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Amplify the good – A new concept for stable wireless network

For each new generation of network, there is a certain technology shift. How can existing wireless network technology be improved, and in what way can it meet the requirements that will be set on the future 6G network? Researchers at The Faculty of Engineering at Lund University suggest a new way of both enhancing and distributing wireless networks with the aid of repeaters.

Susanna Lönnqvist – Published 5 June 2025

Sara Willhammar. Photo.
"A functioning RA-MIMO network would mean a more stable network for many users in densely populated and densely built-up areas, with an equalized access to stable signal strength," says Sara Willhammar. Photo: Susanna Lönnqvist

Researchers active in the strategic research area ELLIIT, Excellence Center at Linköping - Lund in Information Technology, have been instrumental in developing the technology called massive MIMO (multiple-input multiple-output). In 2010 the researchers took a strictly academic idea and developed it into the standardized technology behind 5G today. Massive means that a large number, often hundreds, of antennas are deployed to both send and receive radio signals. This increases the capacity and signal strength of the network, so that numerous persons can use the network at the same time and within the same radio frequency, and with an energy efficiency better than 4G. Massive MIMO is a cornerstone for future 6G networks, and researchers are now investigating how the expansion of network could be done by distributing the multiple antennas.

"There is always a loss of signal in a wireless network, when a signal is sent over a distance that fades it. Large scale fading occurs by larger obstacles, such as big houses standing in the way of signal, and smaller fading when signals bounce in the physical environment. You can effectively reduce the smaller losses of signal with massive MIMO, but a more distributed network could remedy the large scale fading," says Sara Willhammar, postdoc at the Department of Electrical and Information Technology, and first author of the paper.

The concept the researchers now present is a technology being investigated for 6G networks. It is complementary to existing, distributed massive MIMO networks, and constitutes a simpler alternative to a D-MIMO set up (where D stands for distributed). D-MIMO has a central base unit that sends out radiosignals, and supports a certain number of network users, but then the antennas are distributed on a larger geographical area. The distance between the groups of antennas, the access points, and the end users end up shorter, the loss of signal is reduced and the network coverage is improved.

There are technical challenges with D-MIMO such as synchronization of the signals that the access points send and receive. The publication presents the idea of achieving D-MIMO by using network repeaters. Repeaters are simple units that have been used for a long time for enhancement of signal in e.g. Wifi networks. In repeater assisted MIMO, RA-MIMO, the repeaters would be used as active parts of the network. This would enable keeping the existing structures for 5G, and just adding repeaters in various places in a network.

"By using repeaters, the network is both amplified and improved. The signal bounces as if off a building wall, but through a repeater it is amplified instead of losing strength. We can amplify the signal along the signal path, which means a more stable network where more strong signals arrive at the receiver in a reliable way," says Sara Willhammar.

The researchers have discovered that network control is required to ensure that good signals are amplified, so that repeaters do not lead to an amplification of noise in the network. The next step in the research is to investigate the theoretical and practical limits of repeaters as active spreaders of signals, and what performance a repeater assisted network can achieve.

"A functioning RA-MIMO network would mean a more stable network for many users in densely populated and densely built-up areas, with an equalized access to stable signal strength," says Sara Willhammar.


The research is done in collaboration with Linköping University and Ericsson.

Sara Willhammar

Read more about Sara Willhammar's research in Lund University's research portal:
Sara Willhammar - Lund University

The publication is published in IEEE Communications Magazine and can be read here: Achieving Distributed MIMO Performance with Repeater-Assisted Cellular Massive MIMO | IEEE Journals & Magazine | IEEE Xplore

Sara Willhammar is a postdoc in Communication Engineering at LTH and is part of the networks: