查看更多>>摘要：When the number of snapshots used to estimate the Sample covariance matrix (SCM) approaches infinity and the array steering vector is accurately known,the Standard Capon beamformer (SCB) can better suppress spatial noises than data-independent beamformers.On the contrary,the performance of the SCB may decrease.To solve this problem,we propose a two-stage shrinkage scheme for the SCM.Specifically,in the first stage,the SCM is enhanced by the General linear combination (GLC) method,which will be referred to as GLC-SCM;and in the second stage,the GLC-SCM is further improved with the Exponential matrix (EM) method,which will be referred to as GLC-EM-SCM.Compared with the conventional methods,the proposed method can achieve higher signal-to-interference-noise ratio output and more accurate signal power estimate.
查看更多>>摘要：The linear phase is a major characteristic of digital differentiators in many signal processing applications.This study presents a sequential partial optimization method for designing a fullband infinite impulse response digital differentiator with a near linear phase.To achieve a near linear phase,the group delay is treated as an optimization variable,and the maximum phase error is minimized within a constrained domain.During each iteration of the algorithm,in addition to the whole numerator and group delay,only one second-order denominator factor is optimized.The necessary and sufficient stability triangles are applied to insure the stability of the differentiators,and the Gauss-Newton strategy is used to handle the nonconvexity of the design problems.Design examples show that the proposed method outperforms several state-of-the-art methods in terms of the maximum phase deviation from the desired linear phase.
查看更多>>摘要：We focus on the Direct position determination (DPD) of a moving narrowband source based on Doppler frequency shifts of signals with known waveforms.Two common motion models are considered: the Constant velocity (CV) model and the Constant acceleration (CA) model.The DPD cost function is obtained after some algebraic manipulations using the Maximum likelihood (ML) criterion.To develop a computationally efficient optimization algorithm,we present a preliminary mathematical result that plays a fundamental role in development of the proposed algorithm.Subsequently,a Newton iterative algorithm is tailored to the two motion models to determine the moving transmitter's trajectory.When compared with multidimensional grid searching,the proposed algorithm is more computationally attractive without compromising its estimation accuracy.Simulation results confirm the superiority of the proposed algorithm.
查看更多>>摘要：In this work,we report on non-invasive observation of human esophagus,liver,and uterus samples with Full field optical coherence tomography (FFOCT).ln imaging process,fresh human samples were fixed in formalin immediately after excision and then imaged directly without staining and cutting the samples into a serial of thin slices.Tissue microstructures of each type of normal or cancerous tissue as well as their changes with the increase of the depth beneath tissue surface can be identified in the depth-resolved images.The results demonstrate the potential of applications of the en face images in clinic practice.
查看更多>>摘要：In conventional 3D shape retrieval and classification,they differentiate each other in their final stages.We propose a unified feature representation and learning framework for the instance-based shape retrieval and classification.Firstly,we render every 3D model in several directions and use the produced view-sets to represent the 3D models.In this way,both tasks can be tackled by measuring the distances between rendered views of 3D models.Secondly,we construct the view-sets as Symmetric positive definite matrices (SPDMs),which are points on a Riemannian manifold.Thus,the shape retrieval and classification tasks are reduced to a problem of measuring the distances between projected views and SPDMs.To solve this heterogeneous problem,we map them to a Hilbert space using a method of point-to-set matching.In this Hilbert space,the distances are surprisingly easy to calculate.Finally,we use a robust nearest-neighbor approach to unify the instance-based shape retrieval and classification.Our framework combines the state-of-the-art deep learning approaches with traditional mathematical optimization method,makes full use of both advantages,which is much more flexible than pure deep learning methods.Experimental results show the efficiency of our approach.
