Metamaterial-based electronically controlled transmission-line structure as a novel leaky-wave antenna with tunable radiation angle and beamwidth

A metamaterial-based electronically controlled transmission-line structure is presented and demonstrated as a novel leaky-wave (LW) antenna with tunable radiation angle and beamwidth functionalities. This structure is in essence a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. Angle scanning at a fixed frequency is achieved by modulating the capacitances of the structure by adjusting the (uniform) bias voltage applied to the varactors. Beamwidth tuning is obtained by making the structure nonuniform by application of a nonuniform bias voltage distribution of the varactors. A rigorous analysis based on an extension of the CRLH concept is proposed and the corresponding dispersion curves, obtained by equivalent-circuit formulas with LC parameters extracted from full-wave simulation, are shown. A 30-cell LW antenna structure, incorporating both series and shunt varactors for optimal impedance matching and maximal tuning range, is designed. This prototype exhibits continuous scanning capability from 50/spl deg/ to -49/spl deg/ by tuning the bias voltages from 0 to 21 V at 3.33 GHz. A maximum gain of 18 dBi at broadside is also achieved. In addition, it provides half-power beamwidth variation of up to 200% with comparison to the case of uniform biasing. The effect of intermodulation due to the nonlinearity of the varactors is shown to be negligible for antenna applications. The antenna is tested in a 10-Mb/s binary phase-shift key transmission link and successful recovery of the baseband data is demonstrated.     

Improving TCP performance over wireless networks at the link layer

We present the transport unaware link improvement protocol (TULIP), which dramatically improves the performance of TCP over lossy wireless links, without competing with or modifying the transport- or network-layer protocols. TULIP is tailored for the half-duplex radio links available with today's commercial radios and provides a MAC acceleration feature applicable to collision-avoidance MAC protocols (e.g., IEEE 802.11) to improve throughput. TULIP's timers rely on a maximum propagation delay over the link, rather than performing a round-trip time estimate of the channel delay. The protocol does not require a base station and keeps no TCP state. TULIP is exceptionally robust when bit error rates are high; it maintains high goodput, i.e., only those packets which are in fact dropped on the wireless link are retransmitted and then only when necessary. The performance of TULIP is compared against the performance of the Snoop protocol (a TCP-aware approach) and TCP without link-level retransmission support. The results of simulation experiments using the actual code of the Snoop protocol show that TULIP achieves higher throughput, lower packet delay, and smaller delay variance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Security of the Cao-Li public key cryptosystem

The author shows that the Cao-Li cryptosystem proposed [1991] is not secure. Its private key can be reconstructed from its public key using elementary means such as LU-decomposition and the Euclidean algorithm     

The IEEE P1520 standards initiative for programmable networkinterfaces

This article discusses the need for standard software interfaces for programming of networks, specifically for service and signaling control, through programming interfaces. The objective is to enable the development of open signaling, control, and management applications as well as higher-level multimedia services on networks. The scope of this effort includes ATM switches, circuit switches, IP routers, and hybrid switches such as those that provide for fast switching of IP packets over an ATM backbone. The basic ideas represented herein are in the process of development as a standard for application programming interfaces for networks under IEEE Standards Project IEEE P1520     

Reversible energy recovery logic circuit without non-adiabaticenergy loss

The authors propose a reversible energy recovery logic (RERL) circuit for ultra-low-energy consumption, which consumes only adiabatic energy loss and leakage current loss by completely eliminating non-adiabatic energy loss. It is a dual-rail adiabatic circuit using the concept of reversible logic with a new eight-phase clocking scheme. Simulation results show that at low-speed operation, the RERL consumes much less energy than the complementary static CMOS circuit and other adiabatic logic circuits     

A Gunn-Diode Active Leaky-Wave Frequency Scanning Antenna

A frequency tunable active leaky-wave scanning antenna using Gunn-diode voltage control oscillator (VCO) as source is developed. The frequency tuning controlled by changing either the varactor diode dc bias or the Gunn diode dc bias is demonstrated. The measured scanning angle of active antenna is close to 15 degree as the Gunn VCO frequency tuned from 12.58GHz to 12.98GHz. To excite the first higher order mode of the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the middle line of the microstrip leaky wave antenna. This is a prototype of frequency scanning antenna using two terminal device, which can be easily scaled up to millimeter wave frequency region.     

