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  • Articles  (1,341)
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  • Articles  (1,341)
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  • Institute of Electrical and Electronics Engineers (IEEE)  (1,341)
  • Hindawi
  • MDPI Publishing
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  • 1
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: Three-dimensional ultrasound imaging is a promising medical imaging technology because of its ease of use and improved accuracy in diagnosis. However, its high computational complexity and resulting high power consumption has precluded its use in hand-held applications. In this paper, we present a separable beamforming method that greatly reduces computational complexity. Our method is based on decomposing the delay term in a way that minimizes the root-mean-square error caused by the decomposition. We analyze tradeoffs between the approximation error caused by the decomposition and computational complexity. Then, we present enhancements to the Sonic Millip3De hardware accelerator for ultrasound beamforming to implement separable beamforming. Using hardware synthesis targeting standard cells in 45 nm, we show that the proposed method allows us to boost the Sonic Millip3De frame rate from 1–2 Hz to 32 Hz while maintaining power consumption at 15 W. We validate image quality of our method using cyst phantom simulations in Field II. Our evaluation demonstrates that the proposed separable beamforming method can produce 3-D images with high quality that are comparable to those generated by non-separable beamforming.
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  • 2
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: For MIMO systems, due to the deployment of multiple antennas at both the transmitter and the receiver, the design variables, e.g., precoders, equalizers, and training sequences, are usually matrices. It is well known that matrix operations are usually more complicated compared with their vector counterparts. In order to overcome the high complexity resulting from matrix variables, in this paper, we investigate a class of elegant multi-objective optimization problems, namely matrix-monotonic optimization problems (MMOPs). In our work, various representative MIMO optimization problems are unified into a framework of matrix-monotonic optimization, which includes linear transceiver design, nonlinear transceiver design, training sequence design, radar waveform optimization, the corresponding robust design and so on as its special cases. Then, exploiting the framework of matrix-monotonic optimization the optimal structures of the considered matrix variables can be derived first. Based on the optimal structure, the matrix-variate optimization problems can be greatly simplified into the ones with only vector variables. In particular, the dimension of the new vector variable is equal to the minimum number of columns and rows of the original matrix variable. Finally, we also extend our work to some more general cases with multiple matrix variables.
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  • 3
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: This paper investigates the bias of the maximum likelihood target location estimate resulting from the Gaussian data measurement noise and sensor position errors. The bias components from them are interrelated, except when they are independent and identically distributed. The bias behaviors of time of arrival, time difference of arrival, and angle of arrival positionings are contrasted, and geometric conditions under which the location bias becomes zero are elaborated.We illustrate the developed results for bias compensation in improving the performance of target tracking.
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  • 4
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: In a collaborative sensor network (CSN), the conventional target tracking algorithms employed are Kalman filtering (KF) or extended Kalman filtering (EKF). However, these techniques have a presumed probability distribution of the system noise and prediction noise. They also need some a priori information that may be unavailable in some circumstances. Therefore, the system is not flexible for a complicated scenario. With the help of a machine learning technique called expert prediction (EP), a novel target tracking approach for CSNs is developed. This scheme makes use of the aforementioned EP in parameter estimation course for the target of interest, instead of exploiting the filtering method as typically found in available literature. This idea is further unfolded with comparisons regarding the CSN using Kalman filters, extended Kalman filters, and decentralized sigma-point information filters (DSPIFs). The new tracking algorithm is investigated with both linear and nonlinear prediction methods. Simulation results demonstrate that this proposed measure will deliver forecasting output with more precision because of the built-in multimodel mode among different experts, the learning ability, and the self-perfection characteristic. Not only does this performance occur in a more robust way than those of the existing approaches – particularly in the presence of heavy clutter, highly maneuvering targets, and/or multiple targets – but it simultaneously requires the least a priori information and imposes the least limitation on the observation model.
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  • 5
    Publication Date: 2014-12-13
    Description: Hybrid aerial-terrestrial communication networks based on low-altitude platforms are expected to meet optimally the urgent communication needs of emergency relief and recovery operations for tackling large-scale natural disasters. The energy-efficient operation of such networks is important given that the entire network infrastructure, including the battery-operated ground terminals, exhibits requirements to operate under power-constrained situations. In this paper, we discuss the design and evaluation of an adaptive cooperative scheme intended to extend the survivability of the battery-operated aerial-terrestrial communication links. We propose and evaluate a real-time adaptive cooperative transmission strategy for dynamic selection between direct and cooperative links based on the channel conditions for improved energy efficiency. We show that the cooperation between mobile terrestrial terminals on the ground could improve energy efficiency in the uplink, depending on the temporal behavior of the terrestrial and aerial uplink channels. The corresponding delay in having cooperative (relay-based) communications with relay selection is also addressed. The simulation analysis corroborates that the adaptive transmission technique improves overall energy efficiency of the network whilst maintaining low latency, enabling real-time applications.
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  • 6
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: In this paper, a reduced-rank scheme with joint iterative optimization is presented for direction of arrival estimation. A rank-reduction matrix and an auxiliary reduced-rank parameter vector are jointly optimized to calculate the output power with respect to each scanning angle. Subspace algorithms to estimate the rank-reduction matrix and the auxiliary vector are proposed. Simulations are performed to show that the proposed algorithms achieve enhanced performance over existing algorithms in the studied scenarios.
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  • 7
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: Using the dynamic inversion philosophy, a nonlinear partial integrated guidance and control approach is presented in this paper for formation flying. It is based on the evolving philosophy of integrated guidance and control. However, it also retains the advantages of the conventional guidance then control philosophy by retaining the timescale separation between translational and rotational dynamics explicitly. Simulation studies demonstrate that the proposed technique is effective in bringing the vehicles into formation quickly and maintaining the formation.
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  • 8
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: The use of ground-based transmitters (so-called pseudolites) for outdoor and indoor navigation has been under consideration since the origin of the Global Positioning System (GPS). However, one significant limitation of the use of code division multiple access (CDMA) was immediately obvious: one CDMA transmitter signal interferes with another CDMA transmitter signal. This is called the ""near-far problem."" Different methods have been studied in order to mitigate such jamming. This paper presents a new mitigation method based on a principle that can be summed up as follows: the signal and a delayed replica of the signal are broadcast by a ground transmitter antenna. At the receiver stage, the replica signal is used to eliminate the interference caused by the direct signal. This is called the double transmission technique (DTT), and it presents interesting performance features regarding interference mitigation. A signal processing technique corresponding to this method is presented in this paper, considering a GPS L1 C/A-code pseudolite. Performance simulations are also presented.
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  • 9
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: This paper describes a novel framework to determine the relative pose and range of a solid-of-revolution-shaped spacecraft from a single image without any artificial beacons. The translation and the symmetry axis of the spacecraft can be estimated from the imaged cross sections of the spacecraft body. Then the pose and range of the spacecraft are fully determined by means of the images of its solar panels and asymmetric feature. Our method has been validated by both synthetic and real images.
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  • 10
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: Data association, the problem of reasoning over correspondence between targets and measurements, is a fundamental problem in tracking. This paper presents a graphical model formulation of data association and applies an approximate inference method, belief propagation (BP), to obtain estimates of marginal association probabilities. We prove that BP is guaranteed to converge, and bound the number of iterations necessary. Experiments reveal a favourable comparison to prior methods in terms of accuracy and computational complexity.
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  • 11
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-11-08
    Description: Phase reconstruction based on optical ultrafast differentiation is implemented using an integrated-waveguide Mach–Zehnder interferometer to demonstrate self-referenced phase characterization of gigahertz-rate complex modulated signals (e.g., quadrature phase shift keying and amplitude phase shift keying modulation formats), through a single-shot and real-time technique. This method is transparent to both modulation format and bit rate, limited only by the bandwidth capabilities of the temporal intensity measurement instrumentation.
    Print ISSN: 1041-1135
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  • 12
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-11-08
    Description: A 3D lithium niobate integrated electro-optical electric field (E-field) sensor utilizing three optical waveguide Mach–Zehnder interferometers has been designed, fabricated, and characterized for the measurement of lightning electromagnetic impulse (EMP). The linear detected E-fields with the sensor are 15–370 kV/m. Experimental results demonstrate that the half wave E-fields of the 3D probe are all more than 4000 kV/m which means the maximal detectable E-field can be exceed 1000 kV/m. Based on the time domain response for applying the nanosecond EMP, the frequency response of the sensor has been calculated up to 500 MHz.
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  • 13
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-11-08
    Description: RES, a regularized stochastic version of the Broyden–Fletcher–Goldfarb–Shanno (BFGS) quasi-Newton method, is proposed to solve strongly convex optimization problems with stochastic objectives. The use of stochastic gradient descent algorithms is widespread, but the number of iterations required to approximate optimal arguments can be prohibitive in high dimensional problems. Application of second-order methods, on the other hand, is impracticable because the computation of objective function Hessian inverses incurs excessive computational cost. BFGS modifies gradient descent by introducing a Hessian approximation matrix computed from finite gradient differences. RES utilizes stochastic gradients in lieu of deterministic gradients for both the determination of descent directions and the approximation of the objective function's curvature. Since stochastic gradients can be computed at manageable computational cost, RES is realizable and retains the convergence rate advantages of its deterministic counterparts. Convergence results show that lower and upper bounds on the Hessian eigenvalues of the sample functions are sufficient to guarantee almost sure convergence of a subsequence generated by RES and convergence of the sequence in expectation to optimal arguments. Numerical experiments showcase reductions in convergence time relative to stochastic gradient descent algorithms and non-regularized stochastic versions of BFGS. An application of RES to the implementation of support vector machines is developed.
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  • 14
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-11-08
    Description: A high-accuracy fiber-optic Michelson accelerometer based on frequency modulation is demonstrated and a new type of sensing elements is designed in this letter. The interference optical waves are modulated and demodulated. In theory, the sensitivity of the accelerometer goes up with the increase of frequency. The experimental results demonstrate that when the modulation frequency increases from 200 to 800 Hz, the sensitivity increases from 0.188 to 0.751 rad/g and the average error of acceleration measurement is $sim 1$ %.
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  • 15
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: An ultrawideband (UWB) multiple input/multiple output (MIMO) cognitive radar has been developed and demonstrated for the first time. Field-programmable gate array (FPGA) is used for waveform-level computing, while waveform optimization is accomplished in CPU. Working as a closed loop, convex optimization is applied to jointly design (arbitrary) transmitted waveforms and the receiving filters in response to the varying wireless environment. Multiple targets localization in the presence of interference is demonstrated. Shown in the experiment, performance improvement is obvious in all interference patterns.
