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Introduction to WCDMA: Physical Channels, Logical Channels, Network, and Operation

WCDMA Radio Channels

Overview

A radio channel is a communications channel that uses radio waves to transfer information from a source to a destination. A radio channel may transport one or many communication channels and communication circuits.

The WCDMA system uses the same 5 MHz bandwidth size radio channels for WCDMA voice and WCDMA data. To maximize the data transfer rate, the WCDMA forward radio channel can use different types of modulation and different amounts of signal spreading (processing gain). The forward WCDMA channel transmits at maximum power to one user at a time while the reverse WCDMA channel uses precise power control and allows all the active (connected) users to transmit at the same time.

To create a wide digital radio channel from low-speed digital audio or control signals, each bit of the information signal is multiplied (converted) into a long sequence of bits called a spreading code. This spreading code effectively represents each bit of an information signal by multiple RF information signals (chips) over a frequency band that is much wider than the information signal. This is why it is called a wideband system.

Because the WCDMA system use variable spreading sequence for each coded communication channel, data transmission rates can vary based on the amount of spreading that is used. For the user data channels, the information data transmission rate can vary from 7.5 kbps to 960 kbps. While it is theoretically possible to obtain these data transmission rates, the total data transmission rate also varies (is reduced) based...

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