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Arye Nehorai - One of the best experts on this subject based on the ideXlab platform.

  • Acoustic vector-sensor processing in the presence of a reflecting boundary
    IEEE Transactions on Signal Processing, 2000
    Co-Authors: Malcolm Hawkes, Arye Nehorai
    Abstract:

    We consider the passive direction-of-arrival (DOA) estimation problem using arrays of acoustic vector sensors located in a fluid at or near a reflecting boundary. We formulate a general measurement model applicable to any planar surface, derive an expression for the Cramer-Rao bound (CRB) on the azimuth and elevation of a single source, and obtain a bound on the mean-square Angular Error (MSAE). We then examine two applications of great practical interest: hull-mounted and seabed arrays. For the former, we use three models for the hull: an ideal rigid surface for high frequency, an ideal pressure-release surface for low frequency, and a more complex, realistic layered model. For the seabed scenario, we model the ocean floor as an absorptive liquid layer. For each application, we use the CRB, MSAE bound, and beam patterns to quantify the advantages of using velocity and/or vector sensors instead of pressure sensors. For the hull-mounted application, we show that normal component velocity sensors overcome the well-known, low-frequency problem of small pressure signals without the need for an undesirable “stand-off” distance. For the seabed scenario, we also derive a fast wideband estimator of the source location using a single vector sensor

  • effects of sensor placement on acoustic vector sensor array performance
    IEEE Journal of Oceanic Engineering, 1999
    Co-Authors: M Hawkes, Arye Nehorai
    Abstract:

    We consider the role played by the sensor locations in the optimal performance of an array of acoustic vector sensors, First we derive an expression for the Cramer-Rao bound on the azimuth and elevation of a single far-field source for an arbitrary acoustic vector-sensor array in a homogeneous wholespace and show that it has a block diagonal structure, i.e., the source location parameters are uncoupled from the signal and noise strength parameters. We then derive a set of necessary and sufficient geometrical constraints for the two direction parameters, azimuth and elevation, to be uncoupled from each other. Ensuring that these parameters are uncoupled minimizes the bound and means they are the natural or "canonical" location parameters for the model. We argue that it provides a compelling array design criterion. We also consider a bound on the mean-square Angular Error and its asymptotic normalization, which are useful measures in three-dimensional bearing estimation problems. We derive an expression for this bound and discuss it in terms of the sensors' locations. We then show that our previously derived geometrical conditions are also sufficient to ensure that this bound is independent of azimuth. Finally, we extend those conditions to obtain a set of geometrical constraints that ensure the optimal performance is isotropic.

  • vector sensor array processing for electromagnetic source localization
    IEEE Transactions on Signal Processing, 1994
    Co-Authors: Arye Nehorai, E. Paldi
    Abstract:

    The authors present a new approach for localizing electromagnetic sources using sensors where the output of each is a vector consisting of the complete six electric and magnetic field components. Two types of source transmissions are considered: (1) single signal transmission (SST), and (2) dual signal transmission (DST). The model is given in terms of several parameters, including the wave direction of arrival (DOA) and state of polarization. A compact expression is derived for the Cramer-Rao bound (CRB) on the estimation Errors of these parameters for the multi-source multi-vector-sensor model. Quality measures including mean-square Angular Error (MSAE) and covariance of vector Angular Error (CVAE) are introduced, and their lower bounds are derived. The advantage of using vector sensors is highlighted by explicit evaluation of the MSAE and CVAE bounds for source localization with a single vector sensor. A simple algorithm for estimating the source DOA with this sensor is presented along with its statistical performance analysis. >

  • Acoustic vector-sensor array processing
    IEEE Transactions on Signal Processing, 1994
    Co-Authors: Arye Nehorai, E. Paldi
    Abstract:

    A method is presented for localizing acoustic sources using an array of sensors, the output of each being a vector consisting of the acoustic pressure and acoustic particle velocity. The authors derive a compact expression for the Cramer-Rao bound (CRB) on the estimation Errors of the source direction-of-arrival (DOA) parameters in the multi-source multi-vector-sensor model. An explicit expression is found for the mean-square Angular Error (MSAE) bound for source localization with a single vector sensor. The authors present two simple algorithms for estimating the source DOA with this sensor, along with their statistical performance analyses.

Guodong Xie - One of the best experts on this subject based on the ideXlab platform.

