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

A derivation is presented which leads to a new and general class of vector absorbing boundary conditions (ABCs) for use with the finite element method (FEM). The derivation is based on a vector one-way wave equation and a polynomial approximation of the vector radical. Wide-angle absorbing boundary conditions, as proposed in Halpern and Trefethen (1988) for optimal absorption of outward waves, can be obtained in vector forms and their implementation in a FEM formulation can achieve the fifth-order absorbing accuracy with derivatives only up to the second order. >

A general class of vector absorbing boundary conditions for FEM applications

This paper examines the application of the FDTD method to the determination of the DC steady-state current density distribution of arbitrary geometries when the excitation is an impressed current. The term DC is used in this context to denote the response of a system to any waveform which tends asymptotically to a non-zero constant. Thus, more general waveforms than the unit step function can be considered. By concentrating on the steady state only (or, equivalently, the late time response) certain physical and mathematical difficulties can be circumvented. First, by definition of DC, there is no time variation so that the problem can be formulated in terms of an electrostatic potential, which is obviously more convenient than the magnetic vector potential needed in the time-dependent case. Additionally, assuming that the released heat is such that the temperature of the system (and hence the conductivity) remains almost constant, the thermal and electrical problems can be considered to be decoupled.

Determination of the DC steady-state current density distribution using FDTD and analytical techniques

The modeling of wireless channels vary greatly in different propagation environments. For example, the line-of-sight (LoS) radio links and non-line-of-sight (NLoS) are two basic channel models in wireless communications, but they are totally different from each other. For a LoS channel, if the signals propagate in an additive white Gaussian noise (AWGN) environment, it is referred to as an AWGN channel. However, the AWGN channel is seldom available for wireless systems in urban areas. For a mobile wireless system inside a city, since there are many structures between the base station and the mobile station, the signals are transmitted in NLoS channels with strong influence from diffractions and scatterers (Stuber, 2001). Thus, the received signal may arrive from many different directions and different delays. This phenomenon is referred to as multipath propagation. The multipath signals may be constructive or destructive and thus many fading models are proposed to represent it, such as Rayleigh fading and Rician fading. Rician fading is observed when, in addition to multipath signals, a direct path between the transmitter and the receiver exists.

BER of UCA in Rician fading channel

The radar cross section patterns of lossy dihedral corner reflectors are calculated using a uniform geometrical theory of diffraction for impedance surfaces All terms of up to third order reflections are considered for patterns in the principal plane The surface waves are included whenever they exist for reactive surface impedances The dihedral corner reflectors examined have right, obtuse, and acute interior angles, and patterns over the entire 360 deg azimuthal plane are calculated The surface impedances can be different on the four faces of the dihedral corner reflector; however, the surface impedance must be uniform over each face Computed cross sections are compared with a moment method technique for a dielectric/ferrite absorber coating on a metallic corner reflector The analysis of the dihedral corner reflector is important because it demonstrates many of the important scattering contributors of complex targets including both interior and exterior wedge diffraction, half-plane diffraction, and dominant multiple reflections and diffractions

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Constantine A. Balanis

Papers

A general class of vector absorbing boundary conditions for FEM applications

Determination of the DC steady-state current density distribution using FDTD and analytical techniques

BER of UCA in Rician fading channel

Scattering patterns of dihedral corner reflectors with impedance surface impedances

Distinguished Achievement Award [Report of Awards and Fellow Committee]