CDMA Channels Structure - Overview of CDMA Channels As is...

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Overview of CDMA Channels As is typical of channel structure in the North American Common Air Interface Systems, there are two major types of channels: Traffic (voice/data) channels Control Channels However in contrast to the existing narrowband technologies, where separate frequencies physically define the channels, CDMA channels are logically divided among the shared broad bandwidth. Traffic Channels The traffic channels send User Data/Speech between the base station and the mobile along with signaling (Associated Signaling) traffic. User Data/Speech The downlink traffic channel is called the Forward Traffic Channel. On uplink it is called the Reverse Traffic Channel. Four different speech encoder data rates are possible based on the speech energy in each 20ms speech frame: Rate 1, Rate 1/2, Rate 1/4, Rate 1/8. Rate 1 is used when the speech energy is high (typical speech). Rate 1/8 is used when the speech energy is low (silence, background noise). The other rates are used when the speech energy falls in between these two extremes. Associated Signaling When speech information or speech data is replaced by the Associated Signaling, it is called Blank-and-Burst . When part of the speech data is replaced by the signaling it is called Dim-and- Burst . All Associated Signaling is sent at Rate 1.
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Power Control Channel directs the mobile to adjust its transmitted power ± 1dB every 1.25ms (1/16 a 20ms speech frame). Control Channels The 4 Control Channels in a CDMA System and their functions are: CDMA Control Channel Channel Function Pilot Channel (downlink) Allows a mobile station to acquire the timing of the Forward Traffic Channel - the user information. It provides a phase reference for coherent demodulation and signal strength comparisons between base stations for determining when to handoff. Page Channel (downlink) Used for transmitting control information to the mobile. When a mobile is to receive a call it receives a page from the base station on an assigned page channel. Sync Channel (downlink) Used with the Pilot Channel to acquire initial time synchronization Access Channel (uplink) Used for transmitting control information to the base station. When a mobile is to place a call it uses the access channel to inform the base station. This channel is also used when responding to a page. Pilot Channel (Downlink) The pilot channel is the reference for detecting other downlink channels and transmits at a higher power level continuously by each CDMA base station. The pilot channel produces a signal, modulated with a Walsh code of 0, that transmits at all times by the cell site on each active forward CDMA channel. The Pilot channel: is needed to lock onto other channels on same RF carrier. is used to measure signal strength in support of handoff
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This note was uploaded on 08/08/2011 for the course CS 310 taught by Professor Aartisingh during the Spring '11 term at National Institute of Technology, Calicut.

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CDMA Channels Structure - Overview of CDMA Channels As is...

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