Design of signal component separator in mode-multiplexing LINC transmitter using stochastic analysis

A mode-multiplexing transmitter using linear amplification with a nonlinear component (LINC) mode and a balanced mode is analysed. A threshold value of the input signal for mode changing and a constant envelope signal level for the LINC mode in the signal component separator (SCS) are critical variables determining the power efficiency and nonlinear distortion of the mode-multiplexing transmitter. These variables change the probability density function (PDF) of the transmitted signal. The average power efficiencies for power amplifier (PA) and combiner are extracted respectively for the digitally modulated input signal using stochastic analysis. A method to select optimal values of the variables is proposed considering trade-off between efficiency and linearity. A scheme to design a SCS considering the proposed stochastic analysis is suggested. The mode-multiplexing transmitter is designed for WCDMA signal, and efficiency and adjacent channel power ratio (ACPR) are extracted. The result shows that the mode-multiplexing transmitter with the suggested method can improve average power efficiency by 17%, and degrades ACPR only by 4 dBc comparing with the conventional LINC.