Search

This article presents a novel ultra-wideband (UWB) microstrip-fed planar monopole antenna composed of a rectangular patch and a ground-plane π-shape slot structure. Impedance bandwidth of the proposed antenna is ∼147% over an UWB frequency range between 3 and 19.7 GHz satisfying FCC's requirements for an antenna by a factor in excess of twofold. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:870–873, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25072 [ABSTRACT FROM AUTHOR]

A compact printed monopole antenna for WLAN and WiMAX applications is proposed. By combining symmetrical G-shaped strips and a coupling-fed plate, fed by a 50 Ω microstrip transmission line, wide impedance bandwidths covering WLAN/2.4/5.2 and WiMAX/5.75 are achieved. The omnidirectional pattern and good gain over the operating bands have been obtained by the fabricated antenna with a compact size of 20 × 34.5 mm2, which is suitable for wireless communication applications. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:857–861, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25060 [ABSTRACT FROM AUTHOR]

In this article, the analysis of disk patch antenna with two parasitic elements in single layer and in multilayer layer configurations is presented. The bandwidth of the antenna significantly depends on gap separation (s) and thickness h2. Bandwidth of the antenna in single-layer gap-coupled structure is found to be 19.01%, and it improves up to 45.57% in multilayer patch. Further, an enhanced radiation of 8.33 dB is achieved in multilayer patch as compared with simple disk patch. The theoretical results obtained from the analysis are compared with IE3D simulated and experimental results, which are in good agreement. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:865–870, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25076 [ABSTRACT FROM AUTHOR]

In a novel application a slab of S-shaped ring resonators is used to fill a rectangular waveguide for the construction of a band-rejection waveguide filter with adjustable bandwidth and cutoff frequency. Results obtained from theoretical analysis, simulation and measurement of a specific structure are presented. Then, by using finite element simulation, we show that the cutoff frequency and stopband bandwidth of the filter can be controlled by changing the slab substrate properties (permittivity and thickness) and its position inside the waveguide. Results also show that varying the real part of relative permittivity of the slab substrate from 1 to 6, while keeping its physical thickness fixed (0.508 mm), the cutoff frequency drops from 10.6 to 6.9 GHz. On the other hand, when the physical thickness of slab substrate changes from 0.508 mm to 4 mm while keeping its permittivity fixed (εr = 2.2), the filter cutoff frequency decreases from 8.8 to 5.9 GHz. We show that the width of rejection band of the filter can be decreased from about 4.7 GHz to about a few MHz by increasing the distance of the slab from the central plane of the waveguide. [ABSTRACT FROM AUTHOR]

A novel broadband E-plane omni-directional planar antenna is designed and fabricated, which consists of four curved printed dipole radiators with eight parasitical strips. The impedance bandwidth is expanded by properly adding two parasitical strips along the boresight of each dipole radiator. A good omni-directionality is achieved at horizontal plane, and the measured variations of far field-patterns in the E-plane are less than ±1.5 dB, cross polarization levels of all directions in the E-plane better than -10 dB over the operating frequency range 5.1 ∼ 6.8 GHz with the reflection coefficients less than -10 dB. It is demonstrated experimentally that the proposed antenna is suitable for WLAN operation in the 5 GHz band, such as the 5.2 GHz (5.15 ∼ 5.35 GHz) and 5.8 GHz (5.725 ∼ 5.875 GHz) bands. [ABSTRACT FROM AUTHOR]

CPW-fed planar inverted-F antennas (PIFAs) with small ground plane for dual-band performance are proposed. The lower band and upper band can be selected independently: PIFA is for the lower band, and capacitively coupling slot is for the upper band. Moreover, the frequency ratio of upper band to lower band can be obtained from 1 to 3.1. The proposed antenna with wider frequency ratio will enable antenna engineer to design dual-band antenna easily. The radiation patterns for the lower band are decided by the PIFA with the quarter-wavelength electric L-shaped monopole patterns, and those for the upper band are dominant over the coupling slot with the half-wavelength magnetic dipole patterns. Hence, both patterns in the dual-band are near omni-directional. An antenna example is given for WLAN dual-band applications. Simulated data are consistent with the measured ones. Measured impedance bandwidth for 2.4 GHz band is 1090 MHz (47.9%), and that for 5 GHz band is 1180 MHz (20.6%). Additionally, through a suitable adjustment in antenna parameters, a wider bandwidth of 1970 MHz (51.2%) can be obtained with center frequency at 3.845 GHz. The radiation patterns and gains are also studied and analyzed. [ABSTRACT FROM AUTHOR]

This paper focuses on the bandwidth selection in the kernel density estimation in the univariate case. We compared via simulation between the optimal bandwidth selection based on the mean integrated squared error (MISE) and based on the asymptotic mean integrated squared error (AMISE) for various densities and sample sizes. Also, we compared between the MISE and the AMISE in the kernel density estimation. Through simulation, these optimal bandwidths are compared with the bandwidth selection using the methods least squared cross-validation (LSCV), biased cross-validation (BCV), and direct plug-in (DPI). [ABSTRACT FROM AUTHOR]