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  • 16
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: The Maximum Likelihood Probabilistic Multi-Hypothesis Tracker (ML-PMHT) can be used as a powerful multisensor, low-observable, multitarget active sonar tracker. It is a non-Bayesian algorithm that uses a generalized likelihood ratio test to differentiate between clutter and targets. Prior to this paper, the detection threshold used for target discrimination was determined either through trial and error or with lengthy Monte Carlo simulations.We present a new method for determining this threshold by assuming that clutter is uniformly distributed in the search space (which is one of the basic assumptions of the ML-PMHT algorithm) and then treating the log-likelihood ratio (LLR) as a random variable transformation. In this manner we can obtain an expression for the value of any random point on the likelihood surface caused by clutter. We then use extreme value theory to obtain an expression for the probability density function (PDF) of the peak point of the LLR surface due to clutter. From this peak PDF, we can then calculate a threshold based on some desired (small) false track acceptance probability.
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  • 17
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: The Maximum Likelihood Probabilistic Multi-Hypothesis Tracker (ML-PMHT) can be used as a powerful multisensor, low-observable, multitarget active tracker. It is a non-Bayesian algorithm that uses a generalized likelihood ratio test (GLRT) to differentiate between clutter and targets. We use a new method, initially developed to obtain the probability density function (pdf) of the maximum point in theML-PMHT log-likelihood ratio (LLR) due to clutter, to now develop a pdf for the maximum value of the ML-PMHT LLR caused by a target. With expressions for the pdfs of the maximum points caused by both clutter (developed in a companion article) and a target, we can, for a given set of tracking parameters (signal-to-noise ratio, search volume, target measurement probability of detection, etc.), develop ML-PMHT "tracker operating characteristic" curves, similar to receiver operating characteristic curves for a detector. Since ML-PMHT can be thought of as an optimal algorithm in the sense that, as long as the target and the environment match the algorithm???s assumptions, all the information from all the available measurements can be used, and no approximations are necessary to get the algorithm to function, the analysis presented in this paper offers for the first time part of the answer to the fundamental question: Can a particular target be tracked?
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  • 18
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: The goal of a target detection system is to determine the location of potential targets in the field of view of the sensor. Traditionally, this is done using high-quality images from a conventional imager. For wide-field-of-view scenarios, this can pose a challenge for both data acquisition and system bandwidth. In this paper, we discuss a compressive sensing technique for target detection that dramatically reduces the number of measurements that is required to perform the task, as compared with the number of pixels in conventional images. This, in turn, can reduce the data rate from the sensor electronics, and along with it, the cost, complexity, and the bandwidth requirements of the system. Specifically, we discuss a two-stage approach that, first, adaptively searches a large area using shift-invariant masks to determine the locations of potential targets (i.e., the regions of interest) and then revisits each location to discriminate between target and clutter using a different set of specialized masks.We show that the overall process is not only highly efficient (i.e., dramatically reduces the number of measurements as compared with the number of pixels) but does so without appreciable loss in target detection performance.
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  • 19
    Publication Date: 2014-12-13
    Description: Our recently developed nonlinear autopilot controller can make the input???output (I/O) dynamic characteristics of the nonlinear bank-to-turn (BTT) missile system linear and independent of flight conditions. However, relatively slow actuator dynamics can degrade its performance significantly. The proposed compensation method can nearly eliminate the effect of slow actuator dynamics while maintaining the desired linear I/O dynamic characteristics. It considers fully the nonminimum-phase nonlinear BTT missile dynamics but requires no differentiations of noisy variables, unlike other existing control methods.
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  • 20
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: An algorithm is developed for determining the attitude of a spinning sounding rocket. This algorithm is able to track global positioning system (GPS) signals with intermittent availability but with enough accuracy to yield phase observables for the precise, three-axis attitude determination of a nutating rocket. Raw, single-frequency GPS RF front-end data are processed by several filters to accomplish this task. First, a Levenberg-Marquardt algorithm (LMA) estimates GPS observables for multiple satellites by performing a least-squares fit to the accumulation outputs of a bank of correlators. These observables are then used as measurements in a Rauch-Tung-Striebel smoother that optimizes estimates of carrier phase, Doppler shift, and code phase. Finally, attitude determination is carried out by another batch filter that uses the single-differenced optimized carrier phase estimates between two antennas and an Euler dynamics model for the torque-free attitude motion of the spinning rocket. This second batch filter implements a combination of a substantially modified form of the LMA and the least-squares ambiguity decorrelation adjustment (LAMBDA) method. This design enables it to deal with integer ambiguities that change over long data gaps between times of carrier phase availability. The algorithm presented in this paper is applied to recorded RF data from a spinning sounding rocket mission to produce attitude quaternion and spin-rate estimates using a pair of antennas separated by a 0.3-m baseline. These results are confirmed by another set of quaternions and spin-rate vectors independently estimated from magnetometer and horizon crossing indicator data. Attitude precision on the order of several degrees has been demonstrated.
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  • 21
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: This work investigates an online mode shape estimation method to estimate the time-varying modal properties and correct IMU readings in real time using distributed strain measurements of FBG sensor arrays. Compared to the notch filter approach, the proposed method removes structural vibration information without adding phase lag or transient dynamics. Numerical simulations on a flexible rocket attitude control and the experiments on a vertical test beam with configurable mass distribution are used for demonstration.
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  • 22
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: In this paper, we consider multistage look-ahead sensor selection problems for nonlinear dynamic systems such as radar target tracking systems. We investigate the problem for large sensor networks for both independent and dependent Gaussian measurement noises in the presence of temporally separable as well as inseparable constraints, e.g., energy constraints. First, when the measurement noises are uncorrelated between sensors, we derive the optimal solution for sensor selection when the constraints are temporally separable. When constraints are temporally inseparable, we can obtain near-optimal solutions by relaxing the nonconvex problem formulation to a linear programming problem so that the sensor selection problem for a large sensor network can be solved in a computationally efficient manner. For illustration, a radar target tracking problem is considered where it is shown that the new method presented for nonlinear dynamic systems performs better than the method based on linearizing the nonlinear equations and using previous sensor selection methods for large sensor networks. Finally, when the measurement noises are correlated between the sensors, the sensor selection problem with temporally inseparable constraints can be relaxed to a Boolean quadratic programming problem problem,,which can be efficiently solved by a Gaussian randomization procedure along with solving a semidefinite programming problem. Numerical examples show that the proposed method that includes consideration of dependence performs much better than the method that ignores dependence of noises.
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  • 23
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-13
    Description: A transmission line is one of the most hazardous objects to low altitude flying aircraft. Due to its extremely tiny size and unsalient visual features, transmission line detection (TLD) is a well-recognized problem. In this paper, a novel TLD method is proposed with the assistance of the spatial correlation between pylon and line for TLD. First, a unidirectional spatial mapping is built up to describe the pylon line spatial correlation. Then, the proposed pylon line spatial correlation and other line features are integrated into a Bayesian framework, which is trained in advance and used to estimate the probability of one line segment belonging to a transmission line. Compared with three other line-based TLD methods, the experimental results demonstrate that the proposed method can obtain better detection performance with higher detection rates and much lower false alarm rates.
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  • 24
    Publication Date: 2014-12-13
    Description: This paper considers tracking of extended objects using the measurements of down-range and cross-range extent. This type of measurement can be naturally and intuitively expressed in terms of support functions. Based on support functions, we propose a general approach to model smooth shapes of objects. Another approach based on extended Gaussian image is proposed to model nonsmooth shapes such as polygons. Compared with existing approaches, a larger range of object shapes can be modeled by the proposed approaches, which have concise mathematical forms and favorable properties. Specifically for elliptical and rectangular objects, our approaches can be implemented easily utilizing simple parametric representations without the need to assume that the major axis of the object is parallel to its velocity vector. Based on these models, a Bayesian algorithm for extended object tracking is easily obtained, where the kinematic state and object extension can be jointly estimated effectively. The benefits of the proposed modeling approaches are illustrated by simulation results.
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  • 25
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-17
    Description: This paper presents an optimized software implementation of a Successive Cancellation (SC) decoder for polar codes. Despite the strong data dependencies in SC decoding, a highly parallel software polar decoder is devised for x86 processor target. A high level of performance is achieved by exploiting the parallelism inherent in today's processor architectures (SIMD, multicore, etc.). Some optimizations that were originally thought for hardware implementation (memory reduction techniques and algorithmic simplifications) were also applied to enhance the throughput of the software implementation. Finally, some low level optimizations such as explicit assembly description or data packing are used to improve the throughput even more. The resulting decoder description is implemented on different x86 processor targets. An analysis of the decoder in terms of latency and throughput is proposed. The influence of several parameters on the throughput and the latency is investigated: the selected target, the code rate, the code length, the SIMD mode (SSE/AVX), the multithreading mode, etc. The energy per decoded bit is also estimated. The proposed software decoder compares favorably with state of the art software polar decoders. Extensive experimentations demonstrate that the proposed software polar decoder exceeds 1 Gb/s for code lengths $Nleq 2^{17}$ on a single core and reaches multi-Gb/s throughputs when using four cores in parallel in AVX mode.
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  • 26
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-17
    Description: This paper deals with the two-dimensional (2-D) direction-of-arrival (DOA) estimation of a mixture of noncoherent (including uncorrelated and partially correlated) and coherent (i.e., fully correlated) narrowband signals impinging on a planar sensor array composed of two parallel uniform linear arrays (ULAs). An oblique projection based approach for 2-D direction estimation (OPADE) is proposed by using some cross-correlations between the received array data. In the proposed OPADE, the oblique projection is utilized to isolate the coherent signals from the noncoherent ones and the effect of additive noise is alleviated, while the computationally intensive eigendecomposition is avoided, and the estimated elevation and azimuth angles are paired automatically. Further, an iterative alternating scheme is presented to improve the estimation accuracy of the oblique projector and hence that of the DOAs of coherent signals. The Cramér–Rao lower bound (CRB) for the mixture of noncoherent and coherent signals is also derived explicitly, where the prior knowledge of the signal correlation is incorporated into the 2-D DOA estimation of noncoherent signals. Finally the effectiveness of the OPADE and the theoretical analysis are substantiated through numerical examples.
