Intrinsically Embedded Signatures for Multimedia Forensics

This dissertation examines the use of signatures that are intrinsically embedded in media recordings for studies and applications in multimedia forensics. These near-invisible signatures are fingerprints that are captured unintentionally in a recording due to influences from the environment in which it was made and the recording device that was used to make it. We focus on two types of such signatures: the Electric Network Frequency (ENF) signal and the flicker signal. The ENF is the frequency of power distribution networks and has a nominal value of 50Hz or 60Hz. The ENF fluctuates around its nominal value due to load changes in the grid. It is particularly relevant to multimedia forensics because ENF variations captured intrinsically in a media recording reflect the time and location related properties of the respective area in which it was made. This has led to a number of applications in information forensics and security, such as time-of-recording authentication/estimation and ENF-based detection of tampering in a recording. The first part of this dissertation considers the extraction and detection of the ENF signal. We discuss our proposed spectrum combining approach for ENF estimation that exploits the presence of ENF traces at several harmonics within the same recording to produce more accurate and robust ENF signal estimates. We also explore possible factors that can promote or hinder the capture of ENF traces in recordings, which is important for a better understanding of the real-world applicability of ENF signals. Next, we discuss novel real-world ENF-based applications proposed through this dissertation research. We discuss using the embedded ENF signal to identify the region-of-recording of a media signal through a pattern analysis and learning framework that distinguishes between ENF signals coming from different power grids. We also discuss the use of the ENF traces embedded in a video to characterize the video camera that had originally produced the video, an application that was inspired by our work on flicker forensics. The last part of the dissertation considers the flicker signal and its use in forensics. We address problems in the entertainment industry pertaining to movie piracy related investigations, where a pirated movie is formed by camcording media content shown on an LCD screen. The flicker signature can be inherently created in such a scenario due to the interplay between the back-light of an LCD screen and the recording mechanism of the video camera. We build an analytic model of the flicker, relating it to inner parameters of the video camera and the screen producing the video. We then demonstrate that solely analyzing such a pirated video can lead to the identification of the video camera and the screen that produced the video, which can be used as corroborating evidence in piracy investigations

Plug-in Channel Estimation with Dithered Quantized Signals in Spatially Non-Stationary Massive MIMO Systems

As the array dimension of massive MIMO systems increases to unprecedented levels, two problems occur. First, the spatial stationarity assumption along the antenna elements is no longer valid. Second, the large array size results in an unacceptably high power consumption if high-resolution analog-to-digital converters are used. To address these two challenges, we consider a Bussgang linear minimum mean square error (BLMMSE)-based channel estimator for large scale massive MIMO systems with one-bit quantizers and a spatially non-stationary channel. Whereas other works usually assume that the channel covariance is known at the base station, we consider a plug-in BLMMSE estimator that uses an estimate of the channel covariance and rigorously analyze the distortion produced by using an estimated, rather than the true, covariance. To cope with the spatial non-stationarity, we introduce dithering into the quantized signals and provide a theoretical error analysis. In addition, we propose an angular domain fitting procedure which is based on solving an instance of non-negative least squares. For the multi-user data transmission phase, we further propose a BLMMSE-based receiver to handle one-bit quantized data signals. Our numerical results show that the performance of the proposed BLMMSE channel estimator is very close to the oracle-aided scheme with ideal knowledge of the channel covariance matrix. The BLMMSE receiver outperforms the conventional maximum-ratio-combining and zero-forcing receivers in terms of the resulting ergodic sum rate.Comment: submitted to IEEE Transactions on Communication

Development and application of synchronized wide-area power grid measurement

Phasor measurement units (PMUs) provide an innovative technology for real-time monitoring of the operational state of entire power systems and significantly improve power grid dynamic observability. This dissertation focuses on development and application of synchronized power grid measurements. The contributions of this dissertation are as followed:First, a novel method for successive approximation register analog to digital converter control in PMUs is developed to compensate for the sampling time error caused by the division remainder between the desirable sampling rate and the oscillator frequency. A variable sampling interval control method is presented by interlacing two integers under a proposed criterion. The frequency of the onboard oscillator is monitored in using the PPS from GPS.Second, the prevalence of GPS signal loss (GSL) on PMUs is first investigated using real PMU data. The correlation between GSL and time, spatial location, solar activity are explored via comprehensive statistical analysis. Furthermore, the impact of GSL on phasor measurement accuracy has been studied via experiments. Several potential solutions to mitigate the impact of GSL on PMUs are discussed and compared.Third, PMU integrated the novel sensors are presented. First, two innovative designs for non-contact PMUs presented. Compared with conventional synchrophasors, non-contact PMUs are more flexible and have lower costs. Moreover, to address nonlinear issues in conventional CT and PT, an optical sensor is used for signal acquisition in PMU. This is the first time the utilization of an optical sensor in PMUs has ever been reported.Fourth, the development of power grid phasor measurement function on an Android based mobile device is developed. The proposed device has the advantages of flexibility, easy installation, lower cost, data visualization and built-in communication channels, compared with conventional PMUs.Fifth, an identification method combining a wavelet-based signature extraction and artificial neural network based machine learning, is presented to identify the location of unsourced measurements. Experiments at multiple geographic scales are performed to validate the effectiveness of the proposed method using ambient frequency measurements. Identification accuracy is presented and the factors that affect identification performance are discussed

Improved Sensing Accuracy using Enhanced Energy Detection Algorithm with Secondary User Cooperation in Cognitive Radios

Spectrum sensing is indispensable for cognitive radio to identify the available white spaces. Energy detection is considered as a preferred technique for spectrum sensing in cognitive radio networks. It is because of its simplicity, applicability and low computational complexity, energy detection is employed widely for spectrum sensing. This paper proposes an enhanced energy detection based spectrum sensing algorithm which incorporates the features of traditional energy detection and cooperative detection. The false alarm and detection probabilities of the proposed algorithm are derived theoretically under AWGN channel conditions. The performance of the proposed algorithm is evaluated analytically for various decision thresholds. The performance evaluations indicate that the proposed enhanced energy detection algorithm outshines the traditional energy detection algorithm and greatly improves the spectrum sensing accuracy under varying SNR conditions