Abstract
This paper studies the performance of a memoryless power amplifier (PA) linearization technique based on a probabilistic approach. This technique employs a nonparametric method to derive a predistorter function, which does not need any parametric modeling and explicit parameter estimation. It only needs to calculate a probabilistic cumulative distribution function (CDF) and a quantile function (an inverse function of the CDF). Histogram and order statistic methods are proposed to perform the calculation. A rigorous analytic formula is derived for the inter-modulation product power (IMPP) of the PA output signal when a finite number of samples as well as a finite number of bins are used to calculate the CDF and the quantile function. The analytic results show that, with the probabilistic-based technique, the IMPP approaches zero as the number of samples approaches infinity and the bin width approaches zero.
Computer simulations are utilized to verify the theoretical analysis and to compare the performance of the probabilistic-based linearization technique with those of other memoryless PA linearization techniques, while a prototype experiment is carried out to demonstrate its performance in a practical application. Results show that the technique can accurately determine the predistortion function that effectively compensates for the nonlinearity in the PA, and that it achieves a much better linearization performance compared to other existing methods, especially in the presence of a loop delay in the feedback circuit.
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Notes
Note that the probabilistic-based technique estimates the PD function from the CDF of the PA output signal. As the CDF calculation is operated in the statistical domain, the probabilistic-based technique allows the use of a very low sampling rate (lower than the Nyquist sampling rate) in the A/D conversion regardless of the signal bandwidth.
Abbreviations
- AIMPP:
-
Asymptotic inter-modulation product power
- AM/AM:
-
Amplitude-to-amplitude
- AM/PM:
-
Amplitude-to-phase
- CDF:
-
Cumulative distribution function
- PDF:
-
Probability density function
- IMPP:
-
Inter-modulation product power
- IMD:
-
Inter-modulation distortion
- PD:
-
Predistorter
- E[⋅]:
-
Mathematical expectation
- \(\operatorname{Var}{[\cdot]}\) :
-
Variance of random variable
- \(\operatorname{Cov}{[\cdot,\cdot]}\) :
-
Covariance of two random variables
- f X (⋅):
-
PDF of PA input signal
- F X (⋅):
-
CDF of PA input signal
- f Y (⋅):
-
PDF of PA output signal
- F Y (⋅):
-
CDF of PA output signal
- N x :
-
Number of PA input signal samples
- N y :
-
Number of PA output signal samples
- \(\mathcal{G}(\cdot)\) :
-
PA transfer function
- \(\mathcal{G}_{A}(\cdot)\) :
-
AM/AM conversion function of PA
- \(\mathcal{G}_{\varPhi}(\cdot)\) :
-
AM/PM conversion function of PA
- \(\mathcal{H}(\cdot)\) :
-
Predistorter function
- \(\mathcal{H}_{A}(\cdot)\) :
-
AM/AM conversion function of predistorter
- \(\mathcal{H}_{\varPhi}(\cdot)\) :
-
AM/PM conversion function of predistorter
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Acknowledgements
The authors would like to thank the anonymous reviewers for their comments and constructive suggestions, which have been very helpful in improving this paper. The authors would also like to acknowledge Dan Drolet, François Cloutier, and Dhiraj Gangaraju of the Communications Research Centre Canada for their contributions to the prototype development and experiment.
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Zhu, Z., Huang, X. & Caron, M. Theoretical and Experimental Studies of a Probabilistic-Based Memoryless PA Linearization Technique. Circuits Syst Signal Process 32, 3031–3057 (2013). https://doi.org/10.1007/s00034-013-9612-5
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DOI: https://doi.org/10.1007/s00034-013-9612-5