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Bo Liu - One of the best experts on this subject based on the ideXlab platform.

  • orthogonal Discrete Frequency coding waveform set design with minimized autocorrelation sidelobes
    IEEE Transactions on Aerospace and Electronic Systems, 2009
    Co-Authors: Bo Liu
    Abstract:

    The autocorrelation sidelobe peak (ASP) levels of Discrete Frequency-coding waveform with fixed Frequency pulses (DFCW-FF) is very large, which is about 0.21 or -13.2 dB. Replacing the fixed Frequency pulses with linear Frequency modulated (LFM) pulses can lower the ASP. We investigate the autocorrelation function (ACF) and cross-correlation function (CCF) for DFCW with arbitrary Frequency firing order. It is shown that DFCW-LFM has different ACF expression from the DFCW-FF, and the CCF of DFCW-LFM changes distinctly with different Frequency firing order. By setting the relationships between the Frequency step ?f, LFM bandwidth B and subpulse duration T, we can reduce the ASP, as well as nullify the grating lobes. Then, a modified genetic algorithm (GA) is proposed to numerically search optimal Frequency firing order for DFCW-LFM. Some of the designed results are presented. Their correlation properties are effectively improved. Both simulation results and comparisons show that the method of mitigating ASP and the proposed search algorithm are effective for the design of DFCWs with superior aperiodic correlation.

  • orthogonal Discrete Frequency coding waveform design for mimo radar
    Journal of Electronics (china), 2008
    Co-Authors: Bo Liu
    Abstract:

    Design of orthogonal code sets with ideal correlation properties is crucial for orthogonal Multiple Input Multiple Output (MIMO) radar. A modified Genetic Algorithm (GA) is proposed to numerically design orthogonal Discrete Frequency-Coding Waveforms (DFCWs) with good correlation properties for MIMO radar. Some of the designed results are presented, and their correlation properties are better than those presented in literatures. The effect of Doppler Frequency shift on the performance of these signals is simply investigated. Simulation results and comparisons show that the proposed algorithm is more effective for the design of DFCWs with superior aperiodic correlation properties.

  • mitigation of autocorrelation sidelobe peaks of orthogonal Discrete Frequency coding waveform for mimo radar
    IEEE Radar Conference, 2008
    Co-Authors: Bo Liu
    Abstract:

    The autocorrelation sidelobe peak (ASP) levels of Discrete Frequency-coding waveform with fixed Frequency pulses (DFCW_FF) is very large. It is about 0.21 or -13.2dB. Replacing the fixed Frequency pulses with linear FM pulses (LFM) can lower the ASP. We investigate theambiguity function (AF) and cross-AF for DFCW with arbitrary Frequency firing order. It shows that DFCW_LFM have different AF expression with the DFCW_FF. By setting the relationships between the Deltaf, B and T, we can reduce the ASP, as well as nullify the grating lobes. A modified Genetic Algorithm (GA) is proposed to numerically search orthogonal DFCW_LFM with optimal correlation properties. Some of the designed results are presented. Their correlation properties are effectively improved. Both simulation results and comparisons show that the method of mitigating ASP and proposed search algorithm are effective for the design of DFCWs with superior aperiodic correlation.

  • comments on Discrete Frequency coding waveform design for netted radar systems
    IEEE Signal Processing Letters, 2008
    Co-Authors: Bo Liu
    Abstract:

    For original paper see H. Deng, ibid., vol.11, no.2, p.179-182, (2004). This comment points out some errors in the correlation calculations and conclusions in the literature. The ambiguity function and cross-ambiguity function for Discrete Frequency-coding waveform (DFCW) with arbitrary firing order are analyzed in that letter to corroborate the judgement. It shows that range autocorrelation sidelobe peak (ASP) for DFCW fluctuates around 0.21, the Doppler tolerance has sinc function form, while the range cross-correlation peak (CP) between two DFCWs is heavily varied with the different firing order. The correlation values are recalculated.

