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

Several research areas being investigated in the Department of Electrical Engineering at Arizona State University's College of Engineering and Applied Sciences are discussed. The topics of research include antennas, propagation, scattering, microwave circuits and devices, microwave measurements, and optical communications. The University's electromagnetic anechoic chamber, which is designed to perform precision antenna-pattern and radar-cross-section (RCS) measurements in the microwave region, is described. >

Electromagnetics at Arizona State University

Short-pulse microwave level detector.

This work reviews the most recent advancements in the techniqbes utilized for the reduction of Radar Cross Section (RCS) incorporating metasurfaces. Fundamental theory is briefly reviewed then followed by well-known broadband RCS-reduction metasurface designs.

Metasurfaces for Radar Cross-Section Reduction

The moment method-based NEC code is a well-known and widely-used low frequency code. We apply the NEC code to complex structures at high frequencies. At HF, the electrical size of the structural elements become very small, compared to the wavelength. Moreover, these small elements are necessary to represent the geometrical complexity of a structure so that they cannot be ignored in geometry modeling. Thus, at HF, the NEC code has to deal with electrically small elements near its lower limits, which requires careful geometry modeling to minimize numerical inaccuracy. In addition, the prediction of antenna coupling involves near-field calculations that need extra care during the computation process. We discuss geometry modeling guidelines for complex structures. Using these rules, model two HF antennas mounted on an Apache helicopter airframe. We then analyze the coupling effects between the two antennas in terms of radiation patterns, maximum coupling factors and input impedance.

Coupling prediction of HF antennas mounted on helicopter structures using the NEC code

Research was done to investigate the effects of building blockage on signal propagation using the uniform theory of diffraction (UTD) and two models were developed. The first was that of a mobile receiver behind a single row of buildings as a low Earth orbiting (LEO) satellite passed overhead from horizon to horizon transmitting a signal in the L-band. The second model placed a satellite in a geostationary (GEO) orbit transmitting at Ka-band. The mobile would then have a fixed elevation angle to the satellite, but with the path of propagation obstructed. Included rays were: direct, building reflected, ground reflected, building diffracted, and various combinations thereof.

Constantine A. Balanis

Papers

Electromagnetics at Arizona State University

Short-pulse microwave level detector.

Metasurfaces for Radar Cross-Section Reduction

Coupling prediction of HF antennas mounted on helicopter structures using the NEC code

High frequency propagation models for building blockage at L and Ka band