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In this paper, a novel and exact mathematical formulation of three mean level constant false alarm rate (CFAR) detectors has been developed considering a homogeneous gamma-distributed (GM) clutter. These detectors include the cell averaging (CA), the greatest-of (GO), and the smallest-of (SO)-CFAR detection schemes. To do so, we derived closed-form expressions for the probability density function (pdf), and the cumulative distribution function (cdf) of the sum of an exponential fluctuating target submerged in gamma-distributed sea clutter. Then, we developed exact and explicit expressions for the probability of false alarm (Pfa) and probability of detection (Pd) of the optimal fixed threshold detector and the three considered CFAR detectors. The correctness of our expressions is then examined and validated via numerical simulations. Assuming a homogeneous GM background, the detection performance of these three detectors is carried out, discussed, and compared with that of the optimal detector. Experimental results with Sentinel-1 synthetic aperture radar (SAR) data demonstrate the effectiveness of the proposed closed-form expressions and show that the considered CFAR schemes are efficient for ship detection in sea clutter backgrounds. [ABSTRACT FROM AUTHOR]

In this paper, we analyse the performance of infrastructure-based fixed relay with multi-antenna in cognitive radio. We derive the mathematical expression for detection probability of single cooperative relay system over Rayleigh fading channel. Relay and fusion centre may perform either selection combining or maximal ratio combining of the signals. Effect of number of relay antennas for all four combinations of combining schemes has been analysed and as expected, increase in relay diversity improves the sensing performance. This is because, on installing more number of receiving antennas on the relay, it's participation increases, so the detection performance also improves. In the non-cooperative system also, the performance improves on increasing the diversity order but on the other hand, this increment imposes burden on the fusion centre. Whereas in multi-antenna cooperative relay system, the burden of relay gets transferred on relay node and the fusion centre takes advantage of increased diversity order of relay. For cooperative spectrum sensing, we have used soft decision combining scheme in which secondary users send their test statistics calculated from their local observations. [ABSTRACT FROM AUTHOR]

We study the sequential quickest change point detection for systems with multiple possible postchange models. A change point is the time instant at which the distribution of a random process changes. In many practical applications, the prechange model can be easily obtained, yet the postchange distribution is unknown due to the unexpected nature of the change. In this article, we consider the case that the postchange model is from a finite set of possible models. The objective is to minimize the average detection delay (ADD), subject to upper bounds on the probability of false alarm (PFA). Two different quickest change detection algorithms are proposed under Bayesian and non-Bayesian settings. Under the Bayesian setting, the prior probabilities of the change point and prior probabilities of possible postchange models are assumed to be known, yet this information is not available under the non-Bayesian setting. Theoretical analysis is performed to quantify the analytical performance of the proposed algorithms in terms of exact or asymptotic bounds on PFA and ADD. It is shown through theoretical analysis that when PFA is small, both algorithms are asymptotically optimal in terms of ADD minimization for a given PFA upper bound. Numerical results demonstrate that the proposed algorithms outperform existing algorithms in the literature. [ABSTRACT FROM AUTHOR]

Seafloor terrain and water column target detection is of great significance in marine surveys. However, the complex clutter environment can dramatically affect the detection performance of a multi-beam echo sounder. To simultaneously and robustly detect the seafloor terrains and water column targets, this paper proposes a fast two-dimensional double selectivity index-constant false alarm rate (DSI-CFAR) detection method. A two-dimensional cross sliding window, which includes reference cells and guard cells, is used in this paper. The proposed method improves the detection performance by using the appropriate clutter power level estimation strategies in different directions. An exponential model is accurately built by fitting various distributions, so the DSI-CFAR detection performance is greatly ameliorated. To reduce the computational load of the method, this paper uses a fast algorithm based on the global threshold. The region of interest (ROI) is selected by the preset global threshold, and the DSI-CFAR detector is only performed in the region of interest, which significantly reduces the number of pixels that must be calculated. In this paper, the measured results of different sliding windows and CFAR detection methods validate the basic performance of the proposed method. [ABSTRACT FROM AUTHOR]

To perform spectrum sensing in fading environment is one of the most challenging tasks for a CR system. Diversity combining schemes are used to combat the effect of fading and hence detection probability of CR gets improved. Among many diversity combining techniques, switched diversity offers one of the lowest complexity solutions. The receiver embedded with switched diversity looks for an acceptable diversity path (having signal to noise ratio (SNR) above the required threshold) to receive the data. In conventional switch and examine combining (SEC) scheme, when no acceptable path is found after all the paths are examined, the receiver randomly chooses an unacceptable path. Switch and examine combining with post-examining selection (SECp) is a modified version of conventional SEC. In SECp, the conventional SEC scheme is altered in a way that it selects the best path when no acceptable path is found after all paths have been examined. In this paper, formula for probability of detection () is derived using SECp and SEC diversity combining technique over Rayleigh fading channel. Also the performance of SECp is compared with SEC and no diversity case. Performance comparison is done with the help of SNR vs.and complementary receiver operating characteristic curves. [ABSTRACT FROM AUTHOR]

The current practice of multivariate process variability monitoring, when sub-group size is small, has nothing to do with probability of false alarm (PFA). Consequently, the reliability of the existing control charts remains undetermined. In this article, we propose a control chart which is reliable, very sensitive to the change in variance for small or moderate correlation, and provides a root causes analysis of an out-of-control signal. To illustrate these advantages, an industrial example is presented and the results are compared with those issued from the existing methods. [ABSTRACT FROM AUTHOR]

The present article reviews various criteria and approaches for an early detection of abrupt changes in the parameters of stochastic sequences. The discussion focuses on two issues: (i) the distributions of the stopping variables employed; and (ii) the probability of false alarm and the conditional expected delay characteristics. [ABSTRACT FROM AUTHOR]

In addition to the ARL∞, the discussion emphasizes the importance of determining PFA(τ) and CED(τ). An example of such computations is given. When the parameters before and after the change-point are unknown, it is recommended to employ the full Bayesian framework. [ABSTRACT FROM AUTHOR]