Shivakumar Sastry

IEEE 1588 style synchronization over wireless link

We present a technique for synchronizing clocks over a wireless link between a pair of resource constrained nodes. A Kalman filter is used as a pre-processor to a PI controller to mitigate the effects of packet-losses and attenuate noise spikes. This Kalman filter directly tracks the skew, which is the rate of change of offset, between a pair of nodes. The PI controller accepts this skew as input and disciplines the clock on the follower node. Experimental results demonstrate the performance of this technique over a single hop. In the future, this technique can be extended to multihop systems and improve determinism in networked embedded systems.

A cloud middleware for assuring performance and high availability of soft real-time applications

Applications are increasingly being deployed in the cloud due to benefits stemming from economy of scale, scalability, flexibility and utility-based pricing model. Although most cloud-based applications have hitherto been enterprise-style, there is an emerging need for hosting real-time streaming applications in the cloud that demand both high availability and low latency. Contemporary cloud computing research has seldom focused on solutions that provide both high availability and real-time assurance to these applications in a way that also optimizes resource consumption in data centers, which is a key consideration for cloud providers. This paper makes three contributions to address this dual challenge. First, it describes an architecture for a fault-tolerant framework that can be used to automatically deploy replicas of virtual machines in data centers in a way that optimizes resources while assuring availability and responsiveness. Second, it describes the design of a pluggable framework within the fault-tolerant architecture that enables plugging in different placement algorithms for VM replica deployment. Third, it illustrates the design of a framework for real-time dissemination of resource utilization information using a real-time publish/subscribe framework, which is required by the replica selection and placement framework. Experimental results using a case study that involves a specific replica placement algorithm are presented to evaluate the effectiveness of our architecture.

Multipath Dissemination in Regular Mesh Topologies

Mesh topologies are important for large-scale peer-to-peer systems that use low-power transceivers. The quality of service (QoS) in such systems is known to decrease as the scale increases. We present a scalable approach for dissemination that exploits all the shortest paths between a pair of nodes and improves the QoS. Despite the presence of multiple shortest paths in a system, we show that these paths cannot be exploited by spreading the messages over the paths in a simple round-robin manner; nodes along one of these paths will always handle more messages than the nodes along the other paths. We characterize the set of shortest paths between a pair of nodes in regular mesh topologies and derive rules, using this characterization, to effectively spread the messages over all the available paths. These rules ensure that all the nodes that are at the same distance from the source handle roughly the same number of messages. By modeling the multihop propagation in the mesh topology as a multistage queuing network, we present simulation results from a variety of scenarios that include link failures and propagation irregularities to reflect real-world characteristics. Our method achieves improved QoS in all these scenarios.

A Taxonomy of Distributed Real-time Control Systems

Abstract The demands placed on industrial automation systems have grown in many dimensions over the last two decades. Examples of such demands are increased size, functionality, speed, flexibility, simpler programming, quality, and decreased installation and commissioning costs. An emerging approach to meeting such demands is the use of Distributed Real-time Control System (DRCS) architectures and technologies. This chapter discusses key issues that are driving this trend in modern industrial automation systems and provides a framework for discussion and technological research.

Real-Time Sensor-Actuator Networks

Emerging technologies offer new paradigms for computation, control, collaboration, and communication. To realize the full potential of these technologies in industry, defense, and homeland security applications, it is necessary to exploit the real-time distributed computing capabilities of sensor-actuator networks. To reliably design and develop such networks, it is necessary to develop deeper insight into the underlying model for real-time computation and the infrastructure at the node level that supports this model. In this paper, we discuss a new node-level operating system and mechanisms necessary to deploy reliable applications. The overriding issue that guides the design of this operating system is quality of service metric called predictability. A sensor-actuator network is a distributed platform for integrated computation and control in real-time environments. The nodes in such a network are distinguished by being resource constrained. The power of the network arises from the interactions between simple nodes. Such a network extends the popular distributed sensor networks in several dimensions. After identifying a real-time model, we develop a notion of predictability for a sensor-actuator network. We discuss how the node-level operating system is designed in the resource-constrained environment. An efficient multithreading mechanism and scheduling strategy are required to ensure that local tasks are executed within jitter bounds and that end-to-end delays do not violate application constraints. Mechanisms to support communication, monitoring, safety, fault tolerance, programming, diagnosability, reconfiguration, composability, interoperability, and security are discussed.

