Search

The early alert monitoring system for an effective scheduled maintenance strategy based on a wireless technology requires reliable transfer of the diagnostic information between the sensor and the gateway. This paper presents an industrial wireless sensor network (IWSN)-based machine condition monitoring (MCM) system capable of overcoming a false indication caused by temporary loss of data, signal interference, or invalid data. We use multisensor fusion driven by a quality parameter, which is produced by each sensor node according to the data history outliers and the actual state of the node. The fusion node provides a quality evaluation on its output as well. This novel approach enables the propagation of information about the uncertainty of a measured value from the source node to the sink node. Thus, potential degradation of acquired or transferred diagnostic information is minimized. Instead of raw data, the signal features are transferred, so that bandwidth savings are rapidly improved. The proposed concept was experimentally verified on real wireless sensor network (WSN) hardware. The performance evaluated using the signal-to-noise ratio and false-alarm rate detection demonstrates the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]

In order to increase the annual energy yield of a variable-speed wind energy conversion system (WECS), maximum power point tracking (MPPT) control is required at below the rated wind speed. However, the only aspect that has been paid attention to by most of the researchers is the way to accelerate the MPPT speed. In fact, the research of this paper finds out that the faster the MPPT speed is, the larger transient load the turbine shaft bears. Thus, attempts are first made to find out the relationship between the MPPT speed and the transient load through quantity analysis. Then, a principle to choose a proper bandwidth of the MPPT system is given out to optimize the transient load. Furthermore, to ensure that the system can track the varying winds at the designed bandwidth, the design details on how to make the MPPT bandwidth constant are also proposed in this paper. Finally, a 1.2-kW variable-speed WECS, which is based on a permanent-magnet synchronous generator, is established in the laboratory. Theoretical analysis is verified by experimental results performed by it. [ABSTRACT FROM PUBLISHER]

An LCL-type filter is widely used in the grid-connected inverter. However, with only injected grid current control, the current harmonics and low bandwidth caused by the resonance peak cannot be tolerated. The active damping (AD) method with an extra feedback provides a high rejection of the resonance so that the dynamic is improved; however, the high-precision sensing circuit for the extra feedback increases the cost. In this paper, with the signal flow graph and response-fitting methods, an AD method based on the feedback of the injected grid current has been proposed. Then, the novel closed-loop current control requires accurately sensing the injected grid current only, while no observation is needed. Compared with the extra feedback methods, the cost and the complexity are reduced while the reliability is improved. Based on the study of the relation between the controller and the system dynamic, a straightforward design has been proposed. The robustness, harmonic rejection, and digital implementation have been studied. Compared with the conventional control methods, the proposed one promises the satisfactory performance with both analog and digital implementations. Simulations and experiments have verified the proposed control and design strategies. [ABSTRACT FROM PUBLISHER]

This paper discusses the dynamic interaction of multi active power filters (APFs) paralleled with a weak power grid. In order to analyze the dynamic interaction from multi APFs, the output impedance of an APF is solved. The influences of both circuit and control parameters on the output impedance are analyzed. Based on the output impedance of an APF, the dynamic influences of an APF on the other APF connected to the weak grid are discussed. As shown in this paper, the stability of an APF is improved with an increased output filter inductance and some control parameters to reduce its bandwidth. The proposed analysis methods can be used not only for multi APFs but also for the other multi-inverters connected to a weak grid. Experimental tests are carried out using two paralleled three-phase 10-kVA inverters to confirm the validity of the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper describes a new procedure which facilitates the frequency-response curve interpretation in the low-frequency bandwidth. The procedure is able to estimate the magnetization inductance and winding capacitance, for each transformer phase by only using data from its frequency response. The described calculation procedure uses an R-L-C electrical equivalent circuit developed to simulate the impedance measured in the frequency-response test. The procedure takes into account the magnetic coupling among different phases and allows their analysis separately, enabling the identification of a possible failure. This paper describes the procedure to obtain the parameters and its application for interpreting the low-frequency results of frequency-response analysis measurement cases. [ABSTRACT FROM PUBLISHER]

