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

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

Two-dimensional (2-D) measurements of the magnetoquasistatic fields generated from a magnetic dipole (an electrically small current loop) located above the earth are compared to calculations using complex image theory. The magnetoquasistatic coupling between a vertical (i.e., surface normal parallel to the earth) emitting loop and seven vertical receiving loops was measured in a two-dimensional x−y grid of 27.43 m by 27.43 m, all above the earth, where the receiving loops were located outside this grid. Inverting the theoretical expressions to estimate two-dimensional position from measured field values resulted in an average geometric position error of 1.08 m (100th percentile of the measured grid), and an average error of 0.89 m for 95th percentile of measured grid.

Two-dimensional position measurement using magnetoquasistatic fields

Thin films of bismuth substituted iron garnet are fabricated on silicon (100) substrates using the pulsed laser deposition technique. There is a narrow temperature range in which good polycrystalline garnet films can be grown on silicon; it must be higher than 575 °C for the films to crystallize and lower than 700 °C to avoid chemical reaction between the silicon substrate and the deposited materials. Film microstructure and magnetic properties are compared for films grown at different growth conditions and annealing procedures. The films heated during deposition are smooth and dense in contrast to the post‐annealed films, which are characterized by clusters of many smaller grains separated by large cracks and a very small coercivity.

Bismuth substituted iron garnet thin films deposited on silicon by laser ablation

A lens for focusing collimated light. The lens includes a single, optically transmissive material having an aspherical focusing surface (26) and a second surface (28), such that collimated light incident on the aspherical focusing surface is focused in a near-field region of the second surface.

Solid immersion lenses for focusing collimated light in the near-field region

The evaluation of wireless research is challenging because signals traveling through the ether are affected by the physical environment, including movement by people and objects. As a result, testbed experiments are hard to control and are non-repeatable. We have developed a wireless networking testbed based on digital signal propagation emulation that provides control over the signal propagation environment. The testbed has been in regular use for research and education since early 2007. In this paper we present measurements illustrating the properties of the emulator testbed. We also compare the results of various experiments on the emulator with simulation results to shed some light on when the increased accuracy of the emulator testbed is important. Finally, we use the experience gained on the emulator to identify classes of experiments for which the emulator is well suited, compared with other evaluation platforms.

/pdf/experience-with-a-wireless-network-testbed-based-on-signal-3aw2wg7nx8.pdf

Experience with a wireless network testbed based on signal propagation emulation

In this paper, we present the analysis, design and experimental results of /spl lambda//4-patch antennas operating at /spl sim/10 GHz. The ground plane has been adjusted to the patch area in order to drastically reduce the antenna size. Several geometries are presented, with HFSS simulation results. Impedance matching calculations for maximum power transfer between the antenna and the rectifying circuit is also presented. For a 4/spl times/5/spl times/1.6 mm/sup 3/ rectangular antenna fabricated on an RT/Duroid 5880 PCB, the measured maximum gain is 0.75 dB/sub i/ at 10.3 GHz.

/pdf/chip-size-antennas-for-implantable-sensors-and-smart-dust-2lpnjr77nq.pdf

Daniel D. Stancil

Papers

Two-dimensional position measurement using magnetoquasistatic fields

Bismuth substituted iron garnet thin films deposited on silicon by laser ablation

Solid immersion lenses for focusing collimated light in the near-field region

Experience with a wireless network testbed based on signal propagation emulation

"chip-size" antennas for implantable sensors and smart dust