on future enhancements to the first
implementation (Release 0) of EV-DO. EV-DO Revision-A (TIA-856-A) is the first
in a series of planned upgrades for Release 0. The Revision A standard was
approved in March 2004, with commercial services beginning as early as the end
of 2006. EV-DO Revision B logically follows Revision A, with indications that this revision will become a standard in the first quarter
of 2006. Through Revision B, all planned
EV-DO revisions are fully backward and forward compatible. Ultimately, there
could be several “phases” of Revision B, with each
phase introducing greater functionality and
richer feature.
WCDMA/FDD-DS:
Wideband CDMA
(WCDMA) Frequency Division Duplexing-Direct Sequence spreading (FDD-DS) mode, this
has a single 5 MHz channel. WCDMA uses a single carrier per channel and employs
a spreading rate of 3.84 Mcps.
UTRA TDD/
TD-SCDMA:
Universal Mobile Telephone Services
Terrestrial Radio Access (UTRA) and TD-SCDMA. These are Time Division Duplexed
(TDD) standards aimed primarily at asymmetric services used in unpaired (i.e.,
no separate uplink and downlink) bands. TD-SCDMA is based on a synchronous Time
Division scheme for TDD and wireless local loop applications. The frame
and slot structure are the same as W-CDMA. However, in TDD mode each slot can
be individually allocated either the uplink or the downlink.
Source : https://sites.google.com/site/the4gtelecom/cdma
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