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Computationally Efficient Algorithms for Multi-band Power Amplifier Linearization

10/2/2014

 

A. Khanifar | 2012 |

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PROBLEM STATEMENT
  •  In LTE the maximum BW of a single modulated carrier is <=20MHz 3GPP in Release 8/9
  • LTE-Advanced Rel-10 has provisions for aggregation of up to 5 DL carriers.
  • Two or more carriers can be aggregated to support wider transmission of up to100MHz 
  • Spectrum deployment can be contiguous or non-contiguous
  • Higher instantaneous BW may be required due to CA or infrastructure sharing and multi-band operations.
  • So wide instantaneous signal BW is the new challenge in infrastructure design.

A SIMPLIFIED TRANSISTOR MODEL
Picture
IMD GENERTION MECHANISM
Picture
THE ANALYSIS

Assuming a 3rd order non-linearity: 
Picture
If we have a two non-contiguous carriers of 1 and 2 where 2> 1
Picture
PA 3rd order nonlinearity given in generates the 6-terms in-band inter modulations components and these are grouped together to ease the analysis:

Picture
The 2nd batch of IMD terms are generated at 2 1- 2 and 2 2- 1
Picture
However in addition, the same IMD terms are replicated at carrier frequencies and given as:

Picture
Picture
POSSIBLE LINEARIZATION SCHEMES 
Open-loop linearization scheme:
Picture
PRACTICAL RESULTS
Picture
Picture
CONCLUSIONS
  • DPD Feedback processing bandwidth reduction is desirable as:
  • Amplitude variations can hinder broadband linearization Eliminates the need for equalizer and calibration requirements
  • A closer examination of IMD generation mechanism can lead to schemes where feedback BW can be significantly reduced
  • The technique would be particularly attractive in non-contiguous carrier 
configurations

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