Raking the Cocktail Party

We present the concept of an acoustic rake receiver---a microphone beamformer that uses echoes to improve the noise and interference suppression. The rake idea is well-known in wireless communications; it involves constructively combining different multipath components that arrive at the receiver antennas. Unlike spread-spectrum signals used in wireless communications, speech signals are not orthogonal to their shifts. Therefore, we focus on the spatial structure, rather than temporal. Instead of explicitly estimating the channel, we create correspondences between early echoes in time and image sources in space. These multiple sources of the desired and the interfering signal offer additional spatial diversity that we can exploit in the beamformer design. We present several "intuitive" and optimal formulations of acoustic rake receivers, and show theoretically and numerically that the rake formulation of the maximum signal-to-interference-and-noise beamformer offers significant performance boosts in terms of noise and interference suppression. Beyond signal-to-noise ratio, we observe gains in terms of the \emph{perceptual evaluation of speech quality} (PESQ) metric for the speech quality. We accompany the paper by the complete simulation and processing chain written in Python. The code and the sound samples are available online at \url{http://lcav.github.io/AcousticRakeReceiver/}.Comment: 12 pages, 11 figures, Accepted for publication in IEEE Journal on Selected Topics in Signal Processing (Special Issue on Spatial Audio

Energy-Efficient Resource Allocation in Wireless Networks: An Overview of Game-Theoretic Approaches

An overview of game-theoretic approaches to energy-efficient resource allocation in wireless networks is presented. Focusing on multiple-access networks, it is demonstrated that game theory can be used as an effective tool to study resource allocation in wireless networks with quality-of-service (QoS) constraints. A family of non-cooperative (distributed) games is presented in which each user seeks to choose a strategy that maximizes its own utility while satisfying its QoS requirements. The utility function considered here measures the number of reliable bits that are transmitted per joule of energy consumed and, hence, is particulary suitable for energy-constrained networks. The actions available to each user in trying to maximize its own utility are at least the choice of the transmit power and, depending on the situation, the user may also be able to choose its transmission rate, modulation, packet size, multiuser receiver, multi-antenna processing algorithm, or carrier allocation strategy. The best-response strategy and Nash equilibrium for each game is presented. Using this game-theoretic framework, the effects of power control, rate control, modulation, temporal and spatial signal processing, carrier allocation strategy and delay QoS constraints on energy efficiency and network capacity are quantified.Comment: To appear in the IEEE Signal Processing Magazine: Special Issue on Resource-Constrained Signal Processing, Communications and Networking, May 200

Coalitional Game Theory for Communication Networks: A Tutorial

Game theoretical techniques have recently become prevalent in many engineering applications, notably in communications. With the emergence of cooperation as a new communication paradigm, and the need for self-organizing, decentralized, and autonomic networks, it has become imperative to seek suitable game theoretical tools that allow to analyze and study the behavior and interactions of the nodes in future communication networks. In this context, this tutorial introduces the concepts of cooperative game theory, namely coalitional games, and their potential applications in communication and wireless networks. For this purpose, we classify coalitional games into three categories: Canonical coalitional games, coalition formation games, and coalitional graph games. This new classification represents an application-oriented approach for understanding and analyzing coalitional games. For each class of coalitional games, we present the fundamental components, introduce the key properties, mathematical techniques, and solution concepts, and describe the methodologies for applying these games in several applications drawn from the state-of-the-art research in communications. In a nutshell, this article constitutes a unified treatment of coalitional game theory tailored to the demands of communications and network engineers.Comment: IEEE Signal Processing Magazine, Special Issue on Game Theory, to appear, 2009. IEEE Signal Processing Magazine, Special Issue on Game Theory, to appear, 200

Nanodevices for Microwave and Millimeter Wave Applications

The microwave and millimeter wave frequency range is nowadays widely exploited in a large variety of fields including (wireless) communications, security, radar, spectroscopy, but also astronomy and biomedical, to name a few. This Special Issue focuses on the interaction between the nanoscale dimensions and centimeter to millimeter wavelengths. This interaction has been proven to be efficient for the design and fabrication of devices showing enhanced performance. Novel contributions are welcome in the field of devices based on nanoscaled geometries and materials. Applications cover, but not are limited to, electronics, sensors, signal processing, imaging and metrology, all exploiting nanoscale/nanotechnology at microwave and millimeter waves. Contributions can take the form of short communications, regular or review papers

