Autocorrelation analysis of spectral regrowth generated by nonlinear circuits in wireless communication systems

Modern wireless communication systems utilize sophisticated modulation techniques to achieve higher data rates or improvements in overall system capacity. Amplitude variations in the modulated waveforms give rise to distortion products when applied to nonlinear components of the transmitter. Distortion emissions from mobile handsets are limited to prevent system degradation and interference to users in adjacent cells. However, there is an inherent tradeoff between transmitter efficiency and the amount of distortion produced by the power amplifier. Thus when designing an amplifier or transmitter component, it is important to quickly determine the distortion generated by the circuit when a modulated signal is applied.; Estimation of spectral regrowth generated by a digitally modulated carrier passed through a nonlinear RF circuit is analyzed using a formulation of the output autocorrelation function. The estimation is based on developing an analytical expression for the output power spectrum when the nonlinearity is modeled a complex power series model extracted from measured amplitude-to-amplitude (AM-AM) and amplitude-to-phase (AM-PM) characteristics. Comparisons are presented of measured versus predicted ACPR values for a CDMA amplifier.; A statistical technique is presented for the characterization of spectral regrowth at the output of a nonlinear amplifier driven by a digitally modulated carrier in a digital radio system. The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the quadrature input signal transformed by a behavioral model of the amplifier. The amplifier model, a baseband equivalent representation, is derived from a complex radio-frequency envelope model, which itself is developed from readily available measured or simulated amplitude modulation-amplitude modulation and amplitude modulation-phase modulation data. The technique is used in evaluating the spectral regrowth for a CDMA signal.