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

The backscattering from a circular disk is analyzed using the geometrical theory of diffraction (GTD) First-, second-, and third-order diffractions are included in the hard polarization analysis, while first-, second-, and second-order slope diffractions are included for soft polarization Improvements in the prediction of the monostatic radar cross section (RCS) over previous works are noted For hard polarization, an excellent agreement is exhibited between experimental and theoretical results, while a very good agreement is noted for soft polarization To further improve the soft polarization results for wide angles, a model for the creeping wave or circulating current on the edge of the disk is obtained and used to find an additional component of the backscattered field The addition of this component significantly improves the results for wide angles, leading to excellent agreement for soft polarization also An axial-caustic correction method using equivalent currents is also included in the analysis

Higher order diffractions from a circular disk

A hybrid technique of the finite-element method and the method of moments (FEM/ MoM) is used to analyze the effects of multilayered superstrates on cavity-backed slot (CBS) antennas. The spectral-domain approach is used to compute the MoM admittance matrix. An asymptotic extraction technique is applied to improve the computational efficiency of the convolution integrals. Effects on the input impedance, efficiency, gain, and radiation patterns are presented for different antennas. The numerical results are validated with measurements and published data.

Multilayer effects on cavity-backed slot antennas

A scalable and accurate simulation technique to be used for the computer-aided design (CAD) of matching networks employed within high-power RF transistors is presented. A novel measurement methodology is developed and utilized during the validation of the proposed analysis approach. Appropriate segmentation techniques were developed, which are consistent with the design approach of the high-power transistor, that take into account the overall complexity of the internal match of most modern RF high-power transistors, while preserving important electromagnetic interactions. By being able to properly decouple the linear portion of the overall packaged transistor model, an objective accuracy assessment via the comparison of measured versus simulated results of the internal matching network was accomplished. The level of accuracy obtained provides credence to the idea of a full CAD-driven design process of the internal match of high-power RF transistors.

Modeling techniques suitable for CAD-based design of internal matching networks of high-power RF/microwave transistors

A full-wave spectral-domain method with an asymptotic extraction technique is formulated for multilayer microstrip lines. This formulation provides a simple closed-form representation of the asymptotic part of the impedance matrix by using Chebyshev polynomial basis functions with the square-root edge condition and the asymptotic behaviour of the Green's function. The formulation is applied to open microstrip lines. Numerical results, in the form of the effective dielectric constants, are presented for the dominant mode. It is shown that the proposed method significantly reduces the computational time and improves the accuracy over the conventional spectral-domain approach (SDA).

Dispersion characteristics of open microstrip lines using closed-form asymptotic extraction

Reflection phase characteristics of cylindrically curved high impedance surfaces (HISs) are examined. Due to the non-periodicity of the problem, full wave solutions can be time consuming. To overcome this problem, an approximate semi-analytical method, which assumes a homogenized model for the curved HIS, is developed. The model parameters can be extracted from the reflection properties of the flat HIS. For the cases where only Floquet currents are excited, the reflection phase diagram of a curved HIS is independent of the curvature. However, the surface waves generated on HISs, due to their periodic geometry, distorts their reflection phase characteristics within specific frequency intervals. In those intervals, the reflection phase changes as a function of radius of curvature and size of the HIS. These effects are not observed for the flat cases because of the lower radiation resistance of the surface waves. In this paper, the normal incidence case is considered for TEz and TMz polarizations.

Constantine A. Balanis

Papers

Higher order diffractions from a circular disk

Multilayer effects on cavity-backed slot antennas

Modeling techniques suitable for CAD-based design of internal matching networks of high-power RF/microwave transistors

Dispersion characteristics of open microstrip lines using closed-form asymptotic extraction

Reflection Phase Characterization of Curved High Impedance Surfaces