A new dual-polarized microstrip patch antenna fed by probe feed and aperture coupled feed is presented. The hybrid feed, a T-shaped microstrip feedline, is adopted to improve the isolation between two ports, and the “hour-glass” shaped slot is used to improve the input impedance of the proposed antenna. The measured center frequency is 2.37 GHz, the return loss for port 1 is -16.08 dB and -21.92 dB for port 2, and the isolation between the two ports is -24.24 dB. Finally, four slots are embedded along the centerline of the ground plane so that the bandwidth of antenna is greatly improved. Good agreement between the measured and simulated results has been achieved. [ABSTRACT FROM AUTHOR]

Minimizing the number of bandwidth changes of individual stream and enabling the transmission schedule flexible can benefit increasing the number of concurrent multiplexed streams in periodic network without degrading quality of video. However, minimum change bandwidth allocation (MCBA) only provides a fixed transmission schedule for given video and client buffer although it achieves the minimum number of rate changes and the minimum peak rate. So the MCBA schedule cannot be adjusted when multiple streams are multiplexed over a limited bandwidth shared link. In this paper, we propose a relaxing transmission schedule that provides a range of rates for each interval and preserves the minimum number of rate changes without increasing any rate. As a result, the individual schedule can be adjusted by network service to try to satisfy bandwidth constraint when the total required bandwidth of multiplexed streams exceeds the available network capacity. First, we underline that the key of MCBA is to segment video with making each linear trajectory as long as possible. Then we use linear separability and support vector machine under the classification model to compute the longest interval and the required rate, respectively. Due to our proposed decoupled form between segmentation and rate computation, finally, we construct the relaxing schedule bounded by the original MCBA rate and the minimum rate. The simulation using real MPEG4 and H.264 video traces confirms the philosophy and evaluates the relaxing performance of our proposed algorithm. [ABSTRACT FROM AUTHOR]

Digital signal processing technologies are key enablers for realizing high-capacity Optical Transport Network based on over 100 Gb/s and above channels. Novel no-guard-interval OFDM with frequency domain equalization is proposed and shown to offer excellent long-haul transport with capacity well above 10 Tb/s. [ABSTRACT FROM AUTHOR]

We consider the problem of using scattered waves to recover an image of the medium in which the waves propagate. We address the case of scalar waves when the sources and receivers are sparse and irregularly spaced. Our approach is based on the single-scattering (Born) approximation and the generalized Radon transform. The key to handling sparse sources and receivers is the development of a data-weighting scheme that compensates for non-uniform sampling. To determine the appropriate weights, we formulate a criterion for measuring the optimality of the point-spread function, and solve the resulting optimization problem using regularized least squares. Once the weights are determined, they can be used to compute the point-spread function and thus determine resolution, and they can also be applied to the measured data to form an image. Tests of our minimization scheme with different regularization parameters show that, with appropriate weighting, individual scatterers can be resolved at subwavelength scales even when data is noisy and the locations of both sources and receivers are uncertain. We show an example in which the source–receiver geometry and frequency bandwidths correspond to seismic imaging from multiple local earthquakes (passive seismic imaging). The example shows that the weights determined by our method improve the resolution relative to reconstructions with constant weights. [ABSTRACT FROM AUTHOR]

We analysed stability and predictive capabilities of known nitrogen absorption features between plant material prepared for NIRS (dried) and RS (fresh) studies. Grass spectra were taken of the plant canopy, and again after the grass sample was dried and ground. Models were derived using stepwise multiple linear regression (sMLR). Regression values (adj.r2) produced using the dried material were greater than those produced using canopy material. For dried material only wavebands from the SWIR region were selected. Wavebands selected by sMLR on canopy material were located in both the VNIR and SWIR regions. Using wavebands selected for dried material models produced low adj.r2 values when applied to canopy plant material; differences in adj.r2 values are smaller when wavebands selected in canopy material models are applied to dried material. Widening of nitrogen features produced higher adj.r2 values for both dried and canopy material. This work shows that obtaining models with high predictive capabilities for nitrogen concentration is possible, but waveband selection should not be limited to features identified by NIRS studies. To accommodate for variability in absorption features, and instrument errors, absorption features should be widened. [ABSTRACT FROM AUTHOR]

Most of consumer electronic devices, including HDTV/IPTV, multimedia teleconference systems, on-line game stations, and HiFi-audio systems, are expected to be connected through WiFi WLANs in home/office networks. Especially, the realtime multimedia applications are requiring guaranteed bandwidth to provide guaranteed QoS/QoE. As a consequence, correct estimation of the available bandwidth in overlapped WiFi WLANs in home/office network environments is one of the essential functions for efficient provisioning of Qos-guaranteed realtime multimedia applications and optimized network resource utilizations in future internet. in this paper, we propose a cognitive passive estimation of the available bandwidth (cPEAB) by correct measurements of i) the proportion of waiting and backoff delay, ii) packet collision and packet error probability, iii) acknowledgement delay, iv) channel idle time compared to measurement period, and v) traffic from hidden/exposed terminals. Using a series of experiments, we found that the proposed scheme estimates the available bandwidth more accurately compared with other schemes. [ABSTRACT FROM AUTHOR]

