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

Channel Types

The WCDMA system has 3 basic channel types; physical channels, transport channels, and logical channels. Channels can be classified as common channels or dedicated channels. Common channels are accessible and share-able by a variety of communication devices. The WCDMA system uses common channels to send commands or instructions such as system or device identification information to all mobile devices operating in a radio coverage area. Dedicated channels are accessible by one or several designated devices. The WCDMA system uses dedicated channels to send information to a specific device (such as voice or data information).

Physical Channels

Physical channels are the electrical, radio, or optical transmission channels that are connected between transmitters and receivers. Physical channels may be distinguished from other channels by the frequency, code, or time of occurrence of the transmission. The WCDMA system is composed of several physical (coded) and logical (time shared) channels. WCDMA channels may be only used on a forward (downlink) or reverse (downlink) direction or they may be paired for two-way transmission.

Common Pilot Channel (CPICH)

The common pilot channel (CPICH) provides a reference timing signal to assist in the demodulation of the received signal. The CPICH uses a predetermined spreading code that is unique from all other channels. Because the CPICH is always present, it can also be used by mobile devices to estimate the received signal strength. The CPICH has a fixed spreading factor of 256 that provides a data transmission rate of 30 kbps.

The WCDMA system uses two types of...


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