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

The equatorial radiation pattern of a parallel-plate TEM mode axial slot on an infinite cylinder of elliptical cross section is computed using wedge-diffraction and creeping-wave theory. The wedge-diffracted fields are obtained by the diffraction interaction from a set of infinite wedges approximating the parallel-plate-cylinder geometry. Surface-wave propagation on curved bodies commonly used in scattering is employed for the creeping-wave contribution. The total field in the lit region is approximated using superposition of wedge-diffracted and creeping-wave fields and in the shadow region solely by creeping-wave fields. The computed patterns are compared with experimental results since boundary-value solutions are not readily available. Good agreement between theory and experiment is indicated.

Aperture radiation from an axially slotted elliptical conducting cylinder using geometrical theory of diffraction

An accurate technique for remotely determining the internal structure of an object or underground environment would have a significant impact in mining, geoexploration, ultrasonics, and the life sciences. This process of resolving the intrinsic properties of an object or environment by the transmission of radiation or ultrasound through the unknown anomaly is known as reconstructive imaging or tomography. Several efforts have been made to apply imaging (reconstruction) methods to measurements taken between two boreholes on either side of an unknown geophysical structure. However, it became necessary, because of the nature of existing reconstruction methods, to assume a straight-line propagation path from source to receiver. This assumption is not valid in many important applications of geophysical imaging; thus it is desirable to develop a method to account for the radiation mechanisms of refraction and reflection in the unknown medium. An imaging scheme that explicitly incorporates refraction and first-order reflection in the reconstruction process is developed. Several examples of successful reconstruction of multicell underground environments are presented to demonstrate its accuracy.

Electromagnetic geophysical imaging incorporating refraction and reflection

The development of electromagnetic systems to detect and monitor an in situ underground coal gasification process requires a knowledge of the electrical properties of coal. Using a two-path interferometer at microwave frequencies (?9 GHz), the samples of solid eastern bituminous coal were tested as a function of temperature, electric-field polarization, and direction of the coal samples. There were slight decreases in the dielectric constant and conductivity of coal as a function of temperature from ambient up to 700°F. However, there were significant variations in the conductivity as a function of polarization, with the vertical polarization possessing lower conductivity. Only slight changes in conductivity were detected as a function of direction, with the face cleats exhibiting somewhat higher losses. The dielectric constant remained essentially constant as a function of polarization and direction of the electromagnetic wave. Measurements of electrical properties of coal were also made in the 0.5-100-MHz region using capacitance techniques. In general, there was a decrease in the values of dielectric constant and an increase in conductivity as the frequency increased.

Electrical Properties of Eastern Bituminous Coal as a Function of Frequency, Polarization and Direction of the Electromagnetic Wave, and Temperature of the Sample

The wedge-diffraction theory in combination with the creeping wave theory is used to compute the radiation pattern of an axial slot on a circular conducting cylinder. The slot is excited by a parallel-plate waveguide operating in the TEM-mode. The total field in the "lit" region is obtained by the superposition of the wedge-diffracted and creeping wave fields. The total field in the "shadow" region is obtained solely from the creeping wave contribution.

Analysis of aperture radiation from an axially slotted circular conducting cylinder using geometrical theory of diffraction

In this investigation dielectric constant and loss tangent values of coal samples were computed from measurements made at microwave frequencies (8.2–12.4 GHz). Two different waveguide methods were used in the measurements. One technique utilized a finite sample and two reactive terminations, and the other required the use of an infinite sample simulated in the laboratory by a very long specimen. For each of the two Pittsburgh seam coal samples, dielectric constant and loss tangent variations were also measured as a function of moisture. Typical moisture contents of 10% and 15% were examined. Electromagnetic propagation through a single layer of coal seam was then investigated analytically as a function of coal depth.

Constantine A. Balanis

Papers

Aperture radiation from an axially slotted elliptical conducting cylinder using geometrical theory of diffraction

Electromagnetic geophysical imaging incorporating refraction and reflection

Electrical Properties of Eastern Bituminous Coal as a Function of Frequency, Polarization and Direction of the Electromagnetic Wave, and Temperature of the Sample

Analysis of aperture radiation from an axially slotted circular conducting cylinder using geometrical theory of diffraction

Microwave measurements of coal