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


There are two types of radio systems used by the WCDMA system; frequency division duplex (FDD) and time division duplex (TDD). The characteristics of WCDMA radio channels include frequency bands, frequency reuse, channel multiplexing techniques, RF Power levels, RF power control, and channel structure.

WCDMA radio channels are divided into overlapping physical (transport) and logical channels. Each physical radio channel is uniquely identified by a spreading code. The logical channels (e.g. control, voice and data) are divided into groups of bits (fields and frames).

Frequency Division Duplex (FDD) WCDMA

Frequency division duplex (FDD) is a communications channel that allows the transmission of information in both directions via separate bands (frequency division). The WCDMA frequency division duplex (FDD) system pairs two 5 MHz radio channels to provide for simultaneous duplex communication.

FDD operation normally assigns the transmitter and receiver to different communication channels. One frequency is used to communicate in one direction and the other frequency is required to communicate in the opposite direction. The amount of frequency separation between the transmitter and receiver frequency bands varies based on the range of frequencies. Generally, the higher the frequency used, the larger the amount of duplex frequency spacing. The lower frequency band of the pair is generally designated for the mobile because it is easier (and often cheaper) to produce lower frequency devices.

Each radio channel is divided into 10 msec frames and each frame is further divided into 15 time slots (666 usec each). During a typical FDD voice conversation, all...


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