Target Multiplicity Performance Analysis of Radar CFAR Detection Techniques for Partially Correlated Chi-Square Targets

Most radar targets are complex objects and produce a wide variety of reflections. An important class of targets is represented by the so-called moderately fluctuating Rayleigh targets, which, when illuminated by a coherent pulse train, return a train of correlated pulses with a correlation coefficient in the range 0<ρ<1 (intermediate between SWII and SWI models). The detection of this type of fluctuating targets is therefore of great interest. On the other hand, the CFAR detection is one of the desirable features for radar receivers. Because of the simplicity of cell-averaging (CA detectors in their implementation, they are commonly used in modern radar systems to automatically adapt the detection threshold to the local background noise or clutter power in an attempt to maintain an approximately constant rate of false alarm. In this paper, we analyze the performance of these detectors for the case where the radar receiver postdetection integrates M square-law detected pulses and the signal fluctuation obeys chi-square statistics with two degrees of freedom. These detectors include the mean-level ML), the greatest-of (GO) and the smallest-of (SO) schemes. In these processors, the estimation of the noise power levels from the leading and the trailing reference windows is based on the CA technique. Exact formulas for the detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the chi-square fluctuation model with two degrees of freedom. Swerling's well known fluctuation models I and II represent the cases where the signal is completely correlated and completely decorrelated, respectively, from pulse to pulse. Probability of detection curves are presented for the chi-square family of fluctuations, including the Swerling cases I and II. The ML detector has the best homogeneous performance, the SO processor has the best multiple-target performance, while the GO scheme does not offer any merits neither in the absence nor in the presence of outlying targets.     

Semi-supervised superpixel classification for medical images segmentation: application to detection of glaucoma disease

Glaucoma is a disease characterized by damaging the optic nerve head, this can result in severe vision loss. An early detection and a good treatment provided by the ophthalmologist are the keys to preventing optic nerve damage and vision loss from glaucoma. Its screening is based on the manual optic cup and disc segmentation to measure the vertical cup to disc ratio (CDR). However, obtaining the regions of interest by the expert ophthalmologist can be difficult and is often a tedious task. In most cases, the unlabeled images are more numerous than the labeled ones.We propose an automatic glaucoma screening approach named Super Pixels for Semi-Supervised Segmentation “SP3S”, which is a semi-supervised superpixel-by-superpixel classification method, consisting of three main steps. The first step has to prepare the labeled and unlabeled data, applying the superpixel method and bringing in an expert for the labeling of superpixels. In the second step, We incorporate prior knowledge of the optic cup and disc by including color and spatial information. In the final step, semi-supervised learning by the Co-forest classifier is trained only with a few number of labeled superpixels and a large number of unlabeled superpixels to generate a robust classifier. For the estimation of the optic cup and disc regions, the active geometric shape model is used to smooth the disc and cup boundary for the calculation of the CDR. The obtained results for glaucoma detection, via an automatic cup and disc segmentation, established a potential solution for glaucoma screening. The SP3S performance shows quantitatively and qualitatively similar correspondence with the expert segmentation, providing an interesting tool for semi-automatic recognition of the optic cup and disc in order to achieve a medical progress of glaucoma disease.     

Structural Stabilities and Elastic Thermodynamic Properties of SrTe Compound and SrTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Alloy Under High Pressure

The effect of pressure on the structural, elastic, and thermodynamic properties of SrTe in both B1 (rocksalt) and B2 (CsCl-type) phases and the SrTe_1?x Ca _x alloys with Ca dopant concentrations at x = 0.16667, 0.20, 0.33333, 0.42857, 0.44444 and 0.50 have been investigated using the two new gradient-corrected functional developed by Perdew, J.P.; Burke, K.; Ernzerhof named Density-Gradient Expansion for Exchange in Solids (PBEsol) and generalized Wu–Cohen (WC), in a significant range of pressure from 0 GPa to 30 GPa. The structure parameters, elastic stiffness constants c _ij , the bulk modulus (B), Kleinman parameter (\( \xi \)), shear anisotropies A _shear are also determined. Furthermore, as reported in this study, the aggregate elastic modulus (B, G, E), Poisson’s ratio (ν) and the Lame’s coefficients (λ) are estimated. On the other hand, the ductility, brittleness, longitudinal, transverse sound velocities and the Debye temperature Θ_D(T) are also obtained. Importantly, our results are in reasonable agreement with the available theoretical and experimental data. To the best of our knowledge, this is the first study of the effect of the composition on the properties of the SrTe_1?x Ca _x alloys which may encourage other works for the confirmation of the reported results.     

Modification of the electric properties of molecular devices via gradual increase of number of nitrogen atoms: A computational study

This paper introduces a new means to manipulate electronic structures and, consequently, the electrical properties of molecular devices via gradual increase of number of nitrogen atoms in the backbone of conjugated organic molecular systems. Diblock molecules were selected for this purpose. Density functional theory (DFT) was used to investigate geometrical and electronic structures in the absence and presence of external electric field. Furthermore, the tendency of the anchor sulfur atoms toward electrodes in a simulated closed circuit was estimated from the relative condensed Fukui function. The obtained results indicated that HOMO–LUMO gap decreases steadily with increasing the number of nitrogen atoms, which would be used as a means for modifying the electrical properties in a regular mode.     

