The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform

Samir Saoudi - One of the best experts on this subject based on the ideXlab platform.

  • SIC/LMMSE Detector for 3GPP WCDMA enhanced uplink system over multipath fading channels
    International journal of computational science, 2009
    Co-Authors: Mahmoud Ammar, Messaoud El Jamai, Mohamed Et Tolba, Samir Saoudi
    Abstract:

    This paper deals with multiuser detection for the WCDMA enhanced uplink system with low spreading factors over multipath channels. The performance of the conventional Detector is significantly degraded by multiple access interference (MAI) and inter-path interference (IPI) effects. However, these problems can be resolved by the interworking of multiuser Detector with linear minimum mean squared error (LMMSE) filter. In this paper, we propose a new multiuser Detector Structure which is the combination of the successive interference canceller (SIC) with LMMSE chip-level equalizer. The matched filter of the standard SIC is replaced by the LMMSE receiver, in order to decrease the IPI effect. We will show that the new SIC/LMMSE Detector improves the block error rate of the data physical channels performance (BLER edch ). This enhancement achieves, for the modulation and coding scheme 1 (MCS1), almost 4dB at a BLER edch equal to 10−2.

  • Iterative multiuser detection for turbo coded CDMA in uplink UMTS
    2003
    Co-Authors: Ali Al Housseini, Samir Saoudi, Thierry Chonavel, Mahmoud Ammar
    Abstract:

    Multiuser detection and turbo coding are two of the most powerful techniques for enchancing the performance of next generation Code-Division-Multiple-Access (CDMA) systems. In this paper, a new iterative detection and de- coding Structure for asynchronous DS-CDMA communi- cations using convolutive turbo-codes is proposed. The new scheme is based on the combination of a SIC/RAKE Detector Structure together with a turbo decoder. Both elements are associated so as to implement a turbo de- tection/decoding procedure. The complexity of this new scheme is linear with respect to the number of users. Simulation results show that the performance of the pro- posed Detector converges to that of the single user case.

Ioannis Pitas - One of the best experts on this subject based on the ideXlab platform.

  • An Optimal Detector Structure for the Fourier Descriptors Domain Watermarking of 2D Vector Graphics
    IEEE Transactions on Visualization and Computer Graphics, 2007
    Co-Authors: Victor Rodriguez Doncel, Nikos Nikolaidis, Ioannis Pitas
    Abstract:

    Polygonal lines constitute a key graphical primitive in 2D vector graphics data. Thus, the ability to apply a digital watermark to such an entity would enable the watermarking of cartoons, drawings, and geographical information systems (GIS) data in vector graphics format. This paper builds on and extends an existing algorithm that achieves polygonal line watermarking by modifying the Fourier descriptors magnitude in an imperceptible way. Watermarks embedded by this technique can be detected in rotated, translated, scaled, or reflected polygonal lines. The detection of such watermarks had been previously carried out through a correlator Detector. In this paper, analysis of the statistics of the Fourier descriptors is exploited to devise an optimal blind Detector. Furthermore, the problem of watermarking multiple lines, as well as other implementation issues are being addressed. Experimental results verify the imperceptibility and robustness of the proposed method.

  • ICIP (3) - Optimal Detector Structure for DCT and subband domain watermarking
    Proceedings. International Conference on Image Processing, 1
    Co-Authors: Athanasios Nikolaidis, Ioannis Pitas
    Abstract:

    Most of the watermarking schemes that have been proposed until now employ a correlator in the detection stage. The current paper proposes a new Detector scheme that can be applied in the case of additive watermarking in the DCT or DWT domain. Certain properties of the probability density function of the coefficients in these domains are exploited in order to construct an asymptotically optimal Detector based on well known results of the detection theory. Detection is performed without the use of the original image, as in methods employing different Detectors. Experimental results prove the superiority of the proposed Detector over the correlator.