Transient response of premixed methane flames

The response of premixed methane-air flames to transient strain and local variations in equivalence ratio is studied during isolated interactions between a line-vortex pair and a V-flame. The temporal evolution of OH and CH is measured with planar laser-induced fluorescence for N₂-diluted flames with equivalence ratios ranging from 0.8 to 1.2. One-dimensional laminar flame calculations are used to simulate the flame response to unsteady strain and variations in reactant composition. When the reactant composition of the vortex pair and the V-flame are identical, the measurements and predictions show that the peak mole fractions of OH and CH decay monotonically in lean, stoichiometric, and rich flames. We also investigate the effects of a vortex pair with a leaner composition than the V-flame. In a stoichiometric flame, the leaner vortex enhances the decay of both OH and CH. In a rich flame, we observe an abrupt increase in OH-LIF signal and a disappearance of CH-LIF signal that are consistent with a previous experimental investigation. Our results indicate that the previously observed OH burst and CH breakage were caused by a difference in the equivalence ratios of the vortex pair and the main reactant flow. A numerical study shows that N₂ dilution enhances the response of premixed flames to unsteady strain and variations in stoichiometry. Reaction-path and sensitivity analyses indicate that the peak OH and CH mole fractions exhibit significant sensitivity to the main branching reaction, H + O₂ ↔ OH + O. The sensitivity of OH and CH to this and other reactions is enhanced by N₂ dilution. As a result, N₂-diluted flames provide a good test case for studying the reliability of chemical kinetic and transport models.     

Analysis and characterization of traveling-wave electrode in electroabsorption modulator for radio-on-fiber application

Comparing with a lumped electroabsorption modulator (EAM), we show the merits of a long EAM with traveling-wave electrode with high radio-frequency (RF) gain that could be used in high-frequency analog application. By terminating the RF output port with the characteristic impedance of 30 /spl Omega/, the device exhibited a large enhancement of 6 dB above 10 GHz in the electrical-to-optical response and a wide fractional bandwidth as estimated from simulation. In addition, an input impedance matching circuit of stub embedded on the device chip was found to be very effective for improving RF characteristics in the narrow band of frequency.     

Channel Estimation in Long Term Evolution Uplink Using Minimum Mean Square Error-Support Vector Regression

In this paper, minimum mean square error-support vector regression (MMSE-SVR) is proposed, which is shown to be adequate for the estimation of the long term evolution (LTE) uplink channel with nonlinear features. MMSE-SVR was applied to estimate real channel environments such as the vehicular A channels defined by the International Telecommunication Union (ITU). The simulation results show that the proposed method has a better performance than the least squares support vector machine (LS-SVM) and the standard MMSE with linear and spline interpolation.     

Outstanding Low-Temperature Performance of Structure-Controlled Graphene Anode Based on Surface-Controlled Charge Storage Mechanism

The energy and power performance of lithium (Li)-ion batteries is significantly reduced at low-temperature conditions, which is mainly due to the slow diffusion of Li-ions in graphite anode. Here, it is demonstrated that the effective utilization of the surface-controlled charge storage mechanism through the transition from layered graphite to 3D crumpled graphene (CG) dramatically improves the Li-ion charge storage kinetics and structural stability at low-temperature conditions. The structure-controlled CG anode prepared via a one-step aerosol drying process shows a remarkable rate-capability by delivering ≈206 mAh g^–1 at a high current density of 10 A g^–1 at room temperature. At an extremely low temperature of −40 °C, CG anode still exhibits a high capacity of ≈154 mAh g^–1 at 0.01 A g^–1 with excellent rate-capability and cycling stability. A combination of electrochemical studies and density functional theory (DFT) reveals that the superior performance of CG anode stems from the dominant surface-controlled charge storage mechanism at various defect sites. This study establishes the effective utilization of the surface-controlled charge storage mechanism through structure-controlled graphene as a promising strategy to improve the charge storage kinetics and stability under low-temperature conditions.