WCDMA: A high speed 3G mobile wireless technology with capacity to offer higher data rate than CDMA.
WCDMA has the capacity to easily handle bandwidth-intensive applications such as video, data, and image transmission necessary for mobile internet services .
WCDMA was adopted as a standard by the International Mobile Telecommunications-2000 (IMT 2000) with the intention to create a global standard for real time multimedia services and international roaming.
WCDMA is direct spread technology, which means that it will spread its transmissions over a wide, 5MHz carrier.
WCDMA is the leading 3G wireless standard in the world today.
WCDMA users share same radio resources whereas TDMA or FDMA users have their own radio resources allocated.
User signals are differentiated based on codes.
FEATURES OF THE WCDMA (1) The actual data rate achieved is inversely proportional to the coverage and mobility of the user (2) Larger bandwidth of 10 and 20 MHz is proposed for higher data rates. (3) Spreading factor = t b / t c. (4) Scrambling codes permit the handling of multiple users in the network(using the same frequency). (5) Frequency Division Duplex used as there are two different frequency bands, one for the uplink and the second one for the downlink. 144 kbps, 384 kbps, 2 Mbps Data rates FDD Duplexing DL - QPSK UL - BPSK Data Modulation DL- Gold sequences. (len-18) UL- Gold/Kasami sequences (len-41) Scrambling codes Orthogonal variable spreading factor (OVSF) SF: 4-256 Spreading codes 5, 10, 20 MHz Bandwidth
Low power spectral density. As the signal is spread over a large frequency-band, the Power Spectral Density is getting very small, so other communications systems do not suffer from this kind of communications.
Interference limited operation. In all situations the whole frequency-spectrum is used.
Privacy due to unknown random codes. The applied codes are unknown to a hostile user. This means that it is hardly possible to detect the message of another user.
Random access possibilities. Users can start their transmission at any arbitrary time.
In multiple cell system power of each subscriber unit is controlled by the base station of their own cell.
The maximum pilot power among cell sites decides which cell site the subscriber will join.
The interference to a subscriber in another cell site is proportional to the attenuation in the path to the subscriber’s cell and inversely to the attenuation from the interfering user to his own cell site.
Forward link : Power control is essential since signals in adjacent cells fade independently and can cause interference in the near cell boundaries.
Power control in the forward link is the allocation of power to each subscriber according to each subscriber’s needs.