Model-Driven Performance Analysis of Reconfigurable Conveyor Systems Used in Material Handling Applications

Reconfigurable conveyors are increasingly being adopted in multiple industrial sectors for their immense flexibility in adapting to new products and product lines. Before modifying the layout of the conveyor system for the new product line, however, engineers and layout planners must be able to answer many questions about the system, such as maximum sustainable rate of flow of goods, prioritization among goods, and tolerances of failures. Any analysis capability that provides answers to these questions must account for both the physical and cyber artifacts of the reconfigurable system all at once. Moreover, the same system should enable the stakeholders to seamlessly change the layouts and be able to analyze the pros and cons of the layouts. This paper addresses these challenges by presenting a model-driven analysis tool that provides three important capabilities. First, a domain-specific modeling language provides the stakeholders with intuitive artifacts to model conveyor layouts. Second, an analysis engine embedded within the model-driven tool provides an accurate simulation of the modeled conveyor system accounting for both the physical and cyber issues. Third, generative capabilities within the tool help to automate the analysis process. The merits of our model-driven analysis tool are evaluated in the context of an example conveyor topology.

Failure detectors for wireless sensor-actuator systems

Wireless sensor-actuator systems (WSAS) offer exciting opportunities for emerging applications by facilitating fine-grained monitoring and control, and dense instrumentation. The large scale of such systems increases the need for such systems to tolerate and cope with failures, in a localized and decentralized manner. We present abstractions for detecting node failures and link failures caused by topology changes in a WSAS. These abstractions were designed and implemented as a set of reusable components in nesC under TinyOS. Results, which demonstrate the performance and viability of the abstractions, based on experiments on an 80 node testbed are presented. In the future, these abstractions can be extended to detect and cope with larger classes of failures in WSAS.

Networked embedded automation

Purpose – The aim of this research is to investigate whether a collection of tiny, resource constrained, microcontrollers that communicate with each other over wireless links can perform rigorous automation tasks.Design/methodology/approach – We identify three building blocks that are necessary to obtain large conveyor systems. The operation of each building block is regulated by a local microcontroller and the microcontrollers interact via wireless links to coordinate the operations across blocks. We define the actions necessary in each block and discuss two example applications for this method.Findings – It is necessary to fundamentally revisit how automation applications are engineered to get the benefits of new technologies. We show that the three blocks that we call segment, turnaround and crossover are sufficient to obtain a large variety of conveyor systems. By embedding the blocks in a grid, we can simplify the design of the conveyor systems.Research limitations/implications – Extensions of this r...

Spatial Sensing and Cognitive Radio Communication in the Presence of a

We study the feasibility of cognitive radio (CR) communication in the presence of a K-user multi-input multi-output (MIMO) interference channel as the primary network. Assuming that the primary interference network has unused spatial degrees of freedom (DoFs) , we first investigate the sufficient condition on the number of antennas at the secondary transmitter under which the secondary system can communicate while causing no interference to the primary receivers. We show that, to maximize the benefit, the secondary transmitter should have at least the same number of antennas as the spatial DoFs of the primary system. We then derive the secondary precoding and decoding matrices to have zero interference leakage into the primary network while the signal-to-interference plus noise ratio (SINR) at the secondary receiver is maximized. As the success of the secondary communication depends on the availability of unused DoFs, we then propose a fast sensing method based on the eigenvalue analysis of the received signal covariance matrix to determine the availability of unused DoFs or equivalently spatial holes. Since the proposed fast sensing method cannot identify the indices of inactive primary streams, we also provide a fine sensing method based on the generalized likelihood ratio test (GLRT) to decide the absence of individual primary streams. Simulation results show that the proposed CR sensing and transmission scheme can, in practice, provide a significant throughput while causing no interference to the primary receivers, and that the sensing detects the spatial holes of the primary network with high detection probability.

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This paper studies a wire-tap channel in which a source node wants to communicate securely to a destination node in the presence of an eavesdropper and under the aid of an amplify-and-forward (AF) relay operating in full-duplex (FD) mode. The residual self-interference due to FD transmission is explicitly taken into account. The secrecy capacity and the respective optimal power allocation schemes for this system are examined under both individual and joint power constraints. At first, the related optimization problems are shown to be quasi-concave. As such, the globally optimal solution exists and is unique. Due to the non-linearity of the derivative, we apply a simple bisection method for root finding and obtain a simple expression for the optimal power allocation scheme. To further provide some insight on the solutions, we apply the method of dominant balance to analyze the capacity and power allocations in different high power regions. It is then demonstrated that full relay power is only needed when the power at the relay is sufficiently small compared to the power at the source. Comparisons with half-duplex (HD) relaying also revealed that FD can achieve a significantly higher secrecy capacity. Finally, numerical results are presented to confirm the optimality of the solutions.