W-CDMA

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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.

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. Qualcomm collects royalties for both standards. Qualcomm also collects royalties for another standard called TD-SCDMA (Time Division-Synchronous Code Division Multiple Access), which is also based on Qualcomm's CDMA standard.

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 (e.g. GSM's TDMA). Qualcomm's research solved several problems thought to be intractable related to using the multiplexing technique with a cellular phone system (including but not limited to the near-far problem), and thus 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 also uses the CDMA multiplexing technique, due to its advantages over other multiple access techniques such as TDMA, and has many similarities to the Qualcomm standards. Indeed, Qualcomm receives royalties due to the unavoidable use of its patents and research in the implementation of the CDMA multiplexing technique in W-CDMA. However W-CDMA is more than a multiplexing standard. 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, although drawing on Qualcomm's research
The CDMA family of standards (including cdmaOne and CDMA2000) are not compatible with the W-CDMA family of standards

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.