  • optimization of orthogonal Discrete Frequency coding waveform based on modified genetic algorithm for mimo radar
    International Conference on Communications Circuits and Systems, 2007
    Co-Authors: Bo Liu
    Abstract:

    A modified genetic algorithm (GA) is proposed to numerically design orthogonal Discrete Frequency-coding waveforms (DFCWs) which have good aperiodic autocorrelation and cross-correlation properties for orthogonal multiple input multiple output (MIMO) radar. Some of the designed results are presented, and their correlation properties are better than other known in the literature. The effect of Doppler Frequency shift on the performance of these signals and ambiguity function are investigated. The simulation results and comparisons show that the proposed algorithm is more effective for the design of DFCWs with superior aperiodic correlation.

J.m. Cioffi - One of the best experts on this subject based on the ideXlab platform.

  • fdma capacity of gaussian multiple access channels with isi
    IEEE Transactions on Communications, 2002
    Co-Authors: J.m. Cioffi
    Abstract:

    This paper proposes a numerical method for characterizing the rate region achievable with Frequency-division multiple access (FDMA) for a Gaussian multiple-access channel with intersymbol interference. The Frequency spectrum is divided into Discrete Frequency bins and the Discrete bin-assignment problem is shown to have a convex relaxation, making it tractable to numerical optimization algorithms. A practical low-complexity algorithm for the two-user case is also proposed. The algorithm is based on the observation that the optimal Frequency partition has a two-band structure when the two channels are identical or when the signal-to-noise ratio is high. The simulation result shows that the algorithm performs well in other cases as well. The FDMA-capacity algorithm is used to devise the optimal Frequency-division duplex plan for very-high-speed digital subscriber lines.

  • fdma capacity of the gaussian multiple access channel with isi
    International Conference on Communications, 2000
    Co-Authors: J.m. Cioffi
    Abstract:

    This paper proposes a numerical method for characterizing the achievable rate region for a Gaussian multiple access channel with ISI under the Frequency division multiple access restriction. The Frequency spectrum is divided into Discrete Frequency bins and the Discrete bin assignment problem is shown to have a convex programming relaxation, making it tractable to numerical algorithms. The run-time complexity may be further reduced in the two-user case if the two channels are identical, or if the signal-to-noise ratio is high.

Rohit Bhargava - One of the best experts on this subject based on the ideXlab platform.

  • fast infrared chemical imaging with a quantum cascade laser
    Analytical Chemistry, 2015
    Co-Authors: Kevin Yeh, Seth Kenkel, Jui Nung Liu, Rohit Bhargava
    Abstract:

    Infrared (IR) spectroscopic imaging systems are a powerful tool for visualizing molecular microstructure of a sample without the need for dyes or stains. Table-top Fourier transform infrared (FT-IR) imaging spectrometers, the current established technology, can record broadband spectral data efficiently but requires scanning the entire spectrum with a low throughput source. The advent of high-intensity, broadly tunable quantum cascade lasers (QCL) has now accelerated IR imaging but results in a fundamentally different type of instrument and approach, namely, Discrete Frequency IR (DF-IR) spectral imaging. While the higher intensity of the source provides a higher signal per channel, the absence of spectral multiplexing also provides new opportunities and challenges. Here, we couple a rapidly tunable QCL with a high performance microscope equipped with a cooled focal plane array (FPA) detector. Our optical system is conceptualized to provide optimal performance based on recent theory and design rules for h...

  • Discrete Frequency infrared microspectroscopy and imaging with a tunable quantum cascade laser
    Analytical Chemistry, 2012
    Co-Authors: Matthew R Kole, Rohith Reddy, Matthew V Schulmerich, Matthew K Gelber, Rohit Bhargava
    Abstract:

    Fourier-transform infrared (FT-IR) imaging is a well-established modality but requires the acquisition of a spectrum over a large bandwidth, even in cases where only a few spectral features may be of interest. Discrete Frequency infrared (DF-IR) methods are now emerging in which a small number of measurements may provide all the analytical information needed. The DF-IR approach is enabled by the development of new sources integrating Frequency selection, in particular of tunable, narrow-bandwidth sources with enough power at each wavelength to successfully make absorption measurements. Here, we describe a DF-IR imaging microscope that uses an external cavity quantum cascade laser (QCL) as a source. We present two configurations, one with an uncooled bolometer as a detector and another with a liquid nitrogen cooled mercury cadmium telluride (MCT) detector and compare their performance to a commercial FT-IR imaging instrument. We examine the consequences of the coherent properties of the beam with respect t...

