Communication systems

<p>Responsible: <a rel="noopener" href="https://www.chalmers.se/en/persons/hagerc/" target="_blank">Christian Häger</a></p>

<p>Professor <a rel="noopener" href="https://www.chalmers.se/en/persons/graell/" target="_blank">Alexandre Graell i Amat</a></p>

<p><strong>Research area leader:</strong> Professor <a rel="noopener" href="https://www.chalmers.se/en/persons/durisi/" target="_blank">Giuseppe Durisi</a></p>
<h3>About the research area fundamentals</h3>
<div>Within the research area “Fundamentals”, we aim to find mathematically precise answers to practically relevant problems in the areas of wireless and wired communications, signal processing, and machine learning. One of the main tools used in this research area is information theory, a mathematical discipline that deals with optimal methods for representing, communicating, processing, and storing digital information. This involves the study of mathematical models for communication and signals acquisition. Currently, we are targeting the theories behind next generation communication networks. Our research includes the characterization of the ultimate limit on the rate of reliable communications over wireless and wired channels, and the study of the minimum number of measurements necessary to acquire and reconstruct a given signal under a fidelity criterion.</div>
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<h4>Information and Communication Theory</h4>
<div>Wireless and wired communication systems have experienced a formidable growth in the past years. The dramatic increase in the number of mobile subscribers and, in particular, of mobile broadband subscribers resulted in an enormous growth of mobile data traffic. The surge in the use of broadband applications such as video streaming and social media poses a significant challenge on all parts of current communication networks, from the core (backhaul) to the periphery (cellular base stations).</div>
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<div>As already happened in the past, information theory is expected to play a significant role in tackling the challenges ahead. Information theory studies the ultimate limit on the rate of reliable communications, which is usually referred to as channel capacity.</div>
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<div>Our research activity aims at developing an information theory that accounts for the impairments typically encountered in the development of wireless and wired network. Typical research questions include the characterization of the cost of acquiring and distributing channel state information and the impact on capacity of nonlinear phenomena such as phase noise. Our vision is that this theoretical effort will be instrumental for the design of next generation wireless and wired communication networks.</div>
<h4>Compressive sensing</h4>
<div>Compressive sensing is a recently developed theory, which asserts that signals and images that are sparse in an appropriate domain (e.g., frequency, wavelet) can be recovered from far less measurements (samples) than traditionally thought. A classic problem in compressed sensing is to seek - by solving an appropriate convex-optimization problem - the sparsest representation of a given vector, as a linear combination of vectors from a certain set, usually referred to as dictionary. It turns out that this convex-optimization problem yields the unique sparsest representation of a given vector whenever the sparsity level (i.e., the number of nonzero coefficients) of the solution lies below a threshold, which depends on the properties of the dictionary.</div>
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<div><strong>Research area leader: </strong>Professor <a rel="noopener" href="https://www.chalmers.se/en/persons/thomase/" target="_blank">Thomas Eriksson</a>
<h3>About the research area Hardware-constrained communications</h3>
<div>When a communication signal is passed through RF transmitter and receiver hardware, various kind of imperfections in the analog hardware will destroy and distort the signal. The phenomenon is sometimes denoted "Dirty RF", and has increased tremendously in importance lately, due to increased demands on capacity and on cost-effective solutions.<br /><br />Among the most important "Dirty RF" issues are:</div>
<ul>
<li>Nonlinear and inefficient power amplifiers</li>
<li>Phase noise in oscillators</li>
<li>I/Q imbalance in the modulator and demodulator circuits</li>
<li>Cross-talk in the transmitter chain of a MIMO transmitter</li>
</ul>
<div>Of these, we have worked for a long time with the three first issues, and we are currently ramping up our research also in the fourth. We discuss each of these areas briefly below.</div>
<h4>Nonlinear and inefficient power amplifiers</h4>
<div>All power amplifiers are nonlinear to some extent, where the degree varies with the amplifier type and architecture. The nonlinearity is in direct opposition with the efficiency of the amplifier (the consumed power). The amplifier can be made more linear by operating it in backoff (at low output powers), but amplifiers are most efficient when operated close to saturation, with low backoff. We are currently working with these issues, focusing on Digital Predistortion (DPD) and on signal design for high-efficient amplifier architectures (Doherty, Load Modulation,  PWM, delta-sigma etc.).</div>
<h4>Phase noise in oscillators</h4>
<div>An ideal oscillator should oscillate at a single frequency, but in practice all oscillators suffers from phase noise to some degree, leading to an increased bandwidth of the device.  The consequence in the communication system is that the signals get phase-shifted in a random way, leading to problems in designing a good receiver. Our work on phase noise is focused on various ways to analyze and compensate communication systems suffering from phase noise, e.g. by phase-noise modeling, capacity calculations, joint phase noise compensation and detection, phase mitigation in MIMO systems etc.</div>
<h4 class="chalmersElement-H4">I/Q imbalance in modulator and demodulator circuits</h4>
<div>The role of the modulator circuitry is to mix the communication signal with two equal-gain RF signals having 90 degrees phase shift (the I and Q channels). In practice, however, it is difficult to construct analog circuits with exactly 90 degrees phase shift and exactly equal gain. We get I/Q imbalance, which leads to signal distortion. We are working with compensation of all kinds of I/Q imbalance, including frequency dependent gains, I/Q mixing, nonlinear effects and so on. The work is carried out within GHz Centre.</div>
<h4>Cross-talk in MIMO transmitters</h4>