Special Issue on Light Communications: Latest Advances and Prospects

The wireless information carrier shift from the radio frequencies to optical frequencies has been studied in increasing detail since the invention of the laser in the 1960s. With the advent of optical fiber communications and their global use, we have seen a growing interest in the field of optical wireless communications (OWC) for front- and back-haul access networks and beyond as part of fifth-generation (5G) wireless networks. OWC has found niche applications in a wide range of systems, from short-range indoor to long-range outdoor and very long deep space and inter-satellite links. New components, such as visible light-emitting sources, image sensors, advanced signal processing techniques, multi-input multi-output, and machine learning are pushing the OWC technology into new application areas such as vehicular communications, smart environments, medical, manufacturing, etc., as part of 5G wireless networks and the emerging 6G networks and beyond.This Special Issue was put together with the goal of bringing together the latest research and development in wireless light communications. A total of 53 submissions were received, and 24 were selected for publication in this Special Issue. The published works present novel results mainly on outdoor and indoor applications of light communications, while a few papers also address broader areas. We briefly present these works in the following sections

Integrated Sensing and Communications: Towards Dual-functional Wireless Networks for 6G and Beyond

As the standardization of 5G solidifies, researchers are speculating what 6G will be. The integration of sensing functionality is emerging as a key feature of the 6G Radio Access Network (RAN), allowing for the exploitation of dense cell infrastructures to construct a perceptive network. In this IEEE Journal on Selected Areas in Commmunications (JSAC) Special Issue overview, we provide a comprehensive review on the background, range of key applications and state-of-the-art approaches of Integrated Sensing and Communications (ISAC). We commence by discussing the interplay between sensing and communications (S&C) from a historical point of view, and then consider the multiple facets of ISAC and the resulting performance gains. By introducing both ongoing and potential use cases, we shed light on the industrial progress and standardization activities related to ISAC. We analyze a number of performance tradeoffs between S&C, spanning from information theoretical limits to physical layer performance tradeoffs, and the cross-layer design tradeoffs. Next, we discuss the signal processing aspects of ISAC, namely ISAC waveform design and receive signal processing. As a step further, we provide our vision on the deeper integration between S&C within the framework of perceptive networks, where the two functionalities are expected to mutually assist each other, i.e., via communication-assisted sensing and sensing-assisted communications. Finally, we identify the potential integration of ISAC with other emerging communication technologies, and their positive impacts on the future of wireless networks

Editorial

In the past years, digital signal processing (DSP) algorithms and architectures for baseband communication systems have fuelled the delivery of applications such as 3G mobile communications and wireless LAN to mass markets. This was made possible by a tremendous growth in the performance of computational devices such as digital signal processors and FPGAs, as well as an increase in sampling rates of conversion devices to potentially several 100 MHz. While the development of both computational devices and ADCs/DACs continues, thus permitting DSP to be applied at IF sampling rates and possibly beyond, the opportunities for further enhancing radio devices by DSP algorithms and architectures arise. Against this background of development, an IEE/EURASIP conference on “DSP-Enabled Radio” was held at the Institute for System Level Integration (ISLI) in Livingston, Scotland, in September 2003. This very lively one-and-ahalf- day event brought together 120 researchers from both industry and academia with a strong international participation. It was the spirit of this DSP-Enabled Radio conference and the contributions therein that brought to life the idea to this special issue. This issue contains both contributions from the event and responses to an open call for papers

Guest Editorial: Nonlinear Optimization of Communication Systems

Linear programming and other classical optimization techniques have found important applications in communication systems for many decades. Recently, there has been a surge in research activities that utilize the latest developments in nonlinear optimization to tackle a much wider scope of work in the analysis and design of communication systems. These activities involve every “layer” of the protocol stack and the principles of layered network architecture itself, and have made intellectual and practical impacts significantly beyond the established frameworks of optimization of communication systems in the early 1990s. These recent results are driven by new demands in the areas of communications and networking, as well as new tools emerging from optimization theory. Such tools include the powerful theories and highly efficient computational algorithms for nonlinear convex optimization, together with global solution methods and relaxation techniques for nonconvex optimization