Wideband Code Division Multiple Access (WCDMA)

Wideband Code Division Multiple Access (WCDMA) is a third-generation (3G) standard that employs the direct-sequence code division multiple access (DS-CDMA) channel access method and the frequency-division duplexing (FDD) method to provide high-speed and high-capacity service. WCDMA is the most commonly used variant of the Universal Mobile Telecommunications System (UMTS). It was developed by Japan’s NTT DoCoMo and formed the basis of its Freedom of Multimedia Access (FOMA) 3G Network.

The WCDMA system is part of the UMTS. It is developed by the 3G Partnership Program, which is composed of evolved core cellular networks that belong to the Global System for Mobile (GSM) communications networks worldwide.

WCDMA features two modes:

• Frequency Division Duplex (FDD): Separates users by employing both codes as well as frequencies. One frequency is used for the uplink, while another is used for the downlink.
• Time Division Duplex (TDD): Separates users by employing codes, frequencies and time, wherein the same frequency is used for both uplink and downlink.

Although WCDMA is designed to operate on evolved GSM core networks, it uses code division multiple access (CDMA) for its air interface. In fact, the majority of the 3G systems in operation employ CDMA, while the rest use time division multiple access (TDMA). The TDD mode of WCDMA actually employs a combination of TDMA and CDMA.

CDMA allows multiple users to share a channel at the same time, while TDMA allows users to share the same channel by chopping it into different time slots. CDMA offers the benefits of multipath diversity and soft handoffs.

As an air interface technology, WCDMA is able to artificially increase a signal's bandwidth. It does so by modulating each baseband symbol with a binary or quaternary signature with a much higher rate than that of the original data symbol