Networked Supervisor Synthesis Against Lossy Channels with Bounded Network Delays as Non-Networked Synthesis

In this work, we study the problem of supervisory control of networked discrete event systems. We consider lossy communication channels with bounded network delays, for both the control channel and the observation channel. By a model transformation, we transform the networked supervisor synthesis problem into the classical (non-networked) supervisor synthesis problem (for non-deterministic plants), such that the existing supervisor synthesis tools can be used for synthesizing networked supervisors. In particular, we can use the (state-based) normality property for the synthesis of the supremal networked supervisors, whose existence is guaranteed by construction due to our consideration of command non-deterministic supervisors. The effectiveness of our approach is illustrated on a mini-guideway example that is adapted from the literature, for which the supremal networked supervisor has been synthesized in the synthesis tools SuSyNA and TCT.Comment: This paper is under review for Automatic

Simplified Multiuser Detection for SCMA with Sum-Product Algorithm

Sparse code multiple access (SCMA) is a novel non-orthogonal multiple access technique, which fully exploits the shaping gain of multi-dimensional codewords. However, the lack of simplified multiuser detection algorithm prevents further implementation due to the inherently high computation complexity. In this paper, general SCMA detector algorithms based on Sum-product algorithm are elaborated. Then two improved algorithms are proposed, which simplify the detection structure and curtail exponent operations quantitatively in logarithm domain. Furthermore, to analyze these detection algorithms fairly, we derive theoretical expression of the average mutual information (AMI) of SCMA (SCMA-AMI), and employ a statistical method to calculate SCMA-AMI based specific detection algorithm. Simulation results show that the performance is almost as well as the based message passing algorithm in terms of both BER and AMI while the complexity is significantly decreased, compared to the traditional Max-Log approximation method

Covert channels in the HTTP network protocol: Channel characterization and detecting man-in-the-middle attacks

Network covert channels provide two entities the ability to communicate stealthily. Hypertext Transfer Protocol (HTTP), which accounts for approximately half of all traffic on the Internet (Burke, 2007), has become the fertile ground for various network covert channels. Proliferation of network covert channels throughout the World Wide Web and other areas of cyberspace has raised new security concerns and brought both challenges and enhancements to the area of Information Warfare. Covert channels impact our ability to observe and orient in this domain and need to be better understood. They are however, extremely difficult to study as a whole. Network covert channels tend to be protocol, implementation, and/or application specific. Similar to biology or botany, where we classify plants and animals, the first step of research is to define a classification scheme. In the paper, it is intended to define a set of common characteristics, classify and analyze several known covert channels in HTTP with respect to these characteristics. New HTTP based covert channels are discussed and their characteristics presented as well. Although many applications of covert channels are malicious in nature, this paper argues that there are beneficial applications of network covert channels, such as detecting Man-in-the-Middle attacks

Advanced space system concepts and their orbital support needs (1980 - 2000). Volume 3: Detailed data. Part 1: Catalog of initiatives, functional options, and future environments and goals

The following areas were discussed in relation to a study of the commonality of space vehicle applications to future national needs: (1) index of initiatives (civilian observation, communication, support), brief illustrated description of each initiative, time periods (from 1980 to 2000+) for implementation of these initiatives; (2) data bank of functional system options, presented in the form of data sheets, one for each of the major functions, with the system option for near-term, midterm, and far-term space projects applicable to each subcategory of functions to be fulfilled; (3) table relating initiatives and desired goals (public service and humanistic, materialistic, scientific and intellectual); and (4) data on size, weight and cost estimations

Application of automatic vehicle location in law enforcement: An introductory planning guide

A set of planning guidelines for the application of automatic vehicle location (AVL) to law enforcement is presented. Some essential characteristics and applications of AVL are outlined; systems in the operational or planning phases are discussed. Requirements analysis, system concept design, implementation planning, and performance and cost modeling are described and demonstrated with numerous examples. A detailed description of a typical law enforcement AVL system, and a list of vendor sources are given in appendixes

A NOVEL APPROACH FOR COVERT COMMUNICATION OVER TCP VIA INDUCED CLOCK SKEW

The goal of this thesis is to determine the feasibility and provide a proof of concept for a covert communications channel based on induced clock skew. Transmission Control Protocol (TCP) timestamps provide a means for measuring clock skew between two hosts. By intentionally altering timestamps, a host can induce artificial clock skew as measured by the receiver, thereby providing a means to covertly communicate. A novel scheme for transforming symbols into skew values is developed in this work, along with methods for extraction at the receiver. We tested the proposed scheme in a laboratory network consisting of Dell laptops running Ubuntu 16.04. The results demonstrated a successful implementation of the proposed covert channel with achieved bit rates as high as 33 bits per second under ideal conditions. Forward error correction was also successfully employed in the form of a Reed–Solomon code to mitigate the effects of variation in delay over the Internet.Lieutenant, United States NavyApproved for public release; distribution is unlimited

