An Automatically Controlled Predistorter for Multilevel Quadrature Amplitude Modulation

In digital microwave transmission, the nonlinear characteristics in a high power amplifier, such as a TWT (traveling-wave tube) inhibit efficient output use. This note introduces a new predistorter control technique, and assesses the nonlinear compensation capability of a third-order predistorter incorporating this technique. Concerning 16-QAM (quadrature amplitude modulation) a 10 dB reduction in out-of-band emission and larger than 8 dB improvement with respect to symbol error rate can be achieved at 3 dB TWT average output power backoff.