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Date 26-28 Sept. 2007

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Displaying Results 1 - 25 of 214
  • On performance of residue number system coded differential space-time-frequency coding

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (890 KB) |  | HTML iconHTML  

    Space-time-frequency (STF) coding has emerged as a technique for transmitting high data rate over wideband mobile channels. Most of the proposed architectures in the literature maximize diversity gains from one diversity domain and frequency diversity is predominantly dependent on the intrinsic frequency-selective nature of the fading channel In this paper we propose differential space-time-frequency (DSTF) modulation scheme. The available bandwidth is divided into several orthogonal subbands by a frequency encoder and redundancy is added to maximize coding (frequency) gains. For improved non-coherent detection at the receiver, iterative decoding employing hard decision-feedback of differentially encoded space-time block code on each carrier is concatenated with an outer frequency encoder. It is shown through analytical expressions that with appropriate code design, the proposed DSTF coding scheme can maximize the diversity gains over space, time, and frequency domains. View full abstract»

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  • Stabilizing a bicycle below critical speed

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1865 KB) |  | HTML iconHTML  

    This paper discusses the control of a naturally unstable bicycle at stand still based on local linearization of a nonlinear model which results in a 2times2 multiple input multiple output system. It is shown through simulation plus new insights on stabilizing non-minimum phase systems and f-domain design techniques that it is possible to keep the bicycle vertical outside the self stability speed domain where theory in the literature has predicted that it's not possible. In reality the stabilization goal is a skill which can be acquired through practice. View full abstract»

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  • Adaptive inverse quadratics interpolation with applications to vector fitting and the hankel transform of spectral domain green’s functions

    Publication Year: 2007 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (839 KB) |  | HTML iconHTML  

    In this contribution we discuss the translation- invariant interpolation of univariate functions by means of inverse quadratics radial basis functions. For the implementation we use an adaptive interpolation process which is a variant of a recently introduced adaptive residual subsampling method. It is shown that the interpolation process with the inverse quadratics kernel also provides an excellent pre-processing interface when used in conjunction with the popular vector fitting algorithm. This results in a composite algorithm, performing the sampling and modelling of the given function in a fully automatic way. It also provides a platform for calculating the Hankel transform of spectral domain Green's functions. View full abstract»

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  • A bilinear quadrature rule for the finite hankel transform

    Publication Year: 2007 , Page(s): 1 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (809 KB) |  | HTML iconHTML  

    The finite Hankel transform of order zero is evaluated by means of a bilinear quadrature formula. By imposing conditions on the bilinear weight matrix, it is guaranteed that the finite Hankel transform is correct for the class of Fourier- Bessel functions and given interpolation points in the range of the Hankel transform. The algorithm only requires the solution of two linear equations. View full abstract»

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  • Optimizing the performance of an LC oscillator for maximum power delivery to a load

    Publication Year: 2007 , Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1512 KB) |  | HTML iconHTML  

    Using a common Pierce LC oscillator circuit it is demonstrated that by using the technique referred to as a load- line match, commonly used in the design of class A power amplifiers, it is possible to extract the maximum available power from an RF transistor for delivery to a specified load impedance. This results in the transistor being used to its full capacity resulting in the oscillator efficiency approaching the theoretical limit of 50%. View full abstract»

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  • A multi-layered architecture for preventing automated spam in the IP multimedia subsystem

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1053 KB) |  | HTML iconHTML  

    The volume of spam in the Internet has far surpassed legitimate email. Marketers, fraudsters and political parties enjoy positive returns due to the large number of messages that can be transmitted at very low costs. Unfortunately there is an emerging trend that spam is now also being transmitted via instant messaging and voice calls. This is a concern for future next-generation networks, such as the IP multimedia subsystem, because insufficient security and privacy will hinder the take-up of these services. In this paper a multi-layered architecture is presented that blocks automated spammers. This is achieved using a combination of legislation, blacklists, whitelists, call-pattern analysis and Turing tests. The proposed solution is applied to a practical testbed and evaluations demonstrate the effectiveness of this proposal. View full abstract»

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  • Integration effects of multiple microstrip patch antennas into small handsets