Characterization of Ultra Wideband Multiple Access Performance Using Time Hopped-Biorthogonal Pulse Position Modulation

The FCC\u27s release of its UWB First Report and Order in April 2002 spawned renewed interest in impulse signaling research. This work combines Time Hopped (TH) multiple access coding with 4-ary UWB Biorthogonal Pulse Position Modulation (TH-BPPM). Multiple access performance is evaluated in a multipath environment for both synchronous and asynchronous networks. Fast time hopping is implemented by replicating and hopping each TH-BPPM symbol NH times. Bit error expressions are derived for biorthogonal TH-BPPM signaling and results compared with previous orthogonal TH-PPM work. Without fast time hopping (NH = 1), the biorthogonal TH-BPPM technique provided gains equivalent to Gray-coded QPSK; improved BER at a given Eb/No and an effective doubling of the data rate. A synchronized network containing up to NT = 15 transmitters yields an average BER improvement (relative to an asynchronous network) of approximately -6.30 dB with orthogonal TH-PPM and approximately 5.9 dB with biorthogonal TH-BPPM. Simulation results indicate that doubling the number of multipath replications (NMP) reduces BER by approximately 3.6 dB. Network performance degrades as NT and NMP increase and synchronized network advantages apparent in the NMP = 0 case diminish with multipath interference present. With fast time hopping (NH \u3e 1) improves BER performance whenever NMP \u3c NH while reducing effective data rate by 1/NH. Compared to the NH = 1 synchronized network, TH-BPPM modulation using NH = 10 provides approximately 5.9 dB improvement at NMP = 0 and approximately 3.6 dB improvement at NMP = 5. At NMP = 10, the BER for the hopped and NH = 1 cases are not statistically different; with NH = 10 hops, BER improvement varies from approximately 0.57 to 0.14 dB (minimal variation between synchronous and asynchronous network performance)

Secure Control of Cyber-Physical Systems

Cyber-Physical Systems (CPS) are smart co-engineered interacting networks of physical and computational components. They refer to a large class of technologies and infrastructure in almost all life aspects including, for example, smart grids, autonomous vehicles, Internet of Things (IoT), advanced medical devices, and water supply systems. The development of CPS aims to improve the capabilities of traditional engineering systems by introducing advanced computational capacity and communications among system entities. On the other hand, the adoption of such technologies introduces a threat and exposes the system to cyber-attacks. Given the unique properties of CPSs, i.e. physically interacting with its environment, malicious parties might be interested in exploiting the physical properties of the system in the form of a cyber-physical attack. In a large class of CPSs, the physical systems are controlled using a feedback control loop. In this thesis, we investigate, from many angles, how CPSs' control systems can be prone to cyber-physical attacks and how to defend them against such attacks using arguments drawn from control theory. In our first contribution, by considering Smart Grid applications, we address the problem of designing a Denial of Service (DoS)-resilient controller for recovering the system's transient stability robustly. We propose a Model Predictive Control (MPC) controller based on the set-theoretic (ST) arguments, which is capable of dealing with both model uncertainties, actuator limitations, and DoS. Unlike traditional MPC solutions, the proposed controller has the capability of moving most of the required computations into an offline phase. The online phase requires the solution of a quadratic programming problem, which can be efficiently solved in real-time. Then, stemming from the same ST based MPC controller idea, we propose a novel physical watermarking technique for the active detection of replay attacks in CPSs. The proposed strategy exploits the ST-MPC paradigm to design control inputs that, whenever needed, can be safely and continuously applied to the system for an apriori known number of steps. Such a control scheme enables the design of a physical watermarked control signal. We prove that, in the attack-free case, the generators' transient stability is achieved for all admissible watermarking signals and that the closed-loop system enjoys uniformly ultimately bounded stability. In our second contribution, we address the attacker's ability to collect useful information about the control system in the reconnaissance phase of a cyber-physical attack. By using existing system identification tools, an attacker who has access to the control loop can identify the dynamics of the underlying control system. We develop a decoy-based moving target defense mechanism by leveraging an auxiliary set of virtual state-based decoy systems. Simulation results show that the provided solution degrades the attacker's ability to identify the underlying state-space model of the considered system from the intercepted control inputs and sensor measurements. It also does not impose any penalty on the control performance of the underlying system. Finally, in our third contribution, we introduce a covert channel technique, enabling a compromised networked controller to leak information to an eavesdropper who has access to the measurement channel. We show that this can be achieved without establishing any additional explicit communication channels by properly altering the control logic and exploiting robust reachability arguments. A dual-mode receding horizon MPC strategy is used as an illustrative example to show how such an undetectable covert channel can be established