<div>In a multiple-antenna (MIMO) transmitter, it is impossible to avoid some cross-talk between the transmitter chains. Such cross-talk leads to, if left unhandled, to that the separate amplifiers will see a time-varying load, which in turn leads to signal distortion. In a traditional system this is solved by adding isolator circuits between amplifiers and antennas, but this is costly in terms of component costs and reduced efficiency.</div>
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<div>We are currently starting work on compensation MIMO crosstalk using signal processing, avoiding the need for isolators and making efficiency-optimization of the MIMO transmitter possible</div>
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<div><strong>Research area leader:</strong><span> </span>Professor <a rel="noopener" href="https://www.chalmers.se/en/persons/agrell/" target="_blank">Erik Agrell</a></div>
<h3>About the research area Optical communications</h3>
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<div>Fiber-optic communication systems carry most of today’s global internet traffic and other data communication services. This is essential for video conferencing, telemedicine, video-on-demand, data processing and storage in the cloud, “Internet of Things”, and 4G and 5G mobile services. As the potential improvements by legacy wavelength-division multiplexing hardware becomes costlier or even infeasible, optical communications is paving the way to meet the challenges of increasing bandwidth demanded by society.</div>
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<h4 class="chalmersElement-H4">Research</h4>
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<div>Our group focuses on new methods to increase the capacity of existing optical links through software optimizations. Our goal is to extend transmission distances, increase bandwidth, and reduce energy consumption, and through this, we strive to achieve long term social and environmental impact.<br /><br />Our four main focus areas are:<br />
<ul>
<li>Modulation techniques</li>
<li>Understanding and mitigating nonlinear distortion for high power transmissions</li>
<li>Power efficiency for data centers</li>
<li>Adaptive optical networks</li>
</ul>
<a rel="noopener" href="http://publications.lib.chalmers.se/search/index.xsql?doSearch=true&amp;query=optical+communications" target="_blank"></a></div>
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<h5 class="chalmersElement-H5">Research collaboration </h5>
<div>Our research is carried out in the research center <a rel="noopener" href="https://chalmers.se/force" target="_blank">FORCE (Fibre Optic Communications Research Centre)</a>, which facilitate collaboration in the area between different groups at Chalmers and to provide internal and external visibility to this research. Within the FORCE center, we collaborate closely with the Photonics Laboratory at the Department of Microtechnology and Nanoscience, which provides the photonics expertise, including knowledge of lasers, fibers, detectors, and amplifiers. We also collaborate with the VLSI Design Group at the Department of Computer Science and Engineering, which provides expertise in the design and implementation of electronic signal processing. Together, the three groups comprise a truly interdisciplinary research environment in order to address system-wide research challenges and attain innovative solutions. We have together received international attention at the leading international conferences and journals.</div>
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<div>Our collaboration partners outside Chalmers include for example University College London, UK, Royal Institute of Technology in Stockholm, University of Virginia, USA, and University of Toronto in Canada. The collaborations have resulted in numerous research visits, joint projects, and co-authored scientific articles.</div>
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<div>If you are interested to get in touch, please <a rel="noopener" href="https://www.chalmers.se/en/persons/agrell/" target="_blank">contact Professor Erik Agrell</a>.</div>
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<p><strong>Research area leader:&nbsp;</strong>Professor&nbsp;<a rel="noopener" href="https://www.chalmers.se/en/persons/henkw/" target="_blank">Henk Wymeersch</a><a href="/sv/personal/Sidor/henk-wymeersch.html"><span><br></span></a></p>
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<h3>About the research area Radio localization and sensing</h3>
Our research domain is at the forefront of exploring the innovative use of wireless signals for two primary purposes: localizing connected devices and detecting as well as tracking passive objects. The ability to accurately pinpoint the location of devices or objects, known as localization or positioning, is crucial across a wide range of applications. From navigation and transportation to enhancing wireless communication systems themselves, understanding an entity’s position within its environment significantly elevates the efficiency and effectiveness of numerous technological solutions. Our inspiration often stems from the pressing demands of active safety systems, such as those found in autonomous vehicles or drones and in the coordination of autonomous robots. Our investigative scope bifurcates into two main segments. We delve into Integrated Sensing and Communication (ISAC), a realm where we explore the dual utility of communication signals for radar sensing and vice versa. This innovative crossover has the potential to revolutionize how we perceive and utilize signal technology. The second segment of our inquiry focuses on positioning—a critical examination of various methodologies to localize and track users. This often involves techniques such as Simultaneous Localization and Mapping (SLAM), enriching our understanding of both the users and their surrounding environments.<br>&nbsp;<br>Our methodological approach is a rich combination of statistical signal processing, optimization theory, geometric analysis, and machine learning. We consistently follow the latest advances in communication and reflect on their potential for localization and sensing. This multidisciplinary and forward-looking strategy allows us to tackle complex problems with innovative solutions.<br>&nbsp;<br>Collaboration is at the heart of our research approach. By working closely with industry leaders and academic institutions both within Sweden and internationally, we not only broaden our perspective but also ensure our research has tangible, high-impact applications in the real world. Our goal is to pioneer research that not only advances the theoretical framework of our field but also has a profound, practical relevance across industries.</div>

