Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].

/pdf/scaling-up-mimo-opportunities-and-challenges-with-very-large-puqp9v7gzk.pdf

Scaling Up MIMO: Opportunities and Challenges with Very Large Arrays

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

/pdf/high-impedance-electromagnetic-surfaces-with-a-forbidden-3vtu72a5an.pdf

High-impedance electromagnetic surfaces with a forbidden frequency band

http://www.csun.edu/~andrzej/COMP529-S05/papers/Mesh%20Networks%20Survey.pdf

Wireless mesh networks: a survey

This paper surveys recent advances in the area of very large MIMO systems. 
With very large MIMO, we think of systems that use antenna arrays with an order of magnitude more elements than in systems being built today, say a hundred antennas or more. Very large MIMO entails an unprecedented number of antennas simultaneously serving a much smaller number of terminals. The disparity in number emerges as a desirable operating condition and a practical one as well. The number of terminals that can be simultaneously served is limited, not by the number of antennas, but rather by our inability to acquire channel-state information for an unlimited number of terminals. Larger numbers of terminals can always be accommodated by combining very large MIMO technology with conventional time- and frequency-division multiplexing via OFDM. Very large MIMO arrays is a new research field both in communication theory, propagation, and electronics and represents a paradigm shift in the way of thinking both with regards to theory, systems and implementation. The ultimate vision of very large MIMO systems is that the antenna array would consist of small active antenna units, plugged into an (optical) fieldbus.

/pdf/scaling-up-mimo-opportunities-and-challenges-with-very-large-1gai688763.pdf

Scaling up MIMO: Opportunities and Challenges with Very Large Arrays

Almost all mobile communication systems today use spectrum in the range of 300 MHz-3 GHz. In this article, we reason why the wireless community should start looking at the 3-300 GHz spectrum for mobile broadband applications. We discuss propagation and device technology challenges associated with this band as well as its unique advantages for mobile communication. We introduce a millimeter-wave mobile broadband (MMB) system as a candidate next generation mobile communication system. We demonstrate the feasibility for MMB to achieve gigabit-per-second data rates at a distance up to 1 km in an urban mobile environment. A few key concepts in MMB network architecture such as the MMB base station grid, MMB interBS backhaul link, and a hybrid MMB + 4G system are described. We also discuss beamforming techniques and the frame structure of the MMB air interface.

An introduction to millimeter-wave mobile broadband systems

A geometrical optics model for propagation in conducting media requires the determination of the propagation constants for the field transmitted through a plane boundary. In general, the transmitted fiJeld produced by a nonuniform plane wave incident upon a plane boundary between two conducting media propagates with constants which are different from the intrinsic constants of the medium. The expressions for these constants are derived, and data are presented to illustrate when these modified propagation constants must be used to yield valid results.

Modified Propagation Constants for Nonuniform Plane Wave Transmission through Conducting Media

Cavity-backed slot (CBS) antennas are commonly used in Earth-based and space-borne applications. In this manuscript, the finite-difference time-domain (FDTD) method is used to analyze different antenna characteristics of such elements including input impedance, coupling, and radiation patterns. Emphasis is given to coupling calculations, especially to different methods to reduce coupling. Specifically, coupling reduction is attempted using lossy material superstrates or ground plane discontinuities, such as slits. Numerical issues concerning the analysis of CBS antennas in the context of FDTD are also discussed.

Coupling modeling and reduction techniques of cavity-backed slot antennas: FDTD versus measurements

Detection and classification of unmanned aerial vehicles (UAVs) or unmanned aerial systems (UASs) requires an understanding of their characteristics in various regimes. Two relevant UAS characteristics are measured for two consumer-grade UASs: radar cross-section (RCS) and micro-Doppler profile. RCS is measured as a function of frequency, angle, and orientation. Electromagnetic and acoustic micro-Doppler characteristics of the UASs' moving blades are also measured.

Consumer-grade drone radar cross-section and micro-Doppler phenomenology

We develop one-dimensional (1D) and two-dimensional (2D) adaptive algorithms that use gradient projections in selected subspaces for use in antenna beamforming. The 1D algorithm is essentially a significantly enhanced version of an eigenspace projection algorithm (EPA) that was previously developed for controls. The 2D algorithm is new and is based on a stacked configuration of the enhanced 1D algorithm. Both algorithms are applied to antenna beamforming in uniform linear and planar arrays. Simulation results show faster convergence as well as improved beam properties. In addition, results for a more realistic scenario, with a BPSK signal and antenna coupling effects, are also quite promising.

Adaptive eigen-projection beamforming algorithms for 1D and 2D antenna arrays

The study of high frequency diffraction phenomena mostly associated with geometrical theory of diffraction, uniform theory of diffraction, physical theory of diffraction, and their alternatives is reviewed. Several examples illustrate these theories and their applications in antennas and scattering problems. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Constantine A. Balanis

Papers

Modified Propagation Constants for Nonuniform Plane Wave Transmission through Conducting Media

Coupling modeling and reduction techniques of cavity-backed slot antennas: FDTD versus measurements

Consumer-grade drone radar cross-section and micro-Doppler phenomenology

Adaptive eigen-projection beamforming algorithms for 1D and 2D antenna arrays

Fifty years of high frequency diffraction