Baseband Predistortion Linearization of Power Amplifier

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Baseband Predistortion Linearization of Power
Amplifier

• Lei Ding, G. Tong Zhou
• CSIP seminar, April 20

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Outline

• Motivation
• Power Amplifier Modeling
• Predistortion
• RF/DSP Testbed
• Summary

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Motivation

• Recent wireless applications prefer linear
  modulation schemes
• CDMA(IS-95) QPSK
• OFDM QAM
• Better spectral efficiency, need linear power
  amplifier, low power efficiency
• High efficiency nonlinear power amplifier
• Spectral regrowth in adjacent channels

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Power Amplifier Modeling

• Memoryless nonlinear modeling

PA
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Example
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Predistortion
PA
Pred
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Example
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Example
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Adaptive Predistortion

• In real applications, PAs AM/AM and AM/PM are
  not available and are changing with time.
• Adaptive predistortion is needed.

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RF/DSP Testbed
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Table-based adaptive pred.
Given a block of baseband samples, rn rn
1-(k-n)CrEm/Nr ?n ?n
1-(k-n)C?Ep/Nr rn1 rn1 (k-n)CrEm/Nr
?n1 ?n1 (k-n)C?Ep/Nr Where Cr and
C? are constants to control convergence rate and
stability, Nr is the total number of samples
falling into the same amplitude interval rn
rn1.
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Results
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Results
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Results
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Summary

• We developed a flexible RF/DSP testbed, which
  allows us to test a variety of algorithms and RF
  devices.
• We implemented a table-based predistortion
  linearization algorithm and achieved around 9 dB
  suppression on spectral regrowth.
• Next, we will carry out real-time
  implementation and include memory effects in the
  predistortion algorithms