Athanasios G. Kanatas

A Novel Approach to MIMO Transmission Using a Single RF Front End

In this paper we introduce a new perspective to the implementation of wireless MIMO transmission systems with increased bandwidth efficiency. Unlike traditional spatial multiplexing techniques in MIMO systems, where additional information can be sent through the wireless channel by feeding uncorrelated antenna elements with diverse bitstreams, we use the idea of mapping diverse bitstreams onto orthogonal bases defined in the beamspace domain of the transmitting array far-field region. Using this approach we show that we can increase the capacity of wireless communication systems using compact parasitic antenna architectures and a single RF front end at the transmitter, thus paving the way for integrating MIMO systems in cost and size sensitive wireless devices such as mobile terminals and mobile personal digital assistants.

A UTD propagation model in urban microcellular environments

This paper presents a three-dimensional (3-D) propagation model for path-loss prediction in a typical urban site, based on geometrical optics (GO) and uniform theory of diffraction (UTD). The model takes into account numerous rays that undergo reflections from the ground and wall surfaces and diffraction from the corners or rooftops of buildings. The exact location of the reflection and diffraction points is essential in order to calculate the polarization components of the reflected and diffracted fields and their trajectories. This is accomplished by local ray-fixed coordinate systems in combination with appropriate dyadic reflection and diffraction coefficients. Finally, a vector addition of the received fields is carried out to obtain the total received field strength and, subsequently, the path loss along a predetermined route. The model computes the contributions of various categories of rays, as selected, in a flexible manner. Several results-path loss versus distance and power-delay profile-are given, and comparisons with measured data are presented.

Parasitic Antenna Arrays for Wireless MIMO Systems

This book unites two different technologies: parasitic antenna arrays driven via analogue circuits that control the electromagnetic waves generated by the antenna array; and MIMO technology for multi-antenna arrays, typically driven by digital techniques in the baseband domain. The combination of these two technologies has revealed a novel functionality that breaks through the conventional MIMO paradigm, allowing MIMO transmission over the air with the use of antenna arrays that may consist of only a single active element, that is surrounded by a number of passive neighboring antennas. The contributions in the book show the capability of such systems to also perform MIMO transmission. This fact holds the potential of revolutionizing the way small-form wireless terminals operate and seems to set the scene for a win-win situation, achieving MIMO transmission with very small and cheap antenna arrays. The book is structured to provide a well-rounded treatment of the various facets of this newly discovered wireless communication capability. All relevant technical angles, ranging from information theoretic to electromagnetic considerations; from analogue circuit to digital baseband control for signal generation; and from channel modeling to communication theoretic aspects are taken into account. A good balance between theory, practical considerations and over-the-air experimentation is proposed and reflected in the chapter outline. Finally, a discussion and early evidence related to potential applications as well as the relevance to current and upcoming wireless standards is provided.

Beamspace-Domain Analysis of Single-RF Front-End MIMO Systems

It is known that the remarkable implementation complexity of multiple-input-multiple-output (MIMO) architectures limits their wide application to modern communication systems. To facilitate the inclusion of MIMO transceivers in devices with strict cost and size constraints, this paper presents a MIMO scheme built on a single-radio-frequency (RF) chain that uses parasitic antenna structures. After presenting the radiation characteristics of such antennas at the beamspace domain, the functionality and the performance evaluation of the proposed single-RF MIMO architecture is illustrated in detail.

The Land Mobile Earth-Space Channel

Research on mobile satellite and high-altitude platform (HAP) systems (MSHSs) has recently proliferated because of the allocation of additional spectrum, the intense standardization efforts from different international institutes, the detailed studies pursued by the European [European Space Agency (ESA)], French (CNES), and Japanese (JAXA) space agencies, and the commercial impact of some of the corresponding system implementations. A survey of mobile satellite systems is provided. Enhanced land mobile Earth-space (LMES) channels encompassing a variety of geometries, frequency bands, and propagation environments are critical for developing and assessing the performance of these new MSHS paradigms. In this article, we provide a survey of the state-of-the-art measurement campaigns, modeling approaches, and generative methods concerning the LMES channel and pinpoint future research directions. We refer to LMES since, due to the close similarities they exhibit, we present channels from both geostationary (GEO) satellites and quasi-stationary HAPs. Most of the cited models apply in both cases. General emphasis is on statistical/physical narrow-band models, which is the norm in LMES channels.

