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 wideband semi-periodic circular high impedance surface for loop antenna applications is designed. The surface is illuminated with a plane wavw whose electric field is of phi component. A loop antenna is placed above the surface afterwards to find the operational bandwidth of the structure.

Reflection phase characterization of wideband semi-periodic circular high impedance surface

This special issue is devoted to selected papers from the Sixth International Workshop on Finite Element Methods for Microwave Engineering: Antenna, Circuits and Devices. The workshop was held May 30 to June 1, 2002, on the beautiful island of Chios, Greece. The papers focus on the development and various applications of the finite element method (FEM) in electromagnetics, as there is an increasing dependence on modeling and simulation. It is expected that FEM will play an even greater role in the continuous advancement of the technology for the analysis and design of Radio Frequency devices, including antennas and circuits. There are nine papers included in this special issue. Three related to antennas, two to waveguides, and four to FEM methods, and they are presented in that sequence in the journal. Although there were many other outstanding papers presented at the meeting, this issue was limited in size and many other papers could not be included. The guest editors thank all those who participated in the FEM Workshop, and especially those who submitted papers for this special issue.

Introduction to the Special Issue on Finite Element Methods for Microwave Engineering

This paper provides a detailed numerical comparison between two frequency-domain rough-surface scattering models for the reconstruction of a short carrier-free pulse in the time domain. The two scattering models are a Space-Harmonic Model (SHM) and a Full-Wave Model (FWM), both of which assume a sinusoidally corrugated scatterer. To facilitate a time-domain comparison of the scattering algorithms, a Fourier series method is used to sum the scattered harmonics of the incident pulse. Several graphical comparisons are presented for backscattering of a train of square pulses which has been band limited to correspond to an X-band short pulse. The respective algorithmic difficulties and relative computational efficiencies are also briefly discussed. The computational results indicate that at moderate roughness and small incidence angles, the SHM and the FWM agree quite closely. The omission, however, of multiple scattering in the FWM formulation is seen to limit the effectiveness of the FWM for large scattering angles in combination with moderately rough surfaces.

Numerical comparisons of short-pulse scattering models for rough surfaces

In this paper pseudospectral methods are applied to the solution of electromagnetic problems. Specifically, the Chebyshev collocation method is used along with a mapping of the grid to relax the restrictions on the time-step. Entire-domain as well as multi-domain approaches are considered. The system of ordinary differential equations that comes from the spectral method formulation is solved using either the standard Runge-Kutta method of order four (RK4), or a newly developed algorithm from the class of diagonally implicit multistage integration methods. The accuracy of the spectral methods for all the different approaches is compared with that of the classical second-order FDTD scheme. Additionally, the CPU time as well as the memory required to achieve certain accuracy are reported for both the spectral and the FDTD methods.

Pseudospectral methods versus FDTD

Using a variation of the spectral domain technique, a recursion relation for general planar microstrip structures is derived that is simple to formulate and computationally efficient. Using this formulation and the Fourier transform, signal distortion for both simple and complex multilayer, multiconductor lines is investigated as a function of distance and strip spacing. A method for eliminating distortion due to coupling between lines is discussed, and results are presented that confirm the removal of coupling despite the close spacing of the lines. >

Constantine A. Balanis

Papers

Reflection phase characterization of wideband semi-periodic circular high impedance surface

Introduction to the Special Issue on Finite Element Methods for Microwave Engineering

Numerical comparisons of short-pulse scattering models for rough surfaces

Pseudospectral methods versus FDTD

Distortion of transient signals on multilayer coupled symmetric microstrip transmission lines