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  • 27
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: An on-chip error-free 40-Gb/s-aggregated-data-rate link is achieved by transmitting a single wavelength of dual polarization-multiplexed (pol-mux) data at 10 Gb/s through a two-mode mode-division-multiplexing (MDM) chip, with a power penalty of <5 dB/channel. This is the first system-level experimental demonstration of combining pol-mux with MDM to enhance the performance of an on-chip Si photonics network, illustrating the potential to reduce total system electrical power budget by enabling multiple data channels with a single laser.
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  • 28
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: We propose and investigate a generalized quadrature phase-shift keying (QPSK) partitioning algorithm for carrier frequency offset (CFO) estimation in coherent optical 16-quadrature amplitude modulation (QAM) receivers. The algorithm utilizes the phase difference between the samples with different time-domain separations, so that the estimation accuracy can be significantly enhanced. We propose a computationally efficient procedure to implement the generalized CFO estimation algorithm. In a 28-GBd coherent 16-QAM system, simulation results and complexity analysis show that the time span of 16 can realize an optimal balance between performance and complexity. With the optimal time span, the complexity to achieve a normalized variance of $10^{mathrm {mathbf {-8}}}$ for the CFO estimation error can be reduced by 150 times compared with the conventional QPSK partitioning algorithm.
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  • 29
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: A novel and compact magnetic field sensor based on a tapered photonic crystal fiber (PCF) coated with ferrofluid is proposed. It consists of a section of tapered PCF, which is spliced between two single-mode fibers with a waist diameter of $24~mu $ m. The ferrofluid is filled in the capillary to coat the PCF taper. Experimentally, the refractive index (RI) of the ferrofluid increased under increasing magnetic field intensity ( ${H}$ ) with a sensitivity of $mathbf {4 times 10}^{mathbf {-5}}$ RIU/Gs and the RI sensitivity in the evanescent field is 401 nm/RIU. Therefore, the interference spectrum is shifted as the change of $boldsymbol {H}$ ranged from 100 to 600 Gs with a sensitivity of 16.04 pm/Gs and resolution of 0.62 Gs. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference beyond what conventional magnetic field sensors can offer.
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  • 30
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: To reduce the guard interval, short-cyclic-prefix coherent optical orthogonal frequency division multiplexing (CO-OFDM) divides a band into two subbands and precompensates for chromatic dispersion (CD) with timing offset. Implementation using full band inverse discrete Fourier transformations (IDFTs), however, can excessively increase hardware complexity. We propose an efficient hardware implementation of IDFT with timing offsets for short-cyclic-prefix CO-OFDM. In addition, the residual intersubband CD induced by quantized timing offset is compensated using subcarrier-based phase rotation. By increasing the number of subbands efficiently and compensating for the residual intersubband CD, the transmission performance can be improved. Simulation results show 112-Gb/s single-channel transmission over a 2250-km standard single-mode-fiber with polarization division multiplexing 16 quadrature amplitude modulation (PDM-16 QAM) using 128 DFT with a 16 guard interval.
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  • 31
    Publication Date: 2014-12-06
    Description: Bounded Component Analysis (BCA) is a recent framework which enables development of methods for the separation of dependent as well as independent sources from their mixtures. This paper extends a recent geometric BCA approach introduced for the instantaneous mixing problem to the convolutive mixing problem. The paper proposes novel deterministic convolutive BCA frameworks for the blind source extraction and blind source separation of convolutive mixtures of sources which allows the sources to be potentially nonstationary. The global maximizers of the proposed deterministic BCA optimization settings are proved to be perfect separators. The paper also illustrates that the iterative algorithms corresponding to these frameworks are capable of extracting/separating convolutive mixtures of not only independent sources but also dependent (even correlated) sources in both component (space) and sample (time) dimensions through simulations based on a Copula distributed source system. In addition, even when the sources are independent, it is shown that the proposed BCA approach have the potential to provide improvement in separation performance especially for short data records based on the setups involving convolutive mixtures of digital communication sources.
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  • 32
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: This paper investigates the problem of frequency-specific (FS) model approximation of transfer functions using a min-max approach. The objective is to find an approximation model for a transfer function such that the maximum error gain over a specific frequency range is minimized. First, a linear matrix inequality condition characterizing the FS gain of a transfer function is derived by using the generalized Kalman-Yakubovich-Popov lemma, and then a simple iterative approach is proposed to optimize the approximation model. Numerical experiments show that the proposed approach can produce better approximation models over a specific frequency range than some existing approaches. Moreover, it is indicated how to apply the proposed approximation approach to the design problem of infinite impulsive response digital filters, and design examples clearly illustrate that the proposed design flow can generate filters comparable with the latest design method.
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  • 33
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: We address the problem of two-dimensional (2-D) phase retrieval from magnitude of the Fourier spectrum. We consider 2-D signals that are characterized by first-order difference equations, which have a parametric representation in the Fourier domain. We show that, under appropriate stability conditions, such signals can be reconstructed uniquely from the Fourier transform magnitude. We formulate the phase retrieval problem as one of computing the parameters that uniquely determine the signal. We show that the problem can be solved by employing the annihilating filter method, particularly for the case when the parameters are distinct. For the more general case of the repeating parameters, the annihilating filter method is not applicable. We circumvent the problem by employing the algebraically coupled matrix pencil (ACMP) method. In the noiseless measurement setup, exact phase retrieval is possible. We also establish a link between the proposed analysis and 2-D cepstrum. In the noisy case, we derive Cramér–Rao lower bounds (CRLBs) on the estimates of the parameters and present Monte Carlo performance analysis as a function of the noise level. Comparisons with state-of-the-art techniques in terms of signal reconstruction accuracy show that the proposed technique outperforms the Fienup and relaxed averaged alternating reflections (RAAR) algorithms in the presence of noise.
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  • 34
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: In this paper, shrinkage linear complex-valued least mean squares (SL-CLMS) and shrinkage widely linear complex-valued least mean squares (SWL-CLMS) algorithms are devised for adaptive beamforming. By exploiting the relationship between the noise-free a posteriori and a priori error signals, the SL-CLMS method is able to provide a variable step size to update the weight vector for the adaptive beamformer, significantly enhancing the convergence speed and decreasing the steady-state misadjustment. On the other hand, besides adopting a variable step size determined by minimizing the square of the augmented noise-free a posteriori errors, the SWL-CLMS approach exploits the noncircular properties of the signal of interest, which considerably improves the steady-state performance. Simulation results are presented to illustrate their superiority over the CLMS, complex-valued normalized LMS, variable step size, recursive least squares (RLS) algorithms and their corresponding widely linear-based schemes. Additionally, our proposed algorithms are more computationally efficient than the RLS solutions though they may have a slightly slower convergence rate.
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  • 35
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: Downsampling of signals living on a general weighted graph is not as trivial as of regular signals where we can simply keep every other samples. In this paper we propose a simple, yet effective downsampling scheme in which the underlying graph is approximated by a maximum spanning tree (MST) that naturally defines a graph multiresolution. This MST-based method significantly outperforms the two previous downsampling schemes, coloring-based and SVD-based, on both random and specific graphs in terms of computations and partition efficiency quantified by the graph cuts. The benefit of using MST-based downsampling for recently developed critical-sampling graph wavelet transforms in compression of graph signals is demonstrated.
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  • 36
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: We consider mesh networks composed of groups of relaying nodes which operate in decode-and-forward mode. Each node from a group relays information to all the nodes in the next group. We study these networks in two setups, one where the nodes have complete state information about the channels through which they receive the signals, and another when they only have the statistics of the channels. We derive recursive expressions for the probabilities of errors of the nodes and present several implementations of detectors used in these networks. We compare the mesh networks with multihop networks formed by a set of parallel sections of multiple relaying nodes. We demonstrate with numerous simulations that there are significant improvements in performance of mesh over multihop networks in various scenarios.
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  • 37
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: The resolution of many large-scale inverse problems using MCMC methods requires a step of drawing samples from a high dimensional Gaussian distribution. While direct Gaussian sampling techniques, such as those based on Cholesky factorization, induce an excessive numerical complexity and memory requirement, sequential coordinate sampling methods present a low rate of convergence. Based on the reversible jump Markov chain framework, this paper proposes an efficient Gaussian sampling algorithm having a reduced computation cost and memory usage, while maintaining the theoretical convergence of the sampler. The main feature of the algorithm is to perform an approximate resolution of a linear system with a truncation level adjusted using a self-tuning adaptive scheme allowing to achieve the minimal computation cost per effective sample. The connection between this algorithm and some existing strategies is given and its performance is illustrated on a linear inverse problem of image resolution enhancement.
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  • 38
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-12-06
    Description: In this paper, we develop verifiable sufficient conditions and computable performance bounds of $ell_{1}$ -minimization based sparse recovery algorithms in both the noise-free and noisy cases. We define a family of quality measures for arbitrary sensing matrices as a set of optimization problems, and design polynomial-time algorithms with theoretical global convergence guarantees to compute these quality measures. The proposed algorithms solve a series of second-order cone programs, or linear programs. We derive performance bounds on the recovery errors in terms of these quality measures. We also analytically demonstrate that the developed quality measures are non-degenerate for a large class of random sensing matrices, as long as the number of measurements is relatively large. Numerical experiments show that, compared with the restricted isometry based performance bounds, our error bounds apply to a wider range of problems and are tighter, when the sparsity levels of the signals are relatively low.
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  • 39
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-11
    Description: We propose and develop a simple hybrid integration solution for a 100 Gb/s dual polarization quadrature phase shift keying coherent receiver. The cost-effective, precise, and passive alignment technique can be used to couple four output waveguides of planar lightwave circuits (PLCs) based 90 $^{circ}$ optical hybrid (OH) with a 1 $,times,$ 4 photodiode (PD) array directly, adopting an infrared charge-coupled device camera to monitor the light spots, a beam of infrared light to illuminate the light spots and the active areas of PD array, and an epoxy glue to adhere the PLC-based 90 $^{circ}$ OH to the heat sink. Based on this proposed coupling scheme, the responsivity variation for the coherent receiver is less than ${pm}{rm 0.18}~{rm dB}$ for all PD channels in an environment temperature range of ${-}{rm 5}^{circ}{rm C}$ –80 $^{circ}{rm C}$ and the skew of this coherent receiver is only 1.96 ps.
