| This thesis addresses the problem of adaptive linearization of high power amplifiers. The technique considered here is independent of the modulation scheme and is suitable for narrow band signals. In practice, it is applied at base band. In this technique, the low pass equivalent envelope of the modulated signal is distorted prior to amplification (i.e., predistorted), such that the amplified signal is a linear version of the modulated signal. The predistortion is achieved by mapping the modulated signal to a distorted signal using table lookup functions. The mapping is done using the polar representation of the low pass complex envelope of the modulated signal since the amplifier's nonlinearities are a function of the amplitude. The adaptation of the table lookup functions are based on the Least Mean Squared (LMS) algorithm. The adaptation technique is analyzed and tested on a Quadrature Phase Shift Keying (QPSK) modulation system using computer simulation. The results obtained indicate that the technique provides excellent performance. In addition, the technique enjoys the advantages of implementation simplicity, low memory and processing requirements and fast convergence. (Abstract shortened by UMI.). |
