Yuanfang Zhang

Integrated coverage and connectivity configuration in wireless sensor networks

An effective approach for energy conservation in wireless sensor networks is scheduling sleep intervals for extraneous nodes, while the remaining nodes stay active to provide continuous service. For the sensor network to operate successfully, the active nodes must maintain both sensing coverage and network connectivity. Furthermore, the network must be able to configure itself to any feasible degrees of coverage and connectivity in order to support different applications and environments with diverse requirements. This paper presents the design and analysis of novel protocols that can dynamically configure a network to achieve guaranteed degrees of coverage and connectivity. This work differs from existing connectivity or coverage maintenance protocols in several key ways: 1) We present a Coverage Configuration Protocol (CCP) that can provide different degrees of coverage requested by applications. This flexibility allows the network to self-configure for a wide range of applications and (possibly dynamic) environments. 2) We provide a geometric analysis of the relationship between coverage and connectivity. This analysis yields key insights for treating coverage and connectivity in a unified framework: this is in sharp contrast to several existing approaches that address the two problems in isolation. 3) Finally, we integrate CCP with SPAN to provide both coverage and connectivity guarantees. We demonstrate the capability of our protocols to provide guaranteed coverage and connectivity configurations, through both geometric analysis and extensive simulations.

Integrated coverage and connectivity configuration for energy conservation in sensor networks

An effective approach for energy conservation in wireless sensor networks is scheduling sleep intervals for extraneous nodes while the remaining nodes stay active to provide continuous service. For the sensor network to operate successfully, the active nodes must maintain both sensing coverage and network connectivity. Furthermore, the network must be able to configure itself to any feasible degree of coverage and connectivity in order to support different applications and environments with diverse requirements. This article presents the design and analysis of novel protocols that can dynamically configure a network to achieve guaranteed degrees of coverage and connectivity. This work differs from existing connectivity or coverage maintenance protocols in several key ways. (1) We present a Coverage Configuration Protocol (CCP) that can provide different degrees of coverage requested by applications. This flexibility allows the network to self-configure for a wide range of applications and (possibly dynamic) environments. (2) We provide a geometric analysis of the relationship between coverage and connectivity. This analysis yields key insights for treating coverage and connectivity within a unified framework; in sharp contrast to several existing approaches that address the two problems in isolation. (3) We integrate CCP with SPAN to provide both coverage and connectivity guarantees. (4) We propose a probabilistic coverage model and extend CCP to provide probabilistic coverage guarantees. We demonstrate the capability of our protocols to provide guaranteed coverage and connectivity configurations through both geometric analysis and extensive simulations.

Reconfigurable Real-Time Middleware for Distributed Cyber-Physical Systems with Aperiodic Events

Different distributed cyber-physical systems must handle a periodic and periodic events with diverse requirements. While existing real-time middleware such as real-time CORBA has shown promise as a platform for distributed systems with time constraints, it lacks flexible configuration mechanisms needed to manage end-to-end timing easily for a wide range of different cyber-physical systems with both aperiodic and periodic events. The primary contribution of this work is the design, implementation and performance evaluation of the first configurable component middleware services for admission control and load balancing of a periodic and periodic event handling in distributed cyber-physical systems. Empirical results demonstrate the need for, and the effectiveness of, our configurable component middleware approach in supporting different applications with a periodic and periodic events, and providing a flexible software platform for distributed cyber-physical systems with end-to-end timing constraints.

The design and implementation of real-time CORBA 2.0: dynamic scheduling in TAO

In an emerging class of open distributed real-time and embedded (DRE) systems with stringent but dynamic QoS requirements, there is a need to propagate QoS parameters and enforce task QoS requirements across multiple endsystems in a way that is simultaneously efficient and adaptable. The object management groups (OMG) real-time CORBA 2.0 specification (RTC2) defines a dynamic scheduling framework for propagating and enforcing QoS parameters dynamically in standard CORBA middleware. We make two contributions to research on middleware for open DRE systems. First, it describes the design and capabilities of the RTC2 dynamic scheduling framework provided by TAO, which is our open-source CORBA standards-based object request broker (ORB). Second, it describes and summarize the results of empirical studies we have conducted to validate our RTC2 framework in the context of open DRE systems. The results of those experiments show that a range of policies for adaptive scheduling and management of distributable threads can be enforced efficiently in standard middleware for open DRE systems.

