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.

/pdf/a-high-throughput-path-metric-for-multi-hop-wireless-routing-1p4xa8p0kv.pdf

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

Measurements of Ra-226 activity from eight HPGe gamma ray detectors at the NC State University PULSTAR Reactor were analyzed for evidence of periodic variations, with particular attention to annual variations. All measurements were made using the same reference source, and data sets were of varying length taken over the time period from September 1996 through August 2014. Clear evidence of annual variations was observed in data from four of the detectors. Short time periodograms from the data sets suggest temporal variability of both the amplitude and frequency of these variations. The annual variations in two of the data sets show peak values near the first of February, while surprisingly, the annual variations in the other two are roughly out of phase with the first two. Three of the four detectors exhibited annual variations over approximately the same time period. A joint statistic constructed by combining spectra from these three shows peaks approximating the frequencies of solar r-mode oscillations with $\nu_R = 11.74$ cpy, $m=1$, and $l=3,5,6.$ The fact that similar variations were not present in all detectors covering similar time periods rules out variations in activity as the cause, and points to differing sensitivities to unspecified environmental parameters instead. In addition to seasonal variations, the modulation of environmental parameters by solar processes remains a possible explanation of periodogram features, but without requiring new physics.

Search for Possible Solar Influences in Ra-226 Decays

The experimental observation of magnetostatic surface waves (MSSW's) in a rectangular YIG film placed between strips of permalloy and in the plane of the strips is reported. In such a configuration, the DC magnetic field between the permalloy strips is primarily in-plane with a minimum halfway between and increasing toward each strip. In the presence of such a gradient, a series of discrete modes appears near the low frequency end of the normally continuous MSSW band. The frequencies of these modes lie below the bottom of the conventional MSSW band as calculated from the field at the center of the sample where the field is minimum. However, reversing the bias field reduces the coupling to these modes indicating a nonreciprocal surface localization. Estimates of the group velocities of these modes based on the slope of phase vs. frequency data indicate that the discrete modes travel several times faster than conventional MSSW's.

Magnetostatic surface modes in a thin film with nonuniform in-plane fields

An experimental test bed for investigating the hybrid recording process and that allows for the precise visual alignment of the optical spot and magnetic head is described. Using this spin stand experiments have been performed on three types of hybrid recording where the critical bit dimensions are determined by using either, or both, the thermal and magnetic field profiles. By changing the relative alignment of the optical spot and magnetic head in the down track position four distinct types of marks unique to the hybrid recording process are observed.

Experimenatal test bed for hybrid recording

This paper concerns a method of target detection in a cluttered environment where a significantly large number of highly reflective scattering objects exists. With the conventional Radar detection, the detection of a target additional to this highly scattering environment would suffer greatly in their detection dynamic range. In this paper, we present a novel time reversal method that enables automatic destructive interference of the field-probing electromagnetic wave on the reflective scatters of the environment such that the cluttered environment becomes virtually transparent. The experiment in lab tree-scattering environment demonstrates that this time reversal clutter-nulling scheme substantially enhances the detection dynamic range and the signal-to-noise ratio, significantly raising target detectability.

Antenna Array Detection in Highly Cluttered Environment Using Time Reversal Method

Hexagonal Barium Ferrite thin films with perpendicular anisotropy were successfully fabricated on the (111) surface of large lattice constant (LLC) garnet substrates using pulsed laser deposition. Oxygen pressure plays a crucial role in determining film growth characteristics. The film grown at 50 mTorr oxygen pressure has a clear hexagonal structure but is very weakly crystallized due to the lack of oxygen. Increasing the oxygen pressure enhances both crystallization and the in-plane c-axis oriented crystal growth, hence it reduces the perpendicular anisotropy. The optimum pressure is about 180 mTorr which gives a crystallized film with predominantly perpendicular c-axis orientation. The sensitive dependence of film structure on processing gas pressure shown in this work is important in controlling film properties such as anisotropy and grain size for different applications.

Daniel D. Stancil

Papers

Search for Possible Solar Influences in Ra-226 Decays

Magnetostatic surface modes in a thin film with nonuniform in-plane fields

Experimenatal test bed for hybrid recording

Antenna Array Detection in Highly Cluttered Environment Using Time Reversal Method

Oxygen pressure dependence of laser deposited barium ferrite films on LLC(111)