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  • 40
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-11
    Description: Magnetic fluid is a new type of optical functional material, which has interesting optical characteristics under an external magnetic field. In this letter, the magneto-optical characteristic of the magnetic fluid was adopted to form a novel fiber-optic magnetic field sensor. The sensor probe was composed of an extrinsic fiber Fabry–Pérot interferometer and magnetic fluid. The refractive index of the magnetic fluid would be changed with the increase of magnetic field. Preliminary experiment was carried out to verify the feasibility of the sensor. The magnetic field measurement sensitivity was 0.0431 nm/Gs in the experiment. The measurement resolution was better than 0.5 Gs at the measurement range from 0 to 400 Gs. The sensor has the advantages of simple structure, compact size, and easy fabrication.
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  • 41
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: This letter describes a novel configuration and theory for the degree of coherence measurement based on the statistical speckle analysis in coherent optical frequency domain reflectometry. The difference from the previous letter is using a standard phase modulator instead of a single-sideband modulator, which not only simplifies the system configuration, but also yields modulation efficiency, resulting in the operation with lower light source power. A novel theory is presented to describe the operation of the proposed configuration, and experimental results show the validity of the new configuration and theory.
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  • 42
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    Publication Date: 2014-01-15
    Description: Raman-assistance (RA) has been identified as a promising technique to extend the measurement range of Brillouin optical time-domain analysis (BOTDA)-based distributed sensors. Unfortunately, Raman amplification introduces a great amount of relative intensity noise (RIN) to the detected low-frequency probe wave. This RIN transfer problem has been widely identified as a major limitation in RA-BOTDA. In vector BOTDA (VBOTDA), the detected signal is transferred to a high-frequency carrier where the Raman RIN transfer turns out to be much less harmful. In addition, a VBOTDA can also provide information about the phase-shift induced by the local stimulated Brillouin scattering gain curve, paving the way for dynamic measurements. In this letter, we demonstrate, for the first time to our knowledge, the RA in a VBOTDA obtaining gain and phase measurements. Our results show a significant reduction of the RIN transfer effect in RA-VBOTDA compared with standard RA-BOTDA, making this type of scheme particularly interesting for long-range and dynamic distributed sensing.
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  • 43
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    Publication Date: 2014-01-15
    Description: We demonstrate a high-speed and efficient direct modulation of a novel transverse-coupled-cavity vertical cavity surface emitting laser for radio over fiber applications. A bow-tie joint connection between two oxide apertures results in a leaky traveling wave in the lateral direction between the two cavities. The measured L/I characteristics and lasing spectra demonstrate coherent coupling of the two cavities. The small signal response of the fabricated device shows a large enhancement of over 30 dB in the modulation amplitude at frequencies ${>}{rm 25}~{rm GHz}$ . The resonantly enhanced modulation response is suitable for efficient narrow-band modulation in the millimeter wave range over 25 GHz far beyond the intrinsic modulation bandwidth of the laser without optical feedback.
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  • 44
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: In this correspondence, we propose an efficient estimator of optimal memory (averaging interval) for discrete-time finite impulse response (FIR) filters in state-space. Its crucial property is that only real measurements and the filter output are involved with no reference and noise statistics. Testing by the two-state polynomial model has shown a very good correspondence with predicted values. Even in the worst case of the harmonic model, the estimator demonstrates practical applicability.
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  • 45
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    Publication Date: 2014-01-18
    Description: The JPEG compression method is among the most successful compression schemes since it readily provides good compressed results at a rather high compression ratio. However, the decompressed result of the standard JPEG decompression scheme usually contains some visible artifacts, such as blocking artifacts and Gibbs artifacts (ringing), especially when the compression ratio is rather high. In this paper, a novel artifact reducing approach for the JPEG decompression is proposed via sparse and redundant representations over a learned dictionary. Indeed, an effective two-step algorithm is developed. The first step involves dictionary learning and the second step involves the total variation regularization for decompressed images. Numerical experiments are performed to demonstrate that the proposed method outperforms the total variation and weighted total variation decompression methods in the measure of peak of signal to noise ratio, and structural similarity.
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  • 46
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    Publication Date: 2014-01-18
    Description: Stochastic orders are binary relations defined on probability distributions which capture intuitive notions like being larger or being more variable. This paper introduces stochastic ordering of interference distributions in large-scale networks modeled as point processes. Interference is a major performance-limiting factor in most wireless networks, thus it is important to characterize its statistics. Since closed-form results for the distribution of interference for such networks are only available in limited cases, it is of interest to compare network interference using stochastic orders, for two different point processes with different fading or path-loss scenarios between the interferers and the receiver. In this paper, conditions on the fading distribution and path-loss model are given to establish stochastic ordering between interferences. Moreover, Laplace functional ordering is defined between point processes and applied for comparing interference. Monte-Carlo simulations are used to supplement our analytical results. The useful applications of this research are also provided.
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  • 47
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    Publication Date: 2014-01-18
    Description: Screening is the problem of finding a superset of the set of non-zero entries in an unknown $p$ -dimensional vector $beta^*$ given $n$ noisy observations. Naturally, we want this superset to be as small as possible. We propose a novel framework for screening, which we refer to as Multiple Grouping (MuG), that groups variables, performs variable selection over the groups, and repeats this process multiple number of times to estimate a sequence of sets that contains the non-zero entries in $beta^*$ . Screening is done by taking an intersection of all these estimated sets. The MuG framework can be used in conjunction with any group based variable selection algorithm. In the high-dimensional setting, where $p gg n$ , we show that when MuG is used with the group Lasso estimator, screening can be consistently performed without using any tuning parameter. Our numerical simulations clearly show the merits of using the MuG framework in practice.
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    Publication Date: 2014-01-18
    Description: When designing optimal filters it is often unrealistic to assume that the statistical model is known perfectly. The issue is then to design a robust filter that is optimal relative to an uncertainty class of processes. Robust filter design has been treated from minimax (best worst-case performance) and Bayesian (best average performance) perspectives. Heretofore, the Bayesian approach has involved finding a model-specific optimal filter, one that is optimal for some model in the uncertainty class. Lifting this constraint, we optimize over the full class from which the original optimal filters were obtained, for instance, over all linear filters. By extending the original characteristics determining the filter, such as the power spectral density, to “effective characteristics” that apply across the uncertainty class, we demonstrate, for both linear and morphological filtering, that an “intrinsically optimal” Bayesian robust filter can be represented in the same form as the standard solution to the optimal filter, except via the effective characteristics. Solutions for intrinsic Bayesian robust filters are more transparent and intuitive than solutions for model-specific filters, and also less tedious, because effective characteristics push through the spectral theory into the Bayesian setting, whereas solutions in the model-specific case depend on grinding out the optimization.
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  • 49
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    Publication Date: 2014-01-18
    Description: We propose a novel decomposition framework for the distributed optimization of general nonconvex sum-utility functions arising naturally in the system design of wireless multi-user interfering systems. Our main contributions are i) the development of the first class of (inexact) Jacobi best-response algorithms with provable convergence, where all the users simultaneously and iteratively solve a suitably convexified version of the original sum-utility optimization problem; ii) the derivation of a general dynamic pricing mechanism that provides a unified view of existing pricing schemes that are based, instead, on heuristics; and iii) a framework that can be easily particularized to well-known applications, giving rise to very efficient practical (Jacobi or Gauss–Seidel) algorithms that outperform existing ad hoc methods proposed for very specific problems. Interestingly, our framework contains as special cases well-known gradient algorithms for nonconvex sum-utility problems, and many block-coordinate descent schemes for convex functions.
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    Publication Date: 2014-01-18
    Description: The ability to detect change-points in a dynamic network or a time series of graphs is an increasingly important task in many applications of the emerging discipline of graph signal processing. This paper formulates change-point detection as a hypothesis testing problem in terms of a generative latent position model, focusing on the special case of the Stochastic Block Model time series. We analyze two classes of scan statistics, based on distinct underlying locality statistics presented in the literature. Our main contribution is the derivation of the limiting properties and power characteristics of the competing scan statistics. Performance is compared theoretically, on synthetic data, and empirically, on the Enron email corpus.
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  • 51
    Publication Date: 2014-01-22
    Description: In this paper, we propose opportunistic jammer selection in a wireless security system for increasing the secure degrees of freedom (DoF) between a transmitter and a legitimate receiver (say, Alice and Bob). There is a jammer group consisting of $S$ jammers among which Bob selects $K$ jammers. The selected jammers transmit independent and identically distributed Gaussian signals to hinder the eavesdropper (Eve). Since the channels of Bob and Eve are independent, we can select the jammers whose jamming channels are aligned at Bob, but not at Eve. As a result, Eve cannot obtain any DoF unless it has more than $KN_{j}$ receive antennas, where $N_{j}$ is the number of each jammer's transmit antenna, and hence $KN_{j}$ can be regarded as defensible dimensions against Eve. For the jamming signal alignment at Bob, we propose two opportunistic jammer selection schemes and find the scaling law of the required number of jammers for target secure DoF by a geometrical interpretation of the received signals.
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  • 52
    Publication Date: 2014-01-22
    Description: This paper is concerned with the distributed finite-horizon fusion Kalman filtering problem for a class of networked multi-sensor fusion systems (NMFSs) in a bandwidth and energy constrained wireless sensor network. To satisfy the finite communication bandwidth, only partial components of each local vector estimate are allowed to be transmitted to the fusion center (FC) at a particular time, while each sensor intermittently sends information to the FC for reducing energy consumptions. At the FC end, a novel compensation strategy is proposed to compensate the untransmitted components of each local estimates, then a recursively distributed fusion Kalman filter (DFKF) is derived in the linear minimum variance sense. Notice that the designed DFKF update does not need to know the transmitting situation of each component at a particular time, which means that the proposed fusion estimation algorithm is easily implemented for the addressed NMFSs. Since the performance of the designed DFKF is dependent on the selecting probability of each component, some criteria for the choice of probabilities are derived such that the mean squared errors (MSEs) of the designed DFKF are bounded or convergent. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed method.