On rising demand for high quality, mobility and data rate, a considerable effort has been given to develop robust coding techniques for wideband channels. Significant achievements are obtained with multiantenna communications and Orthogonal Frequency Division Multiplexing (OFDM). After the work of Agrawal et al. (1998), the application of Space-Time Block Codes (STBC) to OFDM was suggested by Lee and Williams (2000). Afterwards, the efforts to increase the performance of Multiple-Input Multiple- Output (MIMO) OFDM systems are ongoing. The MIMO OFDM system performance is primarily affected by achieved diversity, and there is a tradeoff between rate, diversity and constellation size. Hence, the only way to increase the diversity in a wideband channel, with unlimited number of channel taps, fixed number of transmit and receive antennas, fixed bandwidth, and bandwidth efficiency, is to extend the constellation of the signals modulating OFDM subcarriers and to encode through these subcarriers. Such systems achieving multipath diversity in wideband channels are the Linear Constellation Precoded (LCP) OFDM and the concatenated LCP and STBC (LCP-STBC) OFDM proposed by Liu et al. (2003; 2002). It is further possible to achieve multipath diversity by trellis encoding through OFDM subcarriers. Such system is the serial concatenated outer convolutional code and LCP-STBC (SC-LCP-STBC) proposed by Wang et al. (2003). The high computational complexity of Maximum Likelihood (ML) sphere decoder (Damen et al., 2000) used with LCP-STBC and turbo decoder used with SC-LCP-STBC leads to a search for techniques with lower decoding complexities. The concatenation of an outer trellis code and STBC (TC-STBC) for OFDM proposed by Gong and Letaief (2003) is an effective coding technique with simple Viterbi decoding. In this system the 8-PSK trellis codes (Jamali and Le-Ngoc, 1991; Schlegel and Costello, 1989) designed for fast fading channels are involved. Gong and Letaief (2003) showed that TC-STBC has superior performance compared to the other trellis coded MIMO OFDM systems (Agrawal et al., 1998; Lu and Wang, 2000). On the other hand, coordinate interleaving (Boulle and Belfiore, 1992; Jelicic and Roy, 1994), applied to MIMO OFDM by Rao et al. (2004), is a powerful technique providing diversity by extending the considered signal constellation. Additionally, the single symbol decodability of Coordinate Interleaved Orthogonal Designs (CIOD) is an important feature ensuring low decoding complexity. In this paper, we propose a concatenated outer trellis code and CIOD (TC-CIOD) OFDM system for high-speed wireless transmission. Our system combines a coordinate interleaver and trellis code to boost the MIMO OFDM performance. The coordinate interleaver provides signal space diversity and improves the Codeword Error Rate (CER) performance of the system in wideband channels. The pairwise error probability analysis of the new system for two transmit antennas shows that the system provides full spatial and multipath diversity, and the TC-CIOD achieves diversity as high as SC-LCPSTBC (Wang et al., 2003) and nearly four times greater than TC-STBC system (Gong and Letaief, 2003), while still preserving the advantage of simple ML Viterbi decoding.… [ABSTRACT FROM AUTHOR]

A broadband circularly polarized (CP) irregular slot antenna with a parasitic slot is proposed. Irregular slot formed by triangles, rectangles and a circle is adopted to achieve both broadband and circularly polarized characteristics. Meanwhile, an accessional slot is cut at proper position to help broadening the bandwidth. A simple 50Ω microstrip line is used to excite this irregular slot. The proposed antenna has a small size of only 25×30×0.8 mm3 and covers a frequency band from 2.35 GHz to 5.95 GHz for S11 less than -10 dB. The 3 dB axial ratio bandwidth is 1.25 GHz (2.65–3.9 GHz) and 0.25 GHz (5.15–5.4 GHz), which are 35.5% and 4.7% respectively. The peak gain of the antenna is 3.19 dB, which appears at 4 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a new configuration of the wide-band amplified spontaneous emission (ASE) source is proposed using dual-stage scheme with a broadband fiber Bragg grating. The ASE source utilizes a Bismuth-based erbium-doped fiber (Bi-EDF) as a gain medium with either forward or backward pumping scheme. A wide-band and flat ASE output is achieved using a forward pumping scheme with the power ripples of less than 4.9 dB and 3 dB bandwidth of 90.5 nm. The ASE spectrum obtained covers the whole C-, L- and extended L-band regions from 1520 to 1620 nm. However, the backward pumping scheme provides a better pumping efficiency as compared to the forward pumping. The total ASE power reaches up to 26.6 mW at maximum pump power of 320 mW with a pumping efficiency of 8%. [ABSTRACT FROM AUTHOR]

