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Wideband CDMA

W-CDMA (Wideband Code Division Multiple Access) is a type of 3G cellular network. W-CDMA is the higher speed transmission protocol used in the Japanese FOMA system and in the UMTS system, a third generation follow-on to the 2G GSM networks deployed worldwide.

More technically, W-CDMA is a wideband spread-spectrum mobile air interface that utilizes the direct sequence Code Division Multiple Access signalling method (or CDMA) to achieve higher speeds and support more users compared to the implementation of time division multiplexing (TDMA) used by 2G GSM networks.

Technical features

Key features of WCDMA include:

Radio channels - 5MHz wide
Chip rate - 3.84 Mcps
Supports two basic modes of duplex, frequency division and time division. Current systems use frequency division, one frequency for uplink and one for downlink. For time division, FOMA uses sixteen slots per radio frame, where as UMTS uses fifteen slots per radio frame.
Employs coherent detection on both the uplink and downlink based on the use of pilot symbols and channels[1].
Supports inter-cell asynchronous operation
Variable mission on a 10 ms frame basis
Multicode transmission
Adaptive power control based on SIR (Signal-to-Interference Ratio)
Multiuser detection and smart antennas can be used to increase capacity and coverage
Multiple types of handoff (or handover) between different cells including soft handoff, softer handoff and hard handoff.

WCDMA Evolution

W-CDMA was developed by NTT DoCoMo as the air interface for their 3G network FOMA.
NTT DoCoMo submitted the specification to the International Telecommunication Union (ITU) as a candidate for the international 3G standard known as IMT-2000.
The ITU accepted W-CDMA as part of the IMT-2000 family of 3G standards, as an alternative to CDMA2000, EDGE, and the short range DECT system.
W-CDMA was selected as the air interface for UMTS, the 3G successor to GSM.

Transmission

W-CDMA transmits on a pair of 5 MHz-wide radio channels, while CDMA2000 transmits on one or several pairs of 1.25 MHz radio channels.

Although W-CDMA uses a direct sequence CDMA transmission technique like CDMA2000, W-CDMA is not simply a wideband version of CDMA2000.

The W-CDMA system is a new design by NTT DoCoMo, and differs in many aspects from CDMA2000.

W-CDMA has been developed into a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how datagrams are structured, and system interfaces are specified allowing free competition on technology elements.

Benefits

Engineering - W-CDMA provides a different balance of costs vs. capacity vs. performance vs. density, and promises to achieve a benefit of reduced cost for video phone handsets.

Deployment - W-CDMA is often better suited for deployment in the very dense cities of Europe and Asia.

Constaints

WCDMA is contrained by:

Incompatibilities with existing air-interface standards
Late introduction as a 3G system
High upgrade cost of deploying an all-new transmitter technology.
Cross-licencing of patents between Qualcomm and W-CDMA vendors due to the features of W-CDMA which remain covered by Qualcomm patents.

Deployment

The world's first commercial W-CDMA service, FOMA, was launched by NTT DoCoMo in Japan in 2001.

As of 2006, W-CDMA had been deployed in 55 countries, including Japan, Europe, USA and Asia.

Elsewhere, W-CDMA deployments have been exclusively UMTS based.

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