Energy efficiency analysis and improvements of MIMO cellular communications

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

L5, can be followed remotely (

Topic of the dissertation

Energy efficiency analysis and improvements of MIMO cellular communications

Doctoral candidate

Master of Science (Tech.) Olli Apilo

Faculty and unit

University of Oulu Graduate School, Faculty of Information Technology and Electrical Engineering, Centre for Wireless Communications - Networks and Systems

Subject of study

Communications Engineering


Professor Loutfi Nuaymi, Institut Mines Télécom / IMT Atlantique


Professor Aarne Mämmelä, VTT Technical Research Centre of Finland Ltd

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Energy efficiency analysis and improvements of MIMO cellular communications

Energy efficiency has been set as one of the main objectives for modern cellular networks. According to the 5G system requirements, energy consumption should not increase from the level of the current networks even though the amount of data in 5G networks is expected to be significantly higher. This thesis contributes in its part to the energy efficiency target by providing tools and methods for analyzing the link energy efficiency as well as proposing energy efficiency improvements for MIMO base stations. The majority of conventional macro base station input power is consumed by its power amplifiers (PAs).

In the first part of the thesis, the average efficiency of PAs is analyzed in power-adaptive spatial diversity systems and a new metric, PA input signal-to-noise ratio (SNR), is proposed. The new metric can capture the effect of non-ideal PA efficiency to the link performance analysis. It is shown with several examples how the benefit from power adaptation vanishes with low-efficiency PAs.

In the second part of the thesis, several energy efficiency improvements are proposed for modern cellular base stations. The focus is on the massive MIMO that is an emerging technology to improve the area spectral efficiency. The energy efficiency of massive MIMO base stations can be improved by adapting the number of active radio frequency (RF) chains according to the number of simultaneously served users. Two new methods are proposed for this kind of adaptive massive MIMO systems in this thesis. These methods have a potential to significantly improve the energy efficiency of a massive MIMO system.
Last updated: 25.11.2020