Modeling and Compensation of Nonlinear Distortion in Multi-Antenna RF Transmitters
Doktorsavhandling, 2018

Multi-antenna systems are utilized as a way to increase spectral efficiency in wireless communications. In a transmitter, the use of several parallel transmit paths and antennas increases system complexity and cost. Cost-efficient solutions, which employ active antenna arrays and avoid expensive isolators, are therefore preferred. However, such solutions are vulnerable to crosstalk due to mutual coupling between the antennas, and impedance mismatches between amplifiers and antennas. Combined with the nonlinear behavior of the power amplifiers, these effects cause nonlinear distortion, which deteriorates the quality of the transmitted signals and can prevent the transmitter from meeting standard requirements and fulfilling spectrum regulations. Analysis, assessment and, if necessary, compensation of nonlinear distortion are therefore essential for the design of multi-antenna transmitters.
In this thesis, a technique for modeling and predicting nonlinear distortion in multi-antenna transmitters is presented. With this technique, the output of every individual transmit path, as well as the radiated far-field of the transmitter can be predicted with low computational effort. The technique connects models of the individually characterized transmitter components. It can be used to investigate and compare the effects of different power amplifier and antenna array designs at early design stages without complicated and expensive measurements.
Furthermore, a digital predistortion technique for compensating nonlinear distortion in multi-antenna transmitters is presented. Digital predistortion is commonly used in transmitters to compensate for undesired nonlinear hardware effects. The proposed solution combines a linear function block with dual-input predistorters. The complexity is reduced compared to existing techniques, which require highly complex multivariate predistorter functions.
Finally, a technique for identifying multi-antenna transmitter models and predistorters from over-the-air measurements using only a small set of observation receivers is presented. Conventional techniques require a dedicated observation receiver in every transmitter path, or one or more observation receivers that are shared by several paths in a time-interleaved manner. With the proposed technique, each receiver is used to observe several transmitter paths simultaneously. Compared to conventional techniques, hardware cost and complexity can be reduced with this approach.
In summary, the signal processing techniques presented in this thesis enable a simplified, low-cost design process of multi-antenna transmitters. The proposed algorithms allow for feasible, low-complexity implementations of both digital and analog hardware even for systems with many antennas, thereby facilitating the development of future generations of wireless communication systems.

multi-antenna transmitter

behavioral modeling

over-the-air characterization

digital predistortion

antenna crosstalk


power amplifier

EB lecture hall, Hörsalsvägen 11, Chalmers
Opponent: Prof. Pere Lluis Gilabert Pinal, Department of Signal Theory and Communications, Universitat Politècnica de Catalunya, Barcelona, Spain


Katharina Hausmair

Chalmers, Elektroteknik, Kommunikationssystem, informationsteori och antenner, Kommunikationssystem

Prediction of Nonlinear Distortion in Wideband Active Antenna Arrays

IEEE Transactions on Microwave Theory and Techniques,; Vol. 65(2017)p. 4550-4563

Artikel i vetenskaplig tidskrift

Digital Predistortion for Multi-Antenna Transmitters Affected by Antenna Crosstalk

IEEE Transactions on Microwave Theory and Techniques,; Vol. 66(2018)p. 1524-1535

Artikel i vetenskaplig tidskrift

Hausmair, K., Gustavsson, U., Fager, C., Eriksson, T. Over-the-Air Linearization of Multi-Antenna Transmitters Affected by Antenna Crosstalk

The research presented in this thesis contributes to the development and implementation of feasible and sustainable multi-antenna transmitters. Transmitters with many antennas are used in modern wireless communication systems to provide reliable transmission and high data rates for large numbers users.
We have developed a method to predict and analyze the performance of multi-antenna transmitters. Usually, such an analysis requires expensive and time-consuming measurements and can only be done once at least a prototype of the transmitter has been built. Our method requires simple measurements, is easy to implement, and can be used at an early design stage. Therefore, our work helps to make the design of transmitters less complicated, faster, and cheaper.
Furthermore, we have designed algorithms that make it possible to build multi-antenna transmitters with fewer and cheaper hardware components. The transmission signals in wireless communication systems have to comply to strictly defined regulations and standards. Transmitters are built with expensive and complex components to meet these regulations, while at the same time achieving high energy efficiency. Our algorithms make it possible to create high quality transmission signals with fewer and less complicated hardware components and, most importantly, without compromising on energy efficiency.


Informations- och kommunikationsteknik

Nanovetenskap och nanoteknik




Annan elektroteknik och elektronik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4369


Chalmers tekniska högskola

EB lecture hall, Hörsalsvägen 11, Chalmers

Opponent: Prof. Pere Lluis Gilabert Pinal, Department of Signal Theory and Communications, Universitat Politècnica de Catalunya, Barcelona, Spain