Khaled Hussien - One of the best experts on this subject based on the ideXlab platform.

  • orthogonal Discrete Frequency coding waveform design based on modified genetic algorithm for mimo sar
    Conference on Industrial Electronics and Applications, 2014
    Co-Authors: Wael Mehany, Licheng Jiao, Khaled Hussien
    Abstract:

    A multi-input multi-output (MIMO) radar can be used to form a synthetic aperture for high resolution imaging. To successfully utilize the MIMO synthetic aperture radar (SAR) system for practical imaging application, the orthogonal waveform design plays a critical role in image formation. Focusing on the SAR application, a definition for synthetic integrated side-lobe level ratio (ISLR) is proposed. In this paper a cost function containing ISLR and peak side-lobe level ratio (PSLR) is presented. A modified genetic algorithm (GA) is proposed to numerically search optimal Frequency firing order for Discrete Frequency-coding waveform (DFCW). Some of the designed results are presented. The obtained waveform can be implemented for MIMO-SAR systems to improve the image contrast.

Tzunglin Lee - One of the best experts on this subject based on the ideXlab platform.

  • Discrete Frequency tuning active filter to suppress harmonic resonances of closed loop distribution power systems
    IEEE Transactions on Power Electronics, 2011
    Co-Authors: Tzunglin Lee
    Abstract:

    Increasing demand of electric-power reliability in industrial parks or in urban areas has led to the development of closed-loop distribution power systems. The harmonic resonance between power-factor-correction capacitors and system inductors may cause significant voltage distortion along the feeder. This paper proposes a Discrete Frequency-tuning active filter installed at the middle point of a closed-loop line for harmonic-resonance suppression. The active filter operates as a variable conductance for individual harmonic Frequency according to the corresponding harmonic-voltage distortion. This algorithm allows the damping conductance of each harmonic Frequency to be separately and autonomously adjusted in response to variation of both harmonic sources and resonant capacitors. Therefore, the unintentional “whack-a-mole” phenomenon, due to mismatching between the active filter and the line, can be avoided even if the active-filter location deviates from the middle point. Voltage distortion throughout the closed-loop line can be definitely maintained below an allowable level with lower peak current and lower rms current compared to the conventional voltage-detection active filter. Computer simulations based on a 11.4 kV/15 MVA system and a scaled-down platform in the laboratory are developed to validate the effectiveness of the proposed approach.

  • Discrete Frequency tuning active filter for power system harmonics
    IEEE Transactions on Power Electronics, 2009
    Co-Authors: Tzunglin Lee, Potai Cheng
    Abstract:

    Severe voltage distortion, due to power system harmonic resonance, has been reported in recent years. This issue becomes more significant in high penetration of a photovoltaic (PV) network. A conventional voltage detection active filter operates as similar conductance for all harmonic frequencies to resolve this problem whether in a fixed conductance command or in an automatic gain adjustment control. However, its filtering capability is impeded by the mismatch between the active filter and the radial line, and the voltage distortion may still be significant. This paper proposes a Discrete Frequency tuning active filter to suppress power system harmonics. The active filter operates as variable conductance for each individual harmonic Frequency. Each harmonic conductance is dynamically adjusted according to the corresponding harmonic voltage distortion of the active filter installation point in response to increase or decrease of nonlinear loads, or variation of resonant Frequency in the power system. The mismatching problem between the feeder impedance and the active filter can be avoided effectively. Therefore, harmonic voltage distortion can be maintained at an allowable level throughout the feeder with lower peak current and lower rms current of the active filter, and loads installed at various locations of the power system receive more uniform voltage waveform.