<p>Professor <a rel="noopener" href="https://www.chalmers.se/en/persons/fredrikb/" target="_blank">Fredrik Brännström</a></p>

<p>Research area leader: Professor<a rel="noopener" href="https://www.chalmers.se/en/persons/tommys/" target="_blank"> Tommy Svensson</a></p>
<h3>About the research area Wireless systems</h3>
<p>Future wireless networks will form the foundation for an intelligent society where people and equipment can be connected anywhere, anytime—with anything. Wireless connectivity is the key for further digitalization and development of innovative technologies and applications in areas such as infotainment, industrial automation, transportation systems, personalized health care, smart grids, smart cities, smart farming and precision agriculture. Mobile networks are also evolving into an integrated communications, computing, storage, sensing and machine learning/artificial intelligence (ML/AI) computing system. Key enablers for such mobile networks will be high transmission speeds, low latency, knowledge of the radio environment, positioning and orientation, integrated sensing, network of networks, and by computational power being decentralized in the mobile networks.</p>
<p>In the research area Wireless systems we focus on design and analysis of mobile communication systems, with a focus on physical layer algorithms, multiple access, resource allocation and cooperative multiple-antenna systems. In particular, we focus on distributed multiple-input multiple-output (D-MIMO) systems and reconfigurable intelligent surfaces (RISs), mm-wave/ sub-THz communications, integrated access and backhaul (IAB), cellular vehicle to everything (C-V2X), joint communication and sensing (JCAS) and context-aided communications, non-terrestrial networks (NTN), trustworthiness and sustainability. We also actively contribute to end-to-end architecture aspects, especially withing top-level EU projects such as WINNER I/II+ (4G), METIS (5G) and Hexa-X/Hexa-X-II (6G). The 6G vision is to connect human, physical, and digital worlds. With 6G, we also aim to meet society’s needs for a sustainable world, in line with the UN’s goals for sustainable development.</p>
<p><strong>Read more about 6G:</strong></p>
<ul>
<li><a href="https://www.chalmers.se/en/current/news/e2-the-future-6g-network-an-important-tool-for-a-sustainable-world/">https://www.chalmers.se/en/current/news/e2-the-future-6g-network-an-important-tool-for-a-sustainable-world/</a></li>
<li><a href="https://www.chalmers.se/en/current/news/e2-eucnc-6g-summit/"> https://www.chalmers.se/en/current/news/e2-eucnc-6g-summit/</a></li>
</ul>
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