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This paper develops, within a general framework that is applicable to rather arbitrary electromagnetic and acoustic remote sensing systems, a theory of time-reversal "MUltiple SIgnal Classification" (MUSIC)-based imaging of extended (nonpoint-like) scatterers (targets). The general analysis applies to arbitrary remote sensing geometry and sheds light onto how the singular system of the scattering matrix relates to the geometrical and propagation characteristics of the entire transmitter-target-receiver system and how to use this effect for imaging. All the developments are derived within exact scattering theory which includes multiple scattering effects. The derived time-reversal MUSIC methods include both interior sampling, as well as exterior sampling (or enclosure) approaches. For presentation simplicity, particular attention is given to the time-harmonic case where the informational wave modes employed for target interrogation are purely spatial, but the corresponding generalization to broadband fields is also given. This paper includes computer simulations illustrating the derived theory and algorithms. [ABSTRACT FROM AUTHOR]

A cooperative spectrum-sensing technique in cognitive radio (CR) networks based on the data fusion of various chaotic stochastic resonance (CSR) energy detectors is proposed in this paper. Due to noisy uncertainty in unpredictable wireless communication environments, detection performance of conventional energy detection cannot be guaranteed. By introducing the CSR system with various CSR noise types, and with the data fusion on these CSR-based energy detectors, the detection probability can be improved under the same constant false-alarm rate (CFAR), particularly under low signal-to-noise ratio (SNR) circumstances. Theoretical analyses and computer simulation results verify the effectiveness of the proposed novel cooperative spectrum-sensing approach under serious wireless conditions. [ABSTRACT FROM PUBLISHER]

It is well known that seven parameters completely describe a circular cone-beam geometry in either flat-panel X-ray computed tomography (CT) or single pinhole SPECT imaging. This paper considers the problem of determining one of the seven parameters only, the detector in-plane rotation or twist angle \eta. We describe a graphical procedure that can determine \eta independently of all other six parameters from a geometric calibration scan of point objects. Our method is exact in the ideal noise-free case and is general in that the other two out-of-plane detector rotation angles \theta and \phi can be nonzero. The calibration scan typically needs at least two point objects and an even number of projection views over a full 360^\circ data acquisition. Under certain conditions, projection data truncation or a short scan acquisition of 180^\circ+ fan angle can be accommodated without affecting the accuracy of the calibration result. The graphical method is equally applicable to rotational multipinhole SPECT geometry. In this case, the final result is averaged from the individual estimates considering each pinhole separately. We use computer simulations and a multipinhole SPECT experiment to demonstrate the accuracy and precision of the proposed method. [ABSTRACT FROM AUTHOR]

The use of multitaper spectrum (MTS) for spectrum sensing in cognitive radio (CR) has been investigated by a number of researchers. Meanwhile, its superior detection performance has been numerically demonstrated. Regardless of their importance, the theoretic performance and thresholds for MTS detectors remain unavailable in the literature. In this paper, we tackle such an issue, ending up with various closed-form analytic formulas for the probabilities of detection and false alarm with different settings including single-sensor and multisensor MTS detectors with perfect or inaccurate noise variance. The validity of theoretical formulas is intensively examined through numerical results and computer simulations. [ABSTRACT FROM PUBLISHER]

In this paper we present two new Non Data Aided (NDA) phase detectors (PDs) for carrier synchronization Phase Locked Loops (PLLs) in M-ary Phase Shift Keying (M-PSK) receivers. The first structure is a self-normalizing modification of the M-th order nonlinearity detector. We investigate this detector theoretically in order to predict its S-curve, self-noise, squaring- loss, and phase-error variance performance. These theoretical predictions are then verified by computer simulations, and the results are contrasted with results obtained using other NDA and Decision Directed (DD) phase detectors. As those comparisons show, the proposed structure offers improved phase- error variance performance that is robust to Automatic Gain Control (AGC) circuit imperfections. Moreover, the new detector has a compact hardware structure suitable for implementation within an FPGA or ASIC. The second phase detector structure presented is an adaptive detector whose principal novelty is that it dynamically adapts the phase detector's gain to allow the PLL to perform optimally at any input Signal-to-Noise Ratio (SNR) at which it can lock. This detector is also robust vis-à-vis the AGC and has a compact hardware implementation suitable for FPGAs and ASICs. [ABSTRACT FROM AUTHOR]

An iterative receiver for a multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system is considered to jointly decode the transmitted bits and estimate the channel state. The receiver consists of a list detector, a turbo decoder, and a channel estimator that is based on the space-alternating generalized expectation-maximization (SAGE) algorithm. This paper proposes a way to improve the convergence of the iterative detection and decoding by using a priori information to also recalculate the candidate list, aside from the log-likelihood ratios (LLRs) of the coded bits. A new list parallel interference cancellation (PlC) detector is derived to approximate an a posteriori probability (APP) algorithm with reduced complexity and minimal losses of performance. Further- more, the organization of spectrally efficient decision-directed (DD) SAGE channel estimation under a constrained number of detector-decoder iterations is optimized by computer simulations, and the SAGE algorithm itself is modified for nonconstant envelope constellations. The list recalculation is shown to improve convergence. It is also shown that the list PlC detector with good initialization outperforms the K-best list sphere detector (LSD) in the case of small list sizes, whereas the complexities of the algorithms are of the same order. Despite the low preamble density and fast-fading channel, the proposed iterative receiver shows robust performance. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem of space-time codebook design for noncoherent communications in multiple-antenna wireless systems. In contrast with other approaches, the channel matrix is modeled as an unknown deterministic parameter at both the receiver and the transmitter, and the Gaussian observation noise is allowed to have an arbitrary correlation structure, known by the transmitter and the receiver. In order to handle the unknown deterministic space-time channel, a generalized likelihood ratio test (GLRT) receiver is considered. A new methodology for space-time codebook design under this non-coherent setup is proposed. It optimizes the probability of error of the GLRT receiver's detector in the high signal-to-noise ratio (SNR) regime by solving a high-dimensional nonlinear nonsmooth optimization problem in a two-step approach. First, a convex semidefinite programming (SOP) relaxation of the codebook design problem yields a rough estimate of the optimal codebook. This is then refined through a geodesic descent optimization algorithm that exploits the Riemannian geometry imposed by the power constraints on the space-time codewords. The results obtained through computer simulations illustrate the advantages of our method. For the specific case of spatio-temporal white observation noise, our codebook constructions replicate the performance of state-of-the-art known solutions. The main point here is that our methodology permits extending the codebook construction to any given correlated noise environment. The simulation results show good performance of these new designed codes in colored noise setups. [ABSTRACT FROM AUTHOR]