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  • 53
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    Publication Date: 2014-01-22
    Description: This paper addresses the joint design of MIMO precoding and decoding matrices for filter bank multicarrier (FBMC) systems based on OQAM, known as FBMC/OQAM. Existing solutions that support multi-stream transmission only give satisfactory performance in scenarios with high coherence bandwidth channels. To make progress towards the application of FBMC/OQAM to MIMO channels, we study the design of novel solutions that provide robustness against the channel frequency selectivity and support multi-stream transmission. To this end, two techniques have been devised under the criterion of minimizing the sum mean square error. The non-circular nature of the OQAM symbols has not been ignored, making evident the convenience of performing a widely linear processing. The first technique keeps the complexity at a reasonable level but in exchange the original problem is relaxed yielding a suboptimal solution. With the objective of performing closer to the optimum solution, the second option iteratively computes precoders and equalizers by resorting to an alternating optimization method, which is much more complex. We have demonstrated via simulations that the first technique nearly achieves the same results as the iterative design. Simulation results show that the proposed low-complexity solution outperforms existing MIMO-FBMC/OQAM schemes in terms of bit error rate. As for the comparison with OFDM, the numerical results highlight that FBMC/OQAM remains competitive, with and without perfect channel state information, while it provides spectral efficiency gains. Under highly frequency selective channels the proposed technique significantly outperforms OFDM.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-22
    Description: Two adaptive Capon methods that jointly estimate the azimuth-angle and polarization of the sources in a closed-form are proposed. It is shown that the azimuth-angles of the sources may be estimated from the roots of a complex-valued polynomial or by rooting a real-valued polynomial, instead. The latter method is particularly useful in tracking arbitrarily polarized sources in a sequential snapshot-by-snapshot manner using root-tracking techniques. The proposed polynomial rooting based methods are applicable to polarization sensitive arrays regardless of the array geometry including conformal arrays, and take into account array nonidealities. A large-sample analysis of the polarimetric Capon method is also provided showing that it converges, up to a multiplicative factor that depends on the interference-plus-noise power, to the polarimetric MUSIC method in the high SINR regime. Such a result gives a new insight into the well-known Capon and MUSIC methods. This paper also shows that employing manifold separation in robust Capon beamforming as well as in transmit beamforming schemes leads to improved performance in terms of received SINR when array calibration measurements are used. Extensive numerical results employing real-world polarimetric arrays are given. Results show that employing manifold separation leads to improved performance in many array processing tasks.
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  • 55
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: Stabilized multi-wavelength emission from a single emitter broad area diode laser (BAL) is realized by utilizing an external cavity with a spectral beam combining architecture. Self-organized emitters that are equidistantly spaced across the slow axis are enforced by the spatially distributed wavelength selectivity of the external cavity. This resulted in an array like near-field emission although the BAL is physically a single emitter without any epitaxial sub-structuring and only one electrical contact. Each of the self-organized emitters is operated at a different wavelength and the emission is multiplexed into one spatial mode with near-diffraction limited beam quality. With this setup, multi-line emission of 31 individual spectral lines centered around and a total spectral width of 3.6 nm is realized with a 1000 &mu;m wide BAL just above threshold. To the best of our knowledge, this is the first demonstration of such a self-organization of emitters by optical feedback utilizing a spectral beam combining architecture.
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  • 56
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: We have designed and fabricated a high speed 850 nm oxide-confined vertical cavity surface emitting laser with an oxide aperture dimension of ${sim}{rm 4}~mu{rm m}$ and a threshold current $I_{rm TH}=0.53~{rm mA}$ at room temperature (20 $^{circ}{rm C}$ ). It demonstrates a modulation bandwidth of 21.2 GHz, and achieves a laser relative intensity noise reaching standard quantum limit $2{rm h}nu/{rm P}_{0}=-154.3~{rm dB}/{rm Hz}$ at high bias ${rm I}/{rm I}_{rm TH}=10$ . Furthermore, error-free data transmission at 40 Gb/s is obtained at $I=6.5~{rm mA}$ which corresponds to an energy/data efficiency of 431 fJ/bit.
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  • 57
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: An all-optical clock recovery (CR) scheme with wide locking range is demonstrated, based on a silicon microring resonator (MRR) and a semiconductor optical amplifier (SOA). The MRR with a free spectral range of 40 GHz works as a comb filter, which removes the modulation information, whereas the SOA operating in the saturation regime performs amplitude equalization to achieve a good optical clock signal. The design of the MRR is investigated according to the tolerance of the subsequent equalizer. Based on the fabricated MRR, single and dual channels CR from 40 Gb/s input data streams can be achieved successfully with root mean square time jitter of ${sim}{rm 900}~{rm fs}$ . Because of the moderate finesse of the MRR, the CR can be achieved with a wide range of several gigahertz.
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  • 58
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: We experimentally demonstrate a soliton wavelength shift of 145 nm through a concatenated pair of higher-order-mode fibers (HOMFs). An input pulse at 1030 nm is used to produce a soliton at 1175 nm that has 3.5 nJ energy and 55 fs duration. Previously, the mode-crossing wavelength of the HOMF limited the range of wavelengths over which soliton shift could be achieved. In this letter, we use two fibers to extend the shifting range beyond the mode-crossing wavelengths of both fibers. Our experiment demonstrates the feasibility of combining HOMFs of different dispersion profiles to provide another degree of freedom for dispersion control.
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  • 59
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: An ultracompact optical fiber sensor based on an S fiber taper Mach–Zehnder interferometer (SFT-MZI) embedded in fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous force and temperature measurement. Experimental results show distinctive spectral sensitivities of ${-}{rm 48.56842}~{rm nm}/{rm N}~({sim}{rm 54.97}~{rm pm}/muvarepsilon)$ and 14.71 pm/ $^{circ}{rm C}$ by the SFT-MZI, and 1.30588 nm/N and 10.13 pm/ $^{circ}{rm C}$ by the FBG. The SFT-MZI, exhibiting an opposite force response as compared with that of the FBG, is highly sensitive to force. The force and temperature calculated by the sensor matrix agree well with the actual force and temperature in the experiment.
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  • 60
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: A multilayer polymeric photodetector fabricated on a paper substrate by inkjet and aerosol jet printing has been demonstrated. It employs a poly(3-hexylthiophene) and C61-butyric acid methyl ester blend (P3HT:PCBM) as a photoactive layer sandwiched between a silver bottom electrode and a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) top electrode. A deoxyribonucleic acid biopolymer interlayer between P3HT:PCBM and PEDOT:PSS top electrode enables the printing of the PEDOT:PSS on P3HT:PCBM. The printed photodetector exhibits a photoresponse when photoexcited by four different light emitting diodes with center wavelengths of 405, 465, 525, and 635 nm. The highest responsivity was observed at 405 nm. The responsivity to pulsed light reveals a strong frequency dependence from 25 to 1000 Hz.
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  • 61
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: A commercially available digital supermode distributed Bragg reflector tunable laser is employed as a fast wavelength switching local oscillator (LO) in a dual polarization (DP) 16-quadrature amplitude modulation (16QAM) coherent burst mode receiver. A digital coherence enhancement technique is used to compensate both the Lorentzian and non-Lorentzian distributed phase noise of the tunable LO laser. It is shown that differential decoding is not sufficient to overcome the substantial bit errors caused by the LO laser phase noise. However, the coherence enhancement technique enables the reception of low symbol rate DP-16QAM bursts, with an average optical signal to noise ratio penalty of 3.5 dB observed relative to theory at the forward error correction threshold $(1.5times 10^{-2})$ .
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  • 62
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: Tunable polymer Bragg grating filters with extremely high tuning efficiency are demonstrated. A buried heating scheme is used to achieve fairly uniform heating conditions in the polymer waveguide. Thermal simulation results indicate that the temperature change per unit heating power at the core of the waveguide can be significantly increased by implementing sufficient thermal buffers around it. Simulated and experimental results are in very good agreement. Tuning efficiency has been improved to a record 425 nm/W, corresponding to a tuning power of 88 mW for a wavelength tuning range of close to 40 nm.
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  • 63
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    Publication Date: 2014-01-18
    Description: Channel statistics based secondary transmission strategy design has been studied intensively in the past. In this work, we consider the same problem but with a carrier sensing multiple access based primary networks, i.e., the primary users that would react to interference. In such primary networks, users always need to perform carrier sensing before accessing the channel. Such networks include 802.11 WLAN and 802.15 WPAN. The secondary transmission strategy design when the primary network uses carrier sensing based network access differs a lot from what has been considered in the literature. Here, we show through experiments with 802.11 networks that under secondary interference, the primary users can experience not only packet collisions but also transmission delay. Under long-term secondary interference, the primary users might even choose to transmit in another channel. This phenomenon is known as the channel capture effect. Next, with this in mind, we formulate a novel transmission strategy design problem that aims to maximize secondary transmission time with design constraints on the probability of packet collision or delay, as well as the probability that the primary user switches channel. Finally, we describe a software-defined radio device that we built to execute the designed transmission strategies on the 2.4 GHz band. The performance of both the primary and secondary users are studied. Results show that our consideration for the primary user reactions is necessary. In particular, the designed transmission strategy better protects the primary user transmission while maintaining secondary user performance.
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  • 64
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: We study distributed algorithms for adapting transmit beamformers and linear receiver filters in a Time-Division Duplex Multiple-Input Multiple-Output (MIMO) interference network. Each transmitter transmits a single beam, and neither the transmitters nor receivers have a priori Channel State Information (CSI). Given a fixed set of powers, we present an adaptive version of the Max-SINR algorithm: pilot symbols are alternately transmitted in the forward direction (transmitters to receivers) and in the reverse direction (receivers to transmitters). Unlike previous channel estimation schemes, transmissions in each direction are synchronized across the source or destination nodes, and the pilots are used to update the filters/beams directly using a least squares criterion. To improve the performance with limited training, we include exponential weighting of the least squares objective across data frames. In addition, bi-directional training can be used to implement analog interference pricing for power control: training in the forward direction is used to measure received signal-to-interference plus noise ratios (SINRs) and interference prices, and those estimates combined with synchronous backward training are used to update the powers. Given sufficient training this method achieves the same performance as interference pricing updates with perfect CSI. Numerical results are presented that illustrate the performance of these methods in different settings.
