Correlation-based Detector Research Articles

A Correlation-Based Joint CFAR Detector Using Adaptively-Truncated Statistics in SAR Imagery.

Traditional constant false alarm rate (CFAR) detectors only use the contrast information between ship targets and clutter, and they suffer probability of detection (PD) degradation in multiple target situations. This paper proposes a correlation-based joint CFAR detector using adaptively-truncated statistics (hereafter called TS-2DLNCFAR) in SAR images. The proposed joint CFAR detector exploits the gray intensity correlation characteristics by building a two-dimensional (2D) joint log-normal model as the joint distribution (JPDF) of the clutter, so joint CFAR detection is realized. Inspired by the CFAR detection methodology, we design an adaptive threshold-based clutter truncation method to eliminate the high-intensity outliers, such as interfering ship targets, side-lobes, and ghosts in the background window, whereas the real clutter samples are preserved to the largest degree. A 2D joint log-normal model is accurately built using the adaptively-truncated clutter through simple parameter estimation, so the joint CFAR detection performance is greatly improved. Compared with traditional CFAR detectors, the proposed TS-2DLNCFAR detector achieves a high PD and a low false alarm rate (FAR) in multiple target situations. The superiority of the proposed TS-2DLNCFAR detector is validated on the multi-look Envisat-ASAR and TerraSAR-X data.

A Phase-Based Audio Watermarking System Robust to Acoustic Path Propagation

Today, comparing audio watermarking systems remain a challenge due to the lack of publicly-available reference algorithms. In addition, robustness against acoustic path transmission is only occasionally evaluated. This jeopardizes the chances of digital watermarking to be adopted in the context of applications where such a feature is vital, e.g., second screen, audience measurement, and so on. In this paper, we introduce a rather simple audio watermarking algorithm, whose source code has been publicized for potential reuse by the watermarking community. We then complement this baseline system with three additional components, namely a psychoacoustic model, a resynchronization framework, and an improved correlation-based detector. Reported experimental results clearly demonstrate that the resulting high-fidelity audio watermarking system manages to survive the acoustic path.

Audio Watermarking Using Independent Component Analysis

This paper presents a blind watermark detection scheme for an additive watermark embedding model. The proposed estimation-correlation-based watermark detector first estimates the embedded watermark by exploiting non-Gaussian of the real-world audio signal and the mutual independence between the host-signal and the embedded watermark and then a correlation-based detector is used to determine the presence or the absence of the watermark. For watermark estimation, blind source separation (BSS) based on independent component analysis (ICA) is used. Low watermark-to-signal ratio (WSR) is one of the limitations of blind detection with the additive embedding model. The proposed detector uses two-stage processing to improve the WSR at the blind detector; the first stage removes the audio spectrum from the watermarked audio signal using linear predictive (LP) filtering and the second stage uses the resulting residue from the LP filtering stage to estimate the embedded watermark using BSS based on ICA. Simulation results show that the proposed detector performs significantly better than existing estimation-correlationbased detection schemes.

Optimal Spectral Feature Detection for Spectrum Sensing at Very Low SNR

Spectrum sensing is one of the enabling functionalities for cognitive radio systems to operate in the spectrum white space. To protect the primary incumbent users from interference, the cognitive radio is required to detect incumbent signals at very low signal-to-noise ratio (SNR). In this paper, we study a spectrum sensing technique based on spectral correlation for detection of television (TV) broadcasting signals. The basic strategy is to correlate the periodogram of the received signal with the a priori known spectral features of the primary signal. We show that this sensing technique is asymptotically equivalent to the likelihood ratio test (LRT) at very low SNR, but with less computational complexity. That is, the spectral correlation-based detector is asymptotically optimal according to the Neyman-Pearson criterion. From the system design perspective, we analyze the effect of the spectral features on the spectrum sensing performance. Through the optimization analysis, we obtain useful insights on how to choose effective spectral features to achieve reliable sensing. Simulation results show that the proposed sensing technique can reliably detect analog and digital TV signals at SNR levels as low as -20 dB.

A Robust Image Watermarking in the Joint Time-Frequency Domain

With the rapid development of computers and internet applications, copyright protection of multimedia data has become an important problem. Watermarking techniques are proposed as a solution to copyright protection of digital media files. In this paper, a new, robust, and high-capacity watermarking method that is based on spatiofrequency (SF) representation is presented. We use the discrete evolutionary transform (DET) calculated by the Gabor expansion to represent an image in the joint SF domain. The watermark is embedded onto selected coefficients in the joint SF domain. Hence, by combining the advantages of spatial and spectral domain watermarking methods, a robust, invisible, secure, and high-capacity watermarking method is presented. A correlation-based detector is also proposed to detect and extract any possible watermarks on an image. The proposed watermarking method was tested on some commonly used test images under different signal processing attacks like additive noise, Wiener and Median filtering, JPEG compression, rotation, and cropping. Simulation results show that our method is robust against all of the attacks.