A microstrip printed monopole antenna with defect ground plane is proposed. It provides wideband performance with radiation pattern similar to ideal monopole antenna. It is compact and has low profile. It is demonstrated that the antenna provides an impedance bandwidth ranging from 2.37 GHz to 6.12 GHz (for VSWR < 2) and supports a monopole type pattern. Extensive simulations are employed through varying its geometric parameters and discussed in the paper. [ABSTRACT FROM AUTHOR]

In highly dynamic and heterogeneous wireless mesh networks (WMN), link quality will seriously affect network performance. Two challenges hinder us from achieving a highly efficient WMN. One is the channel dynamics. As in real network deployment, channel qualities are changing over time, which would seriously affect network bandwidth and reliability. Existing works are limited to the assumption that link quality values are fixed, and optimal scheduling algorithms are working on the fixed values, which would inevitably suffer from the link quality dynamics. Another challenge is the channel diversity. In single channel wireless networks, channel assignment and scheduling are $\mathcal{NP}$ -hard. And in multichannel wireless networks, it could be even harder for higher throughput and efficient scheduling. In this study, we firstly characterize the stochastic behavior on wireless communications in a Markov process, which is based on statistical methodology. Secondly, on exploiting the stochastic behavior on wireless channels, we propose a stochastic programming model in achieving maximized network utilization. Considering the $\mathcal{NP}$ -hardness, we propose a heuristic solution for it. The key idea in the proposed algorithm is a two-stage matching process named “Rematch.” Indeed, our solution to the stochastic network scheduling is a cross-layer approach. Also, we have proved that it is 2-approximate to the optimal result. Moreover, extensive simulations have been done, showing the efficiency of “Rematch” in highly dynamic and distributed wireless mesh networks. [ABSTRACT FROM AUTHOR]

In this paper, we propose a resource-aware solution to achieving reliable and scalable stream diffusion in a probabilistic model, i.e. where communication links and processes are subject to message losses and crashes, respectively. Our solution is resource-aware in the sense that it limits the memory consumption, by strictly scoping the knowledge each process has about the system, and the bandwidth available to each process, by assigning a fixed quota of messages to each process. We describe our approach as gambling in the sense that it consists in accepting to give up on a few processes sometimes, in the hope of better serving all processes most of the time. That is, our solution deliberately takes the risk not to reach some processes in some executions, in order to reach every process in most executions. The underlying stream diffusion algorithm is based on a tree-construction technique that dynamically distributes the load of forwarding stream packets among processes, based on their respective available bandwidths. Simulations show that this approach pays off when compared to traditional gossiping, when the latter faces identical bandwidth constraints. [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents a new slow wave open-loop resonator filters with reduced size and improved stopband characteristics. A comprehensive treatment of different kind of coupling in this structure is demonstrated. Two and four resonator band pass filters at center frequency 2.15 and 2.30GHz with different bandwidth are designed. The simulated results are verified with the help of two different software packages (IE3D and Sonnet Lite). [Copyright &y& Elsevier]

Abstract: A modified band-notched compact printed half-elliptical monopole antenna is presented for ultra-wideband (UWB) applications. Wider impedance bandwidth can be achieved by carving two sectors on top-side of the semi-ellipse-shaped patch. Two connected arc-shaped slots with a variable angle between them are inserted in the patch to act as a filter structure. The proposed antenna is etched on a FR4 substrate with the size of and optimized to operate over the frequency band between 2.5 and 15GHz for , omitting the undesired frequency band of 5.1–5.9GHz. [Copyright &y& Elsevier]

An understanding of the network traffic behavior is essential in the evolution of today's wireless networks and thus leads to a more efficient planning and management of the network's scarce bandwidth resources. Prior reservation of radio resources at future locations of a user'smobile trajectory can assist in optimizing the allocation of the network's limited resources and sustaining a desirable quality-of-service (QoS) level. This can also help to ensure that the network service can be available anywhere and anytime, which is only possible if, at any time, we can predict from where a user is going to make its demands. In this paper, we apply Markov renewal processes for both mobility modeling and predicting the likelihoods of the next-cell transition, along with anticipating the duration between the transitions, for an arbitrary user in a wireless network. Our proposed prediction technique will also be extended to compute the likelihoods of a user being in a particular state after N transitions. The proposed technique can also be used to estimate the expected spatial-temporal traffic load and activity at each location in a network's coverage area. Using some real traffic data, we illustrate how our proposed prediction method can lead to a significant improvement over some of the conventional methods. [ABSTRACT FROM AUTHOR]

Underwater communication is a very challenging topic. Protocols used in terrestrial sensor networks cannot be directly applied in the underwater world. High-bit error rate and large propagation delay make the design of transport protocols especially awkward. ARQ-based reliable transport schemes are not appropriate in underwater environments due to large propagation delay, low communication bandwidth, and high error probability. Thus, we focus on redundancy-based transport schemes in this paper. We first investigate three schemes that employ redundancy mechanisms at the bit and/or packet level to increase the reliability in a direct link scenario. Then, we show that the broadcast property of the underwater channel allows us to extend those schemes to a case with node cooperative communication. Based on our analysis, an adaptive redundancy transport protocol (ARRTP) for underwater sensor networks is proposed. We suggest an architecture for implementation. For two kinds of topologies, namely, regular and random, we show that ARRTP presents a better transmission success probability and energy efficiency tradeoff for single- and multihop transmissions. We also offer an integrated case study to show that ARRTP is not only supplying reliability but also has some positive effect in guiding the deployment of underwater sensor nodes. [ABSTRACT FROM AUTHOR]

