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Moeness G Amin - One of the best experts on this subject based on the ideXlab platform.

  • short time fourier transform receiver for nonstationary interference excision in direct sequence Spread Spectrum Communications
    2001
    Co-Authors: X Ouyang, Moeness G Amin
    Abstract:

    A new adaptive excision approach for nonstationary interference excision in direct sequence Spread Spectrum (DS/SS) Communications is introduced. The proposed excision approach is based on the attractive localization properties of the impulse responses of the multiple pole filters. These impulse responses have Gaussian-like shapes and decrease in bandwidth with higher pole multiplicities. When used as data windows, they field a large class of computationally efficient short-time Fourier transforms (STFTs). Localization measures can be applied to determine the optimum window that maximally concentrates the interference in the time-frequency (t.-f.) domain. Interference mitigation is then achieved by applying a binary excision mask to the corresponding STFT for each data bit. We show that the proposed interference excision method permits both data-dependent windowing and time-varying filtering and leads to improved BER performance of the DS/SS system. The paper also derives the general optimum receiver implementing the STFT-based interference excision system.

  • optimum interference excision in Spread Spectrum Communications using open loop adaptive filters
    1999
    Co-Authors: Moeness G Amin, Chenshu Wang, Alan R Lindsey
    Abstract:

    A generalized approach for interference suppression in PN Spread Spectrum Communications using open-loop adaptive excision filtering is introduced. The excision filter coefficients under this technique depend on the jammer power and its instantaneous frequency (IF) information, and both values can be gained in the time-frequency domain. The dependency of the excision filter characteristics on the interference power, which was absent in past contributions in this area, is of significant importance as it allows optimum tradeoff between interference removal and the amount of self-noise generated from the induced correlation across the PN chip sequence, due to filtering. This tradeoff is bounded by the two extreme cases of no self-noise, which implies preprocessing disabled, and full interference excision, which the case previously considered. In this paper, we derive the FIR excision filters that maximize the receiver signal-to-noise ratio for narrowband interference and discuss the generalization to nonstationary jamming environment.

  • broadband interference excision for software radio Spread Spectrum Communications using time frequency distribution synthesis
    1999
    Co-Authors: S R Lach, Moeness G Amin, Alan R Lindsey
    Abstract:

    A new method is introduced for interference excision in Spread-Spectrum Communications that is conducive to software-radio applications. Spare processing capacity in the receiver permits the use of time-frequency techniques to synthesize a nonstationary interference from the time-frequency domain using least squares methods. The synthesized signal is then subtracted from the incoming data in the time domain, leading to jammer removal and increased signal-to-interference-and-noise ratio at the input of the correlator. The paper focuses on jammers with constant modulus that are uniquely described by their instantaneous frequency characteristics. With this a priori knowledge, the jammer signal amplitude is restored by projecting each sample of the synthesized signal to a circle representing its constant modulus. With the phase matching provided by the least squares synthesis method and amplitude matching underlying the projection operation, a significant improvement in receiver performance/bit-error rates is achieved over the case where no projection is performed. Software-radio aspects including computational complexity and processing modes are also discussed.

  • performance analysis of instantaneous frequency based interference excision techniques in Spread Spectrum Communications
    1998
    Co-Authors: Chenshu Wang, Moeness G Amin
    Abstract:

    Jammers characterized by their instantaneous frequencies can be effectively mitigated in direct sequence Spread Spectrum Communications by using open-loop adaptive excision filters. The primary requirement for these filters is that they must possess a notch in tune with the jammer instantaneous frequency (IF) to annihilate the interference power at every time sample. The interference time-varying frequency can be obtained using existing IF estimators, including quadratic time-frequency distribution methods. Without focusing on any specific estimator, we develop expressions for the receiver performance using a general class of multiple-zero FIR excision filters and show the dependence of the bit error rate (BER) on the filter order and its group delay. The effect of inaccuracies in the jammer instantaneous frequency information on the receiver performance is considered and evaluated as a function of the filter notch bandwidth. The latter is defined by the filter zero multiplicity, which is shown to be an important factor in the analysis of the correlator signal-to-noise ratio (SNR).

Vela Mbele - One of the best experts on this subject based on the ideXlab platform.

  • molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb
    2007
    Co-Authors: Scott A Diddams, Vela Mbele, L Hollberg
    Abstract:

    A broadband frequency 'comb' provides, in a single laser beam, about a million optical modes with very narrow linewidths and precisely known absolute frequency positions. A technique has been developed that enables the resolution of the modes of a frequency comb and the simultaneous detection of them in a parallel manner. The control of the broadband frequency comb1 emitted from a mode-locked femtosecond laser has permitted a wide range of scientific and technological advances—ranging from the counting of optical cycles for next-generation atomic clocks1,2 to measurements of phase-sensitive high-field processes3. A unique advantage of the stabilized frequency comb is that it provides, in a single laser beam, about a million optical modes with very narrow linewidths4 and absolute frequency positions known to better than one part in 1015 (ref. 5). One important application of this vast array of highly coherent optical fields is precision spectroscopy, in which a large number of modes can be used to map internal atomic energy structure and dynamics6,7. However, an efficient means of simultaneously identifying, addressing and measuring the amplitude or relative phase of individual modes has not existed. Here we use a high-resolution disperser8,9 to separate the individual modes of a stabilized frequency comb into a two-dimensional array in the image plane of the spectrometer. We illustrate the power of this technique for high-resolution spectral fingerprinting of molecular iodine vapour, acquiring in a few milliseconds absorption images covering over 6 THz of bandwidth with high frequency resolution. Our technique for direct and parallel accessing of stabilized frequency comb modes could find application in high-bandwidth Spread-Spectrum Communications with increased security, high-resolution coherent quantum control, and arbitrary optical waveform synthesis10 with control at the optical radian level.

  • Molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb
    2007
    Co-Authors: Scott A Diddams, L Hollberg, Vela Mbele
    Abstract:

    The control of the broadband frequency comb emitted from a mode-locked femtosecond laser has permitted a wide range of scientific and technological advances--ranging from the counting of optical cycles for next-generation atomic clocks to measurements of phase-sensitive high-field processes. A unique advantage of the stabilized frequency comb is that it provides, in a single laser beam, about a million optical modes with very narrow linewidths and absolute frequency positions known to better than one part in 10(15) (ref. 5). One important application of this vast array of highly coherent optical fields is precision spectroscopy, in which a large number of modes can be used to map internal atomic energy structure and dynamics. However, an efficient means of simultaneously identifying, addressing and measuring the amplitude or relative phase of individual modes has not existed. Here we use a high-resolution disperser to separate the individual modes of a stabilized frequency comb into a two-dimensional array in the image plane of the spectrometer. We illustrate the power of this technique for high-resolution spectral fingerprinting of molecular iodine vapour, acquiring in a few milliseconds absorption images covering over 6 THz of bandwidth with high frequency resolution. Our technique for direct and parallel accessing of stabilized frequency comb modes could find application in high-bandwidth Spread-Spectrum Communications with increased security, high-resolution coherent quantum control, and arbitrary optical waveform synthesis with control at the optical radian level.

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

  • optimum interference excision in Spread Spectrum Communications using open loop adaptive filters
    1999
    Co-Authors: Moeness G Amin, Chenshu Wang, Alan R Lindsey
    Abstract:

    A generalized approach for interference suppression in PN Spread Spectrum Communications using open-loop adaptive excision filtering is introduced. The excision filter coefficients under this technique depend on the jammer power and its instantaneous frequency (IF) information, and both values can be gained in the time-frequency domain. The dependency of the excision filter characteristics on the interference power, which was absent in past contributions in this area, is of significant importance as it allows optimum tradeoff between interference removal and the amount of self-noise generated from the induced correlation across the PN chip sequence, due to filtering. This tradeoff is bounded by the two extreme cases of no self-noise, which implies preprocessing disabled, and full interference excision, which the case previously considered. In this paper, we derive the FIR excision filters that maximize the receiver signal-to-noise ratio for narrowband interference and discuss the generalization to nonstationary jamming environment.

  • broadband interference excision for software radio Spread Spectrum Communications using time frequency distribution synthesis
    1999
    Co-Authors: S R Lach, Moeness G Amin, Alan R Lindsey
    Abstract:

    A new method is introduced for interference excision in Spread-Spectrum Communications that is conducive to software-radio applications. Spare processing capacity in the receiver permits the use of time-frequency techniques to synthesize a nonstationary interference from the time-frequency domain using least squares methods. The synthesized signal is then subtracted from the incoming data in the time domain, leading to jammer removal and increased signal-to-interference-and-noise ratio at the input of the correlator. The paper focuses on jammers with constant modulus that are uniquely described by their instantaneous frequency characteristics. With this a priori knowledge, the jammer signal amplitude is restored by projecting each sample of the synthesized signal to a circle representing its constant modulus. With the phase matching provided by the least squares synthesis method and amplitude matching underlying the projection operation, a significant improvement in receiver performance/bit-error rates is achieved over the case where no projection is performed. Software-radio aspects including computational complexity and processing modes are also discussed.

Ha H Nguyen - One of the best experts on this subject based on the ideXlab platform.

  • frequency shift chirp Spread Spectrum Communications with index modulation
    2021
    Co-Authors: Muhammad Hanif, Ha H Nguyen
    Abstract:

    This paper introduces a novel frequency-shift chirp Spread Spectrum (FSCSS) system with index modulation (IM). By using combinations of orthogonal chirp signals for message representation, the proposed FSCSS-IM system is very flexible to design and can achieve much higher data rates than the conventional FSCSS system under the same bandwidth. The paper presents optimal detection algorithms, both coherently and non-coherently, for the proposed FSCSS-IM system. Furthermore, a low-complexity non-coherent detection algorithm is also developed to reduce the computational complexity of the receiver, which is shown to achieve near-optimal performance. Results are presented to demonstrate that the proposed system, while enabling much higher data rates, enjoys similar bit-error performance as that of the conventional FSCSS system.

A N Akansu - One of the best experts on this subject based on the ideXlab platform.

  • a novel time frequency exciser in Spread Spectrum Communications for chirp like interference
    1998
    Co-Authors: A Bultan, A N Akansu
    Abstract:

    A novel time-frequency exciser is developed for the removal of chirp-like interferences in direct sequence Spread Spectrum (DSSS) Communications. The chirplet decomposition iteratively expands signals in terms of time-frequency localized waveforms. The interference signal components are highly correlated with chirplets, and are represented by a few of the highest energy components of the decomposition. These components are excised from the received signal, and an excised signal goes through a detector for a decision. The proposed time-frequency exciser outperforms the conventional Fourier transform based excisers for chirp-like interference classes.