Purnendu Sinha

A Diagnostic Tree Approach for Fault Cause Identification in the Attitude Control Subsystem of Satellites

Space and Earth observation programs demand stringent guarantees ensuring smooth and reliable operations of space vehicles and satellites. Due to unforeseen circumstances and naturally occurring faults, it is desired that a fault-diagnosis system be capable of detecting, isolating, identifying, or classifying faults in the system. Unfortunately, none of the existing fault-diagnosis methodologies alone can meet all the requirements of an ideal fault- diagnosis system due to the variety of fault types, their severity, and handling mechanisms. However, it is possible to overcome these shortcomings through the integration of different existing fault-diagnosis methodologies. In this paper, a novel learning-based, diagnostic-tree approach is proposed which complements and strengthens existing efficient fault detection mechanisms with an additional ability to classify different types of faults to effectively determine potential fault causes in a subsystem of a satellite. This extra capability serves as a semiautomatic diagnostic decision support aid to expert human operators at ground stations and enables them to determine fault causes and to take quick and efficient recovery/reconfiguration actions. The developed diagnosis/analysis procedure exploits a qualitative technique denoted as diagnostic tree (DX-tree) analysis as a diagnostic tool for fault cause analysis in the attitude control subsystem (ACS) of a satellite. DX-trees constructed by our proposed machine-learning-based automatic tree synthesis algorithm are demonstrated to be able to determine both known and unforeseen combinations of events leading to different fault scenarios generated through synthetic attitude control subsystem data of a satellite. Though the immediate application of our proposed approach would be at ground stations, the proposed technique has potential for being integrated with causal model-based diagnosis and recovery techniques for future autonomous space vehicle missions.

On the use of formal techniques for validation

The traditional use of formal methods has been for the verification of algorithms or protocols. Given the high cost and limitations in state space coverage provided by conventional validation techniques, we introduce a novel approach to utilize formal verification procedures to drive fault injection based validation of dependable protocols. The paper develops graph structures for representation of information generated through formal processes, as well as a formal framework that facilitates the formulation of specific fault injection experiments for validation.

A novel fault-tree approach for identifying potential causes of satellite reaction wheel failure

Due to unforeseen circumstances and naturally occurring faults, it is desired that an on-board fault-diagnosis system of a space vehicle be capable of detecting, isolating, identifying or classifying faults in the system. In this paper, a novel approach is proposed which strengthens existing efficient fault-detection mechanisms with an additional ability to classify different types of faults to effectively determine potential failure causes in a subsystem. This extra capability ensures a quick and efficient recovery/reconfiguration from disruptions. Our developed diagnosis/analysis procedure exploits a widely used qualitative technique called fault-tree analysis, as a diagnostic aid, for failure analysis in the attitude control subsystem (ACS) of a spacecraft. Constructed fault-trees have been able to represent combinations of events leading to different failures resulting due to artificially injected faults in a MATLAB-Simulink model of the ACS. It is important to emphasize that proposed technique has potentials for being integrated in an on-board health monitoring and diagnosis tool for space vehicles

Modular composition of redundancy management protocols in distributed systems: an outlook on simplifying protocol level formal specification and verification

In recent years, formal methods (FMs) have been extensively used for the verification and validation (V&V) of dependable distributed protocols. In our studies utilizing FMs for V&V, we have observed that a number of protocols providing for distributed and dependable services can often be formulated using a small set of basic functional primitives or their variations. Thus, from the formal viewpoint, the objective of this paper is to introduce techniques, utilizing concepts of category theory, that could effectively identify and reuse basic formal modules in order to simplify formal specification and verification for a spectrum of protocols.

On simplifying modular specification and verification of distributed protocols

Computer systems supporting high assurance and high consequences applications typically utilize dependable distributed protocols to manage system resources and to provide sustained delivery of services in the presence of failures. The inherent complexity entailed in the design and analysis of such protocols, is increasingly necessitating the use of formal techniques in establishing the correctness of the protocol level operations. Exploiting modular design aspects appearing in most dependable distributed protocols, we have introduced techniques utilizing concepts of category theory for constructing formal library routines of a set of constituent functional primitives, and their use in establishing the correctness of the protocol operation. In this paper, we develop on our proposed category-theory-based approach for modular composition through formulating (a) a group membership protocol which can also form the next hierarchical building blocks for other dependable protocol operations, and (b) a checkpointing protocol utilizing the group membership function as one of its building block. Subtleties in building-block interactions and their influence on the overall correctness of the composite protocols are also highlighted.