  • orbital Angular momentum multiplexed free space optical communication link using transmitter lenses
    Applied Optics, 2016
    Co-Authors: Guodong Xie, Peicheng Liao, Marti P J Lavery, Hao Huang, Zhe Zhao, Yongxiong Ren, Yan Yan, Nisar Ahmed, Changjing Bao, Zhe Wang
    Abstract:

    In this paper, we explore the potential benefits and limitations of using transmitter lenses in an orbital-Angular-momentum (OAM)-multiplexed free-space optical (FSO) communication link. Both simulation and experimental results indicate that within certain transmission distances, using lenses at the transmitter to focus OAM beams could reduce power loss in OAM-based FSO links and that this improvement might be more significant for higher-order OAM beams. Moreover, the use of transmitter lenses could enhance system tolerance to Angular Error between transmitter and receiver, but they might degrade tolerance to lateral displacement.

  • performance metrics and design considerations for a free space optical orbital Angular momentum multiplexed communication link
    Optica, 2015
    Co-Authors: Guodong Xie, Marti P J Lavery, Nima Ashrafi, Hao Huang, Zhe Zhao, Long Li, Yongxiong Ren, Yan Yan, Nisar Ahmed, Solyman Ashrafi
    Abstract:

    The capacity of free-space optical (FSO) communication links could potentially be increased by the simultaneous transmission of multiple orbital Angular momentum (OAM) beams. For such an OAM multiplexing approach, one requires the collection of adequate power as well as proportion of the phase front for a system with minimal crosstalk. Here we study the design considerations for an OAM-multiplexed free-space data link, analyzing the power loss, channel crosstalk, and power penalty of the link in the case of limited-size receiver apertures and misalignment between the transmitter and the receiver. We describe the trade-offs for different transmitted beam sizes, receiver aperture sizes, and mode spacing of the transmitted OAM beams under given lateral displacements or receiver Angular Errors. Through simulations and some experiments, we show that (1) a system with a larger transmitted beam size and a larger receiver aperture is more tolerant to lateral displacement but less tolerant to the receiver Angular Error, and (2) a system with a larger mode spacing, which uses larger OAM charges, suffers more system power loss but less channel crosstalk; thus, a system with a small mode spacing shows a lower system power penalty when system power loss dominates (e.g., a small lateral displacement or receiver Angular Error), whereas that with a larger mode spacing shows a lower power penalty when channel crosstalk dominates (e.g., a larger lateral displacement or receiver Angular Error). This work could be beneficial to the practical implementation of OAM-multiplexed FSO links.

  • performance enhancement of an orbital Angular momentum based free space optical communication link through beam divergence controlling
    Optical Fiber Communication Conference, 2015
    Co-Authors: Guodong Xie, Nisa Ahmed, Peicheng Liao, Marti P J Lavery, Nima Ashrafi, Solyma Ashrafi, Zhe Wang, Hao Huang, Zhe Zhao, Ala E Willne
    Abstract:

    Using beam divergence controlling to mitigate Angular Error effects in OAM-based FSO links is investigated through simulation and experiment. Results show that controlling beam divergence allows reducing power loss and Angular Error induced channel crosstalk.

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

  • experimental and numerical study of Angular Error in wire edm taper cutting
    International Journal of Machine Tools & Manufacture, 2008
    Co-Authors: Jose Antonio Sanchez, S Plaza, N Ortega, Marga Marcos, J Albizuri
    Abstract:

    Abstract Wire electro discharge machining (WEDM) has become one of the most popular processes for producing precise geometries in hard materials, such as those used in the tooling industry. The so-called taper-cutting involves the generation of inclined ruled surfaces, and it is especially important in the manufacturing of tooling requiring draft angles. In this paper a new approach to the prediction of Angular Error in wire-EDM taper-cutting is presented. A systematic analysis of the influence of process parameters on Angular Error is carried out using Design of Experiments (DoE) techniques. A quadratic equation for the prediction of Angular Error that takes into account electrical parameters and part geometry is derived. Validation results reveal a dominant influence of the mechanical behaviour of the wire, rather than that of EDM regime. Following this assertion an original finite element model (FEM) to describe the mechanical behaviour of soft wires, typically used in taper-cutting operations, has been developed taking into account non-linear phenomena such as contact mechanics, plastic behaviour, stress-stiffening and large displacements. Both the results of DoE techniques and FEM simulation have been validated through experimental tests in industrial conditions. Deviations of accuracy of WEDM-tapered parts can be reduced to values below 4′ using these models.