A conventional energy harvester typically consists of a cantilevered composite piezoelectric beam, which has a proof mass at its free end while its fixed end is mounted on a vibrating base structure. The resulting relative motion between the proof mass and the base structure produces a mechanical strain in the piezoelectric elements, which is converted into electrical power by virtue of the direct piezoelectric effect. In this article, the harvester is provided with a dynamic magnifier consisting of a spring-mass system that is placed between the fixed end of the piezoelectric beam and the vibrating base structure. The main function of the dynamic magnifier, as the name implies, is to magnify the strain experienced by the piezoelectric elements in order to amplify the electrical power output of the harvester. With proper selection of the design parameters of the magnifier, the harvested power can be dramatically enhanced and the effective bandwidth of the harvester can be improved. The theory governing the operation of this class of cantilevered piezoelectric energy harvesters with dynamic magnifier (CPEHDM) is developed using the Generalized Hamiltons's Principle. Numerical examples are presented to illustrate the merits of the CPEHDM in comparison with the conventional piezoelectric energy harvesters (CPEH). The obtained results demonstrate the feasibility of the CPEHDM as a simple and effective means for enhancing the magnitude and spectral characteristics of CPEH. [ABSTRACT FROM AUTHOR]

A semi-analytical solution for the input reflections, inner field distribution and radiated fields for a wideband traveling-wave antenna based on a tapered half-mode substrate-integrated waveguide (HMSIW) is proposed in this paper. The analysis validates the operation mechanism for this type of traveling-wave antenna which exhibits omni-directional radiation properties with horizontal polarization (“magnetic dipole”). The derived expressions allows the design and efficient optimization of different antennas towards fulfilling various predefined specifications of reflection coefficient and operating bandwidth. The antenna utilizes a wideband transition from coaxial cable to a HMSIW, which is also considered in the model to provide highly accurate semi-analytical results. Utilizing the proposed method, three antennas of different specifications have been optimized, manufactured and tested. The analysis, simulation and measurement results show good correspondences, which verifies the design process and demonstrates the versatility of the concept. [ABSTRACT FROM PUBLISHER]

A new single-layer microstrip dual-resonance conformal loop (DRCL) element is proposed to design a printed beam deflector array for broadband application. By utilizing variable parameters of the DRCL element, a nearly progressive phase-shift ranging more than 550^\circ is achieved for deflecting wave within a wide band. It is important that a small DRCL element can be flexibly used to generate a 360^\circ phase shift, which decreases the cell period between the neighboring elements. The DRCL is less sensitive to the variation of incidence angles for both TE and TM polarizations. An X-band plane wave beam deflector array is designed, fabricated and measured. The results show a significant improvement in gain-bandwidth performance of the deflector array using the new structure element. The 1 dB gain-bandwidth of 20% can be achieved. The measured results agree well with the simulation results. [ABSTRACT FROM PUBLISHER]

Although conventional Yagi antenna has the advantage of unidirectional radiation patterns, it is not suitable for wideband applications due to its drawback of narrow bandwidth. In this communication, a compact wideband planar printed quasi-Yagi antenna is presented. The proposed quasi-Yagi antenna consists of a microstrip line to slotline transition structure, a driver dipole, and a parasitic strip element. The driver dipole is connected to the slotline through a coplanar stripline (CPS). The proposed antenna uses a stepped connection structure between the CPS and the slotline to improve the impedance matching. Two apertures are symmetrically etched in the ground plane to improve the unidirectional radiation characteristics. Simulation and experimental results show that the unidirectional radiation patterns of the proposed antenna are good. A 92.2% measured bandwidth with S 11 < -10~dB from 3.8 to 10.3 GHz is achieved. A moderate gain, which is better than 4 dBi, is also obtained. [ABSTRACT FROM PUBLISHER]

A novel method is presented to design single-feed high-gain EBG resonator antennas (ERAs) with significantly wider bandwidths. Dielectric contrast is introduced to 1-D EBG superstructures composed of unprinted dielectric slabs, and the thicknesses of each of these slabs is optimized to achieve a wideband defect mode in a unit-cell model. Next, antennas are designed and their superstructure areas are truncated to increase the antenna bandwidth and aperture efficiency while decreasing antenna footprint. We demonstrate that a small superstructure area increases the 3-dB bandwidth of ERAs significantly. A prototype ERA designed with a single feed and superstructure area as small as \ 1.5 \lambda_0 \times \ 1.5 \lambda_0 has a measured 3-dB directivity bandwidth of 22% at a peak gain of 18.2 dBi. This prototype antenna was made out of three slabs of different dielectric constants, two of them touching each other. This prototype demonstrates more than 85% reduction in the ERA footprint alongside a drastic improvement in bandwidth over the 3%–4% measured bandwidth of the classical single-feed ERAs with unprinted slabs. [ABSTRACT FROM PUBLISHER]