R. Orava - One of the best experts on this subject based on the ideXlab platform.

  • Charge collection characterization of a 3D silicon radiation Detector by using 3D simulations
    Nuclear Instruments and Methods in Physics Research Section A: Accelerators Spectrometers Detectors and Associated Equipment, 2007
    Co-Authors: Juha Kalliopuska, Simo Eränen, R. Orava
    Abstract:

    Abstract In 3D Detectors, the electrodes are processed within the bulk of the sensor material. Therefore, the signal charge is collected independently of the wafer thickness and the collection process is faster due to shorter distances between the charge collection electrodes as compared to a planar Detector Structure. In this paper, 3D simulations are used to assess the performance of a 3D Detector Structure in terms of charge sharing, efficiency and speed of charge collection, surface charge, location of the primary interaction and the bias voltage. The measured current pulse is proposed to be delayed due to the resistance–capacitance (RC) product induced by the variation of the serial resistance of the pixel electrode depending on the depth of the primary interaction. Extensive simulations are carried out to characterize the 3D Detector Structures and to verify the proposed explanation for the delay of the current pulse. A method for testing the hypothesis experimentally is suggested.

  • 3D simulations of 3D silicon radiation Detector Structures
    Nuclear Instruments and Methods in Physics Research Section A: Accelerators Spectrometers Detectors and Associated Equipment, 2006
    Co-Authors: Juha Kalliopuska, Simo Eränen, R. Orava
    Abstract:

    Abstract The simulations carried out in three dimensions (3D) are becoming important as more and more Detector Structures are fabricated beyond the traditional planar ones. A rectangular 3D Detector Structure is simulated using a finite-element (FE) simulation software ISE-TCAD. The basic characteristics of the Detector Structure simulated in two dimensions (2D) and 3D are compared in order to determine whether there are differences between the two approaches. Effects of the surface charge and surface recombination to the electrostatic potential, electric field, leakage current and capacitance are studied in detail. The 2D and 3D simulations give similar results on IV and CV characteristics when the surface effects are not included in the simulations. The presence of the surface charge at the silicon–oxide interface increases the leakage current while protecting the Detector from the surface currents. It is shown that the vertical spacing of the grid below the surface is playing a critical role in the current results.

  • Simulations of 3D silicon radiation Detector Structures in 2D and 3D
    IEEE Nuclear Science Symposium Conference Record 2005, 1
    Co-Authors: Juha Kalliopuska, Simo Eränen, R. Orava
    Abstract:

    Three dimensional (3D) Detector Structures yield faster charge collection times compared to the ones realized by using the planar (2D) technology. The charge collection time is greatly dependent on the location of the incident ionising radiation. In this paper, the charge collection performance of a rectangular 3D Detector Structure is simulated by using the finite-element simulation software ISE-TCAD. The surface effects, surface charge and surface recombination, are shown to slow down the charge collection by 50% to 70%. The charge sharing between the neighboring pixel is studied by using 2D simulations at 20 V bias and the charge collected by the pixel of the MIP entrance is shown to be more than 95% in a major part of the pixel volume. In addition, it was shown that great care should exercised when analyzing 3D Detector Structures using 2D simulation tools. When the simulated Structure is thinned down, the internal Detector characteristics are altered and, since the RC-constant is proportional to square of the Detector thickness, the charge collection time may decrease unexpectedly

Mahmoud Ammar - One of the best experts on this subject based on the ideXlab platform.

  • SIC/LMMSE Detector for 3GPP WCDMA enhanced uplink system over multipath fading channels
    International journal of computational science, 2009
    Co-Authors: Mahmoud Ammar, Messaoud El Jamai, Mohamed Et Tolba, Samir Saoudi
    Abstract:

    This paper deals with multiuser detection for the WCDMA enhanced uplink system with low spreading factors over multipath channels. The performance of the conventional Detector is significantly degraded by multiple access interference (MAI) and inter-path interference (IPI) effects. However, these problems can be resolved by the interworking of multiuser Detector with linear minimum mean squared error (LMMSE) filter. In this paper, we propose a new multiuser Detector Structure which is the combination of the successive interference canceller (SIC) with LMMSE chip-level equalizer. The matched filter of the standard SIC is replaced by the LMMSE receiver, in order to decrease the IPI effect. We will show that the new SIC/LMMSE Detector improves the block error rate of the data physical channels performance (BLER edch ). This enhancement achieves, for the modulation and coding scheme 1 (MCS1), almost 4dB at a BLER edch equal to 10−2.

