Wireless Future

Many textbook models of communication systems assume that the transmitter and receiver are synchronized in time, frequency, and phase. Achieving and maintaining such synchronization is an often-overlooked practical challenge. However, the importance of synchronization grows as we plan to use larger antenna arrays and distributed MIMO in 6G. In this episode, Emil Björnson and Erik G. Larsson discuss some fundamental principles of synchronization, including the underlying physical phenomena, pilot signaling for phase synchronization, and reciprocity calibration. We especially discuss how the seemingly simplest angular beamforming can be among the hardest features to support from a synchronization perspective, with a digital array. More technical details in the papers https://arxiv.org/abs/2304.05144 and

https://arxiv.org/abs/2401.11730

Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

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 as extended reality services in stadiums and connected factories. The conversation then focuses on hardware aspects, such as how to build a distributed antenna system using plastic microwave fibers and amplifiers so that sub-THz signals can be transmitted from many different locations. You can read more about the EU-funded project and its partners at https://horizon-6gtandem.eu/

Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

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 universal channel decoding and jamming protection. The expected 6G spectrum ranges, energy efficiency in base stations, and new use cases for electromagnetic materials are also covered. You can find slides from the symposium at https://elliit.se/news-and-events/focus-period-lund-2023/ Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

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, Deniz Gündüz (Imperial College London) presents his vision for how artificial intelligence will affect future wireless networks, Henk Wymeersch (Chalmers University of Technology) elaborates on the similarities and differences between communication and positioning, and Luca Sanguinetti (University of Pisa) demystifies holographic MIMO and its relation to near-field communications. Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

It is easy to get carried away by futuristic 6G visions, but what matters in the end is what technology and services the telecom operators will deploy. In this episode, Erik G. Larsson and Emil Björnson discuss a new white paper from SK Telecom that describes the lessons learned from 5G and how these experiences can be utilized to make 6G more successful. The paper and conversation cover network evolution, commercial use cases, virtualization, artificial intelligence, and frequency spectrum. The latest developments in defining official 6G requirements are also discussed. The white paper can be found here:https://www.sktelecom.com/en/press/press_detail.do?idx=1575 The following news article about mmWave licenses is mentioned: https://telecoms.com/521670/south-korea-cancels-skts-28-ghz-5g-licence/ The IMT-2030 Framework for 6G can be found here: https://www.itu.int/en/ITU-R/study-groups/rsg5/rwp5d/imt-2030/Pages/default.aspx Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

The main directions for 6G research have been established and include pushing the communication to higher frequency bands, creating smart radio environments, and removing the conventional cell structure. There are many engineering issues to address on the way to realizing these visions. In this episode, Emil Björnson and Erik G. Larsson discuss the article “The Road to 6G: Ten Physical Layer Challenges for Communications Engineers” from 2021. What specific research challenges did the authors identify, and what remains to be done? The conversation covers system modeling complexity, hardware implementation issues, and signal processing scalability. The article can be found here: https://arxiv.org/pdf/2004.07130 The following papers were also mentioned: https://arxiv.org/pdf/2111.15568 and https://arxiv.org/pdf/2104.15027 Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

The speed of wired optical fiber technology is soon reaching 1 million megabits per second, also known as 1 terabit/s. Wireless technology is improving at the same pace but is 10 years behind in speed, thus we can expect to reach 1 terabit/s over wireless during the next decade. In this episode, Erik G. Larsson and Emil Björnson discuss these expected developments with a focus on the potential use cases and how to reach these immense speeds in different frequency bands – from 1 GHz to 200 GHz. Their own thoughts are mixed with insights gathered at a recent workshop at TU Berlin. Major research challenges remain, particularly related to algorithms, transceiver hardware, and decoding complexity. Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

Research is carried out to obtain new knowledge, find solutions to pertinent problems, and challenge the researchers’ abilities. Two key aspects of the scientific process are reproducibility and replicability, which sound similar but are distinctly different. In this episode, Erik G. Larsson and Emil Björnson discuss these principles and their impact on wireless communication research. The conversation covers the replication crisis, Monte Carlo simulations, best practices, pitfalls that new researchers should avoid, and what the community can become better at. The following article is mentioned: “Reproducible Research: Best Practices and Potential Misuse” (https://arxiv.org/pdf/1905.00645.pdf). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