On improving performance of Network Intrusion Detection Systems by efficient packet capturing

In a PC based network intrusion detection system (NIDS), the packet capturing component is a key bottleneck which reduces its effectiveness. NIDS deployment on multiprocessor or distributed systems that circumvents this bottleneck do not address operating system performance limitations which are the causal factors behind this bottleneck. Completion of intrusion detection task in bounded time at the sensors is also important to detect complex and co-ordinated attack patterns. Existing Linux based packet capturing solutions, NAPI and PFRING, are inefficient and have poor real-time performance. We have implemented a user space network interface (DMA ring) to capture packets under high network load on a modest commodity platform. DMA ring outperforms existing solutions in terms of higher load bearing, packet capturing capacity and superior real-time behavior. We proposed a scheme using DMA ring, which improves the performance of a user space NIDS

On the run-time verification of autonomy software

The mission-critical and dependability aspects of autonomous systems demand formal level of assurance in ascertaining their mission-survivability capabilities. The complete understanding of system autonomy and its verification and validation (V&V) continue to pose technical challenges. In recent years, formal methods have shown considerable promise in the area of V&V of autonomous systems. In this paper, we further explore the applicability of model checking techniques in run-time verification of autonomy software such as automated planning and scheduling algorithms. We illustrate our proposed approach for runtime verification through a case study of FireSat satellite. We also discuss our experiences and ongoing research activities in this direction.

Survey of motion estimation techniques for video compression

The introduction of new, more powerful personal computers and workstations has ushered in a new era of computing. New machines are now capable of supporting full-motion video. The problem of video compression is a difficult and important one, and has inspired a great deal of research and development activity. A number of video compression techniques and standards have been introduced in the past few years, particularly MPEG for interactive multimedia and for digital NTSC and HDTV applications, and H.261/H.263 for video telecommunications. These techniques use motion estimation techniques to reduce the amount of data that is stored and transmitted for each frame of video. This paper is about these motion estimation techniques, their implementations, their complexity, advantages, and drawbacks. An overview of the MPEG video compression standard is first presented with an emphasis on how it utilizes motion compensation to achieve its high compression gains. Then a survey of current motion estimation techniques is presented, including the exhaustive search and a number of fast block-based search algorithms.

Formal verification of dependable distributed protocols

Abstract Dependable distributed systems often employ a hierarchy of protocols to provide timely and reliable services. Such protocols have both dependability and real-time attributes, and the verification of such composite services is a problem of growing complexity even when using formal approaches. Our intention in this paper is to exploit the modular design aspects appearing in most dependable distributed protocols to provide formal level of assurance for their correctness. We highlight the capability of our approach through a case study in formal modular specification and tool-assisted verification of a timestamp-based checkpointing protocol. Furthermore, during the process of verification, insights gained in such a stack of protocols have assisted in validating some additional properties those dealing with failure recovery.

FPGA implementation of fuzzy morphological filters

In this paper, we consider a natural paradigm for lifting of crisp-set binary filters to fuzzy filters for hardware implementation and process the gray-scale realizations of binary images as [0,1]-valued fuzzy binary images. We present the implementation of the filtering algorithms for smoothing, peak detection and edge detection of such fuzzy images using the Xilinx Virtex series of FPGA for real-time processing of image sequences. The erosion filter forms the core for all of the filtering algorithms and the dilation filter itself is implemented as a function of the erosion filter. Smoothing is achieved using fuzzy opening of the input image using the user defined fuzzy structuring element. A fuzzy top-hat transform is used for peak detection. As opposed to gray-scale top-hat, which detects only the narrow peaks, the fuzzy top-hat is shown to detect both the narrow as well as wide peaks within the same image. Edge detection algorithm uses the fuzzy morphological gradient wherein the set minus operation has been performed between the dilated and the eroded images. Pipelined architectures are used for the erosion filter design and the use of flops has been maximized to achieve a high clock rate. The throughput measurements and the results generated by the implemented filters are also presented.