Several graphs are presented to illustrate the effect of the IF bandwidth in the presence of Doppler spread and frequency-selective fading. Go Back To Top 11. These methods are highly sensitive to transmitter power amplifier nonlinearities. The linearity of a power amplifer can be improved by using an adaptive nonlinear predistorter. A modified version of a previously reported polynomial lineariser is presented whichhas a faster rate of convergence by an order of magnitude.
Faster convergence is achieved using postdistorter polynomial functions of two variables.
It is shown analytically that the gain and phase errors in the output demodulator used for adaptation of the predistorter simply result in a phase offset equal to the phase error. Adaptability of the proposed lineariser with changes in the power amplifier, predistorter quadrature modulator and the output demodulator aare tested. Results show that the lineariser can adapt to these changes. The effect of the rotation of the demodulated output signal phase on convergence is studied. It is shown that the optimum value for this rotation is in the range of 15 to 70i .