TAILIEUCHUNG - Adaptive WCDMA (P9)

CDMA network design BASIC SYSTEM DESIGN PHILOSOPHY In Code Division Multiple Access (CDMA) systems, the capacity increase is based on how much interference the desired signal can tolerate. Prior to despreading, the signal level of a desired signal is always below the interference level. All the users have to share the same radio channel. If one user takes more power than needed, then the others will suffer and the system capacity will be reduced. In analog and TDMA systems, the most important key element is the carrier to interference ratio (C/I ). There are two different kinds of C/I . One. | Adaptive WCDMA Theory And Practice. Savo G. Glisic Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-84825-1 9 CDMA network design BASIC SYSTEM DESIGN PHILOSOPHY In Code Division Multiple Access CDMA systems the capacity increase is based on how much interference the desired signal can tolerate. Prior to despreading the signal level of a desired signal is always below the interference level. All the users have to share the same radio channel. If one user takes more power than needed then the others will suffer and the system capacity will be reduced. In analog and TDMA systems the most important key element is the carrier to interference ratio C I . There are two different kinds of C I. One is the measured C I which is used to indicate the voice quality in the system. The higher the measured value the better it is. The other is called the specified C I s which is the required value for a specified performance of the cellular system. For example the C I s in the American mobile phone system AMPS is 18 dB. Since in analog and TDMA systems owing to the spectral and geographical separations the interference I is much lower than the received signal C sometimes we can utilize field strength meter to measure C to determine the coverage of each cell. The field strength meter therefore becomes a useful tool in designing the TDMA system. In CDMA all the traffic channels are served solely by a single radio channel in every cell. In an m-voice channel cell one of the m traffic channels is the desired channel and the remaining m 1 traffic channels are the interference channels. In this case at the receiver front end prior to despreading the interference is much stronger than the desired channel. C I is hard to obtain by using the signal strength meter that will receive more interference than the desired signal. The key elements in designing a CDMA system are different from the key element in designing a TDMA system. We can design the CDMA system based on the specified Eb I0 C

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