Solyman Ashrafi - One of the best experts on this subject based on the ideXlab platform.

  • performance metrics and design considerations for a free space optical orbital Angular momentum multiplexed communication link
    Optica, 2015
    Co-Authors: Guodong Xie, Marti P J Lavery, Nima Ashrafi, Hao Huang, Zhe Zhao, Long Li, Yongxiong Ren, Yan Yan, Nisar Ahmed, Solyman Ashrafi
    Abstract:

    The capacity of free-space optical (FSO) communication links could potentially be increased by the simultaneous transmission of multiple orbital Angular momentum (OAM) beams. For such an OAM multiplexing approach, one requires the collection of adequate power as well as proportion of the phase front for a system with minimal crosstalk. Here we study the design considerations for an OAM-multiplexed free-space data link, analyzing the power loss, channel crosstalk, and power penalty of the link in the case of limited-size receiver apertures and misalignment between the transmitter and the receiver. We describe the trade-offs for different transmitted beam sizes, receiver aperture sizes, and mode spacing of the transmitted OAM beams under given lateral displacements or receiver Angular Errors. Through simulations and some experiments, we show that (1) a system with a larger transmitted beam size and a larger receiver aperture is more tolerant to lateral displacement but less tolerant to the receiver Angular Error, and (2) a system with a larger mode spacing, which uses larger OAM charges, suffers more system power loss but less channel crosstalk; thus, a system with a small mode spacing shows a lower system power penalty when system power loss dominates (e.g., a small lateral displacement or receiver Angular Error), whereas that with a larger mode spacing shows a lower power penalty when channel crosstalk dominates (e.g., a larger lateral displacement or receiver Angular Error). This work could be beneficial to the practical implementation of OAM-multiplexed FSO links.

E. Paldi - One of the best experts on this subject based on the ideXlab platform.

  • vector sensor array processing for electromagnetic source localization
    IEEE Transactions on Signal Processing, 1994
    Co-Authors: Arye Nehorai, E. Paldi
    Abstract:

    The authors present a new approach for localizing electromagnetic sources using sensors where the output of each is a vector consisting of the complete six electric and magnetic field components. Two types of source transmissions are considered: (1) single signal transmission (SST), and (2) dual signal transmission (DST). The model is given in terms of several parameters, including the wave direction of arrival (DOA) and state of polarization. A compact expression is derived for the Cramer-Rao bound (CRB) on the estimation Errors of these parameters for the multi-source multi-vector-sensor model. Quality measures including mean-square Angular Error (MSAE) and covariance of vector Angular Error (CVAE) are introduced, and their lower bounds are derived. The advantage of using vector sensors is highlighted by explicit evaluation of the MSAE and CVAE bounds for source localization with a single vector sensor. A simple algorithm for estimating the source DOA with this sensor is presented along with its statistical performance analysis. >

  • Acoustic vector-sensor array processing
    IEEE Transactions on Signal Processing, 1994
    Co-Authors: Arye Nehorai, E. Paldi
    Abstract:

    A method is presented for localizing acoustic sources using an array of sensors, the output of each being a vector consisting of the acoustic pressure and acoustic particle velocity. The authors derive a compact expression for the Cramer-Rao bound (CRB) on the estimation Errors of the source direction-of-arrival (DOA) parameters in the multi-source multi-vector-sensor model. An explicit expression is found for the mean-square Angular Error (MSAE) bound for source localization with a single vector sensor. The authors present two simple algorithms for estimating the source DOA with this sensor, along with their statistical performance analyses.

  • Acoustic vector sensor array processing
    [1992] Conference Record of the Twenty-Sixth Asilomar Conference on Signals Systems & Computers, 1992
    Co-Authors: A. Nehorai, E. Paldi
    Abstract:

    An approach is proposed for localization of acoustic sources using an array of sensors for which the measurement of each sensor is a vector consisting of the acoustic pressure and acoustic particle velocity. A compact expression is derived for the Cramer-Rao bound (CRB) on the estimation Errors of the source direction-of-arrival (DOA) parameters in the multi-source multi-vector sensor model. An explicit expression is found for the mean-square Angular Error bound for source localization with a single vector sensor. Two simple algorithms for estimating the source DOA with this sensor are presented along with their statistical performance analysis.