Factors Affecting Spectral Regrowth in DS-CDMA Signals Due to PD-HPA Nonlinear Distortion

When passed through a high power amplifier (HPA), downlink direct sequence-code division multiple access (DS- CDMA) signals result in additional out-of-band emissions, or spectral regrowth, which could affect adjacent channels. In this paper, we explore which characteristics of the input CDMA signal, in relation to the amplifier characteristics, contribute to spectral regrowth. These characteristics represent the key features of the signal´s interplay with the HPA, which give the system designer/operator the ability to minimize the spectral regrowth in the transmitted signal. The amplifier chain considered in this paper includes a predistorter (PD), namely PD- HPA. Assuming that the baseband CDMA signal is characterized as a band-limited Gaussian process, we develop analytic expressions for the characteristics contributing to spectral regrowth. Finally, simulation experiments are presented to demonstrate the effect of the established signal characteristics on spectral regrowth.