A novel theoretical framework for uplink simulations is proposed. It allows investigations which have to cover a very long (real -) time and which at the same time require a certain level of accuracy in terms of radio resource management, quality of service, and mobility. This is of particular importance for simulations of self-organizing networks. For this purpose, conventional system level simulators are not suitable due to slow simulation speeds far beyond real-time. Simpler, snapshot-based tools are lacking the aforementioned accuracy. The runtime improvements are achieved by deriving abstract theoretical models for the MAC layer behavior. The focus in this work is long term evolution, and the most important uplink effects such as fluctuating interference, power control, power limitation, adaptive transmission bandwidth, and control channel limitations are considered. Limitations of the abstract models will be discussed as well. Exemplary results are given at the end to demonstrate the capability of the derived framework. [ABSTRACT FROM AUTHOR]

In this paper, we present IAC, an interference aware admission control algorithm for use in wireless mesh networks. The core concept of IAC is to use a low overhead dual threshold based approach to share the bandwidth information with its neighbors in the interfering range. As a result, IAC guarantees that the shared wireless bandwidth is not overutilized and the quality of all existing flows are preserved. Moreover, IAC takes into account the intraflow interference effect to estimate the bandwidth consumption of the flow in a multihop path. We have further proposed two approaches of bandwidth allocation, FCFS and MCU, and demonstrated that proper tuning of thresholds can lead to high performance of both schemes. Simulation results illustrate that IAC effectively limits the overutilization of channel resources which in turn results in high throughput, low delay and low packet loss rate for all admitted flows. [ABSTRACT FROM AUTHOR]

Resonator antennas made from simple radiating devices placed between a woodpile and a ground plane are studied. A woodpile is a dielectric three-dimensional electromagnetic bandgap material that presents large stop-bands. A woodpile superstrate and a metallic plane, placed at an appropriate distance from each other, are equivalent to a woodpile cavity, the transmission response of which presents peaks inside the bandgaps. This property can be exploited to obtain highly directive radiators from low-directivity antennas. The cavity is fed by a double-slot antenna. The role of the permittivity of the constituent material of the rods is investigated. An evaluation of the bandwidth is performed for the directivity enhancement of the studied antennas, and the role of the woodpile covering area is pointed out. [ABSTRACT FROM AUTHOR]

Resonators are traditionally characterised by their quality factor Q, which is inversely proportional to the relative bandwidth. Small antennas are often resonant, so they can be characterised by a Q, except for the fact that the correct quality measure of an antenna is the inverse Q, that is the relative bandwidth, rather than Q. Still, it has become common to study fundamental size limitations of small antennas in terms of a so-called radiation Q (or antenna Q). This study explains how this intrinsic radiation Q relates to: (i) the bandwidth–efficiency product of small single-resonance-type antennas, (ii) the gradual cut-off of spherical waves for wideband gradual-transition-type small antennas and (iii) the number of resonances needed to cover a certain frequency band for wideband cascaded-resonance-type small antennas. The study also introduces one intrinsic radiation Q for basic single TE and TM spherical mode sources, and another for combined TE and TM sources. [ABSTRACT FROM AUTHOR]

Distance resolution of cooperative sensors is limited by the signal bandwidth. For the transmission mainly lower frequency bands are used which are more narrowband than classical radar frequencies. To compensate this resolution problem the combination of a pseudo-noise coded pulse compression system with superresolution time of arrival estimation is proposed. Coded pulsecompression allows secure and fast distance measurement in multi-user scenarios which can easily be adapted for data transmission purposes (Morhart and Biebl, 2009). Due to the lack of available signal bandwidth the measurement accuracy degrades especially in multipath scenarios. Superresolution time of arrival algorithms can improve this behaviour by estimating the channel impulse response out of a band-limited channel view. For the given test system the implementation of a MUSIC algorithm permitted a two times better distance resolution as the standard pulse compression. [ABSTRACT FROM AUTHOR]

The Scanning Synthetic Aperture Radar (ScanSAR) is very useful for Earth observation because of its wider imaging swath and shorter revisit time. However, ScanSAR is sometimes affected by the following three artifacts: 1) scalloping, which often appears as repeating weak azimuth stripes at both edges of the focused burst image; 2) azimuth ambiguity (i.e., a form of ghosting that appears over the adjacent uniform area when the pulse repetition frequency is below the Doppler bandwidth); and 3) radiometric discontinuity (i.e., banding) between two adjacent scans. This paper proposes three methods to correct these artifacts, which are, specifically, the proposal for scalloping correction using Amazon Rainforest data, band limitation, and the correction for the inter SCAN banding using the dynamic gain correction algorithm. Several corrected sample data sets of the Phased-Array L-band SAR onboard the Advanced Land-Observing Satellite are presented to demonstrate the validity of the proposed methods. [ABSTRACT FROM AUTHOR]

