In what ways could we improve cellular-massive-MIMO based 5G? Well, to start with, this technology is already pretty good. But coverage holes, and difficulties to send multiple streams to multi-antenna users because of insufficient channel rank, remain issues. Perhaps the ultimate solution is distributed MIMO (also known as cell-free massive MIMO). But while this is at heart a powerful technology, installing backhaul seems dreadfully expensive, and achieving accurate phase-alignment for coherent multiuser beamforming on downlink is a difficult technical problem. Another option is RIS – but the ..read more

I started analyzing reconfigurable intelligent surfaces (RISs) in 2019, just when the hype began in the communication community. I was mostly interested in understanding the fundamentals of this technology because some claims that I found in papers were too good to be true. In 2020, we summarized our thoughts in the paper “Reconfigurable Intelligent Surfaces: Three Myths and Two Critical Questions,” which corrected three misconceptions that flourished then. More importantly, we identified two open research problems that we found particularly important to solve if the RIS technology should beco ..read more

The academic research into wireless communication is fast-paced, enabled by the fact that one can write a paper in just a few months if it only involves mathematical derivations and computer simulations. This feature can be a strength when it comes to identifying new concepts and developing know-how, but it also leaves a lot of research results unproven in the real world. Even if the math is correct, the underpinning models simplify the physical world. The models can have served us well in the past, but might have to be refined to keep delivering accurate insights as wireless technology become ..read more

I receive many questions from students and researchers on social media, including this blog, YouTube, and ResearchGate. I do my best to answer such questions while commuting to work or having few minutes between meetings. I receive some questions quite frequently, making it worth creating videos where I try to answer them once and for all. Below, you can find the first video in that series, and it answers the question: How many beams can you send from a MIMO array? As you will notice when watching the video, we obtain a more appropriate question if “can you send” is replaced by “do you want to ..read more

We have now released the 39th episode of the podcast Wireless Future. It has the following abstract: Massive bandwidths are available in the sub-terahertz bands, but the coverage of a cellular network exploiting those frequencies will be spotty. The 6GTandem project tries to circumvent this issue by developing a dual-frequency system architecture that jointly uses the sub-6 GHz and sub-THz bands. In this episode, Erik G. Larsson and Emil Björnson are visited by Dr. Parisa Aghdam, Technical Lead of 6GTandem and Research Manager at Ericsson. The discussion starts with potential use cases, such ..read more

The research community often praises reconfigurable intelligent surfaces (RISs) as a transformative technology. By controlling parts of wireless propagation channels, we can improve the bit rates by increasing the received signal strength, mitigating interference, enhancing channel ranks, etc. The potential benefits RISs can bring to wireless networks are now well documented, and several of them have also been demonstrated experimentally. However, the RIS technology also introduces several practical complications that one must be mindful of. In this blog post, I will give two examples of the ..read more

The way that mobile communication networks are designed changed dramatically with the advent of 5G. In the past, it was all about utilizing large bandwidths and deploying many base stations. Nowadays, we are instead equipping each base station and smartphone with multiple antennas, which enables us to use signal processing algorithms to improve signal strength, enhance reliability, and send more data of the same spectrum by controlling the spatial direction of each signal layer. In essence, we refine the hardware and algorithms instead of deploying more infrastructure and requiring more signal ..read more

We have now released the 38th episode of the podcast Wireless Future. It has the following abstract: Many topics are studied within the 6G research community, from hardware design to algorithms, protocols, and services. Erik G. Larsson and Emil Björnson recently attended the ELLIIT 6G Symposium in Lund, Sweden. In this episode, they discuss ten things that they learned from listening to the keynote speeches. The topics span from integrated sensing, positioning, and localization via machine-learning applications in communications to fundamental communication theory, such as circuits for univer ..read more

The golden frequencies for wireless access are in the band below 6 GHz. Why are these frequencies so valuable? The reasons, of course, are rooted in the physics. First, the wavelength is short enough that a (numerically) large array has an attractive form factor, enabling spatial multiplexing even from a single antenna panel. At the same time, the wavelength is large enough that a sufficiently large aperture can be obtained with a reasonable number of antennas – which, in turn, directly translates into a favorable link budget and high ..read more

We have now released the 37th episode of the podcast Wireless Future. It has the following abstract: We celebrate the three-year anniversary of the podcast with a live recording from the Wireless Future Symposium that was held in September 2023. A panel of experts answered questions that we received on social media. Liesbet Van der Perre (KU Leuven) discusses the future of wireless Internet-of-Things, Fredrik Tufvesson (Lund University) explains new channel properties at higher frequencies, Jakob Hoydis (NVIDIA) describes differentiable ray-tracing and its connection to machine learning, Deni ..read more