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.

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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

Ultrafast clock speeds and short rise times of digital signals give them a very large bandwidth. With clock speeds in the Gigabit /second range and rise times on the order of 10 picoseconds, these signals will have significant frequency components in the tens to hundreds of GHz. This wide frequency range requires a full-wave analysis, rather than a a quasi-static one, to accurately predict the distortion and coupling of highspeed digital signals. High speed circuits also have small inter-line spacing to increase packing density, which in turn increases coupling distortion and crosstalk. Successful design of these high-speed circuits requires accurate prediction of pulse distortion and coupling, as well as a technique to reduce coupling over a very wide band of frequencies.

Wide-Band Reduction of Coupling and Pulse Distortion in Multi-Conductor Integrated Circuit Lines

Some of the problems associated with perfect electric conductor (PEC) boundary conditions in the context of FDTD(2,4) are discussed. Also, a hybrid technique of FDTD(2,4) with subgrid FDTD(2,2) is formulated and applied to practical engineering problems. FDTD(2,2) is the standard FDTD, second-order accurate both in time and space, whereas FDTD(2,4) is second-order accurate in time and fourth-order accurate in space. Two important EMI problems are examined. First, the shielding effectiveness of a simplified scale model of a Boeing 757 aircraft is calculated. A critical EMI/EMC issue, that is relevant to all aviation, concerns the penetration of high intensity radiated fields (HIRF) into conducting enclosures via apertures. Second, the coupling of personal electronic devices (PEDs) is examined for the scaled fuselage by modeling the coupling between a PED antenna inside the fuselage and an antenna mounted on the exterior skin of the fuselage. The EMI generated by PEDs is another very important issue for all aviation. In the two cases, both the standard and hybrid FDTD methods are applied and the predictions are validated by comparison with measurements.

HIRF penetration and PED coupling analysis for fuselage models using a hybrid subgrid FDTD(2,2)/FDTD(2,4) method

Harold A. Wheeler was a pioneer and innovator in electromagnetics, including antennas and microwaves. Two of his fundamental contributions on antennas were on the topics of Small Antennas and Radian Sphere, which are briefly discussed in this paper.

Small Antennas and Wheeler's radian sphere

In this paper, we investigate the bit error-rate (BER) of adaptive arrays in Rayleigh fading with Doppler shift. This will represent well a moving receiver in an urban area. The multipath signals are assumed uniformly distributed in 360 degrees around the receiver in a Rayleigh fading model. Therefore, the uniform circular array (UCA) is selected because it has symmetrical field of view. It is shown that the adaptive UCA system does have good BER performance in Rayleigh fading and the trellis coded modulation (TCM) improves it.

BER performances of UCA in fading channel

In this issue of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IEEE Antennas and Propagation Magazine</i> , we are very fortunate to have an invited article by Prof. Constantine A. Balanis on his journey from Greece to the United States as a young man with very little knowledge of English and becoming a world-famous researcher and author of an antenna book that is used as a reference and textbook in numerous antenna classes around the world. This is an inspiring story for all IEEE Young Professionals around the world to read and take motivation from. I would like to thank Prof. Balanis for taking the time and contributing such a great article for the column. 

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Constantine A. Balanis

Papers

Wide-Band Reduction of Coupling and Pulse Distortion in Multi-Conductor Integrated Circuit Lines

HIRF penetration and PED coupling analysis for fuselage models using a hybrid subgrid FDTD(2,2)/FDTD(2,4) method

Small Antennas and Wheeler's radian sphere

BER performances of UCA in fading channel

Coming to America: My Journey From Greece to the United States and to the Fascinating World of Electromagnetics and Antennas