Sathish Gopalakrishnan

Cyber-Physical Systems: A New Frontier

The report of the Presidents Council of Advisors on Science and Technology (PCAST) has placed CPS on the top of the priority list for federal research investment [6]. This article first reviews some of the challenges and promises of CPS, followed by an articulation of some specific challenges and promises that are more closely related to the sensor networks, ubiquitous and trustworthy computing conference.

Template-based real-time dwell scheduling with energy constraint

This paper addresses the scheduling problem of radar dwells in multi-function phase array radars. Well-known and new challenges make it difficult to provide predictable performance for real-time dwell scheduling. We developed the template-based scheduling algorithm to guarantee the performance requirement with low on-line overhead. Simulation results show that the template-based scheduling approach increases utilization and provides predictable performance.

Optimal Sampling Rate Assignment with Dynamic Route Selection for Real-Time Wireless Sensor Networks

The allocation of computation and communication resources in a manner that optimizes aggregate system performance is a crucial aspect of system management. Wireless sensor network poses new challenges due to the resource constraints and real-time requirements. Existing work has dealt with the real-time sampling rate assignment problem, under single processor case and network case with static routing environment. For wireless sensor networks, in order to achieve better overall network performance, routing should be considered together with the rate assignments of individual flows. In this paper, we address the problem of optimizing sampling rates with dynamic route selection for wireless sensor networks. We model the problem as a constrained optimization problem and solve it under the network utility maximization framework. Based on the primal-dual method and dual decomposition technique, we design a distributed algorithm that achieves the optimal global network utility considering both dynamic route decision and rate assignment. Extensive simulations have been conducted to demonstrate the efficiency and efficacy of our proposed solutions.

Scheduling real-time dwells using tasks with synthetic periods

This paper addresses the problem of scheduling real-time dwells in multi-function phase array radar systems. To keep track of targets, a radar system must meet its timing and energy constraints. We propose a new task model for radar dwells to accurately characterize their timing parameters. We develop an algorithm of transforming every dwell task as a semi-period task so the dwell task can meet its timing constraint and the interarrival times of the task will not be a constant. We also develop an enhanced template-based scheduling algorithm to schedule such tasks to meet the timing and energy constraints. Simulation results show that this algorithm can significantly improve the resource utilization.

Fuzzy Algorithms for Maximum Lifetime Routing in Wireless Sensor Networks

We address the maximum lifetime routing problem in wireless sensor networks (WSNs) and propose two online routing algorithms based on fuzzy logic, namely fuzzy maximum lifetime algorithm and fuzzy multiobjective algorithm. The former attempts to maximize the WSN lifetime objective, whereas the latter strives to simultaneously optimize the lifetime as well as the energy consumption objectives. The distinguishing aspect of this work is the novel use of fuzzy membership functions and rules in the design of cost functions for the routing objectives considered in this work. A range of simulation results obtained under various network scenarios show that the proposed approach is superior to a number of other well-known online routing heuristics, both in terms of the obtained network lifetime as well as the average energy consumption.

Task Partitioning with Replication upon Heterogeneous Multiprocessor Systems

The heterogeneous multiprocessor task partitioning with replication problem involves determining a mapping of recurring tasks upon a set consisting of different processing units in such a way that all tasks meet their timing constraints and no two replicas of the same task are assigned to the same processing unit. The replication requirement improves the resilience of the real-time system to a finite number of processor failures. This problem is NP-hard in the strong sense. We develop a Fully Polynomial-Time Approximation Scheme (FPTAS) for this problem.

A Switch Design for Real-Time Industrial Networks

The convergence of computers and the physical world is the theme for next generation networking research. This trend calls for real-time network infrastructure, which requires a high-speed real-time WAN to serve as its backbone. However, commercially available high-speed WAN switches (routers) are designed for best-effort Internet traffic. A real-time switch design for the aforementioned networks is missing. We propose a real-time switch design using a crossbar switching fabric. The proposed switch can be implemented by making minimal modification, or even simplification, to the widely implemented iSLIP crossbar switch scheduler. Our real-time switch serves periodic and aperiodic traffic with real-time virtual machine tasks, which simplifies analysis, provides isolation, and facilitates future hierarchical scheduling and flow aggregation. Taking advantage of the fact that most industrial real-time network flows rarely change, our switch is better adapted to providing high bandwidths and low latencies.

ORTEGA: An Efficient and Flexible Software Fault Tolerance Architecture for Real-Time Control Systems

Fault tolerance is an important aspect in real-time computing. In real-time control systems, tasks could be faulty due to various reasons. Faulty tasks may compromise the performance and safety of the whole system and even cause disastrous consequences. In this paper, we describe ORTEGA (On-demand Real-TimE GuArd), a new software fault tolerance architecture for real-time control systems. ORTEGA has high fault coverage and reliability. Compared with existing real-time fault tolerance architectures, such as Simplex, ORTEGA allows more efficient resource utilizations and enhances flexibility. These advantages are achieved through the on-demand detection and recovery of faulty tasks. ORTEGA is applicable to most industrial control applications where both efficient resource usage and high fault coverage are desired.

Switch Scheduling and Network Design for Real-Time Systems

The rapid need for high bandwidth and low latency communication in distributed real-time systems is driving system architects towards high-speed switches developed for high volume data transfer on the Internet. These switches employ complex scheduling algorithms for transferring data cells from the input line to the output line. From a real-time systems perspective, it is necessary to understand the behavior of these switching algorithms and obtain worst-case delay bounds for message transfer across these switches. Many researchers have derived average-case delay bounds for switching algorithms but mission-critical systems require guarantees for the worst-case. In this context, we derive upper bounds on cell delays across commonly available switches. Our bounds provide a starting point for research in this direction. Moreover, we use the delay bounds to construct low-cost networks of switches given a set of processors and their real-time communication requirements. Experiments with the heuristic algorithm that we propose for network design have produced encouraging results. Importantly, the algorithm is independent of the delay analysis technique and better techniques can be incorporated trivially. By addressing the network design problem, we hope to transform the system architecting process from a manual, ad-hoc operation to a simple and automated step that will result in better designs and cost savings.

An Online Multipath Routing Algorithm for Maximizing Lifetime in Wireless Sensor Networks

We address the maximum lifetime routing problem in wireless sensor networks, and present an online multipath routing algorithm. The proposed algorithm strives to maximize the network lifetime metric by distributing the source-to-sink traffic for a given routing request along a set of paths. Fuzzy membership function is used for designing the edge weight function. Simulation results obtained under a variety of network scenarios show that the proposed multipath scheme is able to achieve better lifetime results than those obtained by its predecessor single-path fuzzy routing scheme as well as by another well-known online routing scheme, namely the Online Maximum Lifetime heuristic.