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”).

 CDMA2000 1xEV-DO:

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.





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