Behavior forensics with side information for multimedia fingerprinting social networks

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In multimedia social networks, there exists complicated dynamics among users who share and exchange multimedia content. Using multimedia fingerprinting as an example, this paper investigates the human behavior dynamics in the multimedia social networks with side information. Side information is the information other than the colluded multimedia content that can help increase the probability of detection. We study the impact of side information in multimedia fingerprinting and show that the statistical means of the detection statistics can help the fingerprint detector significantly improve the collusion resistance. We then investigate how to probe the side information and model the dynamics between the fingerprint detector and the colluders as a two-stage extensive game with perfect information. We model the colluder-detector behavior dynamics as a two-stage game and find the equilibrium of the colluder-detector game using backward induction and show that the min-max solution is a Nash equilibrium, which gives no incentive for everyone in the multimedia fingerprint social network to deviate. This paper demonstrates that the proposed side information can significantly help improve the system performance to almost the same as the optimal correlation-based detector. Such result opens up a new scope in the research of fingerprinting system that given any fingerprint code, leveraging side information can improve the collusion resistance. Also, we provide the solutions to how to reach optimal collusion strategy and the corresponding detection, thus lead to a better protection of the multimedia content. </para>

Robust MC-CDMA-Based Fingerprinting Against Time-Varying Collusion Attacks

The design of robust fingerprinting systems for traitor tracing against time-varying collusion attacks in protecting continuous media, such as audio and video, is investigated in this research. We first show that it can be formulated as a multiuser detection problem in a wireless communication system with a time-varying channel response. Being inspired by the multicarrier code-division multiaccess technique, we propose a fingerprinting system that consists of three modules: 1) codeword generation with a multicarrier approach, 2) colluder weight estimation (CWE), and 3) advanced message symbol detection. We construct embedding codes with code spreading followed by multicarrier modulation. For CWE, we show that the weight estimation is analogous to channel response estimation, which can be solved by inserting pilot signals in the embedded fingerprint. As to advanced message symbol detection, we replace the traditional correlation-based detector with the maximal ratio combining detector and the parallel interference cancellation multiuser detector. The superior performance of the proposed fingerprinting system in terms of number of users/identified colluders and the bit-error probability of symbol detection is demonstrated by representative audio and video examples.

Spread spectrum watermark detection in DRT-domain

The traditional correlation-based detector is optimal only for Gaussian data, but the Laplacian Probability Density Function (PDF) is more appropriate to model the coefficients in the Discrete Ridgelet Transform (DRT) domain. An additive maximum-likelihood detector based on the Laplacian PDF is analyzed and the theoretical result of its performance is given. The experiments show that the error of the Laplacian model for the DRT coefficients of many images is smaller than that of the Gaussian model. The experiments also prove that the Laplacian detector is superior to the traditional correlation-based detector.

Salamander locomotion-induced head movement and retinal motion sensitivity in a correlation-based motion detector model

We report on a computational model of retinal motion sensitivity based on correlation-based motion detectors. We simulate object motion detection in the presence of retinal slip caused by the salamander's head movements during locomotion. Our study offers new insights into object motion sensitive ganglion cells in the salamander retina. A sigmoidal transformation of the spatially and temporally filtered retinal image substantially improves the sensitivity of the system in detecting a small target moving in place against a static natural background in the presence of comparatively large, fast simulated eye movements, but is detrimental to the direction-selectivity of the motion detector. The sigmoid has insignificant effects on detector performance in simulations of slow, high contrast laboratory stimuli. These results suggest that the sigmoid reduces the system's noise sensitivity.

Efficient Spatial Image Watermarking via New Perceptual Masking and Blind Detection Schemes

The aim of this paper is to improve the performance of spatial domain watermarking. To this end, a new perceptual mask and a new detection scheme are proposed. The proposed spatial perceptual mask is based on the cover image prediction error sequence and matches very well with the properties of the human visual system. It exhibits superior performance compared to existing spatial masking schemes. Moreover, it allows for a significantly increased strength of the watermark while, at the same time, the watermark visibility is decreased. The new blind detection scheme comprises an efficient prewhitening process and a correlation-based detector. The prewhitening process is based on the least-squares prediction error filter and substantially improves the detector's performance. The correlation-based detector that was selected is shown to be the most suitable for the problem at hand. The improved performance of the proposed detection scheme has been justified theoretically for the case of linear filtering plus noise attack and through extensive simulations. The theoretical analysis is independent of the proposed mask and the derived expressions can be used for any watermarking technique based on spatial masking. It is shown though that in most cases the detector performs better if the proposed mask is employed.

BER sensitivity to mistiming in ultra-wideband impulse radios - part II: fading channels

We investigate timing tolerances of ultra-wideband (UWB) impulse radios. We quantify the bit-error rate (BER) sensitivity to epoch timing offset under different operating conditions, including frequency-flat fading channels, dense multipath fading channels, multiple access with time hopping, and various receiver types including sliding correlators and RAKE combiners. For a general correlation-based detector, we derived in Part I unifying expressions for the decision statistics as well as BER formulas under mistiming, given fixed channel realizations. In Part II, we provide a systematic approach to BER analysis under mistiming for fading channels. The BER is expressed in terms of the receiver's energy capture capability, which we quantify under various radio operating conditions. We also develop the optimal demodulator in the presence of timing offset and show a proper design of the correlation-template that is robust to mistiming. Through analyses and simulations, we illustrate that the reception quality of a UWB impulse radio is highly sensitive to both timing acquisition and tracking errors.

Fast Watermarking of MPEG-1/2 Streams Using Compressed-Domain Perceptual Embedding and a Generalized Correlator Detector

A novel technique is proposed for watermarking of MPEG-1 and MPEG-2 compressed video streams. The proposed scheme is applied directly in the domain of MPEG-1 system streams and MPEG-2 program streams (multiplexed streams). Perceptual models are used during the embedding process in order to avoid degradation of the video quality. The watermark is detected without the use of the original video sequence. A modified correlation-based detector is introduced that applies nonlinear preprocessing before correlation. Experimental evaluation demonstrates that the proposed scheme is able to withstand several common attacks. The resulting watermarking system is very fast and therefore suitable for copyright protection of compressed video.