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2304 KB) |  | HTML iconHTML  

    This paper describes the integration of multiple microstrip patch antenna elements into a small handset. The antenna system has been developed for multiple-input multiple- output (MIMO) applications in WLAN systems at 5 GHz. Four square microstip patches are printed on the top area of a 45mmxl05 mm ground plane, representing the back side of a typical small handset. The small ground plane integration effects on input return loss, mutual coupling, envelope correlation and radiation pattern, are evaluated. An antenna prototype has been fabricated and tested. Good agreement has been obtained between numerical simulations and experimental results. View full abstract»

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  • Example of undervoltage load shedding implementation

    Publication Year: 2007 , Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1604 KB) |  | HTML iconHTML  

    After deregulation of power systems, large problems with voltage stability incurred due to the large transits of power transmitted to large distances. Systems are very stressed and often work on their limits. Therefore, single contingency is sometimes enough to cause system collapsing. One of the most economic methods to prevent larger scale voltage collapse is undervoltage load shedding (UVLS). In this article, implementation of UVLS scheme is tested in New England Test System and then modeled in part of Croatian power system. Simulation of system behavior is presented as well. View full abstract»

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  • RF-MEMS dielectric charging: Dependence on dielectric film polarization procedures

    Publication Year: 2007 , Page(s): 1 - 6
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1444 KB) |  | HTML iconHTML  

    The paper demonstrates the advantages arising from the simultaneous assessment of RF-MEMS capacitive switches and MIM capacitors. The application of simple capacitive-voltage characteristics and thermally stimulated depolarization current methods, respectively, allow the discrimination of the contribution of injected charges induced space charge polarization and the dipolar polarization. The proposed method allows the direct determination of device degradation sources and can be used for the dielectric material improvement. View full abstract»

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  • Recovery of small bursts of voice packets using RS erasure code with low decoding delay

    Publication Year: 2007 , Page(s): 1 - 7
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1387 KB) |  | HTML iconHTML  

    It is well known that packet losses in the networks are mainly due to congestion because of the finite buffer capacity of queues in routers. Forward error correction (FEC) can recover from losses without retransmissions of lost packets. However, FEC faces with two main drawbacks: firstly, the redundancy generated by the sender increases the overall load of the network resulting in an increase of loss rate and secondly, waiting for redundant information to be able to recover lost packets results in additional delay. In this paper we employ the Reed Solomon erasure (RSE (7, 4)) code to recover lost packets. We apply the adaptive differential pulse code modulation (ADPCM) compression technique to make room for the redundant packets and thus reduce the additional load due to redundancy. We further modify the recovery scheme to bring down the decoding delay from a maximum of 6 packets to a maximum of 3 packets. Results of informal mean opinion score (MOS) listening test show that the modified RSE code is capable of correcting any burst of two packets and provides a tradeoff between quality, network load and decoding delay. View full abstract»

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  • The design of an electro-optic control circuit for photonic packet switching applications

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1712 KB) |  | HTML iconHTML  

    We demonstrate the design and experimental implementation of an electro-optic control system that is used to detect the arrival of packets at the optical switch input, process the headers of the packets, and control switching according to the header content for both fixed and variable length packets. We also demonstrate the flexibility of the electro-optic crosspoint switch for implementation in a photonic packet switching (PPS) network. Furthermore, contention resolution is demonstrated in the electro-optic crosspoint switch by detecting packets at the input ports and controlling the switch operation accordingly. By incorporating this control system into the crosspoint switch it is possible to route contending packets to a re-circulating fiber delay line and control the switch output in a flexible manner for any type of traffic depending on the applied switching algorithm. The experiments are carried out with 155 Mbit/s headers and 10 Gbit/s payloads transmitted on a single wavelength with a guard time of 12.8 ns between header and payload. PPS with bit error rate (BER) less than 10-9 is demonstrated. Error free contention resolution is shown with the main signal degradation being from the switch cell attenuation and amplifier ASE that can be alleviated by eliminating fiber-to-fiber transmission loss in the crosspoint. View full abstract»

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  • Indicative RES-E targets for the year 2010 and their fulfillment in slovenia

    Publication Year: 2007 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1486 KB) |  | HTML iconHTML  