End-to-End Scheduling Strategies for Aperiodic Tasks in Middleware

Many mission-critical distributed real-time applications must handle aperiodic tasks with hard end-to-end deadlines. Existing middleware such as RT-CORBA lacks schedulability analysis and run-time scheduling mechanisms that can provide real-time guarantees to aperiodic tasks. This paper makes the following contributions to the state of the art for end-to-end aperiodic scheduling in middleware. First, we compare two approaches to aperiodic scheduling, the deferrable server and the aperiodic utilization bound, using representative workloads. Numerical results show that the deferrable server analysis is less pessimistic than the aperiodic utilization bounds when applied offline. Second, we propose a practical approach to tuning deferrable servers for end-to-end tasks. Third, we describe deferrable server mechanisms we have developed for TAOs federated event channel. Finally, we present empirical results from a Linux testbed that demonstrate the efficiency of those deferrable server mechanisms. Type of Report: Other Department of Computer Science & Engineering Washington University in St. Louis Campus Box 1045 St. Louis, MO 63130 ph: (314) 935-6160 End-to-End Scheduling Strategies for Aperiodic Tasks in Middleware Yuanfang Zhang, Chenyang Lu, and Christopher Gill Department of Computer Science and Engineering Washington University, St. Louis, MO, USA yfzhang,lu,cdgill @cse.wustl.edu Patrick Lardieri and Gautam Thaker Advanced Technology Laboratories Lockheed Martin, Cherry Hill, NJ, USA plardieri,gthaker @atl.lmco.com

Real-Time Performance and Middleware for Multiprocessor and Multicore Linux Platforms

An increasing number of distributed real-time applications are running on multicore platforms. However, existing real-time middleware (e.g., Real-Time CORBA) lacks adequate support for ensuring the timing constraints of soft real-time tasks on multicore platforms, and thus is dependent on (potentially inadequate) support from the underlying operating system. This paper makes three contributions to the state of the art in real-time system software for multicore platforms. First, it offers what is to our knowledge the first experimental analysis of real-time performance of vanilla Linux primitives on multicore platforms. Second, it presents MC-ORB, the first real-time object request broker (ORB) designed to address the nuances of multiprocessor (and especially multicore) platforms with a novel core-aware middleware thread architecture and allocation service for soft real-time tasks. Third, it evaluates MC-ORBs performance on a Linux multicore testbed, the results of which demonstrate its efficiency and effectiveness.

Middleware Support for Aperiodic Tasks in Distributed Real-Time Systems

Many mission-critical distributed real-time applications must handle aperiodic tasks with end-to-end deadlines. However, existing middleware (e.g., RT-CORBA) lacks schedulability analysis and run-time enforcement mechanisms needed to give online real-time guarantees for aperiodic tasks. The primary contribution of this work is the design, implementation, and performance evaluation of the first realization of deferrable server and admission control mechanisms for aperiodic tasks in middleware. Empirical results on a KURT-Linux testbed demonstrate the efficiency and effectiveness of our deferrable server and admission control mechanisms in TAOs federated event service

A real-time performance comparison of distributable threads and event channels

No one middleware communication model completely solves the problem of ensuring schedulability in every DRE system. Furthermore, there have been few studies to date of the trade-offs between alternative middleware communication models under different application scenarios. This paper makes three contributions to the state of the art in middleware for distributed real-time and embedded systems. First, it describes what we believe is the first example of integrating release guards directly with CORBA distributable threads to ensure appropriate release times for sub-tasks along an end-to-end computation. Second, it presents empirical results in which release guards improve schedulability of distributable threads compared to a greedy protocol in which arriving tasks simply begin to run as soon as they can. Third, we offer the first empirical comparisons of the distributable thread and event channel models under three different communication scenarios and then using a randomized workload.

Configurable Middleware for Distributed Real-Time Systems with Aperiodic and Periodic Tasks

Different distributed real-time systems (DRS) must handle aperiodic and periodic events under diverse sets of requirements. While existing middleware such as Real-Time CORBA has shown promise as a platform for distributed systems with time constraints, it lacks flexible configuration mechanisms needed to manage end-to-end timing easily for a wide range of different DRS with both aperiodic and periodic events. The primary contribution of this work is the design, implementation, and performance evaluation of the first configurable component middleware services for admission control and load balancing of aperiodic and periodic event handling in DRS. Empirical results demonstrate the need for, and the effectiveness of, our configurable component middleware approach in supporting different applications with aperiodic and periodic events, and providing a flexible software platform for DRS with end-to-end timing constraints.

Practical Schedulability Analysis for Generalized Sporadic Tasks in Distributed Real-Time Systems

Existing off-line schedulability analysis for real-time systems can only handle periodic or sporadic tasks with known minimum inter-arrival times. Modeling sporadic tasks with fixed minimum inter-arrival times is a poor approximation for systems in which tasks arrive in bursts, but have longer intervals between the bursts. In such cases, schedulability analysis based on the existing sporadic task model is pessimistic and seriously overestimates the tasks time demand. In this paper, we propose a generalized sporadic task model that characterizes arrival times more precisely than the traditional sporadic task model, and we develop a corresponding schedulability analysis that computes tighter bounds on worst-case response times. Experimental results show that when arrival time jitter increases, the new analysis more effectively guarantees schedulability of sporadic tasks.