| Power amplifiers are essential components in communication systems and are inherently nonlinear. The nonlinearity creates spectral growth (broadening) beyond the signal bandwidth, which interferes with adjacent channels. It also causes distortions within the signal bandwidth, which decreases the bit error rate at the receiver. Newer transmission formats, such as wideband code division multiple access (WCDMA) or orthogonal frequency division multiplexing (OFDM), are especially vulnerable to the nonlinear distortions due to their high peak-to-average power ratios (PAPRs). If we simply back-off the input signal to achieve the linearity required for the power amplifier, the power amplifier efficiency will be very low for high PAPR signals. Another choice is to linearize a nonlinear power amplifier so that overall we have a linear and reasonably efficient device.Based on the complete and deep study of radio power amplifier, this dissertation focuses on predistortion technique, one of the most cost effective ways among all linearization techniques. Main achievements are as follows: An effective electric circuit is proposed, This design proposition of analogue predistortion which is simple and low-cost has been utilized successfully in a mobile communications optimization product, and the analogue predistorter will also be able to be applied in gapfillers of digital television terrestrial network;The research on digital predistortion system concentres on adaptive algorithms, this paper proposes an improved successive substitution method. The simulation results prove that the new algorithm has more advantages compared with the original algorithm. What's more, a new RLS algorithm of adaptive filter theory is also applied in the digital predistortion system. |
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