    To reduce the reliance on imported fossil energy sources and combat climate change, to foster domestic technology development and harmonize the national support policies for renewable energy sources (RES) in its Member States, the European Commission introduced the Directive 2001/77/EC, defining renewable portfolio standards for the Member States. The indicative target for Slovenia is the 33,6 % contribution of RES in total gross electrical energy consumed by 2010. In this study, we review the mid-term possibility of achieving the Slovenian objectives, considering factors crucial for forecasting hydropower production. It is apparent that in order to achieve the RES-support policy goals and to break the spell of their weather-dependency, the support schemes in Slovenia need to be re-assessed and appropriately amended. View full abstract»

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  • High-power extended cavity narrow linewidth laser

    Publication Year: 2007 , Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1608 KB) |  | HTML iconHTML  

    We present a compact extended cavity laser (ECL) system based on a high-power laser diode with reduced linewidth and stabilized to the rubidium D1 line at the 794.74 nm. The laser system was derived from an arrangement designed for optical pumping of Rb and production of hyperpolarized gasses. We concentrated on the ECL system optimization - linewidth narrowing effects with the broad-area power laser diode. We show that the intensity of optical feedback in the ECL laser influences linewidth and output power and it is possible to find an optimum value for the highest power spectral density and eventually adjust the linewidth over wide range. The emission linewidth was reduced approximately 10 times with only half of the total optical power loss. The ECL system is controlled by electronic servo-loop for laser frequency stabilization. View full abstract»

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  • Generation and detection of hyperpolarized xenon

    Publication Year: 2007 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1576 KB) |  | HTML iconHTML  

    We present the experimental results of generation and of detection of hyperpolarized xenon obtained by 4.7 T, 200 MHz magnetic resonance (MR) system. Xenon 129 was hyperpolarized by the spin-exchange with Rubidium pumped first by Ti:Sa laser and also by extended cavity laser system based on a high-power laser diode optimized for maximum efficiency of the optical pumping process. The application of the arrangement with semiconductor laser system is oriented medicine, especially to continuous production of hyperpolarized Xenon (HpXe) which serves as an contrast media in MR imaging systems. View full abstract»

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  • A contribution to the IEEE STD. 1451.2-1997 revision and update

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1513 KB) |  | HTML iconHTML  

    After a technical overview of the IEEE 1451 family of standards, detailed descriptions of implemented smart transducers interface modules (STIM) and transducer interface modules (TIM) either using 10-wire transducer independent interface (TII) or USB are presented. These experimental research results aim to be a small contribution for the IEEE STD. 1451.2-1997 revision and update. View full abstract»

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  • MATLAB, LabVIEW and FPGA linear control of an inverted pendulum

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1529 KB) |  | HTML iconHTML  

    Linearized model, pole placement and LQR linear controllers are derived for the inverted pendulum bytronic plant. Investigation of the real-time controller implementation using different PC (MATLAB/LabVIEW) and field programmable gate array (FPGA) CompactRIO (cRIO) platforms is done to prove and verify the FPGA capabilities in real-time control. The dynamic behaviour of the inverted pendulum under the same control, realized by the above various real-time platforms is obtained to be identical. View full abstract»

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  • Diode mounting topologies for X-band waveguide switches

    Publication Year: 2007 , Page(s): 1 - 7
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1106 KB) |  | HTML iconHTML  

    Diode mounting topologies for waveguide switches are presented and utilized to design and fabricate two evanescent- mode X-band modules of approximately 15 and 25% fractional bandwidth, comprising two packaged PIN diodes, with varying isolation, insertion loss and VSWR. View full abstract»

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  • A plasma torch converter based on the partial series resonant converter

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2371 KB) |  | HTML iconHTML  

    Converters for plasma torches generally operate at power levels above 30 kW, and hard switching topologies are normally used. The switching frequency at these power levels is restricted due to high switching losses and the unavailability of suitable high power transformers. While significant progress was made in soft switching by using resonant techniques, the applications were restricted mostly to lower power applications. The zero voltage switching partial series resonant converter has properties that make the application at high power levels attractive. In this paper the converter is applied to a plasma torch application where power levels can go up into the megawatt range. To increase the power rating per unit, a distributed transformer and parallel operation of a number of converters are proposed. An improved dynamic controller is introduced and experimental results are presented on a 30 kW, 40 kHz, DC plasma torch converter using an IGBT partial series resonant converter. View full abstract»

