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Merge: date=January 2009
W-CDMA (Wideband Code Division Multiple Access) is an air interface found in 3G mobile telecommunications networks. 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.
Technical features
Only key features are cited below.
- Radio channels are 5MHz wide.
- Chip rate of 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, whereas 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.
- 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.
Development
W-CDMA was developed by NTT DoCoMo as the air interface for their 3G network FOMA. Later 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 eventually 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. Later, W-CDMA was selected as the air interface for UMTS, the 3G successor to GSM.
Code Division Multiple Access communication networks have been developed by a number of companies over the years, but development of cell-phone networks based on CDMA (prior to W-CDMA) was dominated by Qualcomm, the first company to succeed in developing a practical and cost-effective CDMA implementation for consumer cell phones, its early IS-95 air interface standard. IS-95 evolved into the current CDMA2000 (IS-856/IS-2000) standard.
In the late 1990s, NTT DoCoMo began work on a new wide-band CDMA air interface for their planned 3G network FOMA. FOMA's air interface, called W-CDMA, was selected as the air interface for UMTS, a newer W-CDMA based system designed to be an easier upgrade for European GSM networks compared to FOMA. FOMA and UMTS use essentially the same air interface, but are different in other ways; thus, handsets are not 100% compatible between FOMA and UMTS, but roaming is supported.
Qualcomm created an experimental wideband CDMA system called CDMA2000 3x which unified the W-CDMA (3GPP) and CDMA2000 (3GPP2) network technologies into a single design for a worldwide standard air interface. Compatibility with CDMA2000 would have beneficially enabled roaming on existing networks beyond Japan, since Qualcomm CDMA2000 networks are widely deployed, especially in the Americas, with coverage in 58 countries . However, divergent requirements resulted in the W-CDMA standard being retained and deployed.
