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April 03, 2005

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From Wikipedia, the free encyclopedia.


This page explains the technological aspects of W-CDMA (the air interface technology, the protocol that defines the over-the-air transmissions between mobile phones and towers), and general information of the family of 3G implementations that based on W-CDMA, including UMTS and FOMA. For other aspects (business, users, political, or implementation-specific issues) surrounding the various W-CDMA networks or standards, or issues specific to those variants, please refer to their respective pages.


General Information

W-CDMA (Wideband Code Division Multiple Access), a wideband spread-spectrum 3G mobile telecommuncation air interface that utilizes code division multiple access (or CDMA the general multiplexing scheme, not to be confused with CDMA the standard), is a 3G mobile communications standard allied with the GSM standard. W-CDMA is the technology behind UMTS (aka 3GSM). Networks using W-CDMA are a form of cellular network.


Brief History

W-CDMA was developed by NTT DoCoMo as the air interface for their 3G network FOMA. Later NTT Docomo submitted the specificication to ITU as a candidate for the international 3G standard known as IMT-2000. The ITU eventually accepted W-CDMA as part of the IMT-2000 family of 3G standards. Later, W-CDMA is selected as the air interface for UMTS, the 3G successor to GSM.



Despite the similarity in name, W-CDMA has very little to do with CDMA. How little depends on the point of the viewer.

In the mobile phone world, the term CDMA can refer to either the Code Division Multiple Access spread spectrum multiplexing technique, or the CDMA family of standards developed by Qualcomm, including cdmaOne (or IS-95) and CDMA2000 (or IS-2000).

The CDMA multiplexing technique existed long before Qualcomm used it for its IS-95 protocol. However, this protocol is now widely referred to as "CDMA" because for its principal characteristic of using the CDMA multiplexing scheme to share multiple connections over the same spectrum, as opposed to other spectrum division schemes (eg. GSM's TDMA).

W-CDMA also uses the CDMA multiplexing technique, but has no other similarities to Qualcomm's CDMA standards. W-CDMA is 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, etc.

In summary:

  • The term CDMA in the mobile world typically refers to the CDMA family of standards developed by Qualcomm. They are protocols, sets of defined specifications of mobile communications
  • CDMA (the multiplexing technique) is used as the principle of the W-CDMA air interface protocol, as well as Qualcomm's CDMA protocols
  • W-CDMA strictly refers to a mobile phone protocol with detailed specifications, as defined in IMT-2000
  • The W-CDMA protocol was developed independently of the CDMA protocol developed by Qualcomm
  • The CDMA family of standards (including cdmaOne and cdma2000) are not compatible with the W-CDMA family of standards


Real-World Implementations

The world's first commercial W-CDMA service, FOMA, was launched by NTT DoCoMo in Japan in 2001. FOMA is not compatible with UMTS.

J-Phone Japan (now Vodafone) soon followed by launching their own W-CDMA based service, now branded "Vodafone Global Standard" and claiming UMTS compatibility (although as of 2004 this is debatable).

Beginning in 2003, Hutchinson Whompoa gradually launched their upstart UMTS networks (simply called 3) worldwide.

Most Western European GSM providers plan to offer UMTS sometime in the future, though few have committed to an actual timeline. Some of them have begun launching UMTS networks at the end of 2003.

Vodafone launched several UMTS networks in Europe in February 2004.

AT&T Wireless has announced plans to launch a UMTS service in the United States by the end of 2004.

Please see UMTS for more



W-CDMA may use unpaired or paired spectrum, though the current implementations of W-CDMA (i.e. FOMA and UMTS) all use a pair of 5MHz spectrum, one for uplink and one for downlink. See Spread spectrum for more information.


Comparison with other standards

In contrast to CDMA2000, which can use multiple 1.25 MHz carriers, W-CDMA uses 5MHz channels.

In the ITU's IMT-2000 standard, W-CDMA is known as CDMA Direct Spread.

The family of standards commonly known as W-CDMA (e.g. FOMA, UMTS) is not compatible with the family of standards common known as CDMA (e.g. IS-95 and cdma2000).



Last update: April 03, 2005
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