High Efficient And Linearized Techniques For Power Amplifier In High Peak-to-Average-Power Ratio System

OFDM is one of the key technologies in the next generation communication systems, and it has been widely used as it has the advantages of anti-multipath fading and high spectrum efficiency. But OFDM has some huge disadvantages, one of which is high Peak-to-Average-Power Ratio problem. The power of peak signal is higher than that of average signal, which makes OFDM signal very sensitive to the nonlinear and saturation distortion of power amplifier (PA). In another hand, when the communication system is wideband, the distortion of PA becomes memory. The instantaneous output signal of PA has the relationship not only with the instantaneous input signal but also with the previous signals. Therefore, the existence of PA's memory nonlinear distortion makes huge negative effect to OFDM system.A frequency domain predistorter based on the special modulation scheme of OFDM is proposed to compensate the memory nonlinear distortion of PA firstly. Since the memory distortion can be seen as the frequency-selective distortion and the frequencies of sub-carriers of OFDM are different from each other, the signal in each sub-carrier can be predistorted which would reach the goal of memory nonlinear distortion elimination. Secondly, we connect the frequency domain and time domain predistorter together. A frequency-time domain combination predistorter is proposed, which has better BER performance than frequency domain predistorter. At last, based on Filter Look-Up Table method, we propose a more common Simplified Filter Look Up Table method, which has simpler structure and higher convergence speed than the original one.To compensate the saturation distortion of PA, A parallel multi-PA structure is proposed, which can eliminate the nonlinear and saturation distortion. Firstly, we propose a combined two PAs structure for the Class B amplifier, which extends the dynamic range by cutting the signal into two segments and eliminates the nonlinear distortion due to the inherent characteristic of PA. Secondly, we extend the multiple PA structure to the Class AB amplifier, and propose a novel predistorter which can eliminate the memory, nonlinear and saturation distortion at the same time.Since the PA consumes a large part of energy consumption, the reduction of PA's energy cost can remarkably decrease the energy consumption of the total communication system. To solve the problem of low power efficiency of PA in the high peak-to-average-power ratio communication system, a novel structure is proposed in order to decrease the energy consumption and increase the power efficiency of PA. The high PAPR signal would be decomposed into several low PAPR branch signals, linearized and amplified in parallel. This structure could reduce the PAPR of branch signals and improve the power efficiency of PA. The simulation results indicate that the power efficiency will be remarkably increased.