In this paper, we present a class of nonlinear signal-processing schemes to reduce the envelope fluctuations in the downlink transmission within code-division multiple-access (CDMA) systems. These schemes are compatible with conventional CDMA receivers since they just require some modifications at the transmitter side. The proposed transmitter structure includes a nonlinear operation in the time-domain followed by a linear frequency-domain filtering operation. We also include a semi-analytical statistical characterization of the transmitted signals, which takes advantage of the Gaussian-like nature of CDMA signals with a high number of users. This characterization is used for an analytical performance evaluation of the proposed techniques. A set of performance results is presented showing that we can reduce significantly the envelope fluctuations of the transmitted signals, while maintaining the spectral occupation of the corresponding conventional CDMA signals. Moreover, the performance degradation due to the nonlinear distortion effects on the transmitted signals can be kept relatively low.

In this paper we develop signal processing techniques to reduce the PMEPR for downlink transmission (i.e., from the BS to the mobile terminals) within synchronous CDMA systems using orthogonal spreading codes. These techniques are compatible with conventional CDMA receivers since just require some modifications at the transmitter side. The proposed transmitter structure includes a nonlinear operation in the time-domain followed by a linear, frequency-domain filtering operation. We also include a semi-analytical statistical characterization of the transmitted signals, which takes advantage of the Gaussian-like nature of CDMA signals with a high number of users. This characterization is used for an analytical performance evaluation of the proposed techniques. Our performance results show that we can reduce significantly the PMEPR of the transmitted signals, while maintaining the spectral occupation of the corresponding conventional CDMA signals.