A novel planar octagonal-shaped antenna with reduced radar cross section (RCS) for ultra-wideband (UWB) applications is designed and demonstrated experimentally. The proposed antenna is modified using the geometrical shaping method in order to get the RCS reduction. This method is based on the subtraction of metal areas which have the minimum current distributions on the surface of printed antenna. Both of the reference and modified octagonal-shaped antennas are operating at 2.5–18 GHz frequency range with %151 fractional bandwidths. The full-wave electromagnetic simulations and laboratory measurements are performed to characterize their RCSs as a function of frequency, radiation patterns and scattering characteristics. The radiation performance of modified antenna is stable and consistent with the reference antenna. Also the results show that the designed UWB antenna has lower RCS compared to the reference antenna. About 10 dBsm RCS reduction is obtained in the whole operation bandwidth. The designed antenna has very large RCS reduction up to 25 dBsm, especially in the low frequency range. [ABSTRACT FROM PUBLISHER]

A compact hyper-band (>10:1 impedance bandwidth) printed antenna design is investigated numerically and experimentally. It is based on an elliptical-slot antenna augmented with a parasitic oval patch and driven with a specially engineered microstrip-line-fed elliptical tuning fork element. The parasitic and driven elements are adjusted along with the elliptical slot to create additional resonance modes; adjust the coupling strengths among all of the design components; facilitate the overlap of adjacent resonance modes; and fine tune the input impedance. The total size of the final optimized antenna is only 30\times40 mm^2. It exhibits a -10-dB impedance bandwidth from 2.26 to 22.18 GHz. Desirable radiation performance characteristics, including relatively stable and omni-directional radiation patterns, are obtained over this range. A prototype was fabricated and tested. The experimental results confirm the predicted input impedance bandwidth and radiation characteristics. While the hyper-band performance could be used for high fidelity short pulse applications, the antenna could also be used for multi-band operations from 3.1–10.6 GHz since it covers that entire ultra-wideband (UWB) spectral range. [ABSTRACT FROM PUBLISHER]

Random arrays bound by a spherical volume are rigorously analyzed through a stochastic approach for uniform and Gaussian element distributions. The full mathematical derivation and process to determine the array characteristics are discussed and a key result is the form solution which describes both the sidelobe behavior and main beam characteristics. It is also shown that the proposed approach shares many conceptual similarities to the probabilistic approach applied to circular random arrays and comparisons are made. The 3-dB beamwidth, directivity, grating lobes, and sidelobe level are examined analytically and in numerical simulation for a conceptual system of isotropic wide-band radiators with a 100:1 bandwidth. [ABSTRACT FROM PUBLISHER]

We propose a slot array antenna for dual-polarization operation in the 60 GHz band. To realize the dual-polarization, cross-shaped radiating slots and a multilayer feeding structure are employed. A 16\,\times\,16-element array is fabricated by diffusion bonding of laminated thin copper plates, which has the advantages of high precision and low loss characteristics. To suppress the grating lobes, we employ several design techniques, such as a thick cavity structure and dense element spacing. The high antenna gain higher than 32.0 dBi and the antenna efficiency near 80.0% are obtained over 60.0–64.0 GHz for two different polarizations. The 1-dB-down gain bandwidths reach 10.4% and 10.9%. High isolation above 50 dB is achieved between the two input ports. [ABSTRACT FROM PUBLISHER]

The IEEE Wireless Access in Vehicular Environment, or WAVE, system uses 5.9 GHz band. Recently, however, the FCC announced its intention to share the band for WLANs based on new standards such as IEEE 802.11ac. In this article, we discuss the problems in the possible coexistence scenario of WAVE and WLAN, such as direct competition between WLAN and WAVE devices for bandwidth and the hidden terminal problem. The problems are exacerbated by the different bandwidth used by the two technologies, so the only usable sensing method between them is energy detection. In this article, we consider one way to address the problems within the current standards framework, which is the combined control of interframe space and the receiver sensitivity on the WLAN devices cued by the energy detection. [ABSTRACT FROM PUBLISHER]

