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

Scalar Holographic Artificial Impedance Surface (HAIS) is a modulated slow leaky-wave antenna whose surface impedance profile is obtained using holographic principle. The surface impedance modulation functions aid in the formation of the desired radiation pattern, polarization, aperture efficiency and bandwidth of the radiating structure. This paper compares the bandwidth of phase crossover and non-phase crossover frequency operations of scalar HAIS. It is shown that the non-phase crossover frequency operation provides an additional degree of freedom of structural modification to achieve desired polarization along with larger operational bandwidth.

Bandwidth analysis of phase crossover and non-phase crossover frequency operations of HAIS

Using the geometrical theory of diffraction, the traditional method of high frequency scattering analysis, the prediction of the radar cross section of a perfectly conducting, flat, rectangular plate is limited to principal planes. Part A of this report predicts the radar cross section in nonprincipal planes using the method of equivalent currents. This technique is based on an asymptotic end-point reduction of the surface radiation integrals for an infinite wedge and enables nonprincipal plane prediction. The predicted radar cross sections for both horizontal and vertical polarizations are compared to moment method results and experimental data from Arizona State University's anechoic chamber. In part B, a variational calculus approach to the pattern control of the horn antenna is outlined. The approach starts with the optimization of the aperture field distribution so that the control of the radiation pattern in a range of directions can be realized. A control functional is thus formulated. Next, a spectral analysis method is introduced to solve for the eigenfunctions from the extremal condition of the formulated functional. Solutions to the optimized aperture field distribution are then obtained.

Nonprincipal plane scattering of flat plates and pattern control of horn antennas

In this paper, a flexible reconfigurable antenna mounted on curved cylindrical configurations is presented. The proposed design is based on a folded slot antenna printed on a flexible Polyethylene Terephthalate (PET) substrate. One PIN-diode is incorporated to the antenna surface to make it reconfigurable in terms of its resonant frequencies and polarizations. The impact of curved cylindrical geometries, such as circumferential and axial configurations, on the antenna radiation characteristics is discussed.

Radiation characteristics of flexible reconfigurable antenna with curved cylindrical configurations

Backscatter analysis of a corner reflector using GTD and PTD

Existing microwave radiometer technology now provides a suitable method for remote determination of the ocean surface's absolute brightness temperature To extract the brightness temperature of the water from the antenna temperature equation, an unstable Fredholm integral equation of the first kind was solved Fast Fourier Transform techniques were used to invert the integral after it is placed into a cross-correlation form Application and verification of the methods to a two-dimensional modeling of a laboratory wave tank system were included The instability of the Fredholm equation was then demonstrated and a restoration procedure was included which smooths the resulting oscillations With the recent availability and advances of Fast Fourier Transform techniques, the method presented becomes very attractive in the evaluation of large quantities of data Actual radiometric measurements of sea water are inverted using the restoration method, incorporating the advantages of the Fast Fourier Transform algorithm for computations

/pdf/application-and-sensitivity-investigation-of-fourier-13vth4ty9u.pdf

Constantine A. Balanis

Papers

Bandwidth analysis of phase crossover and non-phase crossover frequency operations of HAIS

Nonprincipal plane scattering of flat plates and pattern control of horn antennas

Radiation characteristics of flexible reconfigurable antenna with curved cylindrical configurations

Backscatter analysis of a corner reflector using GTD and PTD

Application and sensitivity investigation of Fourier transforms for microwave radiometric inversions