In the field of design and engineering education, the fast and expansive evolution of information and communication technologies is steadily converting traditional learning approaches into more advanced ones. Facilitated by Broadband (high bandwidth) personal computers, distance learning has developed into web-hosted electronic learning. The emergence of portable communication devices, wireless, and ad hoc networks has enabled electronic learning to develop into mobile and ubiquitous learning. In the literature there is a fuzziness in terms of the concepts and goals of these advanced learning solutions, mainly because the technological platforms and methodological approaches are not clearly distinguished. This paper attempts to demarcate them based on the level of flexibility in processing courseware and the extent of blending technological heterogeneity. These descriptors allowed us to highlight their differences, not only in terms of the types of interaction devices and communication platforms, but also in terms of the development and manner of using advanced learning solutions. What this paper goes on to illuminate is that by the process of the demarcation based upon the level of flexibility in processing courseware and the extent of blending technological heterogeneity, a more rational, useful and common understanding can be developed. [ABSTRACT FROM AUTHOR]

In this paper, we present the development of an even-mode matching network for a Marchand balun to achieve 50-Ωmatch and high isolation at the balanced ports. A very wide matching bandwidth can be accomplished with the novel addition of an open-circuit stub to the network. Experimental results demonstrate that the even-mode matched balun achieves return losses that are greater than 15 dB at the balanced ports from 6 to 17 GHz. The measured isolation between the balanced ports is greater than 15 dB from 4 to 19 GHz. For the unbalanced port, the return loss is greater than 15 dB from 4 to 19 GHz. The measured insertion loss is less than 1 dB, and amplitude and phase imbalances are ±0.5 dB and ±5° from 4 to 18 GHz, respectively. [ABSTRACT FROM AUTHOR]

This paper is concerned with the blind identification of passband and baseband Hammerstein channels using cumulants of the received sequence. The channel is excited by common communication signals such as QAM, PSK and OFDM; sparseness of the higher order cumulant lags is exploited. Exact expressions and algorithms involving the output cumulants are developed. Performance is assessed by simulations. [ABSTRACT FROM AUTHOR]

Investigations of a wideband balanced antenna for mobile handsets covering three bands—GSM1800, GSM1900, and UMTS—are presented. Balanced antennas have advantages in handset applications as they are less affected by juxtaposition with human tissue than unbalanced types. The antenna is a slotted planar dipole with its arms folded and not connected at their ends. The antenna is fed by a balanced voltage source. The antenna impedance was investigated using two different methods, including an S-parameter method and a mirror image method. For the purpose of antenna stability evaluation and power gain measurement, a wide bandwidth planar balun was adopted and modified to feed the antenna from an unbalanced source. For validation, prototypes of the antenna were fabricated and tested. The calculated and measured results in terms of return loss show good agreement and the results also show good wideband characteristics. [ABSTRACT FROM AUTHOR]

A miniature printed sleeve meander antenna used in tire pressure monitoring system (TPMS) is proposed in this paper. By using the meander structures including the radiation patch and ground plane, the antenna provides a degree of 78% miniaturization. Meanwhile, a L-shaped stub is loaded on the meander ground to improve the impedance bandwidth, thus a wide bandwidth of 24.2% (VSWR < 3.0) and 13.8% (VSWR < 2.0) for TPMS application is obtained. The antenna has good radiation pattern characteristic, and its performance is relatively stable. Design details of the proposed antenna and results of both simulations and experiments are presented and discussed. [ABSTRACT FROM AUTHOR]

Low-frequency radio astronomy has become a fascinating research area in the field of astronomy, including on its instrumentation development. In this paper, a multiband VHF antenna for low-frequency transient radio telescope is developed. The multiband has been achieved by combining V-shape half-wavelength dipole, traps, and parasitic elements. Measurement result shows that the antenna can work properly in three different frequencies designated by International Telecommunication Union (ITU) for radio astronomical purposes. [ABSTRACT FROM AUTHOR]

This paper presents a new design of wideband filter for X-band application using hybrid hairpin resonator and half wave coupled line resonator in multilayer microstrip configuration. Different resonator shapes were put on two substrates with different dielectric constants. In this work R/T Duroid 6010 and R/T Duroid 5880 with dielectric constant 10.2 and 2.2 respectively were used as the substrates, producing a very small filter size, only at 10 × 10 cm2. This configuration is not only producing compact size filter, but also high bandwidth since the overlapping gap between two resonators produces a tight coupling which is needed for wideband filter. The filter can cover whole X-band frequencies by producing 44% bandwidth at 10.2 GHz center frequency with excellent responses, where the measured passband return loss for this filter is better than –12.5 dB and the insertion loss is better than 2.3 dB. [ABSTRACT FROM AUTHOR]

