Skip to content

Advertisement

Open Access

Prototype Implementation of Two Efficient Low-Complexity Digital Predistortion Algorithms

  • Ernst Aschbacher1, 2Email author,
  • Mei Yen Cheong3,
  • Peter Brunmayr2,
  • Markus Rupp2 and
  • Timo I. Laakso3, 4
EURASIP Journal on Advances in Signal Processing20072008:473182

https://doi.org/10.1155/2008/473182

Received: 1 February 2007

Accepted: 16 September 2007

Published: 11 November 2007

Abstract

Predistortion (PD) lineariser for microwave power amplifiers (PAs) is an important topic of research. With larger and larger bandwidth as it appears today in modern WiMax standards as well as in multichannel base stations for 3GPP standards, the relatively simple nonlinear effect of a PA becomes a complex memory-including function, severely distorting the output signal. In this contribution, two digital PD algorithms are investigated for the linearisation of microwave PAs in mobile communications. The first one is an efficient and low-complexity algorithm based on a memoryless model, called the simplicial canonical piecewise linear (SCPWL) function that describes the static nonlinear characteristic of the PA. The second algorithm is more general, approximating the pre-inverse filter of a nonlinear PA iteratively using a Volterra model. The first simpler algorithm is suitable for compensation of amplitude compression and amplitude-to-phase conversion, for example, in mobile units with relatively small bandwidths. The second algorithm can be used to linearise PAs operating with larger bandwidths, thus exhibiting memory effects, for example, in multichannel base stations. A measurement testbed which includes a transmitter-receiver chain with a microwave PA is built for testing and prototyping of the proposed PD algorithms. In the testing phase, the PD algorithms are implemented using MATLAB (floating-point representation) and tested in record-and-playback mode. The iterative PD algorithm is then implemented on a Field Programmable Gate Array (FPGA) using fixed-point representation. The FPGA implementation allows the pre-inverse filter to be tested in a real-time mode. Measurement results show excellent linearisation capabilities of both the proposed algorithms in terms of adjacent channel power suppression. It is also shown that the fixed-point FPGA implementation of the iterative algorithm performs as well as the floating-point implementation.

Keywords

Field Programmable Gate ArrayField Programmable Gate Array Implementation3GPP StandardAmplitude CompressionWiMax Standard

Publisher note

To access the full article, please see PDF.

Authors’ Affiliations

(1)
MED-EL Medical Electronics, Research and Developement, Innsbruck, Austria
(2)
Institute of Communications and Radio-Frequency Engineering, Vienna University of Technology, Vienna, Austria
(3)
Signal Processing Laboratory, Helsinki University of Technology, Espoo, Finland
(4)
National Board of Patents and Registration of Finland, Helsinki, Finland

Copyright

© Ernst Aschbacher et al. 2008

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Advertisement