W-CDMA(Wideband Code Division Multiple Access)
W-CDMA(Wideband Code Division Multiple Access) is a type of 3G cellular network. W-CDMA is the technology behind the 3G UMTS standard and is allied with the 2G GSM standard with the International Telecommunication Union - ITU.
More technically, W-CDMA is a wideband spread-spectrum 3G mobile telecommunication air interface that utilizes code division multiple access (or CDMA the general multiplexing scheme, not to be confused with CDMA the US standard).
History
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. Later, W-CDMA was selected as the air interface for UMTS, the 3G data part of GSM. Attempts were made to unify W-CDMA (3GPP) and CDMA-1X (3GPP2) standards in order to provide a single worldwide standard, however, divergent requirements resulted in the two incompatible standards being retained.
Features
Only key features are cited below.
- Supports two basic modes of duplex: FDD (frequency division duplex) and TDD (time division duplex) modes
- Employs coherent detection on uplink and downlink based on the use of pilot symbols
- Inter-cell asynchronous operation
- Variable mission: on a 10 ms frame basis
- Multicode transmission
- Adaptive power control based on SIR
- Multiuser detection and smart antennas can be used to increase capacity and coverage
- Multiple types of handoffs between different cells including soft handoff, softer handoff and hard handoff
Misconceptions
W-CDMA is based on the Direct Spread CDMA technique. Code Division Multiple Access has been developed by a number of companies, and in the US this is dominated by Qualcomm. However, the ITU standard is not a Qualcomm implementation, but one where Qualcomm has been invited to participate. Other standards, such as TD-SDMA/TD-CDMA has been developed by Siemens and the Chinese independent of both the ITU and Qualcomm and bears no relationship with the US technology other than the name others have assigned to it.
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 (IS-95) and CDMA2000 (IS-2000 and IS-856).
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" for its principal characteristic of using the CDMA multiplexing scheme to share multiple connections divided by different codes (PN sequences) over the same spectrum channel, as opposed to other spectrum division schemes
Qualcomm was able to introduce the first mobile protocol relying upon the CDMA multiplexing technique, associating the multiplexing technique with the name of the protocol.
W-CDMA is used in 3G as a political compromise made by the more advanced non-US companies to allow the US to participate in the rollout of 3G services. Since it now is part of the International Telecommunication Union's standards it is part of a larger suite of 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, and system interfaces are specified allowing free competition on technology elements.
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 that are based on ITU standards.
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. But the effort for migrating the FOMA specifications to UMTS are indicated by Japan.
J-Phone Japan (now Vodafone) soon followed by launching their own W-CDMA based service, originally branded "Vodafone Global Standard" and claiming UMTS compatibility. The name of the service was changed to "Vodafone 3G" in December 2004.
Beginning in 2003, Hutchison Whampoa gradually launched their upstart UMTS networks.
Most countries have since the ITU approved of the 3G mobile service either "auctioned" the radio frequencies to the company willing to pay the most, or conducted a "beauty contest" - asking the various companies to present what they intend to commit to if awarded the licenses. This strategy has been criticised for aiming to drain the cash of operators to the brink of bankruptcy in order to honour their bids or proposals. Most of them have a time constraint for the rollout of the service - where a certain "coverage" must be achieved within a given date or the license will be revoked.
Vodafone launched several UMTS networks in Europe in February 2004. MobileOne of Singapore commercially launched its 3G (W-CDMA) services in February 2005. New Zealand in August 2005 and Australia in October 2005.
AT&T Wireless (now a part of Cingular Wireless) has deployed UMTS in several cities. Though advancements in its network deployment have been delayed due to the merger with Cingular, Cingular began offering HSDPA service in December 2005.
Rogers in Canada is currently trialing HSDPA on W-CDMA at 1900MHz and plan the launch the service commercial in Q3, 2006.
TeliaSonera opened W-CDMA service in Finland October 13th 2004 with speeds up to 384 kbit/s. Availability only in main cities. Pricing is approx. 2€/MB. [citation needed]SK Telecom and KTF, two largest mobile phone service providers in South Korea, have each started offering W-CDMA service in December 2003. Due to poor coverage and lack of choice in handhelds, the W-CDMA service has barely made a dent in the Korean market which was dominated by CDMA2000.
In Norway, Telenor introduced W-CDMA in major cities by the end of 2004, while their competitor, NetCom, followed suit a few months later. Both operators have 98 % national coverage on EDGE, but Telenor has parallel WLAN roaming networks on GSM, where the UMTS service is competing with this. For this reason Telenor is dropping support of their WLAN service in Austria (2006).
Maxis Communications and Celcom, two mobile phone service providers in Malaysia, started offering W-CDMA services in 2005.
In Sweden, Telia introduced W-CDMA March 2004.
Technology
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. FOMA uses 16 slots per radio frame, where as UMTS uses 15 slots per radio frame.
