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].

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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

An electromagnetic band gap checkerboard surface including a first quadrant, a second quadrant, a third quadrant, and a fourth quadrant The first and third quadrants each include a multiplicity of first dual-band electromagnetic band gap structures having a first resonant frequency and a second resonant frequency The second and fourth quadrants each include a multiplicity of second dual-band electromagnetic band gap structure having a third resonant frequency and a fourth resonant frequency The first quadrant is directly adjacent to the second quadrant and the fourth quadrant; the third quadrant is directly adjacent to the second quadrant and the fourth quadrant; the first quadrant and the third quadrant are diagonally juxtaposed; and the second quadrant and the fourth quadrant are diagonally juxtaposed

Electromagnetic bandgap checkerboard designs for radar cross section reduction

This paper presents simulation and measurement of a flexible bow-tie which is fabricated at the Flexible Display Center (FDC) of Arizona State University (ASU). The substrate is heat stabilized polyethylene naphthalate (PEN) which allows the antenna to be flexible. The antenna is flexed in the form of a cylinder and its radiation properties are obtained for different radii of curvature. The return loss, radiation patterns and realized gain of the flexed antenna were compared with those of the flat antenna.

Radiation characteristics of a flexible bow-tie antenna

In this paper a new silicon-based antenna structure with an embedded back cavity is presented. The basic antenna with an optimized geometry has good impedance matching with return loss of -40 dB and gain of 7.6 dBi at the resonant frequency of 60 GHz. The linear arrays of four antennas with the corporate feed network have been built with three different forms of rectangular back cavity to compare its impact on the directivity and total efficiency of the antenna. As a result, the array with closed-box cavity gives the best performance with directivity of 16.51 dBi with total efficiency of -1.22 dB.

Millimeter-wave antenna array on silicon with embedded cavity-backed structure

Geometrical scale modeling is often necessary to perform measurements of parameters and figures-of-merit of antennas and radar targets with large physical dimensions that cannot be accommodated in indoor and controlled experimental facilities. The measured and simulated parameters and figures-of-merit of the scaledmodels can then be translated to represent, if transformed properly, those of the full-scale models. In this paper, the basic theory is summarized which relates the gain and the echo area (RCS) of scaled models to those of their full-scale counterparts. Simulations and measurements are performed on scaled models, for both gain and RCS, and compared with those of full-scale models to verify the geometrical scaling. For the gain, a quarter-wavelength monopole on a scaled helicopter airframe, and for the RCS, a flat plate of complex configuration, are considered for simulations, measurements and comparisons. A very good agreement has been obtained for both gain and RCS between both sets of data.

Geometrical Scale Modeling of Gain and Echo Area: Simulations, Measurements and Comparisons

This letter introduces a signal processing procedure that improves the performance of the basic Global Positioning System (GPS) receivers. The proposed signal process incorporates fixed nonuniform tap delays to a seven-element spherical array to mitigate the degrading impact of multipath propagation in satellite communications. Contrary to the time-consuming tap-delay-tracking algorithms, the proposed nonuniform tap delays do not increase the complexity of the signal processing when compared to those of the uniform spaced delays. Using standardized channel models, it is shown that, for a bit error rate (BER) of 10 $ ^{-3}$ , the system can operate with 1–2 dB less signal-to-noise ratio (SNR) when an exponential distribution is used instead of the uniform.

Constantine A. Balanis

Papers

Electromagnetic bandgap checkerboard designs for radar cross section reduction

Radiation characteristics of a flexible bow-tie antenna

Millimeter-wave antenna array on silicon with embedded cavity-backed structure

Geometrical Scale Modeling of Gain and Echo Area: Simulations, Measurements and Comparisons

Nonuniform Tap Spacing in a GPS Spherical Adaptive Array