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  • 65
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    Publication Date: 2014-01-18
    Description: Consider a multi-user orthogonal frequency division multiple access (OFDMA) system where multiple users share multiple discrete subcarriers, but at most one user is allowed to transmit power on each subcarrier. To adapt fast traffic and channel fluctuations and improve the spectrum efficiency, the system should have the ability to dynamically allocate subcarriers and power resources to users. Assuming perfect channel knowledge, two formulations for the joint subcarrier and power allocation problem are considered in this paper: the first is to minimize the total transmission power subject to the quality of service constraints and the OFDMA constraint, and the second is to maximize some system utility function subject to the total transmission power constraint per user and the OFDMA constraint. In spite of the existence of various heuristics approaches, little is known about the computational complexity status of the above problem. This paper aims at filling this theoretical gap, i.e., characterizing the complexity of the joint subcarrier and power allocation problem for the multi-user OFDMA system. It is shown in this paper that both formulations of the joint subcarrier and power allocation problem are strongly NP-hard. Several subclasses of the problem which can be solved efficiently in polynomial time are also identified. These complexity results suggest that there are not polynomial time algorithms that are able to solve the general joint subcarrier and power allocation problem to global optimality (unless ${rm P}={rm NP}$ ), and determining an approximately optimal subcarrier and power allocation strategy is more realistic in practice.
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  • 66
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: Multicell cooperation has recently attracted tremendous attention because of its ability to eliminate intercell interference and increase spectral efficiency. However, the enormous amount of information being exchanged, including channel state information and user data, over backhaul links may deteriorate the network performance in a realistic system. This paper adopts a backhaul cost metric that considers the number of active directional cooperation links, which gives a first order measurement of the backhaul loading required in asymmetric Multiple-Input Multiple-Output (MIMO) cooperation. We focus on a downlink scenario for multi-antenna base stations and single-antenna mobile stations. The design problem is minimizing the number of active directional cooperation links and jointly optimizing the beamforming vectors among the cooperative BSs subject to signal-to-interference-and-noise-ratio (SINR) constraints at the mobile station. This problem is non-convex and solving it requires combinatorial search. A practical algorithm based on smooth approximation and semidefinite relaxation is proposed to solve the combinatorial problem efficiently. We show that semidefinite relaxation is tight with probability 1 in our algorithm and stationary convergence is guaranteed. Simulation results show the saving of backhaul cost and power consumption is notable compared with several baseline schemes and its effectiveness is demonstrated.
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  • 67
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    Publication Date: 2014-01-18
    Description: We develop new and optimal algorithms for distributed detection in sensor networks over fading channels with multiple receive antennas at the Fusion Centre (FC). Sensors observe a hidden physical phenomenon over fading channels and transmit their observations using the amplify-and-forward scheme over fading channels to the FC which is equipped with multiple antennas. We derive the optimal decision rules and the associated probabilities of detection and false alarm for three scenarios of Channel State Information (CSI) availability. For the most difficult case of unknown CSI, we develop two new algorithms to derive the optimal decision rule. The first is based on a Gaussian approximation method where we quantify the approximation error and its rate of convergence (to a true Normal distribution) via a multivariate version of the Berry-Esseen bound. The second is based on a multivariate Saddle-point (Laplace) approximation which is obtained via a non-convex optimisation problem which is solved efficiently via Bayesian Expectation-Maximisation method. We show under which system configuration which algorithm is suitable and should be used. For cases where the distribution of the optimal decision rule can not be derived exactly, we develop a Laguerre series expansion to approximate the resulting distribution. The performance of the proposed algorithms is evaluated via analytic bounds and numerical simulations. We show that the detection performance of the proposed algorithms is significantly superior to a local vote decision fusion based algorithms.
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  • 68
    Publication Date: 2014-01-22
    Description: In this paper, we study the joint design of Doppler robust transmit sequence and receive filter to improve the performance of an active sensing system dealing with signal-dependent interference. The signal-to-noise-plus-interference (SINR) of the filter output is considered as the performance measure of the system. The design problem is cast as a max-min optimization problem to robustify the system SINR with respect to the unknown Doppler shifts of the targets. To tackle the design problem, which belongs to a class of NP-hard problems, we devise a novel method (which we call DESIDE) to obtain optimized pairs of transmit sequence and receive filter sharing the desired robustness property. The proposed method is based on a cyclic maximization of SINR expressions with relaxed rank-one constraints, and is followed by a novel synthesis stage. We devise synthesis algorithms to obtain high quality pairs of transmit sequence and receive filter that well approximate the behavior of the optimal SINR (of the relaxed problem) with respect to target Doppler shift. Several numerical examples are provided to analyze the performance obtained by DESIDE.
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  • 69
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    Publication Date: 2014-01-22
    Description: We consider distributed optimization in random networks where $N$ nodes cooperatively minimize the sum $sum _{i=1}^{N} f_{i}(x)$ of their individual convex costs. Existing literature proposes distributed gradient-like methods that are computationally cheap and resilient to link failures, but have slow convergence rates. In this paper, we propose accelerated distributed gradient methods that 1) are resilient to link failures; 2) computationally cheap; and 3) improve convergence rates over other gradient methods. We model the network by a sequence of independent, identically distributed random matrices ${W(k)}$ drawn from the set of symmetric, stochastic matrices with positive diagonals. The network is connected on average and the cost functions are convex, differentiable, with Lipschitz continuous and bounded gradients. We design two distributed Nesterov-like gradient methods that modify the D–NG and D–NC methods that we proposed for static networks. We prove their convergence rates in terms of the expected optimality gap at the cost function. Let $k$ and $ {cal K}$ be the number of per-node gradient evaluations and per-node communications, respectively. Then the modified D–NG achieves rates $O(log k/k)$ and $O(log {cal K}/ {cal K})$ , and the modified D–NC rates $O(1/k^{2})$ and $O(1/ {cal K}^{2-xi })$ , where - tex Notation="TeX"〉$xi 〉0$ is arbitrarily small. For comparison, the standard distributed gradient method cannot do better than $Omega (1/k^{2/3})$ and $Omega (1/ {cal K}^{2/3})$ , on the same class of cost functions (even for static networks). Simulation examples illustrate our analytical findings.
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  • 70
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    Publication Date: 2014-01-22
    Description: We consider the problem of phase retrieval, namely, recovery of a signal from the magnitude of its Fourier transform, or of any other linear transform. Due to the loss of Fourier phase information, this problem is ill-posed. Therefore, prior information on the signal is needed in order to enable its recovery. In this work we consider the case in which the signal is known to be sparse, i.e., it consists of a small number of nonzero elements in an appropriate basis. We propose a fast local search method for recovering a sparse signal from measurements of its Fourier transform (or other linear transform) magnitude which we refer to as GESPAR: GrEedy Sparse PhAse Retrieval. Our algorithm does not require matrix lifting, unlike previous approaches, and therefore is potentially suitable for large scale problems such as images. Simulation results indicate that GESPAR is fast and more accurate than existing techniques in a variety of settings.
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  • 71
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    Publication Date: 2014-01-22
    Description: Cooperation between nodes sharing a wireless channel is becoming increasingly necessary to achieve higher throughputs in a wireless network. The problem of determining the feasibility and stability of cooperation between rational nodes in a wireless network is of great importance in understanding cooperative behavior. This paper addresses the stability of the grand coalition of transmitters signaling over a multiple access channel using the framework of cooperative game theory. The external interference experienced by each TX is represented accurately by modeling the cooperation game between the TXs in partition form. Single user decoding and successive interference cancelling strategies are examined at the receiver. Transmitter cooperation is stable, if and only if the core of the game (the set of all divisions of grand coalition utility such that no coalition deviates) is nonempty. Determining the stability of cooperation is a co-NP-complete problem in general. For a single user decoding receiver, transmitter cooperation is shown to be stable at both high and low SNRs, while for an interference cancelling receiver with a fixed decoding order, cooperation is stable only at low SNRs and unstable at high SNR. When time sharing is allowed between decoding orders, it is shown using an approximate lower bound to the utility function that TX cooperation is also stable at high SNRs. Thus, this paper demonstrates that ideal zero cost TX cooperation over a MAC is stable and improves achievable rates for each individual user.
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  • 72
    Publication Date: 2014-01-22
    Description: Synthetic transmit aperture (STA) has been widely investigated in ultrasound system recently with characteristics of high frame rate and low hardware cost. Since the high-resolution image (HRI) of STA is formed by summation of low-resolution images (LRIs), it is susceptible to inter-firing motions. In this paper, we propose a low-complexity global motion compensation algorithm. We use the common region of interest $({rm ROI}_{{rm com}})$ between different transmissions of STA imaging to beamform backward and forward beam vectors. Then, the magnitude and direction of motion can be evaluated by cross-correlations between specific beam vectors in STA imaging. Compared with the uncompensated image in two-dimentional (2D) motion environment, the proposed motion compensation algorithm can improve the contrast ratio (CR) and contrast-to-noise ratio (CNR) by 13.73 and 2.04 dB, respectively. Also, the proposed algorithm improves the CR and CNR about 7.84 and 1.36 dB comparing with the reference work, respectively. In the Field II breath model, the proposed method also improves the CR and CNR about 6.65 and 1.04 dB than the reference method, respectively. Moreover, we propose a low-complexity delay generator in the architecture design to further reduce the computational complexity of the whole beamforming system. Finally, we verify the proposed low-complexity motion compensation beamforming engine by using the VLSI implementation with CMOS 90 nm technology. In the post-layout result, the core size is 2.39 mm $^2$ at 125 MHz operating frequency and the frame rate of the beamforming system is 42.23 frames per second.
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  • 73
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    Publication Date: 2014-01-11
    Description: We present 18 months of field observations on the state-of-polarization (SOP) and polarization-mode dispersion (PMD) on three routes monitored using deployed coherent 40 Gb/s transponders. Two fiber paths were monitored on each of three different routes, ranging from 30 km with one amplified span to 273 km with seven amplified spans. In general, the changes in SOP and PMD were slow, with the autocorrelation half-width-half-maxima ranging from 1.3 to 4.1 days for the differential-group-delay and from 0.18 to 1.7 days for the SOP. We observed the largest correlation of active periods between fiber paths sharing the same cable and weak correlation with fiber paths sharing an office. With over 10,000 hours of measurements spanning an 18-month period, we believe this to be the most extensive study published on the polarization behavior of buried fiber.
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  • 74
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    Publication Date: 2014-01-11
    Description: We report wavelength-division-multiplexed transmission of ninety 128-Gb/s polarization-multiplexed quadrature-phase-shift-keyed channels in a seamless 73 nm band over 60 $,times,$ 100 km of ultra-large-area fiber. Co- and counter-pumped all-Raman amplification in the fiber spans, single-stage discrete Raman amplifiers, and broadband wavelength selective switch and channel equalizer were utilized to achieve optical signal-to-noise-ratio margin of more than 3 dB after 6000 km transmission of the 9 Tb/s capacity.
