Recent years have seen the emergence of wireless sensor network systems that must support high data rate and realtime queries of physical environments. This paper proposes Real-Time Query Scheduling (RTQS), a novel approach to conflict-free transmission scheduling for real-time queries in wireless sensor networks. First, we show that there is an inherent trade-off between prioritization and throughput in conflict-free query scheduling. We then present three new real-time scheduling algorithms. The non-preemptive query scheduling algorithm achieves high throughput while introducing priority inversions. The preemptive query scheduling algorithm eliminates priority inversion at the cost of reduced throughput. The slack stealing query scheduling algorithm combines the benefits of preemptive and non- preemptive scheduling by improving the throughput while meeting query deadlines. Furthermore, we provide schedulability analysis for each scheduling algorithm. The analysis and advantages of our scheduling algorithms are validated through NS2 simulations.

/pdf/real-time-query-scheduling-for-wireless-sensor-networks-3bwtnbftk3.pdf

Real-Time Query Scheduling for Wireless Sensor Networks

Real-time systems comprise computers that must generate correct results in a timely manner. This involves a wide spectrum of computing systems found in our everyday life ranging from computers in rockets to our mobile phones. The criticality of producing timely results defines the different types of realtime systems. On one hand, we have the so-called hard real-time systems, where failing to meet deadlines may result in a catastrophe. In this thesis we are, however, concerned with firm and soft real-time systems, where missing deadlines is acceptable at the expense of degraded system performance. The usage of firm and soft real-time systems has increased rapidly during the last years, mainly due to the advent of applications in multimedia, telecommunication, and e-commerce. These systems are typically data-intensive, with the data normally spanning from low-level control data, typically acquired from sensors, to high-level management and business data. In contrast to hard real-time systems, the environments in which firm and soft real-time systems operate in are typically open and highly unpredictable. For example, the workload applied on a web server or base station in telecommunication systems varies according to the needs of the users, which is hard to foresee. In this thesis we are concerned with quality of service (QoS) management of data services for firm and soft real-time systems. The approaches and solutions presented aim at providing a general understanding of how the QoS can be guaranteed according to a given specification, even if the workload varies unpredictably. The QoS specification determines the desired QoS during normal system operation, and the worst-case system performance and convergence rate toward the desired setting in the face of transient overloads. Feedback control theory is used to control QoS since little is known about the workload applied on the system. Using feedback control the difference between the measured QoS and the desired QoS is formed and fed into a controller, which computes a change to the operation of the real-time system. Experimental evaluation shows that using feedback control is highly effective in managing QoS such that a given QoS specification is satisfied. This is a key step toward automatic management of intricate systems providing real-time data services.

http://liu.diva-portal.org/smash/get/diva2:16753/FULLTEXT01.pdf

QoS Control of Real-Time Data Services under Uncertain Workload

Previous years have seen rapid growth of online services that rely on large-scale server clusters to handle high volume of requests. Such clusters must adaptively control the CPU utilizations of many processors in order to maintain desired soft real-time performance and prevent system overload in face of unpredictable workloads. This paper presents DUC-LB, a novel distributed utilization control algorithm for cluster-based soft real-time applications. Compared to earlier works on utilization control, a distinguishing feature of DUC-LB is its capability to handle system dynamics caused by load balancing, which is a common and essential component of most clusters today. Simulation results and control-theoretic analysis demonstrate that DUC-LB can provide robust utilization control and effective load balancing in large-scale clusters

/pdf/distributed-utilization-control-for-real-time-clusters-with-37hjtmgla4.pdf

Distributed Utilization Control for Real-Time Clusters with Load Balancing

Many distributed real-time systems face the challenge of dynamically maximizing system utility and meeting stringent resource constraints in response to fluctuations in system workload. Thus, online adaptation must be adopted in face of workload changes in such systems. We present the multiparametric rate adaptation (MPRA) algorithm for discrete rate adaptation in distributed real-time systems with end-to-end tasks. The key novelty and advantage of MPRA is that it can efficiently produce optimal solutions in response to workload variations such as dynamic task arrivals. Through offline preprocessing MPRA transforms an NP-hard utility optimization problem to the evaluation of a piecewise linear function of the CPU utilization. At run time MPRA produces optimal solutions by evaluating the function based on the CPU utilization. Analysis and simulation results show that MPRA maximizes system utility in the presence of varying workloads, while reducing the online computation complexity to polynomial time.

/pdf/optimal-discrete-rate-adaptation-for-distributed-real-time-48km5nfkv8.pdf

Optimal Discrete Rate Adaptation for Distributed Real-Time Systems

The use of feedback control techniques has been gaining importance in real-time scheduling as a means to provide predictable performance in the face of uncertain workload. In this paper, we propose and analyze a feedback scheduling algorithm, called double-loop feedback scheduler, for distributed real-time systems, whose objective is to keep the deadline miss ratio near the desired value and achieve high CPU utilization. This objective is achieved by an integrated design of a local and a global feedback scheduler. We provide the stability analysis of the double-loop system. We also carry out extensive simulation studies to evaluate the performance and stability of the proposed double-loop scheduler. Our studies show that the proposed scheduler achieves high CPU utilization with low miss ratio and stays in steady state after a step change in workload, characterized by change in actual execution time of tasks.

Double-loop feedback-based scheduling approach for distributed real-time systems

Many real-time systems must control their CPU utilizations in order to meet end-to-end deadlines and prevent overload. Utilization control is particularly challenging in distributed real-time systems with highly unpredictable workloads and a large number of end-to-end tasks and processors. This paper presents the decentralized end-to-end utilization control (DEUCON) algorithm that can dynamically enforce desired utilizations on multiple processors in such systems. In contrast to centralized control schemes adopted in earlier work, DEUCON features a novel decentralized control structure that only requires localized coordination among neighbor processors. DEUCON is systematically designed based on recent advances in distributed model predictive control theory. Both control-theoretic analysis and simulations show that DEUCON can provide robust utilization guarantees and maintain global system stability despite severe variations in task execution times. Furthermore, DEUCON can effectively distribute the computation and communication cost to different processors and tolerate considerable communication delay between local controllers. Our results indicate that DEUCON can provide scalable and robust utilization control for large-scale distributed real-time systems executing in unpredictable environments

/pdf/decentralized-utilization-control-in-distributed-real-time-4vkgktoply.pdf

Decentralized utilization control in distributed real-time systems

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Decentralized utilization control in distributed real-time systems