3G cellular communication systems have superseded 2G systems in many areas. Currently 3G is being researched and developed into 4G. At present W-CDMA (Wide Band Code Division Multiple Access) is the most common interface for this technology. 3GPP (3rd Generation Partnership Project) is the standardization body in Europe, which is similar to ITU (International Telecommunication Union) and IMT-2000 (International Mobile Telecommunication).

2G superseded 1G by using digital signals while 1G used analog signals. 3G also uses digital signals. 2G is divided into TDMA (Time Division Multiple Access) based and CDMA (Code Division Multiple Access) standards depending on the type of multiplexing used. 2.5G networks (GPRS, cdma2000 1x) are the enhanced versions of 2G networks with data rates up to about 144kbit/s. 3G networks (UMTS FDD and TDD, cdma2000 1x EVDO, cdma2000 3x, TD-SCDMA, Arib WCDMA, EDGE, IMT-2000 DECT) are the latest cellular networks that have data rates 384kbit/s and more.

The main 2G standards are GSM (Global System for Mobile Communication), iDEN (Integrated Digital Enhanced Network), IS-136 aka D-AMPS, and PDC (Personal Digital Cellular). All of the previous standards are TDMA based. The only CDMA based standard on 2G is IS95 aka cdmaOne.

By using digital signals between the handset and the towers system capacity can be increased in two ways: Voice can be digitized, compressed, and multiplexed in greater efficiency than analog by using compression CODECS, allowing more calls to be used in the same bandwidth. Another feature is digital transmission uses less radio power from the handsets, allowing for smaller sets to be developed that uses less battery power.

3G, using W-CDMA, theoretically supports up to 14 Mbit/s data transfer using HDSPA (High Speed Downlink Data Access), although real world benchmarks varies from 384 kbit/s to 3.6 Mbit/s. This is still an impressive improvement over 2G which supports 14.4 kbit/s using cdmaONE. In 2.5G, GPRS (General Packet Radio Switch) was introduced, which is theoretical to support 140 kbit/s with real world benchmarks averaging 56 kbit/s.

E-GPRS, aka EGDE (Enhanced Data Rates for Mobile Evolution) is an upgrade to GPRS, which employs more modern coding algorithms. With EDGE data rates can reach 180 kbit/s, Edge is considered to be 2.5G but is often referred as 2.75G, It employs TDMA (Time Division Multiple Access).

Edge uses Gaussian minimum-shift keying (GMSK), additionally; it uses higher-order PSK/8 phase shift keying (8PSK) for the upper 5 of its 9 modulation schemes. EDGE creates a 3-bit word during every change in carrier phase. Consequently, this will triple the data rate offered by GSM.

CDMA (Code Division Multiple Access) is a channel access method used by various radio communication technologies. It should not be confused with CDMA2000. The main concept behind CDMA is allowing many transmitters to send information concurrently over a single communication channel. As a result, this allows several users to share a bandwidth of frequencies. This concept is referred to as multiplexing. CDMA uses spread spectrum technology and special coding where each transmitters is assigned a code to allow multiple users to be multiplexed over the same channel.

In contrast, TDMA (Time Division Multiple Access) divides access by time while FDMA (Frequency Division Multiple Access) divides access by frequency. CDMA uses spread spectrum signaling, since the signal has higher bandwidth than the data being transmitted.

To simplify the above concept consider people sitting in room and they wish to communicate with each other. In order to avoid confusion, people will take turns to speak, which is considered time division, or speak in different a pitch, which is frequency division, or speak in different direction, which is spatial division. In CDMA, they would speak different languages. Perople speaking the same language will understand each other but not other people. CDMA2000 is a mixture of 2.5 and 3G technologies to send voice and data between mobile phones and towers.

CDMA2000 uses 2.5G technology in 1xRTT and 3G in EVDO (Evolution Data Optimized Evolution Data Only). CDMA2000 has a somewhat long technical history and is compatible with older CDMA technologies. CDMA2000 1xRTT is the core standard for wireless interfaces, aka 1x 1xRTT and IS-2000.

1x means 1 times Radio Transmission Technology. Another designation is 1xMC which is 1 times multi carrier. 1xMC uses a duplex pair of 1.25 MHz radio channels. In contrast 3xMC uses channels 3 times as wide equating to 3.75 MHz. 1xMC can double its capacity by adding 64 more traffic channels to the forward link and orthogonal to the original set of 64.

Although CDMA2000 is theoretically able to give more performance, real deployments register a 144kbit/s transfer rate. 1xMC qualifies as 3G but is considered a 2.5G or sometimes as 2.75G.

CDMA2000 3xMC is AKA EVDO which offers the following specifications:
• Higher rates per carrier (up to 4.9 Mbit/s on the downlink per carrier). Typical deployments are expected to include 3 carriers for a peak rate of 14.7 Mbit/s

• Uses statistical multiplexing across channels to further reduce latency, enhancing the experience for latency-sensitive services such as gaming, video telephony, remote console sessions and web browsing.
• Increased talk-time and standby time
• Hybrid frequency re-use which reduces the interference from the adjacent sectors and improves the rates that can be offered, especially to users at the edge of the cell.
• Efficient support for services that have asymmetric download and upload requirements (i.e. different data rates required in each direction) such as file transfers, web browsing, and broadband multimedia content delivery.

W-CDMA has its market mainly in Japan and Europe, while CDMA2000 is utilized by the rest of the world.

Quick market facts for CDMA2000
• 257 commercial operators
• 98 countries
• 252 commercial 1X networks
• 24 1X networks in deployment
• 99 commercial 1xEV-DO Rel. 0 networks
• 44 1xEV-DO Rel. 0 networks in deployment
• 35 commercial 1xEV-DO Rev. A network
• 33 1xEV-DO Rev. A networks in deployment
• 417,500,000 CDMA2000 subscribers (4Q 2007)
• 90,534,000 CDMA2000 1xEV-DO subscribers (4Q 2007)
• 1,980 devices have been introduced in to the market including 515 1xEV-DO Rel. 0 and 56 1xEV-DO Rev A devices (as of May 16, 2008)

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References:
http://www.3gpp.org/
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V8B-4DS7YGS-2&_user=536372&_rdoc=1&_fmt=&_orig=search&_sort=d&view=
  \ c&_acct=C000027078&_version=1&_urlVersion=0&_userid=536372&md5=4de16500169d4bec52dc6b86e704c48a
http://en.wikipedia.org/wiki/2G
http://en.wikipedia.org/wiki/3G
http://en.wikipedia.org/wiki/CDMA2000
http://www.cdg.org/

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