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

A design procedure is introduced where a refined algorithm is developed and employed on single-band AMCs leading to a 10-dB RCS-reduction bandwidth of 80%. The AMC circuit model is utilized cleverly to reduce the substrate thickness while simultaneously increasing the bandwidth of AMC surfaces. Furthermore, dual-band AMC surfaces are synthesized and utilized in combination with single-band AMC surfaces to extend the 10-dB RCS-reduction bandwidth from 80% to about 99%.

Design of Ultra-Broadband RCS-Reduction Checkerboard Surface Using AMC Circuit Model

The ElectroMagnetic Anechoic Chamber (EMAC) facility has been in operation at Arizona State University (ASU) since 1988. In addition to providing experimental verification for theoretical prediction of radiation and scattering targets, this multi-purpose facility acts as a testbed for a unique, semicompact antenna test range. Antenna patterns of a scale model helicopter have been measured at 500 MHz and compared to Numerical Electromagnetics Code (NEC) prediction. These measurements demonstrate that accurate antenna patterns can be measured at frequencies much lower than expected according to the conventional wisdom concerning rectangular anechoic chambers and compact ranges. Measurements made at EMAC of a scale model helicopter at UHF demonstrate remarkable agreement with theoretical prediction, particularly in the case of the electrically small reflector, absorber, and chamber. >

Scale model helicopter antenna pattern measurements at ASU's EMAC Facility

In this paper, a wearable reconfigurable antenna based on the concept of folded slot antennas is reported. The antenna is designed over Artificial Magnetic Conductor (AMC) to reduce the impedance mismatch due to the presence of human body and also to minimize the Specific Absorption Rate (SAR). The antenna and AMC surface are designed on a flexible substrate so that the antenna structure can be curved and mounted on human body.

A wearable and reconfigurable folded slot antenna for body-worn devices

The ability of the finite-difference time-domain (FDTD) method to readily handle complex structures having a complex mix of materials makes it suitable for predicting the penetration of high intensity radiated fields (HIRF) fields into aircraft fuselages. This paper summarizes the next step in ASU's on-going research into developing the computational tools that are needed to predict this HIRF penetration. The shielding effectiveness, a measure of field penetration, of a 1:20 scaled simplified aircraft fuselage was predicted using the FDTD method and was compared with measurements. To accelerate the FDTD solution of this relatively high-Q structure, a resistive source model was used, and the time-domain fields were windowed prior to Fourier transformation into the frequency domain. A reasonable level of agreement was observed between measurement and prediction at the lower frequencies of the 0.25 GHz to 9 GHz band considered. At the higher frequencies, the measurement and prediction are not in close agreement, deterministically. However, the envelope of the predicted shielding effectiveness continues to compare favorably at the higher frequencies with that measured, suggesting that a statistical approach may be appropriate.

HIRF penetration into a fuselage-like body: FDTD predictions vs. measurements

Modeling of ferrite-loaded CBS antennas often makes use of the simplifying assumptions which involve some kind of averaging of the magnetic bias field. Simulations and measurements presented here demonstrate that failure to account for the non-uniform magnitude, as well as direction, of the bias field leads to inaccurate predictions of not only the input impedance, but also of the amplitude radiation patterns.

Constantine A. Balanis

Papers

Design of Ultra-Broadband RCS-Reduction Checkerboard Surface Using AMC Circuit Model

Scale model helicopter antenna pattern measurements at ASU's EMAC Facility

A wearable and reconfigurable folded slot antenna for body-worn devices

HIRF penetration into a fuselage-like body: FDTD predictions vs. measurements

The Impact of Non-Uniform Bias Field on the Radiation Patterns of Ferrite-Loaded CBS Antennas