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Maneuvering target detection is a challenging task for radar due to its maneuverability and weak energy. Long-term coherent integration can remarkably increase signal energy to improve the target detection ability. Unfortunately, high velocity and acceleration of the target will produce linear range migration (LRM), quadratic range migration (QRM), and Doppler frequency migration (DFM), which seriously degrades the coherent integration gain and further deteriorates target detection performance. To solve this problem, a method based on second-order Keystone transform (SKT) and Lv's distribution (LVD), also combined with Radon Fourier transform (RFT), i.e., SKTLVD, is proposed in this paper. The LRM is firstly corrected by using RFT. Then, the SKT is employed to remove QRM. Finally, LVD is utilized to eliminate the DFM and achieve coherent integration. Compared with several representative methods, the SKTLVD consumes low computation and obtains good target detection performance, striking a balance between computational cost and target detection ability. Numerical simulations and real measured radar data demonstrate that the proposed method can obtain considerable coherent integral gain under acceptable computational complexity. [ABSTRACT FROM AUTHOR]

A fast and low-complexity blind chromatic dispersion (CD) estimation method is proposed by a stepwise optimal order search of fractional Fourier transform (FrFT) in coherent optical communications. The method can track the cumulative dispersion over time in future dynamic and flexible scenarios. The validity of the FrFT method is verified by analogy to the field of CD estimation from the energy concentration property of the chirp signal, and the estimation equation of the CD value is obtained by parameter transformation. Numerical simulations have been carried out in the CD range of 1600 ps/nm to 32,000 ps/nm for 28 GBaud PM-QPSK and 14 GBaud PM-16QAM signals. The results show that the proposed algorithm achieves a high CD estimation accuracy with an average estimation error of less than 50 ps/nm within the 4096 sampling points and an order search interval of 0.0001. The effects of the polarization mode dispersion, optical signal-to-noise ratio and nonlinearity on CD estimation performance are discussed. In addition, the stepwise optimal order search method can achieve the purpose of greatly reducing the computational complexity under the premise of ensuring the accuracy of CD estimation. [ABSTRACT FROM AUTHOR]

Highlights • The problems of quadratic range migration and Doppler frequency migration for the maneuvering target are addressed. • A method based on TSS-FrFT is proposed to achieve the coherent integration and it has superior detection performance and low computational complexity. • The acceleration matched filter is presented to remove the DFRC caused by the sudden change of targets acceleration. Abstract This paper considers the detection problem of radar maneuvering target with the range migration (RM) and Doppler frequency migration (DFM) and proposes an coherent integration method based on two steps scaling and fractional Fourier transform, i.e., TSS-FrFT. To be specific, this method corrects the quadratic RM (QRM) and DFM based on FrFT and a scaling processing of the rotation angle firstly. Then, it eliminates the coupling between the range frequency variable and FrFT domain (FrFD) variable via a second scaling processing. In the end, the coherent integration is achieved by the inverse Fourier transform (IFT) with respect to the range frequency variable. Compared with the existing methods, the proposed TSS-FrFT method has superior detection performance and low computational complexity. Moreover, considering the sudden change of the target acceleration within the coherent integration interval, this paper also presents an acceleration matched filter (AMF) to remove the Doppler frequency rate change (DFRC) caused by this acceleration change. Computer simulation results are also given to demonstrate the effectiveness of the proposed method from different aspects, i.e., computational complexity, coherent integration for a single target and multiple targets and detection performance for a uniform acceleration and non-uniform accelerations. [ABSTRACT FROM AUTHOR]

Detection of weak maneuvering target often suffers from the problems of the range migration (RM) and the Doppler frequency migration (DFM) within the coherent pulse interval. In order to eliminate the RM and DFM, a new coherent integration method based on keystone transform (KT) and matched filtering process (MFP), i.e., KT-MFP, is proposed. Specifically, this method firstly corrects the linear RM caused by the unambiguous velocity via KT and then the MFP, which jointly searching in the fold factor and acceleration domain, is carried out to remove the residual RM and compensate the DFM. At last, coherent integration of the target’s energy is achieved through the slow time Fourier transform (FT). The advantage of the proposed method is that it can obtain superior coherent integration and detection performance for both the slow-moving and fast-moving target, in comparison with the existing algorithms. In addition, KT-MFP could avoid the blind speed sidelobe (BSSL) effect. Numerical simulations are performed to assess the performance from different aspects, i.e., computational complexity, coherent integration for a low-speed target, detection performance for a low-speed target, coherent integration for a high-speed target, detection performance for a high-speed target and coherent integration for multi-targets. [ABSTRACT FROM AUTHOR]

The efficient numerical simulation of population balance equations requires sophisticated techniques in order to combine accuracy with efficiency. We will focus on the numerical treatment of aggregation integrals that often dominate the overall time in population balance simulations. Following a finite element approach, the density distribution is discretized through a piecewise polynomial of order p > 0 on a nested grid that is refined locally toward an arbitrary point. The proposed method conserves mass while reducing the quadratic complexity (in the dimension of the solution space) of the direct computation to an almost linear complexity. The complexity improvement is based on recursion formulas exploiting orthogonality properties of basis functions along with FFT on locally equidistant portions of the grid. We present numerical results for various initial conditions and provide heuristic criteria for the choice of polynomial degree and grid refinement. [ABSTRACT FROM AUTHOR]

