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

This paper presents the expected transmission count metric (ETX), which finds high-throughput paths on multi-hop wireless networks. ETX minimizes the expected total number of packet transmissions (including retransmissions) required to successfully deliver a packet to the ultimate destination. The ETX metric incorporates the effects of link loss ratios, asymmetry in the loss ratios between the two directions of each link, and interference among the successive links of a path. In contrast, the minimum hop-count metric chooses arbitrarily among the different paths of the same minimum length, regardless of the often large differences in throughput among those paths, and ignoring the possibility that a longer path might offer higher throughput.This paper describes the design and implementation of ETX as a metric for the DSDV and DSR routing protocols, as well as modifications to DSDV and DSR which allow them to use ETX. Measurements taken from a 29-node 802.11b test-bed demonstrate the poor performance of minimum hop-count, illustrate the causes of that poor performance, and confirm that ETX improves performance. For long paths the throughput improvement is often a factor of two or more, suggesting that ETX will become more useful as networks grow larger and paths become longer.

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A high-throughput path metric for multi-hop wireless routing

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

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Wireless vehicular communication has the potential to enable a host of new applications, the most important of which are a class of safety applications that can prevent collisions and save thousands of lives. The automotive industry is working to develop the dedicated short-range communication (DSRC) technology, for use in vehicle-to-vehicle and vehicle-to-roadside communication. The effectiveness of this technology is highly dependent on cooperative standards for interoperability. This paper explains the content and status of the DSRC standards being developed for deployment in the United States. Included in the discussion are the IEEE 802.11p amendment for wireless access in vehicular environments (WAVE), the IEEE 1609.2, 1609.3, and 1609.4 standards for Security, Network Services and Multi-Channel Operation, the SAE J2735 Message Set Dictionary, and the emerging SAE J2945.1 Communication Minimum Performance Requirements standard. The paper shows how these standards fit together to provide a comprehensive solution for DSRC. Most of the key standards are either recently published or expected to be completed in the coming year. A reader will gain a thorough understanding of DSRC technology for vehicular communication, including insights into why specific technical solutions are being adopted, and key challenges remaining for successful DSRC deployment. The U.S. Department of Transportation is planning to decide in 2013 whether to require DSRC equipment in new vehicles.

Dedicated Short-Range Communications (DSRC) Standards in the United States

In this work we characterize the magnetoquasistatic waves in an anisotropic, indefinite metamaterial used in wireless power applications. We show that the magnetic resonances in the metamaterial are volume mode waves and calculate the expected complex wave number, which represents the wavelength and attenuation, versus frequency from the complex permeability of the metamaterial. We then compare the calculated wavenumber to an experimentally extracted number. Our results show that the loss of the metamaterial increases with frequency due to the shortening of the wavelength even though the imaginary part of μ is lower at these frequencies.

Experimental characterization of volume-mode waves in near-field anisotropic metamaterials with application to wireless power transfer

Pedestrian navigation is readily enabled by GPS in outdoor environments. However, there are many locations - indoors, urban canyons and underground - where the GPS signal is unreliable or unavailable. Compact, MEMS inertial navigation, augmented by a Shoe Ranging Sensor (SRS) that measures scalar range between shoes, greatly reduces navigational error over large distances in simulations. Existing sensors have insufficient measurement dynamic range or environmental resiliency. Here, the authors report on an SRS based on stepped-frequency continuous wave radar with RMS ranging accuracy of 0.59 mm and 1 m range. This is an order-of-magnitude more accuracy over recent ultra-wideband rangers.

A stepped-frequency continuous wave ranger for aiding pedestrian navigation

An antenna that has a number of co-located elements, with no (or very small) coupling between the various elements. The antenna may comprise one or more electric dipole elements, such as an electric tripole, co-located with one or more magnetic dipole elements, such as a magnetic tripole. The antenna has the property that although all of the electric and magnetic dipole elements are co-located, there is substantially no coupling between the elements. Some of the antenna elements may operate as transmitters and the others may act as receivers. The antenna elements may be tuned to different frequencies. The antenna may comprise less than six antenna elements. Also disclosed are example devices and systems that may utilize the antenna structure, such as a handheld wireless communication device and an access point of a HVAC wireless communication system.

Antenna with multiple co-located elements with low mutual coupling for multi-channel wireless communication

A microstrip T-transducer excites forward volume magnetostatic waves (MSWs) in a [BiLu]3Fe5O12 film An optical beam is edge coupled into the film and the transverse MSW–optical interaction is observed at high microwave power levels Using the coupled mode equations, we demonstrate that a T-transducer causes the intensity of the diffracted beam to be a product of terms involving the magneto-optic coupling coefficient (κ) and the phase mismatch between the optical guided modes and the MSWs Taylor series expansions for κ and the MSW wave number (β) are used to obtain an analytic expression for the MSW–optical interaction The dependence on β causes a shift in the interaction spectrum with increasing power After correcting for this shift, the residual dependence on power is attributed to a quadratic correction to the dynamic magnetization which in turn affects κ We demonstrate how the quadratic dependence plays an important role in accurately determining an expansion for the MSW dispersion relation

Quadratic power corrections to the dynamic magnetization using the transverse magnetostatic wave-optical interaction

In Chapter 4 we solved for the magnetostatic modes in a variety of geometries. These geometries were characterized by simple boundary shapes, uniform bias fields, and uniform materials. In some cases, however, material and field nonuniformities may be needed to control the dispersion or to guide and localize the magnetostatic mode energy. In other cases the effects of undesired inhomogeneities need to be assessed. Such problems are not easily attacked by the classical boundary value techniques used in Chapter 4. Consequently, this chapter is devoted to a variational approach capable of treating arbitrary inhomogeneities in a relatively simple and elegant way.

Daniel D. Stancil

Papers

Experimental characterization of volume-mode waves in near-field anisotropic metamaterials with application to wireless power transfer

A stepped-frequency continuous wave ranger for aiding pedestrian navigation

Antenna with multiple co-located elements with low mutual coupling for multi-channel wireless communication

Quadratic power corrections to the dynamic magnetization using the transverse magnetostatic wave-optical interaction

Variational Formulation for Magnetostatic Modes