Three-Dimensional HAP-MIMO Channels: Modeling and Analysis of Space-Time Correlation

High-altitude platforms (HAPs) are one of the most promising alternative infrastructures for realizing next-generation high-data-rate wireless networks. This paper investigates the application of multiple-input-multiple-output (MIMO) techniques to HAP-based systems and proposes a 3-D geometry-based single-bounce reference model for Ricean fading channels. From this model, the space-time correlation function is derived for a 3-D nonisotropic scattering environment. The statistical properties of the reference model are analytically studied in terms of various parameters such as the elevation angle of the platform, the array configuration, the Doppler spread, and the distribution of the scatterers. Using the theoretical expressions, one can easily numerically evaluate the HAP antenna interelement spacing required to achieve uncorrelated responses in the HAP-MIMO channel matrix. The proposed model provides guidelines for the system design and performance analysis of HAP-MIMO communication systems with line-of-sight (LoS) and non-line-of-sight (NLoS) connections at the L and S frequency bands.

Energy consumption and trade-offs on wireless sensor networks

Wireless sensor networks (WSN) belong to a special category of networks where the nodes are size-limited and operate on small batteries that in most cases cannot be replaced. As a result ensuring the viability of these networks is usually a much more important task than achieving greater performance in terms of quality of services (QoS), capacity (C) or bandwidth efficiency. In this paper we consider the energy consumption according to the modulation schemes used in order to transmit the data. The trade-offs needed in order to achieve energy-efficiency and especially the case of the trade-off between bandwidth and energy consumption are examined. Furthermore, a model to measure the energy dissipation per transmitted bit will be presented including not only the analog but also the digital blocks of the transceiver. The description of the energy model is followed by the evaluation of the energy consumption introduced by M-ary frequency shift keying modulation (M-ary FSK), depended upon values of parameters such as the compromise in terms of bandwidth and transmission time

Selecting array configurations for MIMO systems: an evolutionary computation approach

This paper presents an antenna selection method for multiple-input multiple-output wireless systems. By exploitation of the channel transfer matrix, the antenna selection criterion is the maximization of the instantaneous capacity achieved using a specific number of transmitting and receiving antenna array elements. For each environment, the proposed method applies a genetic algorithm which seeks the most advantageous subset of antenna elements. The results are based on measured and simulated channels and show that the proposed method selects array configurations that yield superior performance compared to the arrays usually employed. Furthermore, comparative analysis results are presented, with respect to a state-of-the-art algorithm.

A Stochastic Beamforming Algorithm for ESPAR Antennas

Beamforming capabilities of ESPAR antenna structures have attracted considerable attention in recent literature. In this letter, we consider a different beamforming approach, presenting an efficient optimization algorithm which enables such antennas to create desired transmit radiation patterns in real time, rather than patterns aiming at signal to interference ratio maximization. The proposed algorithm may be used in any beamforming, diversity or multiuser system. In order to demonstrate the algorithms efficiency, we investigate a scenario with mobile handsets equipped with ESPAR antennas, considering a beamspace multiple inputmultiple output architecture. It is shown that the algorithm may enforce even cost and size sensitive devices to efficiently operate in closed loop communication environments.

Spatial multiplexing by decomposing the far-field of a compact ESPAR antenna

A framework for implementing spatial multiplexing using an electronically steerable parasitic array radiator (ESPAR) antenna is presented. While traditional multi-element arrays (MEA) show great potential for meeting the increasing demand for higher data rates, they come at the expense of computationally demanding signal processing, larger size, and higher consumption of DC power, making traditional MEA impractical at userspsila hand-held devices. In this work, we introduce a novel methodology for using ESPAR antennas as a compact, cheap and less power-hungry MEA, for spatially multiplexing BPSK symbols, while still providing comparable spectral efficiency and performance as traditional MEA. The main idea is to exploit the strong mutual coupling among the ESPAR antenna elements at the transmitter side to create a linear combination of orthogonal patterns (beams), onto which the symbols are directly mapped, instead of the traditional approach of sending the symbols toward different locations within the antenna domain. On the other side, the receiver (base-station (BS) or access point (AP)) is equipped with a traditional uniform linear array (ULA), and decodes the received signal using the Vertical Bell labs layered space time (VBLAST) algorithm.