We present a theoretical study on optoelectronic properties ofn-type monolayer MoS2under long-wavelength light radiation. The optical conductance for such material system is evaluated using the energy-balance equation derived from the Boltzmann equation in the presence of linearly polarized radiation field. Forn-type monolayer MoS2, the optical absorption in terahertz bandwidth can be achieved via intra spin-conserved transitions and inter spin-flip transitions at K and K′ valleys. More importantly, we find that there is a terahertz absorption peak in the radiation frequency range 2–10 THz. The intensity and width of this absorption peak depend sensitively on temperature and the position of the peak can be tuned via changing the electron density. This study shows thatn-type monolayer MoS2can be applied as frequency tunable THz optical and optoelectrical devices. [ABSTRACT FROM AUTHOR]

ABSTRACT A complementary staked microstrip antenna with a modified Minkowski fractal shaped defect is presented which has a wide bandwidth of 1.8-6.4 GHz with a fractional BW of 89.1%. The concept of the complimentary stacked parasitic fractal patch has been incorporated to enhance the impedance bandwidth in comparison to the conventional stacked patch antenna. The antenna has a dimension of 42 × 55 × 4.8 mm3, which is printed on a low cost FR4 substrate of dielectric constant 4 and a height of 1.6 mm. The gain of the antenna varies from 5 to 7 dBi throughout the operating band. Simulated and experimental characteristics of the antenna are in good agreement. The proposed antenna can be a potential candidate for wideband communication systems and also capable to operate satisfactorily in 3.3-3.7 GHz (WiMAX), 3.7-4.2 GHz (C-Band), and 5.15-5.825 GHz (WLAN) frequency bands. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:944-947, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, we propose the design of a coplanar waveguide (CPW)-fed circular slot antenna, with dual frequency rejection characteristics for ultra-wideband communication applications. The dual frequency rejection function is realized by inserting a stepped impedance stub (SIS) inside the circular ring radiation patch and by using an arc-shaped parasitic element (ASPE) along the circular ring radiation patch. The center frequencies of these rejection bands can be controlled by adjusting the dimensions of the SIS and the ASPE. The antenna has been designed, optimized, and fabricated, and its performance has been verified through measurements, which show that it can operate across a wide bandwidth ranging from 2.7 to 11.6 GHz with a VSWR < 2, and that it provides dual-band rejection characteristics at both the WLAN band and the X-band. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:783-787, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a set of CAD oriented closed form expressions to predict accurately the effect of radome (superstrate) on resonant frequency, input impedance, bandwidth, and gain of rectangular patch antenna. Merits of this model include low computation cost and mathematical simplicity. The numerical values obtained with the present method are compared with experimental and different theoretical values. The accuracy of this model is verified with electromagnetic software (HFSS) computation and with the experimental values. The present model shows very close agreements with the experimental and software computation values compared to the other models for wide range of thickness and permittivity of substrates and superstrates. This model is directly applicable for the integration of patch antennas beneath plastic covers or protective superstrates in portable wireless equipment and aircraft radome. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:883-893, 2014 [ABSTRACT FROM AUTHOR]

Ad hoc networks are characterized by limited resources (e.g. energy, bandwidth). Efficient information dissemination while avoiding excessive energy cost can be achieved through the suitable design of a network. To this end we propose an information dissemination scheme which couples epidemic dissemination with adaptive modulation and coding (AMC). The proposed scheme tunes the message forwarding probability and the coding and modulation mode in order to achieve a balance between maximum coverage over the network and minimum energy expenditure. We achieve this based on the evaluation of suitably defined indicators related to the lower network layers and exploiting information on the current status of the wireless medium. Building on established previous AMC-related work, our simulation results indicate that our scheme brings significant improvement over non-adaptive approaches, comparable with other adaptive epidemic dissemination schemes. Our findings are quite promising for adaptive epidemic-based information dissemination schemes with a strong cross-layer component. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a study of Global Navigation Satellite System (GNSS) receiver correlation performance in the presence of phase noise (PN) originating from the radio front-end's phase-locked loop (PLL). Various constituent PLL sub-blocks, such as the reference oscillator (RO), phase and frequency detector (PFD), voltage controlled oscillator (VCO), loop filter and frequency dividers contribute to the overall PN of the PLL. The PLL phase noise modeling is covered in detail. Correlation performance of GNSS baseband tracking loops is then calculated as a function of several PLL design parameters, such as the VCO thermal PN, loop filter bandwidth (BW), frequency division ratio (FDR), and the receiver correlator's pre-detection integration times (PIT). The effects of these parameters on the signal to noise ratio (SNR) of the correlation product are described and simulated. Based on the results of these simulations, we present guidelines for radio front-end PLL circuit design in order to maintain a minimum baseband correlation performance within the GNSS receiver. Copyright © 2014 Institute of Navigation. [ABSTRACT FROM AUTHOR]

