Technique for Peak to Average Power Ratio Reduction suited for M-carrier WCDMA Base Station Transmitters

Network operators are allowed in some countries to transmit on adjacent frequency channels multiple WCDMA signals simultaneously. For this kind of application a base-station transmitter operating with a single analog up-conversion path shared by all WCDMA channels represents an attractive solution. In particular sharing a single power amplifier (PA) can largely reduce the costs of a base station. The M-carrier WCDMA signal has on the other hand the disadvantage of a large peak to average power ratio (PAPR). Efficient transmission of such wide band signals is limited by the non-linearity of the PA which causes interference within and outside the signal band. Without any measures this interference can be reduced only with a sufficient back off of the PA input. In order to achieve a better efficiency in the PA, in addition to pre-distortion methods, the signal PAPR should be reduced. This work proposes an algorithm which limits the PAPR without introducing additional out of band emission. Simulations for the WCDMA downlink signal for the case of a 3-carrier base-station indicates that the PAPR can be reduced by 4 dB ensuring still a secure margin on the maximum distortion allowed by the standard.