  • Iterative multiuser detection for turbo coded CDMA in uplink UMTS
    2003
    Co-Authors: Ali Al Housseini, Samir Saoudi, Thierry Chonavel, Mahmoud Ammar
    Abstract:

    Multiuser detection and turbo coding are two of the most powerful techniques for enchancing the performance of next generation Code-Division-Multiple-Access (CDMA) systems. In this paper, a new iterative detection and de- coding Structure for asynchronous DS-CDMA communi- cations using convolutive turbo-codes is proposed. The new scheme is based on the combination of a SIC/RAKE Detector Structure together with a turbo decoder. Both elements are associated so as to implement a turbo de- tection/decoding procedure. The complexity of this new scheme is linear with respect to the number of users. Simulation results show that the performance of the pro- posed Detector converges to that of the single user case.

Sanjay Krishna - One of the best experts on this subject based on the ideXlab platform.

  • Antimonid Based Mid-Infrared Detectors and Focal Plane Arrays
    Frontiers in Optics 2016, 2016
    Co-Authors: Sanjay Krishna
    Abstract:

    The use of “unipolar barrier engineering” to realize high performance infrared Detectors and focal plane arrays will be discussed. A metamaterial Detector Structure will be demonstrated using Type II superlattices.

  • inassb based nbn photoDetectors lattice mismatched growth on gaas and low frequency noise performance
    Semiconductor Science and Technology, 2015
    Co-Authors: Adam P Craig, Sanjay Krishna, Michael Dermot Thompson, Zhaobing Tian, A Krier, Andrew R J Marshall
    Abstract:

    An InAsSb nBn Detector Structure was grown on both GaAs and native GaSb substrates. Temperature dependent dark current, spectral response, specific detectivity (D*) and noise spectral density measurements were then carried out. Shot-noise-limited D*figures of 1.2 10 Jones × 10 and 3.0 10 Jones × 10 were calculated (based upon the sum of dark current and background photocurrent) for the sample grown on GaAs and the sample grown on GaSb, respectively, at 200 K. Noise spectral density measurements revealed knee frequencies of between 124–337 Hz and ∼8 Hz, respectively. Significantly, these devices could support focal plane arrays capable of operating under thermoelectric cooling.

  • Molecular beam epitaxy growth and characterization of type-II InAs/GaSb strained layer superlattices for long-wave infrared detection
    Journal of Vacuum Science & Technology B Nanotechnology and Microelectronics: Materials Processing Measurement and Phenomena, 2010
    Co-Authors: Elena Plis, A. Khoshakhlagh, Stephen Myers, Ha Sul Kim, Nutan Gautam, Yagya D. Sharma, Sanjay Krishna, S. J. Lee, S. K. Noh
    Abstract:

    The authors report on investigation of type-II InAs/GaSb and InAs/InxGa1−xSb strained layer superlattices (SLSs) for long-wave infrared detection. Growth conditions were optimized to obtain nearly lattice matched (Δa/a∼0.03%) 13 ML InAs/7 ML GaSb SLS nBn Detector Structure with cutoff wavelength of ∼8.5 μm (77 K). Dark current density was equal to 3.2×10−4 A/cm2 (Vb=+50 mV, 77 K) for this Detector Structure. Thin 10 ML InAs/6 ML In0.35Ga0.65Sb SLS was grown with zero lattice mismatch achieved by incorporation of 2.5 ML of GaAs in every SLS period.