We have now released the 16th episode of the podcast Wireless Future, with the following abstract:
The research community’s hype around 5G has quickly shifted to hyping the next big thing: 6G. This raises many questions: Did 5G become as revolutionary as previously claimed? Which physical-layer aspects remain to be improved in 6G? To discuss these things, Erik G. Larsson and Emil Björnson are visited by Professor Angel Lozano, author of the seminal papers “What will 5G be?” and “Is the PHY layer dead?”. The conversation covers the practical and physical limits in communications, the role of machine learning, the relation between academia and industry, and whether we have got lost in asymptotic analysis. Please visit Angel’s website.
You can watch the video podcast on YouTube:
You can listen to the audio-only podcast at the following places:
We have now released the 15th episode of the podcast Wireless Future, with the following abstract:
Machine learning builds on the collection and processing of data. Since the data often are collected by mobile phones or internet-of-things devices, they must be transferred wirelessly to enable machine learning. In this episode, Emil Björnson and Erik G. Larsson are visited by Carlo Fischione, a Professor at the KTH Royal Institute of Technology. The conversation circles around distributed machine learning and how the wireless technology can evolve to support learning applications via network slicing, information-aware communication, and over-the-air computation. To learn more, they recommend the article “Wireless for Machine Learning”. Please visit Carlo’s website and the Machine Learning for Communications ETI website.
You can watch the video podcast on YouTube:
You can listen to the audio-only podcast at the following places:
We have now released the 14th episode of the podcast Wireless Future, with the following abstract:
In this episode, Emil Björnson and Erik G. Larsson answer questions from the listeners on the topics of distributed MIMO, THz communications, and non-orthogonal multiple access (NOMA). Some examples are: Is cell-free massive MIMO really a game-changer? What would be its first use case? Can visible light communications be used to reach 1 terabit/s? Will Massive MIMO have a role to play in THz communications? What kind of synchronization and power constraints appear in NOMA systems? Please continue asking questions and we might answer them in later episodes!
You can watch the video podcast on YouTube:
You can listen to the audio-only podcast at the following places:
We have now released the 13th episode of the podcast Wireless Future, with the following abstract:
Wireless devices normally connect to a single access point, deployed at one location. The access points are deployed sparsely to create large cell regions, each controlled by the nearest access point. This architecture was conceived for mobile telephony and has been inherited by today’s networks, even if those mainly transfer wireless data. However, future wireless networks might be organized entirely differently. In this episode, Erik G. Larsson and Emil Björnson discuss how one can create cell-free networks consisting of distributed massive MIMO arrays. The vision is that each user will be surrounded by small access points that cooperate to provide uniformly high service quality. The conversation covers the key benefits, how the network architecture can be evolved to support the new technology, and what the main research challenges are. To learn more, they recommend the article “Ubiquitous Cell-Free Massive MIMO Communications” and the new book “Foundations of User-Centric Cell-Free Massive MIMO”.
You can watch the video podcast on YouTube:
You can listen to the audio-only podcast at the following places:
Mobile networks are divided into semi-autonomous cells. It is essentially a divide-and-conquer approach to network operation, where each cell becomes simple to operate and the reuse of radio resources over the cells can be planned in advance. This network structure was proposed already in the 1950s and has been vital for the wide-spread adoption of mobile network technology. However, the weaknesses of the cellular architecture have become increasingly apparent as mobile data has replaced voice calls as the main type of traffic. While the peak data rates are high in contemporary networks, the user-guaranteed rates are very modest, due to the largest pathloss variations and inter-cell interference that is inherent in the cellular architecture.
A promising solution to these issues is to leave the cellular paradigm behind and create a new network architecture that is free from cells. This vision is called Cell-free Massive MIMO.
This is a technology that essentially combines three main components that have been previously considered separately: 1) the efficient physical-layer operation with many antennas that enabled wide-spread adoption of Massive MIMO in cellular networks; 2) the vision of deploying many access points close to the users, to create a reality where users are surrounded by access points instead of the opposite; 3) the joint transmission and reception from distributed access points, that have been analyzed under many names over the last two decades, including coordinated multipoint (CoMP).
This blog post is about the first book on the topic: “Foundations of User-Centric Cell-Free Massive MIMO” by Özlem Tuğfe Demir, Emil Björnson, and Luca Sanguinetti. We provide the historical background, theoretical foundations, and state-of-the-art signal processing algorithms. The book is 300 pages long and is accompanied by a GitHub repository with all the simulation code. We hope that this book will serve as the starting point for much further research. The last section of the book outlines many future research directions.
NOW publishers is offering a free PDF until April 2, 2021. To obtain it, go to the book’s website, create a free account, and then click on download. For the same period, they are offering printed copies for the special prize of $40 (including non-trackable shipping). To purchase the printed version, go to the secure Order Form and use the Promotion Code 584793.
Since 5G is designed to be future-proof and enable decoupling of the control signaling and data transmissions, I believe that the 5G networks will become increasingly cell-free during this decade, while beyond 5G networks will embrace the cell-free architecture from the outset.
We have now released the twelfth episode of the podcast Wireless Future, with the following abstract:
The data that flows through wireless networks are protected by encryption, but there are anyway privacy and security issues inherent in wireless technologies. In this episode, Erik G. Larsson and Emil Björnson are visited by Panos Papadimitratos, a Professor at the KTH Royal Institute of Technology. The conversation focuses on location privacy and spoofing; what the practical issues are, what countermeasures exist, and which tradeoffs must be made when building wireless technologies.
You can watch the video podcast on YouTube:
You can listen to the audio-only podcast at the following places:
Consider the following simulation example, where the respective path losses are indicated:
Case 1 represents a weak direct path and Case 2 represents a direct path that is of the same strength as the paths to/from the RIS. When adding more and more elements in the RIS, the spectral efficiency behaves as follows (“baseline” is the case without RIS):
The RIS can improve the performance by a lot in Case 1 (weak direct channel), while the improvements are mediocre in Case 2 (stronger direct channel). (You can download the simulation code here.) Hence, we should utilize an RIS to improve the SNR when the channel quality is otherwise low. This might not be so surprising but it means that we must deploy the RIS strategically to get good channels both to and from it.
Criterion 2: Line-of-sight channels to and from the RIS
A more subtle point is that we should deploy the RIS to have line-of-sight channels to the transmitter and the receiver. There are three main reasons for this:
Criterion 1 is likely to be satisfied, at least if the direct path is non-line-of-sight.
The RIS can be used over wideband channels (e.g., tens of MHz) since most of the energy comes from one angular direction and should be delivered in one angular direction.
The channel estimation can be vastly simplified by exploiting angular sparsity.
The following paper contains recent experimental results that demonstrate the feasibility of the RIS technology: “RIS-Aided Wireless Communications: Prototyping, Adaptive Beamforming, and Indoor/Outdoor Field Trials“. The paper describes outdoor field trials over 50 and 500 meters in scenarios satisfying the two conditions above. The paper proposes an algorithm for RIS configuration that is explicitly utilizing the angular channel sparsity and provided large SNR improvements.
I talk more about these measurements and underlying theory in the following video (which is also based on my new tutorial article):