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  • A novel approach to improve sparse data models

    Publication Year: 2007 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (842 KB) |  | HTML iconHTML  

    This paper implements the recently introduced measure of sparseness with a specific feedback mechanism to improve the large standard deviation that current random data sources suffer from. The authors will show the drawbacks of the current, frequently used random data sources and suggest a novel approach to rectify these disadvantages. Simulation results are presented for various blocklengths typically used in 3G UMTS/WCDMA systems, showing how the standard deviation may be significantly reduced by up to 33% by using an optimal feedback length. These optimal feedback lengths are also presented, as well as some conclusions regarding communication system simulation and future View full abstract»

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  • Simulator of an optical communication system

    Publication Year: 2007 , Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1426 KB) |  | HTML iconHTML  

    The need for higher bandwidth in a global scale for the transmission of real-time video, will change the role of optical communication systems from the high bit-rate international and intercontinental digital networks to local area networks, using also the immunity of such systems to electromagnetic interference. However the proficiency of students of electrical engineering in optical systems is hampered by the cost and maintanence of university and high school optical labs. The computer simulator can constitute an answer for a portable, safe and low cost optical lab. This paper presents the framework of a functional simulator of an optical communication system. The blocks of such systems are represented by behavioural multilevel models with input, output and internal parameters. View full abstract»

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  • Zeros and the output-zeroing problem in a LTI system with single state delay

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1659 KB) |  | HTML iconHTML  

    The concept of invariant zeros in a linear time- invariant system with state delay is considered. The problem of zeroing the system output is discussed and a general formula for output-zeroing inputs is provided. View full abstract»

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  • Low density parity check irreducible Goppa codes

    Publication Year: 2007 , Page(s): 1 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB) |  | HTML iconHTML  

    In this paper, whose earlier version was presented at SAMSA 05 conference, we present some of the results obtained in the on-going research on low density parity check (LDPC) irreducible Goppa codes. The objective of the research is to find irreducible Goppa codes with sparse parity check matrices to which LDPC decoding can be applied. If such codes are found then they would permit efficient encoding and decoding algorithms. We use two methods to come up with a sparse parity check matrix. The first method involves changing the basis of the splitting field of the Goppa polynomial. In the other method, we build the parity check matrix using low weight codewords in the dual code of the Goppa code. View full abstract»

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  • Feasibility of using stochastic adaptive congestion control in computer networks

    Publication Year: 2007 , Page(s): 1 - 8
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (836 KB) |  | HTML iconHTML  

    The paper presents a novel approach for congestion control and avoidance in computer networks. The approach is based on stochastic search, as opposed to systematic-like search employed by existing mechanisms. Our approach forms basis for more informed heuristics and promises to be more adaptive. We employ the Weibull distribution density function to continuously define the search space. In this paper we develop a single simple heuristic, based on the approach, and evaluate its performance in terms of congestion window evolution, response time and throughput. View full abstract»

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  • Examining power line communication on Egypt’s low voltage grid for AMR network

    Publication Year: 2007 , Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1498 KB) |  | HTML iconHTML  

    Electrical energy consumers are demanding better customer service, higher power quality, higher energy measurement accuracy and more timely data. Utility companies all over the world are being forced to find solutions giving greater information on the population's power consumption. The Automatic Meter Reading system (AMR) is one of the ways in which utilities are go-getting to achieve these goals. Power lines are one of the communication mediums used in the AMR system. However, power lines are a hostile communication environment. This paper describes a prototype for AMR system using power lines showing performance and reliability tests. The measurements are carried out on a sample of Egypt's low voltage network. View full abstract»

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  • Experience in using MALTLAB Power System Toolbox (PST) for transient stability study of an AC/DC interconnected power system

    Publication Year: 2007 , Page(s): 1 - 4
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1415 KB) |  | HTML iconHTML  

    This paper discusses the experience of the authors in using Matlab power system toolbox for the transient stability studies of an AC/DC interconnection power system. The modified two-area power system model with HVDC Link is used in the investigation. It is shown that as the AC line became weaker (as compared to the DC line), the transient stability of the interconnected AC/DC system is negatively affected. The use of power system stabilizer (PSS) was critical in maintaining the stability of the system. View full abstract»

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