Information theory is the research discipline that establishes the fundamental limits for information transfer, storage, and processing. Major advances in wireless communications have often been a combination of information-theoretic predictions and engineering efforts that turn them into mainstream technology. Erik G. Larsson and Emil Björnson invited the information-theorist Giuseppe Caire, Professor at TU Berlin, to discuss how the discipline is shaping current and future wireless networks. The conversation first covers the journey from classical multiuser information theory to Massive MIMO technology in 5G. The rest of the episode goes through potential future developments that can be assessed through information theory: distributed MIMO, orthogonal time-frequency-space (OTFS) modulation, coded caching, reconfigurable intelligent surfaces, terahertz bands, and the use of ever larger numbers of antennas. The following papers are mentioned: “OTFS vs. OFDM in the Presence of Sparsity: A Fair Comparison” (https://doi.org/10.1109/TWC.2021.3129975) , “Joint Spatial Division and Multiplexing”(https://arxiv.org/pdf/1209.1402.pdf), and “Massive MIMO has Unlimited Capacity” (https://arxiv.org/pdf/1705.00538.pdf). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

A wave of digitalization is sweeping over the world, but not everything benefits from a transformation from analog to digital methods. In this episode, Emil Björnson and Erik G. Larsson discuss the fundamentals of analog modulation techniques to pinpoint their key advantages. Particular attention is given to how analog modulation enables over-the-air aggregation of data, which can be used for computations, efficient federated training of machine learning models, and distributed hypothesis testing. The conversation covers the need for coherent operation and power control and outlines the challenges that researchers are now facing when extending the methods to multi-antenna systems. Towards the end, the following paper is mentioned: “Optimal MIMO Combining for Blind Federated Edge Learning with Gradient Sparsification” (https://arxiv.org/pdf/2203.12957.pdf). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

Many assumptions must be made when simulating a communication link, including the modulation format, channel coding, multi-antenna transmission scheme, receiver processing, and channel modeling. In this episode, Emil Björnson and Erik G. Larsson are visited by Jakob Hoydis, Principal Research Scientist at NVIDIA, to discuss the fundamentals of link-level simulations. Jakob has led the development of the new open-source simulator Sionna, which is particularly well suited for machine learning research. The conversation covers the needs and means for making accurate simulations, channel modeling, reproducibility, and how machine learning can be used to improve standard algorithms. Other topics that are discussed are MIMO decoding and technical debt. Sionna can be downloaded from https://nvlabs.github.io/sionna/ and the white paper that is mentioned in the episode is found here: https://arxiv.org/pdf/2203.11854.pdf Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

The research towards 6G is intense and many new technology components are being proposed by academia and industry. In this episode, Erik G. Larsson and Emil Björnson identify the key selling points of six of these 6G technologies. They discuss the potential for major breakthroughs and what the main challenges are. The episode covers: 1) Semantic communications; 2) Distributed/cell-free Massive MIMO; 3) Reconfigurable intelligent surfaces; 4) Full-duplex radios; 5) Joint communication and sensing; and 6) Orbital Angular Momentum (OAM). The following paper is mentioned: “Is Orbital Angular Momentum (OAM) Based Radio Communication an Unexploited Area?” by Edfors and Johansson (https://lup.lub.lu.se/search/ws/files/4023050/2339120.pdf). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

The reliability of an application is determined by its weakest link, which often is the wireless link. Channel coding and retransmissions are traditionally used to enhance reliability but at the cost of extra latency. 5G promises to enhance both reliability and latency in a new operational mode called ultra-reliable low-latency communication (URLLC). In this episode, Erik G. Larsson and Emil Björnson discuss URLLC with Petar Popovski, Professor at Aalborg University, Denmark. The conversation pinpoints the physical reasons for latency and unreliability, and viable solutions related to network deployment, diversity, digital vs. analog communications, non-orthogonal network slicing, and machine learning. Further details can be found in the article “Wireless Access in Ultra-Reliable Low-Latency Communication (URLLC)” (https://doi.org/10.1109/TCOMM.2019.2914652) and its companion video (https://youtu.be/XGbe_ckKKpE). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