A new, fast and computationally efficient lateral subpixel shift registration algorithm is presented. It is limited to register images that differ by small subpixel shifts otherwise its performance degrades. This algorithm significantly improves the performance of the single-step discrete Fourier transform approach proposed by Guizar-Sicairos and can be applied efficiently on large dimension images. It reduces the dimension of Fourier transform of the cross correlation matrix and reduces the discrete Fourier transform (DFT) matrix multiplications to speed up the registration process. Simulations show that our algorithm reduces computation time and memory requirements without sacricing the accuracy associated with the usual FFT approach accuracy. [ABSTRACT FROM AUTHOR]

The Gray-Scott model is the representative bistable system in many reaction–diffusion models. Numerical simulation of this model is very difficult especially for space fractional case. In this paper, a novel numerical approach is introduced. We introduce the Runge–Kutta method for time discretization and Fourier transform for spatial discretization. The error has been reduced effectively by using Richardson Extrapolation. We perform stability and convergence analysis for the present method. Numerical experiments show that present method has low computational complexity and higher precision. Long time diffusion behavior of pattern can be observed. [ABSTRACT FROM AUTHOR]

By using Fractional Fourier Transform (FRFT) for detecting multicomponent linear frequency-modulated (LFM) signals, weak signal components are usually shadowed by the sidelobes of strong ones and cannot be detected effectively. The CLEAN technique is widely used to improve such a situation via subtracting the detected strong signal component from the multicomponent signals iteratively and applying detection algorithm to the remainder signals. Thus the adverse effect of strong components can be eliminated and weak signal components may be detected. However, since only the strongest LFM component is detected and subtracted in each iteration, the number of detection iteration will be directly proportional to the number of LFM components. Using concept of shading coefficient, a novel threshold setting method for rapid detection of multicomponent LFM signals has been proposed by analyzing the shading relation among the fourth-order origin moment of fractional spectrum (OMFrS) of different LFM components. By employing the proposed method, several LFM components whose fourth-order OMFrS at their own optimal rotation angles are not shadowed by strong components can be detected at the same time in one iteration. Consequently, the number of detection iteration and the computational complexity are reduced dramatically. Simulation results are given to verify that this new approach is valid. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a modified widely linear selective mapping (MWL-SLM) scheme is proposed to reduce the peak-to-average power ratio (PAPR) of the orthogonal frequency-division multiplexing (OFDM) systems. In the proposed MWL-SLM scheme, through partition one complex signals into two real signals and combining the linear properties of the Fourier Transform, at most 4M 2 candidate signals can be obtained but only require M inverse fast Fourier transform (IFFT) operations. As a result, the proposed SLM scheme has the ability to generate more candidates when compared with conventional SLM (C-SLM) and widely linear SLM (WL-SLM). Therefore, MWL-SLM outperforms C-SLM and WL-SLM for the same computational cost of IFFT operations. Alternatively, for a given number of candidates, MWL-SLM has slightly inferior PAPR reduction performance to C-SLM and WL-SLM but requires less IFFT operations to be implemented, thus resulting in a lower computational complexity. Simulation results demonstrate the effectiveness of the proposed scheme. [Copyright &y& Elsevier]

Abstract: This paper presents a time–frequency-domain filtered-x LMS (FXLMS) algorithm for active noise control (ANC) based on the short-time Fourier transform (STFT). We show that proposed algorithm has much reduced computational complexity and better convergence performance, as compared with the time-domain FXLMS algorithm. Additionally, computer simulations show that a time–frequency-domain FXLMS algorithm for ANC is effective in canceling non-stationary noise while a frequency-domain FXLMS algorithm remains inadequate at this task. [Copyright &y& Elsevier]

SUMMARY A framework for a computationally efficient single-carrier frequency-division multiple access (SC-FDMA) transmitter is proposed in this paper. Compared with a wide system bandwidth, the uplink allocation for each user is supposed to be relatively small because of multiple user access, which makes each user's signal vector to be sparse. When the localized subcarrier allocation is used for SC-FDMA, the inverse fast fourier transform can take advantage of the sparse user input vector to reduce its complexity. The analytical and simulation results show that the proposed framework can provide a significant complexity reduction compared with the conventional SC-FDMA transmitter. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: A thin gaseous disk has often been investigated in the context of various phenomena in galaxies, which point to the existence of starburst rings and dense circumnuclear molecular disks. The effect of self-gravity of the gas in the disk can be important in confronting observations and numerical simulations in detail. For use in such applications, a new method for the calculation of the gravitational force of a disk is presented. Instead of solving the complete potential function problem, we calculate the force in infinite planes in Cartesian and polar coordinates by a reproducing kernel method. Under the limitation of a disk, we specifically represent the force as a double summation of a convolution of the surface density and a fundamental kernel and employ a fast Fourier transform technique. In this method, the entire computational complexity can be reduced from to , where N is the number of zones in one dimension. This approach does not require softening. The proposed method is similar to a spectral method, but without the necessity of imposing a periodic boundary condition. We further show this approach is of near second order accuracy for a smooth surface density in a Cartesian coordinate system. [Copyright &y& Elsevier]