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    Publication Date: 2014-01-11
    Description: Guided-mode resonant filters (GMRFs) are promising narrowband filters with high peak efficiency, but their practical applications have been restricted by their natural high angular sensitivity. We investigated the influence of incident angle and azimuthal angle on the spectral response of GMRF, and found that the resonant peaks are mainly influenced by the incident angle. A polymer-dispersed liquid crystal layer was introduced to compensate the shift of resonant wavelength through applying proper voltage in real time, and numerical results show that a large angular compensation range of about ${pm}{rm 4.2}^{circ}$ can be obtained while maintaining high performance of the spectral response.
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  • 76
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    Publication Date: 2014-01-11
    Description: Random lasing (RL) characteristics of second-order random fiber laser formed solo by dispersion compensated fiber are studied. It is found that the threshold of first-order RL is only 0.45 W. In addition, a special route to stable second-order lasing is revealed, i.e., a special arc-shape output spectrum of second-order RL and three chaotic regimes during evolution from the first RL to the second-order one with increased pump power.
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  • 77
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    Publication Date: 2014-01-11
    Description: A compact singlemode-multimode-singlemode fiber tip (SMST) refractive index sensor is demonstrated. Focused ion beam milling is exploited to have a clean fiber tip cut which is then coated by a layer of gold to increase reflection. An average sensitivity of 265 nm/RIU and a resolvable index change of $3.77times 10^{-5}$ are obtained experimentally with a ${sim}{rm 2.94}~mu{rm m}$ diameter SMST. Because of its compactness, ease of fabrication, linear response, good sensitivity, easy connectivity to other in-fiber optical components, and low cost, this refractometer could find various applications in chemical and biological sensing.
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  • 78
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    Publication Date: 2014-01-11
    Description: The highly sensitive nature of slot waveguide micro-resonator power couplers is discussed with respect to the resonator geometry and evanescent coupler design. A modified, tri-bar, evanescent field coupler is demonstrated that shows reduced sensitivity to ring radius as compared with conventional couplers, while maintaining a compact beat-length of only a few micrometers. With the measurement of bending losses of curved slot waveguides, critically coupled ring resonators were designed and fabricated, exhibiting a resonance extinction exceeding 22 dB.
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    Publication Date: 2014-01-11
    Description: We propose a new method to change the resonant status of the microring by modifying the light-absorption ability of the waveguide. A conception of a 2 $,times,$ 2 microring switch based on the graphene-silicon-waveguide is presented by inserting a single graphene flake inside the lateral slot waveguide. The resonance procedure of the microring is thoroughly blocked when the graphene is tuned to be a zero-permittivity material, which significantly enhances the waveguide's loss. Neither a high quality factor nor a large driving voltage of the microring is needed. According to the numerical analysis, an extinction ratio for ${>}{rm 50}~{rm dB}$ is obtained in the drop port with a broad bandwidth. The extinction ratio in the through port is 34 dB. The radius of the microring is 5.1 $mu{rm m}$ and the driving voltage is 2.38 V.
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  • 80
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    Publication Date: 2014-01-15
    Description: Wavelength conversion of a 10-Gb/s (9.35 Gb/s net rate) return-to-zero ON-OFF keying signal is demonstrated using a simple InP photonic crystal H0 nanocavity with Lorentzian line shape. The shifting of the resonance induced by the generation of free-carriers enables the pump intensity modulation to be transferred to a continuous-wave probe with a sufficiently high quality so that the converted signal can be detected with a conventional telecommunication receiver. A clear eye diagram is observed for the converted signal showing a pre-forward error correction bit-error-ratio down to $10^{-3}$ .
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  • 81
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: We propose an efficient time-domain adaptive decision-directed channel equalizer (TD-ADDCE) for reduced-guard-interval dual-polarization coherent optical orthogonal frequency-division-multiplexing (RGI-DP-CO-OFDM) transmission systems. TD-ADDCE estimates the phase noise in a decision-directed scheme by extracting and averaging the phase drift of OFDM subcarriers. It updates the channel state information (CSI) using the decision data and previous estimated CSI in time domain on a symbol-by-symbol basis. In addition, TD-ADDCE can perform efficiently without any matrix inversion. We numerically compare the performance of TD-ADDCE with frequency domain ADDCE (FD-ADDCE) for a 112-Gb/s RGI-DP-CO-OFDM system at laser linewidth of 100 kHz. The simulation results show that TD-ADDCE attains a superior performance than FD-ADDCE. At a forward error correction threshold of $38times 10^{{-3}}$ , TD-ADDCE can increase the maximum transmission reach by ${sim}{29%}$ as compared with FD-ADDCE. We also show that only small additional computational efforts are required for TD-ADDCE as compared with FD-ADDCE.
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  • 82
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: We demonstrate effective four-wave mixing in a 2- $mu{rm m}$ microfiber attached onto a graphene film by using two continuous-wave pump lasers at wavelengths near 1550 nm. With a contact length of 10 mm between the microfiber and the graphene film and input powers of 600 and 100 mW for the two pumps, we achieve a conversion efficiency that varies from ${-}{28}$ to ${-}{rm 34}~{rm dB}$ as the wavelength difference between the two pump lasers varies from 0.5 to 4.5 nm. Graphene-attached microfibers could find applications as miniaturized nonlinear devices in optical signal processing.
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  • 83
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: In this letter, a novel two-stage digital feed forward carrier recovery algorithm for 64-ary quadrature amplitude modulation (QAM) is proposed and analyzed. Due to the absence of any feedback loop, the approach shows a high tolerance toward laser phase noise. Different steps involving partition, selection, and rotation of symbols are also discussed. For an OSNR penalty of 1 dB at bit error rate of $10^{-3}$ , the proposed scheme can tolerate linewidth times symbol duration product equal to $3.3times 10^{-5}$ and hence can be used with the commercially available state-of-the-art tunable lasers for 64-QAM transmission at 400 Gb/s.
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  • 84
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: A lithium niobate $({rm LiNbO}_{3})$ -based integrated optical $E$ -field sensor utilizing Mach-Zehnder optical waveguide interferometer and bow-tie antenna has been designed and fabricated for the detection of nanosecond intense pulsed electric field. Experimental data demonstrate that the average rise time, fall time, and pulsewidth of the input/output electromagnetic pulse (EMP) are 1.31/1.28, 3.63/3.61, and 34.19/34.25 ns, respectively. Correspondingly, the relative errors are 2.3%, 0.6%, and 0.2%, respectively. In addition, the input/output of the sensor system shows a linear relationship as the correlation coefficient between measured and fitting is 0.9991. The minimum and maximum measured EMP fields are approximately equal to 3 and 50 kV/m, respectively.
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  • 85
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: We demonstrated a novel highly efficient polarized combining technique, enabling combing power scaling by increasing the number of individual lasers. With commercial polarization rotators, up to 98.7% combining efficiency has been obtained using three linearly polarized pulsed lasers. The beam quality of the combined laser was 12 ${rm mm}cdot{rm mrad}$ at 109 W, which was comparable with starting ones. To the best of our knowledge, these results represent the highest power combining efficiency to date for scalable polarized combining system.
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  • 86
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-15
    Description: An in-fiber modal interferometer based on coaxial dual-waveguide optical fiber was demonstrated for temperature sensing. The modal interferometer is composed of a coaxial fiber, which is sandwiched in between two single mode fibers with small lateral core-offsets. Such a modal interferometer is insensitive to external refractive index (RI) and can work when the surrounding RI is larger than the RI of the fiber cladding. It has high temperature sensitivity of 78 ${rm pm}/^{circ}{rm C}$ and low cross-sensitivity to strain of 0.004 $^{circ}{rm C}/muvarepsilon$ .
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  • 87
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: With the electromagnetic theory as a basis, we present a sensor model for three-axis magnetometers suitable for localization and tracking as required in intelligent transportation systems and security applications. The model depends on a physical magnetic dipole model of the target and its relative position to the sensor. Both point target and extended target models are provided as well as a heading angle dependent model. The suitability of magnetometers for tracking is analyzed in terms of local observability and the Cramér–Rao lower bound as a function of the sensor positions in a two sensor scenario. The models are validated with real field test data taken from various road vehicles which indicate excellent localization as well as identification of the magnetic target model suitable for target classification. These sensor models can be combined with a standard motion model and a standard nonlinear filter to track metallic objects in a magnetometer network.
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  • 88
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: Polarimetric weather radars provide additional measurements that allow better characterization of the targeted medium. Because ground clutter has different polarimetric characteristics from weather echoes, dual-polarization measurements can be used to distinguish one from the other. Ground clutter and weather signals also have different statistical properties which can be utilized to distinguish one from the other. A test statistic, obtained from the generalized likelihood ratio test (GLRT), and a simple Bayesian classifier (SBC), with inputs from the mean and covariance of the received signals, are developed to detect ground clutter in the presence of weather signals. It is found that the test statistic produces false detections caused by narrow-band zero-velocity weather signals while the SBC can effectively neutralize them. This work is aimed at detecting ground clutter based solely on data from each resolution volume. The performances of the test statistic and SBC are shown by applying them to radar data collected with the University of Oklahoma-Polarimetric Radar for Innovation in Meteorology and Engineering.
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  • 89
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: During the late 1990s, Huang introduced the algorithm called Empirical Mode Decomposition, which is widely used today to recursively decompose a signal into different modes of unknown but separate spectral bands. EMD is known for limitations like sensitivity to noise and sampling. These limitations could only partially be addressed by more mathematical attempts to this decomposition problem, like synchrosqueezing, empirical wavelets or recursive variational decomposition. Here, we propose an entirely non-recursive variational mode decomposition model, where the modes are extracted concurrently. The model looks for an ensemble of modes and their respective center frequencies, such that the modes collectively reproduce the input signal, while each being smooth after demodulation into baseband. In Fourier domain, this corresponds to a narrow-band prior. We show important relations to Wiener filter denoising. Indeed, the proposed method is a generalization of the classic Wiener filter into multiple, adaptive bands. Our model provides a solution to the decomposition problem that is theoretically well founded and still easy to understand. The variational model is efficiently optimized using an alternating direction method of multipliers approach. Preliminary results show attractive performance with respect to existing mode decomposition models. In particular, our proposed model is much more robust to sampling and noise. Finally, we show promising practical decomposition results on a series of artificial and real data.