查看更多>>摘要：Ultrasound computed tomography (USCT) is a promising approach for early breast cancer screening.Existing studies that estimate breast images using Waveform inversion (WI) methods utilize a Circular ultrasonic transducer element array (CUTA) to collect the measurement data.However,very accurate transducer element positioning and directivity are required for signal calibration in the hardware system of these studies,thereby causing difficulties in hardware manufacturing.The purpose of this study is to estimate high-resolution USCT images using a WI method with a Square border ultrasonic transducer element array (SUTA),which reduces the difficulty of hardware manufacturing and creates accurate correspondence between the continuous and discrete forms of the transducer element positions.Therefore,in this study,an SUTA is adopted to collect the measurement data of breast imaging using the WI method.A penalized least-squares optimization problem is constructed to obtain the numerical solution of a sound speed distribution.Computer simulations are conducted to compare images reconstructed from the measurement data that are collected using an SUTA and a CUTA.The performance is evaluated using a numerical breast phantom.Results suggest that the biases of the images reconstructed are less than 1％ with the evenly distributed SUTA and 1％ with the CUTA,under a noise condition.
查看更多>>摘要：This paper proposes a flexible design scheme for H.265/HEVC encoding based on FPGA,which allows an easy incorporation of a variety of algorithms applied to different scenarios.In particular,we present an H.265/HEVC intra encoder as an instantiation of our proposed scheme.The key idea is to develop an encoder system by configuring basic Processing elements (PEs) of fundamental algorithms.Our intra encoder using the flexible framework is structured with four-stage CTU based pipeline.Pixel-level PEs are designed to unify the intra prediction of 35 modes and a multi-scale compatible transform array is proposed to process variable size transform.32 PEs are paralleled for intra mode decision to support 35 combinations of modes and partitions.In the reconstruction stage,16 PEs are paralleled for intra prediction and a 16 × 16 multiplier array is configured for transforms of variable sizes with a constant 16 pixels/cycle throughput.Implementation results show that our proposed architecture costs about 63K Lookup tables and 62KB on-chip memories on Xilinx Kintex-7 platform with the maximum working frequency at 175MHz,which is sufficient for real-time encoding of 1920 × 1080@60fps video at 160MHz.The flexibility and extension capability of our framework provides a great potential for future FPGA solutions serving for different purposes.
查看更多>>摘要：In this paper,we study double circulant codes of length 2n over the non-chain ring R =Fq + vFq + v2Fq,where q is an odd prime power and v3 =v.Exact enumerations of self-dual and LCD double circulant codes of length 2n over R are derived.When n is an odd prime,using random coding,we obtain families of asymptotically good self-dual and LCD codes of length 6n over Fq.
查看更多>>摘要：Ultralightweight mutual authentication protocols (UMAP) of Radio frequency identification (RFID) systems have attracted much attention from researchers.Many studies reveal that most of UMAP suffer malicious attack.To improve security of UMAP,formal analysis is performed with Simple promela interpreter (SPIN).Two typical UMAPs,which are RCIA and RAPP,are selected as our case study.A protocol abstract modeling method is presented to make UMAP can be formalized simply.Using SPIN,verification results show that RCIA and RAPP are both vulnerable against desynchronization attack.A Generalized model of UMAP (G-UMAP) and a general patching scheme are presented for resisting the attack.To validate the patching scheme,formal verification is then performed for the improved protocol.SPIN verification shows that the improved RCIA and RAPP both gain higher security.The above proposed modeling method has great significance for similar UMAP analyzing,and the proposed patching scheme is proved to be practical and reliable.
查看更多>>摘要：A variety of web services have emerged with the rapid development of the Internet.These services are often of a single function.The value-added services can be achieved by combing with multiple services.The processing speed and stability of existing methods in service composition were not very well and seldom consider the fault diagnosis and handling methods for the service,which results in a greater probability of the service composition failure at run time.We use spiking neural P systems with colored spikes to model the fault of available service,component,and connector in the service composition.The proposed model can be used to locate a fault and handle it correctly when the service combination fails,the advantage of efficiency and stability of proposed method has been proved by comparing with the method of Petri net.
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