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 hybridization of the finite element method (FEM) [Jin, 1993] and the spectral domain method of moments (MoM) [Zavosh and Aberle, 1994; Aberle and Zavosh 1994] is utilized in the analysis of cavity-backed patch antennas mounted on an infinite ground plane. The spectral domain MoM models the fields in the external region of the cavity through the use of the half-space Green's function whereas the FEM models the fields inside the cavity using linear edge-based tetrahedral elements. The two regions are coupled through the continuity of the fields in the aperture. The MoM formulation can be completely decoupled from the FEM formulation with the use of the physical equivalence principle after a surface magnetic current is introduced just above and below the aperture plane. The use of edge-based tetrahedral elements inside the cavity volume results in a triangular discretization of both the aperture and patch surfaces. The spectral domain implementation of the Rao, Wilton and Glisson [1982] basis functions with triangular support is one of the most appropriate choices in our case, if indeed arbitrary shaped apertures and/or patches are to be considered in the analysis.

Analysis of arbitrary shaped cavity-backed patch antennas using a hybridization of the finite element and spectral domain methods

The authors present a program developed at Arizona State University to generate automatically three-dimensional surface FDTD (finite-difference time-domain) mesh for a complex object. The program is based on an efficient ray-tracing algorithm and has been tested in various numerical simulations. The mesh generator can be used for a complex object enclosed by conducting and thin-dielectric surfaces. The high efficiency of the algorithm allows the mesh generation to be performed on a special computer. As an example, the mesh generation for a scale helicopter is shown. >

Three-dimensional automatic FDTD mesh generation on a PC

When applying moment method solutions to electromagnetic problems, an integration requiring numerical evaluation is usually encountered. A numerically efficient technique for this evaluation is outlined. The technique involves expanding the intergrand in a binomial series for large arguments and in a Taylor series for small arguments. The proposed technique for evaluating the large argument integral has been tested, and it yields an approximately 30% percent reduction of computation time without any loss in accuracy, as compared with techniques currently in common use. >

An efficient numerical integral in three-dimensional electromagnetic field computations

Because of the design limitations of conventional high impedance surfaces (HIS), it is not possible to miniaturize the HIS and increase the bandwidth, simultaneously. To overcome this, a novel HIS is proposed with a periodically perforated ground plane. The magnetic flux flowing through the perforations results in an extra inductance which increases the fractional bandwidth and decreases the center frequency.

A novel HIS with a perforated ground plane for miniaturization and bandwidth enhancement

A system model is presented of adaptive arrays with trellis coded modulation (TCM) to investigate the bit-error-rate (BER) of a wireless system in a co-channel interference environment. Adaptive arrays with different geometries, uniform circular array (UCA), uniform rectangular array (URA) and UCA with center element (UCA-CE), are implemented with the least mean square (LMS) algorithm to combat interference at the same frequency. The wireless systems are investigated in well-separated signals and random direction signals scenarios with additive white Gaussian noise. The URA and UCA-CE have faster convergence and their BERs, in some cases, are slightly influenced by the number of interferers. However, although the UCA converges slowly and its performance degrades as the number of interferers increases, it generally has the best BER. The recursive least square (RLS) algorithm is also investigated. It achieves much better performance than the LMS algorithm when the training sequences are short. However, the optimum BERs attained by these two algorithms are the same.

Constantine A. Balanis

Papers

Analysis of arbitrary shaped cavity-backed patch antennas using a hybridization of the finite element and spectral domain methods

Three-dimensional automatic FDTD mesh generation on a PC

An efficient numerical integral in three-dimensional electromagnetic field computations

A novel HIS with a perforated ground plane for miniaturization and bandwidth enhancement

BER of Adaptive Arrays in AWGN Channel