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

A novel hybrid circular ground plane integrated with a loop antenna is presented. The ground plane is composed of two different rings: a ring with periodic gaps and an annular concentric ring. The combination of the two rings into one ground plane improves significantly the radiation performance of the radiating element. The proposed antenna is designed to resonate at 2.9 GHz with a return loss of $-\text{24}$ dB and a realized gain of 10.5 dB. To experimentally verify the simulated results, a prototype was fabricated and measured. The simulations and the measurements are in excellent agreement.

Hybrid Circular Ground Planes for High-Realized-Gain Low-Profile Loop Antennas

A wideband uniform circular array (UCA) in azimuth is proposed. The UCA consists of omnidirectional antenna elements, each one of them connected to a single multiplying weight. The array is operating within a desired frequency bandwidth. Using an easy to implement LMS algorithm, we demonstrate that filtering of the incoming wave in both frequency and space domains is achieved. The method provides fully spatial signal processing with a combination of beamforming and null steering in the desired frequency range.

Wideband beamforming using circular arrays

Edge diffraction effects in TEM axially slotted finite ground plane on radiation pattern in waveguides of different geometries

Equatorial plane pattern of an axial-TEM slot on a finite size ground plane

In this paper, high-intensity radiated fields (HIRF) penetration into aircraft fuselage is studied using a reverberation chamber approach. A mode-stirrer is constructed and placed inside a simplified scale fuselage model. Measurements of the penetrating field are performed for different mode-stirrer positions. The collected sets of data are statistically processed and their probability distributions are investigated. Goodness-of-fit tests are performed between data empirical cumulative density functions and existing theoretical probability models which govern the electromagnetic field variations inside reverberation chambers.

HIRF penetration into simplified fuselage using a reverberation chamber approach

A new approach to domain truncation without reflection is proposed for finite methods. The open-space Maxwell's equations, along with boundary conditions, are transformed to an equivalent system with a homogeneous closed boundary; the latter is then solved numerically. Like the popular perfectly matched layer (PML), the new method is independent of frequency and incident angle. Its uniqueness is that it does not need the extra absorption region, since the field attenuation takes place in the domain of the subject.

Constantine A. Balanis

Papers

Hybrid Circular Ground Planes for High-Realized-Gain Low-Profile Loop Antennas

Wideband beamforming using circular arrays

Equatorial plane pattern of an axial-TEM slot on a finite size ground plane

HIRF penetration into simplified fuselage using a reverberation chamber approach

Transparent absorbing boundary (TAB) for the truncation of the computational domain