The decades-old synchronous memory bus interface has restricted many innovations in the memory system, which is facing various challenges (or walls) in the era of multi-core and big data. In this paper, we argue that a message based interface should be adopted to replace the traditional bus-based interface in the memory system. A novel message interface based memory system called MIMS is proposed. The key innovation of MIMS is that processors communicate with the memory system through a universal and flexible message packet interface. Each message packet is allowed to encapsulate multiple memory requests (or commands) and additional semantic information. The memory system is more intelligent and active by equipping with a local buffer scheduler, which is responsible for processing packets, scheduling memory requests, preparing responses, and executing specific commands with the help of semantic information. Under the MIMS framework, many previous innovations on memory architecture as well as new optimization opportunities such as address compression and continuous requests combination can be naturally incorporated. The experimental results on a 16-core cycle-detailed simulation system show that: with accurate granularity message, MIMS can improve system performance by 53.21% and reduce energy delay product (EDP) by 55.90%. Furthermore, it can improve effective bandwidth utilization by 62.42% and reduce memory access latency by 51% on average. [ABSTRACT FROM AUTHOR]

Abstract: We propose a novel bandwidth expansion technique for cascode amplifiers, that exploits positive capacitive feedback (PCF) applied to the cascade of common base and common collector stages to increase the overall amplification at high frequencies. The resulting amplifier has a nearly unchanged input impedance, that we enhance introducing a second PCF loop. We present an ac model of the topology to better understand the behavior of the proposed technique and to compare it with other PCF-based amplifiers. Simulations, carried out using a 230GHz-fT SiGe technology, have shown a 40% bandwidth extension rate with respect to a simple cascode differential pair when a 50Ω source resistance is used, and up to 59% for a 200Ω source resistance. This is a 15–20% more than what can be achieved with other PCF techniques in the literature. The proposed topology is robust against process variations, and retains its advantages when accurate layout parasitics are taken into account. [Copyright &y& Elsevier]

Folded waveguide (FWG) traveling wave tubes (TWTs) are potential sources of wideband, high-power millimeter and terahertz wave radiation. However, low efficiency limits its application. In this paper, we discuss a design strategy to improve efficiency of the FWG TWT meanwhile how to avoid instability is also discussed. The critical factors for the slow-wave structure design and the sever design are analyzed. A phase velocity taper profile incorporating a positive period followed by a negative period is introduced into the design to improve the efficiency. A Ka-band FWG TWT was developed, which demonstrated the output power up to >1~KW in 2-GHz bandwidth and electronic efficiency up to >9.4\%. [ABSTRACT FROM AUTHOR]

Network mobility (NEMO) enables a group of nodes to connect to the back-end infrastructure during the movement. Because a vehicle must provide passengers good enough transmission quality, various access techniques, for example, 3 G/3.5 G, Wi-Fi or dedicated short range communication, can be simultaneously equipped to aggregate bandwidth and tolerate link failure. This paper extends the Session Initiation Protocol (SIP)-based NEMO framework to support multihoming. First, IEEE 802.21 Media Independent Handover (MIH) is integrated to manage multiple egress interfaces in an on-board unit (OBU). Second, a dynamic synchronization mechanism using the SIP SUBSCRIBE and NOTIFY methods is proposed to manage multiple OBUs in a vehicle. Furthermore, the framework is applied to public transportation systems, for example, bus, train, or mass rapid transit. Passengers may need to transit several times during their journeys. The transit behavior must induce a flood of signaling messages for location update. In this paper, the SIP REFER method is exploited to reduce signaling messages while a group of passengers have scheduled their transit in advance. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT The channel capacity and the bit error rate of ultra-wide bandwidth transmitted-reference systems are optimized with respect to time delay between the reference and the adjacent data pulses. Approximate and theoretical expressions for the signal-to-interference-plus-noise ratio are derived. Numerical results show that optimizing the receiver can provide a significant capacity improvement of up to 2.2 bits/s/GHz and a bit error rate performance gain of up to 2 dB in effective signal-to-noise ratio. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we study how multiple users can balance their traffic loads to share common resources in an efficient and distributed manner, without message exchanges. Specifically, we study a deployment scenario where users deploy delay-sensitive applications over a wireless multipath network and aim to minimize their own expected delays. Since the performance of a user's load balancing strategy depends on the strategies that are deployed by other users, it becomes important that a user considers the multiuser coupling when making its own load balancing decisions. We model this multiuser interaction as a load balancing game (LBG) and show that users can converge to a \varepsilon-consistent conjectural equilibrium by building near-accurate beliefs about the remaining capacities on each path. Based on these beliefs, users can make load balancing decisions without explicitly knowing the actions of the other users. In such a conjecture-based LBG, we analytically show that, if a leader is elected to build beliefs about how the users' aggregate transmission strategies affect the remaining resources, then this leader can use this knowledge to shape its traffic such that the multiuser interaction can achieve an efficient allocation across paths. Even if no leader is present in the game, as long as the users follow a set of prescribed rules for building beliefs, they can reach efficient outcomes in a distributed manner. Importantly, the proposed distributed load balancing solution can be also applied to other multiuser communication and networking problems where message exchanges are prohibited (or prohibitively expensive in terms of delay or bandwidth), ranging from multichannel selection in wireless networks to relay assignment in multivehicle networks. [ABSTRACT FROM PUBLISHER]