Mobile network technology builds on open standards, but it is nevertheless a major effort to implement the required software protocols and interface them with actual hardware. Many algorithmic choices must also be made in the implementation, leading to each vendor having its proprietary solution. The OpenAirInterface Alliance wants to change the game by providing open-source software implementations of the wireless air interface and core network. In this episode, Emil Björnson and Erik G. Larsson are discussing these prospects with a Board Member of the Alliance: Florian Kaltenberger, Associate Professor at EURECOM, France. The conversation covers the fundamentals of air interfaces, how anyone can build a 5G network using their open-source software and off-the-shelf hardware, and the pros and cons of implementing everything in software. The connections to Open RAN, functional splits, and patent licenses are also discussed. Further details can be found at https://openairinterface.org and in the paper “OpenAirInterface: Democratizing innovation in the 5G Era” (https://doi.org/10.1016/j.comnet.2020.107284). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

In the near future, we will be able to deploy new wireless networks without installing new physical infrastructure. The networks will instead be virtualized on shared hardware using the new concept of network slicing. This will enable tailored wireless services for businesses, entertainment, and devices with special demands. In this episode, Erik G. Larsson and Emil Björnson discuss why we need multiple virtual networks, what the practical services might be, who will pay for it, and whether the concept might break net neutrality. The episode starts with a continued discussion on the usefulness of models, based on feedback from listeners regarding Episode 25. The network slicing topic starts after 10 minutes. Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

The statistician George Box famously said that “All models are wrong, but some are useful”. In this episode, Emil Björnson and Erik G. Larsson discuss what models are useful in the context of wireless communications, and for what purposes. The conversation covers modeling of wireless propagation, noise, hardware, and wireless traffic. A key message is that the modeling requirements are different for algorithmic development and for performance evaluation. Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

In this episode, Emil Björnson and Erik G. Larsson answer ten questions from the listeners. The common theme is predictions of how 5G will evolve and which technologies will be important in 6G. The specific questions: Will Moore’s law or Edholm’s law break down first? How important will integrated communication and sensing become? When will private 5G networks start to appear? Will reconfigurable intelligent surfaces be a key enabler of 6G? How can we manage the computational complexity in large-aperture Massive MIMO? Will machine learning be the game-changer in 6G? What is 5G Dynamic Spectrum Sharing? What does the convergence of the Shannon and Maxwell theories imply? What happened to device-to-device communications, is it an upcoming 5G feature? Will full-duplex radios be adopted in the future? If you have a question or idea for a future topic, please share it as a comment to the YouTube version of this episode. Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

For each wireless generation, we are using more bandwidth and more antennas. While the primary reason is to increase the communication capacity, it also increases the network’s ability to localize objects and sense changes in the wireless environment. The localization and sensing applications impose entirely different requirements on the desired signal and channel properties than communications. To learn more about this, Emil Björnson and Erik G. Larsson have invited Henk Wymeersch, Professor at Chalmers University of Technology, Sweden. The conversation covers the fundamentals of wireless localization, the historical evolution, and future developments that might involve machine learning, terahertz bands, and reconfigurable intelligent surfaces. Further details can be found in the articles “Collaborative sensor network localization” (https://doi.org/10.1109/JPROC.2018.2829439) and “Integration of communication and sensing in 6G” (https://arxiv.org/pdf/2106.13023). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

Wireless signals look different when observed near to versus far from the transmitter. The notions of near and far also depend on the physical size of the transmitter and receiver, as well as on the wavelength. In this episode, Erik G. Larsson and Emil Björnson discuss these fundamental phenomena and how they can be utilized when designing future communication systems. Concept such as near-field communications, finite-depth beamforming, mutual coupling, and new spatial multiplexing methods such as orbital angular momentum (OAM) are covered. To get more technical details, you can read the paper “A Primer on Near-Field Beamforming for Arrays and Reconfigurable Intelligent Surfaces” (https://arxiv.org/pdf/2110.06661.pdf). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/

The latest wireless technologies rely heavily on beamformed data transmissions, implemented using antenna arrays. Since the signals are spatially directed towards the location of the receiver, the transmitter needs to know where to point the beam. Before the wireless link has been established, the transmitter will not have such knowledge. Hence, the geographical coverage of a network is determined by how we can transmit in the absence of beamforming gains. In this episode, Emil Björnson and Erik G. Larsson discuss how to achieve wide-area coverage in wireless networks without beamforming. The conversation covers deployment fundamentals, pathloss characteristics, beam sweeping, spatial diversity, and space-time codes. To learn more, you can read the textbook “Space-Time Block Coding for Wireless Communications” (https://doi.org/10.1017/CBO9780511550065). Music: On the Verge by Joseph McDade. Visit Erik’s website https://liu.se/en/employee/erila39 and Emil’s website https://ebjornson.com/