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  • 90
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: In this paper, we present energy-efficient architectures for decoders of low-density parity check (LDPC) codes using the differential decoding with binary message passing (DD-BMP) algorithm and its modified variant (MDD-BMP). We also propose an improved differential binary (IDB) decoding algorithm. These algorithms offer significant intrinsic advantages in the energy domain: simple computations, low interconnect complexity, and very high throughput, while achieving error correction performance up to within 0.25 dB of the offset min-sum algorithm. We report on fully parallel decoder implementations of (273, 191), (1023, 781), and (4095, 3367) finite geometry-based LDPC codes in 65 nm CMOS. Using the MDD-BMP algorithm, these decoders achieve respective areas of 0.28 ${rm mm}^{2}$ , 1.38 ${rm mm}^{2}$ , and 15.37 ${rm mm}^{2}$ , average throughputs of 37 Gbps, 75 Gbps, and 141 Gbps, and energy efficiencies of 4.9 pJ/bit, 13.2 pJ/bit, and 37.9 pJ/bit with a 1.0 V supply voltage in post-layout simulations. At a reduced supply voltage of 0.8 V, these decoders achieve respective throughputs of 26 Gbps, 54 Gbps, and 94 Gbps, and energy efficiencies of 3.1 pJ/bit, 8.2 pJ/bit, and 23.5 pJ/bit. We also report on a fully parallel implementation of IDB for the (2048, 1723) LDPC code specified in the IEEE 802.3an (10GBASE-T) standard. This decoder achieves an area of 1.44 ${rm mm}^{2}$ , average throughput of 172 Gbps, and an energy efficiency of 2.8 pJ/bit with a 1.0 V supply voltage; at 0.8 V, it achieves throughput of 116 Gbps and energy efficiency of 1.7 pJ/bit.
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  • 91
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-18
    Description: Energy efficiency optimization of wireless systems has become urgently important due to its impact on the global carbon footprint. In this paper we investigate energy efficient multicell multiuser precoding design and consider a new criterion of weighted sum energy efficiency, which is defined as the weighted sum of the energy efficiencies of multiple cells. This objective is more general than the existing methods and can satisfy heterogeneous requirements from different kinds of cells, but it is hard to tackle due to its sum-of-ratio form. In order to address this non-convex problem, the user rate is first formulated as a polynomial optimization problem with the test conditional probabilities to be optimized. Based on that, the sum-of-ratio form of the energy efficient precoding problem is transformed into a parameterized polynomial form optimization problem, by which a solution in closed form is achieved through a two-layer optimization. We also show that the proposed iterative algorithm is guaranteed to converge. Numerical results are finally provided to confirm the effectiveness of our energy efficient beamforming algorithm. It is observed that in the low signal-to-noise ratio (SNR) region, the optimal energy efficiency and the optimal sum rate are simultaneously achieved by our algorithm; while in the middle-high SNR region, a certain performance loss in terms of the sum rate is suffered to guarantee the weighed sum energy efficiency.
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  • 92
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-22
    Description: We present a new class of highly effective and low complexity digital filters for processing very wideband signals. Digital filtering for wideband signals is often limited by the number of arithmetic operations that has to be performed per input sampling interval. We will show the new architecture permits filtering to be performed on partitioned spectral segments of the input signal at significantly reduced sample rate. The digital filtering will be shown to include various tasks such as linear/non-linear phase finite impulse response (FIR) filtering, fractional delay filter among others. The proposed technique utilizes the framework of non-maximally decimated filter banks (NMDFBs) with perfect reconstruction (PR) property, which makes the filter bank design simpler and more flexible. Compact representation for the generalized DFT based NMDFBs as well as its efficient polyphase implementation will be provided. The digital filtering is made possible by incorporating the desired intermediate processing elements in between the analysis and synthesis filter banks. We will show this embedded intermediate processing elements can achieve spectral shaping/signal manipulation task, which is a generalization of the concept of manipulating a digital filter in the frequency domain. We also analyze both analytically and experimentally, the spectral shaping accuracy based on different design strategies.
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  • 93
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-01-22
    Description: Long-time coherent integration technique is one of the most important methods for the improvement of radar detection ability of a weak maneuvering target, whereas the integration performance may be greatly influenced by the across range unit (ARU) and Doppler frequency migration (DFM) effects. In this paper, a novel representation known as Radon-fractional Fourier transform (RFRFT) is proposed and investigated to solve the above problems simultaneously. It can not only eliminate the effect of DFM by selecting a proper rotation angle but also achieve long-time coherent integration without ARU effect. The RFRFT can be regarded as a special Doppler filter bank composed of filters with different rotation angles, which indicates a generalization of the traditional moving target detection (MTD) and FRFT methods. Some useful properties and the likelihood ratio test detector of RFRFT are derived for maneuvering target detection. Finally, numerical experiments of aerial target and marine target detection are carried out using simulated and real radar datasets. The results demonstrate that for integration gain and detection ability, the proposed method is superior to MTD, FRFT, and Radon-Fourier transform under low signal-to-clutter/noise ratio (SCR/SNR) environments. Moreover, the trajectory of target can be easily obtained via RFRFT as well.
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  • 94
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-03-14
    Description: In this letter, we demonstrate a proof of concept fully loaded bidirectional ultrahigh capacity coherent passive optical network (2 $,times,$ 1008 $,times,$ 8.3 Gb/s). This was achieved using partial spectrum overlap, Nyquist shaping, digital frequency shifting, self-homodyne detection, and pilot tone remodulation. Upstream burst mode operation is also demonstrated.
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  • 95
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-03-14
    Description: We report a hybrid silicon optical gate array based on a silicon waveguide with a III-V gain medium and two vertical grating couplers. The gates show a fast switching time, a high extinction ratio, and a positive fiber-to-fiber optical gain. The dynamic behavior of such a device is evaluated under electrically controlled gating. We further focus on a single gate performance in a packet-switched network. We demonstrate subwavelength switching operations with multiformat and multibit-rate optical packet based on direct and coherent detection.
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  • 96
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-03-14
    Description: We demonstrate a broadband wavelength converting system for incoherent amplified spontaneous emission (ASE) sources. It is based on single-pass difference frequency generation using a periodically poled stoichiometric lithium tantalate crystal placed inside the cavity of a tuneable self-injection-locked diode-pumped ${rm Cr}^{3+}{:}{rm LiCAF}$ laser. A spectral bandwidth of ${sim}{rm 30}~{rm nm}$ around 1550 nm is converted within a tuneable shift of ${sim}{rm 12}~{rm nm}$ . The technique we propose does not only provide ASE sources in new spectral allocations but it also opens up a way to perform spectral shaping.
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  • 97
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-03-14
    Description: A promising technique for inscribing long period fiber gratings (LPFGs) was demonstrated by only using a commercial splicer. The commercial splicer was developed secondarily to build up a new program for periodically tapering a single mode fiber. High-quality LPFGs with a low insertion loss of ${sim}{rm 1}~{rm dB}$ and a large resonant attenuation of more than ${-}{rm 30}~{rm dB}$ were achieved. The achieved periodic tapers exhibited an excellent reproducibility with a small error of less than ${pm}{rm 0.3}~mu{rm m}$ . To the best of our knowledge, it is the minimum reproducibility error of tapers achieved by arc discharge technique so far. Near mode fields of three LPFG samples with different pitches were observed to investigate the mode coupling in the taper-inscribed LPFGs. In addition, the resonant wavelengths of our taper-inscribed LPFGs exhibited a blue shift first and then red shift with an increased number of grating periods, resulting from residual stress relaxation together with physical deformation.
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  • 98
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-03-14
    Description: A 3-D polarizing beam splitter based on a silicon nitride $({rm Si}_{3}{rm N}_{4})$ vertical directional coupler is experimentally demonstrated. A new planarization technique by incorporating conventional chemical-mechanical lapping with a dry-etching process is developed, in order to obtain a flat film surface for the second ${rm Si}_{3}{rm N}_{4}$ core deposition after the first-layer waveguide is formed. Both the ${rm Si}_{3}{rm N}_{4}$ layer thicknesses are 200 nm. As there is a material refractive index mismatch between the vertically separated waveguides, the polarization splitter can be realized with a bottom waveguide width of 1.55 $mu{rm m}$ and a top core width of 1.35 $mu{rm m}$ . The transverse electric (TE) polarized light can be transmitted completely to the cross-layer output-port, whereas the transverse magnetic (TM) polarized wave outputs mostly from the port at the input layer. A high-extinction ratio and a wide operation bandwidth can be achieved. An extinction ratio of 26 dB for the cross-layer output-port at 1550-nm wavelength and that of 16 dB for the input-layer output-port are obtained. There is an excess coupling loss of ${〈}{rm 0.1}~{rm dB}$ for the TE light, but a 1-dB loss for the TM wave.
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  • 99
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-03-14
    Description: In this letter, we demonstrate a novel monolithically integrated photonic multiwavelength transmitter that was realized by integrating an arrayed waveguide grating-based laser with selective distributed Bragg reflector mirrors and Mach-Zehnder modulators. The integrated circuit was designed according to a generic integration model, by utilizing standardized photonic building blocks, and was fabricated on an InP-based platform in a multiproject wafer run. The device delivers above 1 mW of optical power into the fiber with a side mode suppression ratio better than 40 dB. The linewidth of the generated signals is 275 kHz. We achieved error free 50-km transmission at the modulation data rate of 10 Gb/s per channel, for a received power of ${-}{26.5}~{rm dBm}$ .
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  • 100
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2014-03-14
    Description: Optical (de)multiplexers that can provide low insertion loss, low crosstalk, high thermal stability, and insensitivity to fabrication tolerances are essential components for silicon photonics integration. In this letter, we demonstrate the integration of an angled multimode interferometer coarse wavelength division multiplexer with germanium $phbox{-}{rm i}hbox{-}n$ photodetectors to form a 50 Gb/s receiver with a low insertion loss of ${〈}{-}{rm 0.5}~{rm dB}$ and crosstalk of ${〈}{-}{rm 15}~{rm dB}$ . The angled multimode interferometer has the flexibility to be designed on a platform with a wide range of waveguide thicknesses with little variation in performance, which allows for the optimization of other optical components in the photonics integrated circuit.
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