A new design of broadband circularly polarized antenna is proposed. The antenna is composed of a square patch and a horizontal L-shaped stripline that feeds the patch at two orthogonal directions by two probes. The L-shaped feeding structure provides excitements of approximately equal amplitude and 90° phase difference and then good circularly polarized characteristics are obtained. Measured results show that the proposed antenna has 10-dB impedance bandwidth of 14.3% (2.27-2.62 GHz) and 3-dB axial-ratio bandwidth of 13.1% (2.3 -2.62 GHz). Moreover, the measured gain is over 7 dBic within the effective band. [ABSTRACT FROM AUTHOR]

A self-phase-locked degenerate femtosecond optical parametric oscillator (OPO) based on the birefringent nonlinear material, bismuth triborate, BiB3O6, synchronously-pumped by a Kerr-lens-mode-locked Ti:sapphire laser at 800 nm is described. By exploiting versatile phase-matching properties of BiB3O6, including large spectral and angular acceptance for parametric generation and low group velocity dispersion in the optical xz plane, stable self-phase-locked degenerate OPO operation centered at 1600 nm is demonstrated using collinear type I ( e → oo) interaction in a 1.5-mm crystal at room temperature. The degenerate OPO output spectrum extends over 46 nm (∼5.4 THz) with 190 fs pulse duration for input pump pulses of 155 fs with a bandwidth of 7 nm. Phase coherence between the pump and degenerate output is verified using f-2f interferometry, and discrete frequency beats caused by different carrier-envelope-offset frequencies are measured using radio frequency measurements. Photo shows a 1.5-mm BiB3O6 crystal used as a nonlinear gain medium in a degenerate self-phase-locked femtosecond OPO operating at room temperature. The green beam is the result of non-phase-matched sum-frequency mixing between the pump light and the sub-harmonic OPO field at degeneracy. [ABSTRACT FROM AUTHOR]

Semiconductor microcircular lasers have been investigated as potential light sources for photonic integrated circuits and optical interconnections for more than two decades. However, the direct modulation bandwidths of the circular microlasers remain a challenge, especially when being compared with other microlasers, such as photonic crystal lasers. In this paper, microcircular lasers connected to an output waveguide are investigated for high-speed direct modulation with optimized mode Q factors. Small signal modulation with a resonance frequency of fR = 12.5 GHz is realized for a AlGaInAs/InP circular microlaser with a radius of 10 µm at 290 K. Furthermore, clear eye diagrams are observed at 12.5 Gbit/s for a 15-µm radius circular microlaser with fR = 6.9 GHz. [ABSTRACT FROM AUTHOR]

Telecom infrastructure development has been enabled greatly by different forms of collaborations or synergies between the public and the private sector. These synergies in most cases are exigent measures employed to enable the diffusion of telecom infrastructure into underserved and un-served areas. This paper examines the role of different public-private interplay that exists in Africa that were aimed at developing telecom infrastructure and why this public-private interplay could help in extending broadband connectivity to rural areas. Ghana is identified as a country with almost 80% penetration of mobile telephony. This has been made possible by the public-private collaborations fostered towards telecom infrastructure development. Ghana is used as a case to examine the strategies and identify possibilities for more of these collaborations. Data was gathered qualitatively. The significance of the paper is to narrate the possibility of using PPP to develop broadband infrastructure in Africa. [ABSTRACT FROM AUTHOR]

