Digital Predistortion of Power Amplifiers for Wireless Applications

handchief581

再来一个DPD的博士论文
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. Digital predistortion is one of the most cost effective
ways among all linearization techniques. However, most of the existing designs treat the
power amplifier as a memoryless device. For wideband or high power applications, the
power amplifier exhibits memory effects, for which memoryless predistorters can achieve
only limited linearization performance.
In this dissertation, we propose novel predistorters and their parameter extraction algorithms.
We investigate a Hammerstein predistorter, a memory polynomial predistorter,
and a new combined model based predistorter. The Hammerstein predistorter is designed
specifically for power amplifiers that can be modeled as a Wiener system. The memory
polynomial predistorter can correct both the nonlinear distortions and the linear frequency
response that may exist in the power amplifier. It is a robust predistorter, which has demonstrated
good performance on several nonlinear system models. Real-time implementation
aspects of the memory polynomial predistorter are also investigated in the dissertation.
The new combined model includes the memory polynomial model and the Murray Hill
model, thus extending the predistorter’s ability to compensate for strong memory effects inthe power amplifier. Performance of the new model is demonstrated through experimental
measurements.
The predistorter models considered in this dissertation include both even- and oddorder
nonlinear terms. In the literature, most of the power amplifier and predistorter
models consider only the odd-order terms. Here, we show that it is beneficial to include
even-order nonlinear terms in both the baseband power amplifier and predistorter models.
By including these even-order nonlinear terms, we have a richer basis set, which offers
appreciable improvement.
The ideal performance of digital predistortion certainly relies on robust predistorters
that can completely compensate for the nonlinearities of the power amplifier. In reality,
however, the performance can also be affected by the analog imperfections in the transmitter,
which are introduced by the analog components; mostly analog filters and quadrature
modulators. There are two common configurations for the upconversion chain in the transmitter:
two-stage upconversion and direct upconversion. For a two-stage upconversion
transmitter, we design a band-limited equalizer to compensate for the frequency response
of the surface acoustic wave (SAW) filter which is usually employed in the IF stage. For a
direct upconversion transmitter, we develop a model to describe the frequency-dependent
gain/phase imbalance and dc offset. We then develop two methods to construct compensators
for the imbalance and dc offset. These compensation techniques help to correct for
the analog imperfections, which in turn improve the overall predistortion performance.

huatiantian

:victory::victory:

kevinwjs

qq

starwave

下载学习下技术。谢谢分享。

huatiantian

dddddddddddddddddddddddddd

wuchenghe

好，謝謝，下載中

cuky

非常感谢楼主的奉献

wc_buaa

顶一下！

lownbin

好东西啊
歇息

fklj

好像以前看过。确认一下