A via stitching (VS)-electromagnetic bandgap (EBG) is analyzed with the compact circuit modeling method. From this analysis, a compact EBG structure is proposed to mitigate wideband simultaneous switching noise (SSN) in mobile phones. This EBG structure is compact enough to be used in mobile phones. Simulations and measurements show that the proposed EBG structure meets the requirements of stopband characteristics, having a stopband range from 750 MHz to 3.25 GHz with –60 dB suppression. [ABSTRACT FROM AUTHOR]

Recently, various uncommon materials such as metamaterials have been the subject of intensive research. In this paper, we introduce a new class of materials called double zero materials (DZR) having the real parts of both its epsilon and mu equal to zero and investigate the electromagnetic wave propagation in them, particularly the propagation constant k and intrinsic impedance η. We investigate the reflection and transmission coefficients from multilayer structures made of DZR material located in various media. It is shown that the DZR constants namely k and η and also the reflection and transmission coefficients from the multilayer structures are all real quantities. Several numerical examples are provided for both dispersive and nondispersive DZR materials. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel type of annular ring Printed Monopole Antenna (PMA) for ultra wideband (UWB) applications. The proposed antenna consists of a truncated ground plane and radiating patch with dual annular structure, which provides a wide usable bandwidth with high radiation pattern stability. Moreover, the effects of a double-fed structure inserted in the radiating patch, on the impedance matching and radiation behavior is investigated. Its impedance bandwidth, defined by measured voltage standing wave ratio (VSWR) less than 2, is from 3.1 to 16 GHz with a ratio of about 5.15 : 1. This novel monopole antenna has ultrawide impedance bandwidth, compact size (18 mm × 14 mm), low fabrication lost, and omni-directional H-plane radiation patterns, which are suitable for various broadband applications. [ABSTRACT FROM AUTHOR]

A compact single-layer planar antenna is proposed for dualband operation. The antenna is a coplanar waveguide-fed patch with dual embedded inverted-L shaped slots. The effects of the proposed antenna with/without the embedded slots in the patch on impedance matching condition have been examined theoretically. Prototype of the proposed antenna has been fabricated and measured for the electromagnetic performance including the impedance bandwidth, radiation pattern, and antenna gain. The designed antenna, which, including the ground, is only 18 × 22.5 mm2, leads to good dual bandwidths covering 2.4/5 GHz WLAN operation. Also, a stable radiation pattern and high average gains of about 3.6 and 4.3 dBi, respectively, over the two operating bands have been obtained. [ABSTRACT FROM AUTHOR]

In this paper, a novel method is proposed to design wideband bandpass filters with compact size. Combining half mode substrate integrated waveguide (HMSIW) and periodic dumbbell-shaped defected ground structure (DGS), two compact wideband bandpass filters with different HMSIW-microstrip transitions are fabricated and measured. The filters are found to possess wide passband bandwidth and compact size. Good agreement between the measured and simulated results demonstrates the validity of this technique. [ABSTRACT FROM AUTHOR]

In this paper, a wideband compact planar balun with impedance-transforming ratio of 2 : 1 is developed for push pull applications. The proposed balun is composed of broadside coupled strip lines and lumped capacitors. In this design, by utilizing broadside coupled strip lines with large enough spacing between strip and ground plane, even mode impedance of the transmission line and bandwidth is increased. Size reduction is effectively obtained by the use of discrete capacitors. As an example, one balun on a double-sided PCB is designed, simulated, fabricated and measured. Measured results show that the return loss is better than 15 dB over the frequency band from 470 MHz to 860 MHz, or around 59% bandwidth. The amplitude and phase imbalance between the two balanced output ports at worth case are 0.7 dB and 6 degree, respectively, over the operating frequency band. [ABSTRACT FROM AUTHOR]

A broadband planar antenna fed by coplanar waveguide (CPW) with gradually changed central feeder line is proposed. Central feeder line of the CPW and the ground plane are designed to be graded structure, which endow the proposed antenna with better impedance matching characteristic and broader bandwidth than microstrip line (MSL) fed antenna. Compared with antennas in previous researches, this proposed antenna has smaller size but covers wider bandwidth, which can operate from 0.7 GHz to 5.9 GHz for return loss less than –10 dB, and shows omni-directivity in azimuth plane. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to investigate the demand for broadband services in Greece and to estimate the price elasticity of the demand for ADSL and ISDN services as well as the cross-price elasticity between the two services. The empirical analysis uses the 384kbps connections since for the period examined, over 85% of the total ADSL customers in Greece are connected at this bandwidth. The empirical analysis is based on an ad-hoc specification of the demand equation, with no reference to the utility maximization problem of the representative consumer. The results of the analysis show that both demands are inelastic. In addition, cross-price elasticity for ADSL is negative, indicating that ISDN is a complement to ADSL, whereas the demand for ISDN is almost neutral to ADSL. [Copyright &y& Elsevier]

