Adaptive digital predistortion for power amplifier linearization
Author(s)
Advisor
Atalar, AbdullahDate
2008Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
High power amplification of linear modulation schemes which exhibit fluctuating
envelopes, invariably leads to the generation of distortion and intermodulation
products. In order to avoid these effects, maintaining both power and spectral
efficiency, it is necessary to use linearization techniques. By using linearization
techniques, the amplifier can be operated near the saturation with good efficiency
and linearity.
The technique proposed here is predistortion based on a look-up table (LUT)
method using input and output signal envelopes. The predistortion is implemented
using a LUT and an address generation block that selects the appropriate
coefficient from the LUT, given the magnitude of the input signal. The testing
of the predistorter is done by using a baseband system model which consists of
a 16-QAM modulator, an upsampler, a raised cosine filter, the predistorter and
a baseband behavioural amplifier model. The performance of the predistorter
with a new LUT update method is evaluated in terms of power efficiency and
spectrum efficiency. MATLAB simulations show that to obtain up to 25-30 dB
improvement in power spectrum is possible and sufficiently large LUT size is
needed to reduce the background noise level. Furthermore, the performance of
the predistorter in the case of an amplifier with memory is also investigated.
The algorithms have been implemented on an FPGA chip. The performance of
the system is as predicted in MATLAB simulations.
Keywords
Aptive Digital PredistortionLook-up Table Predistortion
Linearization
Amplifier Nonlinearity
Spectrum Efficiency
FPGA