The increasing use of streaming applications and wide variety of devices, such as handheld personal organizers, have raised new challenges, such as the provision of access to multimedia content for devices with limited computing and bandwidth capabilities. In this paper, we propose a technique for periodic broadcasting. Our technique allows clients with low bandwidth capability to be served in the same period as high-bandwidth clients, using peer-to-peer streaming between clients, and also works for clients with downstream capability below the video bit rate. In the proposed system, the server builds multicast trees of clients that allow clients with low bandwidth to be served by other clients with sufficient upstream bandwidth. Clients below the video bit rate will suffer additional, but only moderately noticeable, delays that occur as video is converted to lower quality. We performed extensive simulation and showed that our system can provide improved service performance for heterogeneous clients on periodic broadcasting protocols. [ABSTRACT FROM AUTHOR]

The rendering of effects such as motion blur and depth-of-field requires costly 5D integrals. We accelerate their computation through adaptive sampling and reconstruction based on the prediction of the anisotropy and bandwidth of the integrand. For this, we develop a new frequency analysis of the 5D temporal light-field, and show that first-order motion can be handled through simple changes of coordinates in 5D. We further introduce a compact representation of the spectrum using the covariance matrix and Gaussian approximations. We derive update equations for the 5x5 covariance matrices for each atomic light transport event, such as transport, occlusion, BRDF. texture, lens, and motion. The focus on atomic operations makes our work general, and removes the need for special-case formulas. We present a new rendering algorithm that computes 5D covariance matrices on the image plane by tracing paths through the scene, focusing on the single-bounce case. This allows us to reduce sampling rates when appropriate and perform reconstruction of images with complex depth-of-field and motion blur effects. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, we introduce the continuous phase modulations mode of the second-generation broadband satellite communications return link Digital Video Broadcast Interactive Satellite System standard. Starting from a detailed discussion about the impairments faced in a typical broadband satellite system user set-up, we introduce the waveform selection rationale, the design trade-offs, and the waveform performance under realistic system assumptions. We show that the designed continuous phase modulations mode exhibits an excellent trade-off between performance and robustness to nonlinear distortions at low and medium spectral efficiency thus suggesting its adoption for the consumer market profile of the Digital Video Broadcast Interactive Satellite System. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A self-phase-locked degenerate femtosecond optical parametric oscillator (OPO) based on the birefringent nonlinear material, bismuth triborate, BiB3O6, synchronously-pumped by a Kerr-lens-mode-locked Ti:sapphire laser at 800 nm is described. By exploiting versatile phase-matching properties of BiB3O6, including large spectral and angular acceptance for parametric generation and low group velocity dispersion in the optical xz plane, stable self-phase-locked degenerate OPO operation centered at 1600 nm is demonstrated using collinear type I ( e → oo) interaction in a 1.5-mm crystal at room temperature. The degenerate OPO output spectrum extends over 46 nm (∼5.4 THz) with 190 fs pulse duration for input pump pulses of 155 fs with a bandwidth of 7 nm. Phase coherence between the pump and degenerate output is verified using f-2f interferometry, and discrete frequency beats caused by different carrier-envelope-offset frequencies are measured using radio frequency measurements. Photo shows a 1.5-mm BiB3O6 crystal used as a nonlinear gain medium in a degenerate self-phase-locked femtosecond OPO operating at room temperature. The green beam is the result of non-phase-matched sum-frequency mixing between the pump light and the sub-harmonic OPO field at degeneracy. [ABSTRACT FROM AUTHOR]

A novel triple-frequency fork-shaped antenna for WLAN/WiMAX applications is proposed and investigated in this paper. The presented antenna is simply composed of three radiating elements viz. Stub1, Stub2, Stub3. By adjusting the lengths of the three stubs, three desired resonant frequencies can be achieved and adjusted independently. Experimental results show that the antenna impedance bandwidths for S11 ≤ -10 dB are 2.4{2.65 GHz, 3.3-4.05 GHz, and 5-5.98 GHz, covering the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands. Furthermore, nearly omnidirectional radiation patterns over the operating bands have been obtained. [ABSTRACT FROM AUTHOR]