Performance Analysis of MIMO Based CDMA Code Acquisition Over Rayleigh Fading Channels

This paper proposes a new MIMO based CDMA code acquisition scheme. The pilot codes consist of a number of short Gold code sequences which are transmitted in parallel using a group of transmit antennas. Reception diversity is performed by multiple receive antennas at the receiver. Three different acquisition detection techniques are proposed and compared. Corresponding threshold optimizations are investigated as well. Detection and false alarm probabilities are derived in closed form based on the outputs of non-coherent matched filters. The acquisition performance is evaluated in terms of mean acquisition time (MAT) in Rayleigh fading environment. It is shown that the proposed MIMO acquisition scheme exhibits a much better MAT performance than the conventional single-antenna acquisition scheme. The results reveal that multiple receive antennas can be utilized to significantly reduce the MAT at the expense of receiver complexity increase. On the other hand, increasing the number of transmit antennas makes the MAT performance more robust in the presence of strong interference.     

Analytical expressions for blocking and dropping probabilities for mobile streaming users in wireless cellular networks

We consider a wireless cellular network serving streaming traffic. We study in this context the effect of the users mobility on their quality of service (QoS). If the arrival of a new user violates the capacity constraint, then his call is blocked. If the user is first admitted but the capacity constraint is violated later when he attempts to move, then his call is dropped. The blocking and dropping probabilities are the main QoS indicators in this model called forced termination (FT). We introduce an alternative model, called transitions backtrack (TB), where a user backtracks when his motion violates the capacity constraint. In this model, a relevant QoS indicator is the number of times the user backtracks called number of motion blocking per call. We propose some explicit expressions for the above QoS indicators as functions of the mean user speed. These expressions are validated by simulations. In particular we observe that the dropping probability in the FT model is well approximated by the number of motion blocking per call in the TB model which is expressed analytically.     

A Uniform Balancing Energy Routing Protocol for Wireless Sensor Networks

In wireless sensor network, the power supply is, generally, a non-renewable battery. Consequently, energy effectiveness is a crucial factor. To maximize the battery life and therefore, the duration of network service, a robust wireless communication protocol providing a best energy efficiency is required. In this paper, we present a uniform balancing energy routing protocol. In this later the transmission path is chosen for maximizing the whole network lifetime. Every transmission round, only the nodes which have their remaining energies greater than a threshold can participate as routers for other nodes in addition to sensing the environment. This choice allows the distribution of energy load among any sensor nodes; thus extends network lifetime. The experimental results shows that the proposed protocol outperforms some protocols given in the literature.     

Symbol error rate calculation and data pre‐distortion for 16‐QAM transmission over nonlinear memoryless satellite channels

This paper presents a simplified mathematical approach to evaluate the performance of any given circular constellation of 16‐level quadrature amplitude modulation (16‐QAM) in terms of symbol error rate (SER). Following this approach, with the aim to work with memoryless nonlinear satellite channels, a model is derived as a generalized form for both linear and nonlinear channels in the presence of down link additive white Gaussian noise (AWGN). The analysis provides means to calculate the optimal ring ratio (RR) and phase difference (PD) for several possible candidates of 16‐QAM circular constellations. The effects of RR and PD on the SER performance are investigated in the analysis. To overcome the nonlinear distortion, data pre‐distortion is taken into account in the study. The paper gives a general procedure for data pre‐distortion implementation for all circular 16‐QAM constellations. The analytical formulation has been extended for total degradation (TD) performance measure as a function of input back‐off (IBO) of the nonlinear amplifier. A SER performance‐comparison between different constellations for 16‐QAM systems has also been presented in this paper. The analytical results are validated by simulation. Copyright © 2006 John Wiley & Sons, Ltd.     

An Enhanced A-MSDU Frame Aggregation Scheme for 802.11n Wireless Networks

The main goal of the IEEE 802.11n standard is to achieve a minimum throughput of 100 Mbps at the MAC service access point. This high throughput has been achieved via many enhancements in both the physical and MAC layers. A key enhancement at the MAC layer is frame aggregation in which the timing and headers overheads of the legacy MAC are reduced by aggregating multiple frames into a single large frame before being transmitted. Two aggregation schemes have been defined by the 802.11n standard, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). As a consequence of the aggregation, new aggregation headers are introduced and become parts of the transmitted frame. Even though these headers are small compared to the legacy headers they still have a negative impact on the network performance, especially when aggregating frames of small payload. Moreover, the A-MSDU is highly influenced by the channel condition due mainly to lack of subframes sequence control and retransmission. In this paper, we have proposed an aggregation scheme (mA-MSDU) that reduces the aggregation headers and implements a retransmission control over the individual subframes at the MSDU level. The analysis and simulations results show the significance of the proposed scheme, specifically for applications that have a small frame size such as VoIP.     

Detail preserving impulsive noise removal

Most image processing applications require noise elimination. For example, in applications where derivative operators are applied, any noise in the image can result in serious errors. Impulsive noise appears as a sprinkle of dark and bright spots. Transmission errors, corrupted pixel elements in the camera sensors, or faulty memory locations can cause impulsive noise. Linear filters fail to suppress impulsive noise. Thus, non-linear filters have been proposed. Windyga's peak-and-valley filter, introduced to remove impulsive noise, identifies noisy pixels and then replaces their values with the minimum or maximum value of their neighbors depending on the noise (dark or bright). Its main disadvantage is that it removes fine image details. In this work, a variation of the peak-and-valley filter is proposed to overcome this problem. It is based on a recursive minimum–maximum method, which replaces the noisy pixel with a value based on neighborhood information. This method preserves constant and edge areas even under high impulsive noise probability. Finally, a comparison study of the peak-and-valley filter, the median filter, and the proposed filter is carried-out using different types of images. The proposed filter outperforms other filters in the noise reduction and the image details preservation. However, it operates slightly slower than the peak-and-valley filter.