The authors assume a linear equidistance antenna array as the receiver for a fixed frame-length multiple-access system, which employs variable-gain receiver power and repetition encoding. They propose a robust maximum a posteriori probability (MAP) blind bit-rate detector (BBRD). This detector considers the rate detection (RD) as a multi-hypothesis test and maximises the likelihood functions (LFs) to find the true bit-rate, whereas the complex amplitude of the received signal, the noise variance and the direction of arrival are unknown parameters. First, assuming that the location parameter is known and the information sequence are independent and uniformly distributed random variables, the authors propose a hybrid likelihood ratio test (HLRT). The proposed HLRT requires to solve a set of non-linear equations that have no closed-form solution. Thus, an iterative numerical algorithm is proposed. In addition, a quasi-HLR detector which has a significantly lower computational complexity is also proposed. In the case of unknown location parameter, the authors develop two quasi-HLR methods. They use fast Fourier transform and search to estimate the unknown location. In Q-HLRT-Method-I, the non-linear equation similar to the one in known location parameter is iteratively solved. In Q-HLRT-Method-II, a low complexity solution is proposed. Simulation examples evaluate and compare the performances of the proposed BBRDs. [ABSTRACT FROM AUTHOR]

By adopting the pseudo-random noise (PN) sequences as the guard interval (GI) as well as the training sequence, time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) outperforms the conventional OFDM using the cyclic prefix (CP) in the spectral efficiency at the cost of the iterative padding subtraction (IPS) in channel estimation (CE). To avoid the high computational complexity of the IPS, an improved frequency domain CE scheme based on a newly designed frame structure is proposed. To further improve the CE accuracy, the time domain training sequences, which are frequency binary (FB) after the fast Fourier transform (FFT), are flexibly padded as the frame header instead of the PN sequences. Theoretical analyses and computer simulations show that the proposed scheme can improve the system performance under the time frequency doubly selective channels, even in the presence of large channel delays in the single frequency networks. [ABSTRACT FROM AUTHOR]

In this paper, we have presented a comparative study of four different Rayleigh fading channel simulation methods with respect to computational complexity and accuracy. Fidelity of the various simulators is examined in terms of confidence interval also. The sum-of-sinusoids (SOS)-based simulation method can accurately generate a very long sequence without any impact on computer memory usage. The inverse discrete Fournier transform (IDFT)-based simulator is relatively fast and able to generate a sequence corresponding to a given autocorrelation function (ACF). However, its applicability is limited due to large memory spare requirement. For small sequences, algorithm based on covariance matrix is most efficient but its time complexity grows many folds as the sequence length is increased. Autoregressive modelling (AR) of fading process is needed when time evolution of fading process is exploited for channel tracking. The accuracy of the generated sequence ACF using the above four methods is also compared through an example. [ABSTRACT FROM AUTHOR]

Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitter's output signal. The selected mapping (SLM) approach provides good performance for PAPR reduction, but it requires a bank of inverse fast Fourier transforms (lFFTs) to generate a set of candidate transmission signals, and this requirement usually results in high computational complexity. In this paper, we propose a kind of low-complexity conversions to replace the IFFT blocks in the conventional. SLM method. Based on the proposed conversions, we develop two novel SLM schemes with much lower complexity than the conventional one; the first method uses only one IFFT block to generate the set of candidate signals, while the second one uses two IFFT blocks. Computer simulation results show that, as compared to the conventional SLM scheme, the first proposed approach has slightly worse PAPR reduction performance and the second proposed one reaches almost the same PAPR reduction performance. [ABSTRACT FROM AUTHOR]

In recent years, recurrent networks have been attracting attention as a processing mechanism of spatiotemporal patterns by neural networks. Although learning algorithms based on the steepest descent method have been proposed by Williams and Zipser and by Pearlmutter, that of Williams and Zipser has a problem of increased computational complexity for large-scale networks, and Pearlmutter's has a flaw in that learning cannot be completed in a real time. In this paper, gradients of objective functionals are derived by variational calculus and a real-time computation method of gradients is proposed. With this methods it is expected that the real-time learning, requiring less computational complexity compared to conventional learning algorithms, will become possible. [ABSTRACT FROM AUTHOR]

Quantum image encryption offers major advantages over its classical counterpart in terms of key space, computational complexity, and so on. A novel double quantum image encryption approach based on quantum Arnold transform (QAT) and qubit random rotation is proposed in this paper, in which QAT is used to scramble pixel positions and the gray information is changed by utilizing random qubit rotation. Actually, the independent random qubit rotation operates once, respectively, in spatial and frequency domains with the help of quantum Fourier transform (QFT). The encryption process accomplishes pixel confusion and diffusion, and finally the noise-like cipher image is obtained. Numerical simulation and theoretical analysis verify that the method is valid and it shows superior performance in security and computational complexity. [ABSTRACT FROM AUTHOR]