In video transmission, the compressed signal is extremely vulnerable to bit errors. Error concealment is widely used in video decoder to recover corrupted frames. Due to the use of variable length codes (VLCs), a single bit error in block-based bitstream may propagate to following of this slice. Especially, the effectiveness of error concealment technique relies heavily on correctly locating errors. In this paper an error detector based on syntax and continuity which consists of two stages is proposed. The first stage is to find erroneous slice according to checking constraints imposed on video bitstream syntax or detecting special error patterns. In the second stage, the precise position of the first erroneous macroblock (MB) is found based on the continuity of spatial or temporal data of neighbor MBs. Simulation results demonstrate that the proposed method improves performance of error detection significantly compared with the traditional syntax-based method'. [ABSTRACT FROM AUTHOR]

This paper presents a study on the effectiveness of strained contact-etch-stop-layer (CESL) technologies in aggressively scaled dense structures. The focus is on nested transistors, which is a technologically very important structure that consists of a chain of gates on one active area. It will be shown that the two main channel stress components introduced by CESL, which are the vertical and parallel stresses, have a different sensitivity toward layout variations, which accordingly leads to different scaling guidelines to obtain a layout-insensitive strained CESL technology. Decreasing the CESL thickness is not enough for technology scaling; also, adapting the spacer dimensions is indispensable to scale a strained CESL technology from one technology node to the next. [ABSTRACT FROM AUTHOR]

The problem of blind separation of overdetermined mixtures of sources, that is, with fewer sources than (or as many sources as) sensors, is addressed in this paper. A new method, called Independent Component Analysis using Redundancies in the quadricovariance (ICAR), is proposed in order to process complex data. This method, without any whitening operation, only exploits some redundancies of a particular quadricovariance matrix of the data. Computer simulations demonstrate that ICAR offers in general good results and even outperforms classical methods in several situations: ICAR i) succeeds in separating sources with low signal-to-noise ratios, ii) does not require sources with different second-order or/and first-order spectral densities, iii) is asymptotically not affected by the presence of a Gaussian noise with unknown spatial correlation, iv) is not sensitive to an over estimation of the number of sources. [ABSTRACT FROM AUTHOR]

Multicarrier spread spectrum (MC-SS) is an alternative to the conventional spread spectrum (SS) techniques that be- have significantly better when the system is subject to narrow- or partial-band interference. However, successful implementation of the optimum detector requires knowledge of noise and interference variance in each subcarrier band. In this paper, we propose a suboptimal detector for MC-SS that keeps the significant gain of MC-SS over the conventional SS, with a relatively low loss compared with the optimum MC-SS detector. Theoretical analysis and computer simulations that corroborate the theory are presented. [ABSTRACT FROM AUTHOR]

A novel multi-sensor information fusion methodology for intelligent terrain classification is presented. The focus of this research is to analyze safety characteristics of the terrain using imagery data obtained by on-board sensors during spacecraft descent. This information can be used to enable the spacecraft to land safely on a planetary surface. The focus of our approach is on robust terrain analysis and information fusion in which the terrain is analyzed using multiple sensors and the extracted terrain characteristics are combined to select safe landing sites for touchdown. The novelty of this method is the incorporation of the T-Hazard Map, a multi-valued map representing the risk associated with landing on a planetary surface. The fusion method is explained in detail in this paper and computer simulation results are presented to validate the approach. [ABSTRACT FROM AUTHOR]

List mode image reconstruction is attracting renewed attention. It eliminates the storage of empty sinogram bins. Howe ever, a single back projection of all LORs is still necessary for the pre-calculation of a sensitivity image. Since the detection sensitivity is dependent on the object attenuation and detector efficiency, it must be computed for each study. Exact computation of the sensitivity image can be a daunting task for modern scanners with huge numbers of LORs. Thus, some fast approximate calculation may be desirable. In this paper, we analyze the error propagation from the sensitivity image into the reconstructed image. The theoretical analysis is based on the fixed point condition of the list mode reconstruction. The nonnegativity constraint is modeled using the Kuhn-Tucker condition. With certain assumptions and the first order Taylor series approximation, we derive a closed form expression for the error in the reconstructed image as a function of the error in the sensitivity image. The result shows that the error response is frequency-dependent and provides a simple expression for determining the required accuracy of the sensitivity image calculation. Computer simulations show that the theoretical results are in good agreement with the measured results. [ABSTRACT FROM AUTHOR]