We analyze the spatial-frequency dependence of the gain of phase-insensitive and phase-sensitive optical parametric amplifiers with plane-wave pumping. We discuss the dependence of their spatial bandwidths on pump power and crystal length, L, and observe that the well-known (ks/L)1/2 approximation of spatial bandwidth is not very accurate (here ks is the signal beam's wavevector magnitude). We derive an alternative approximation that is highly accurate at large gains and moderately accurate at low gains. The differences between the phase-insensitive and phase-sensitive amplifier bandwidths are shown to be insignificant for gains above several dB. Maximum phase-sensitive gain and bandwidth are realized by imposing an optimum phase profile onto the input signal's spatial spectrum, which has nearly parabolic shape with added series of π/2 phase discontinuities at spatial frequencies outside the main bandwidth of the amplifier. We show that, apart from the discontinuities, such a profile can be closely approximated by placing the image plane into the middle of the nonlinear crystal (converging input beam). The phase discontinuities contribute an additional narrow component to the point-spread function of the phase-sensitive amplifier. [ABSTRACT FROM AUTHOR]

Peer-to-peer (P2P) media streaming quickly emerges as an important application over the Internet. A plethora of approaches have been suggested and implemented to support P2P media streaming. In our study, we first classified existing approaches and studied their characteristics by looking at three important quantities: number of upstream peers (parents), number of downstream peers (children), and average number of links per peer. In existing approaches, peers are assigned with a fixed number of parents without regard to their contributions, measured by the amount of outgoing bandwidths. Obviously, this is an undesirable arrangement as it leads to highly inefficient use of the P2P links. This observation motivates us to model the peer selection process as a cooperative game among peers. This results in a novel peer selection protocol such that the number of upstream peers of a peer is related to its outgoing bandwidth. Specifically, peers with larger outgoing bandwidth are given more parents, which make them less vulnerable to peer dynamics. Simulation results show that the proposed protocol improves delivery ratio using similar number of links per peer, comparing with existing approaches under a wide range of system parameters. [ABSTRACT FROM AUTHOR]

A novel study of ultra wideband (UWB) communication over the indoor powerline channel, in a wide frequency range up to 1 GHz is presented. An exhaustive measurement campaign was conducted on a test bed that replicated the environment of an indoor powerline network. The aim of this study was to observe and analyse the transmission and noise properties of such a broadband powerline channel. A time domain channel model has been used to study the broadband channel response of the powerline. Measurement and modelling results show that the indoor powerline channel provides a communication link in the 50–550 MHz frequency range. Channel capacity is greatly enhanced by exploiting the 500 MHz bandwidth. The conclusions of this study indicate that gigabit per second data rate transmission are possible over the indoor powerline channel in 50–550 MHz. [ABSTRACT FROM AUTHOR]

In March 2008 the ITU-T approved a new wideband speech codec called ITU-T G.711.1. This Recommendation extends G.711, the most widely deployed speech codec, to 7 kHz audio bandwidth and is optimized for voice over IF applications. The most important feature of this codec is that the G.711.1 bitstream can be transcoded into a G.711 bitstream by simple truncation. G.711.1 operates at 64, 80, and 96 kbls, and is designed to achieve very short delay and low complexity. ITU-T evaluation results show that the codec fulfils all the requirements defined in the terms of reference. This article presents the codec requirements and design constraints, describes how standardization was conducted, and reports on the codec performance and its initial deployment. [ABSTRACT FROM AUTHOR]

The paper presents the design of a compact ultra wideband antenna composed of two circular coplanar strips which enclose slot aperture of the similar shape. The antenna is fed with three coplanar strip-lines of 50 Ω. The effect of the outer strip edge on the antenna bandwidth is investigated. This antenna configuration has been modeled and experimentally tested, showing good performance in 1.7–15.5 GHz frequency range where return losses |S11| < –10 dB are achieved. Stable radiation patterns across the whole band is also observed. [ABSTRACT FROM AUTHOR]

Comprehensive characterization of wideband ultrasonic transducers and specifically optoacoustic detectors is achieved through the analysis of their frequency response as a function of the incident angle. The tests are performed under well-defined, repeatable operating conditions. Backillumination of a blackened, acoustically matched planar surface with a short laser pulse creates an acoustic impulse which is used as a wideband ultrasonic source. Upon illumination with a short laser pulse, the bandwidth of our source shows a -6 dB point of 12 MHz and a low-frequency roll-off around 300 kHz. Using proprietary software, we examine thoroughly the planarity of the emitted wave front within a specified amplitude cutoff and phase incoherence. Analysis of the angular dependence of the frequency response yields invaluable directivity information about the detector under study: a necessary component toward accurate optoacoustic image reconstruction and quantitative tomography. The laser ultrasonic source we developed is the main feature of our directivity measurement setup. Due to its simplicity, it can easily be adapted to various calibration devices. This paper focuses on the development and characterization of the flatness and the bandwidth of our wideband ultrasonic source. [ABSTRACT FROM AUTHOR]