Control-Based Adaptive Middleware for Real-Time Image Transmission over Bandwidth-Constrained Networks

Real-time image transmission is crucial to an emerging class of distributed embedded systems operating in open network environments. Examples include avionics mission replanning over Link-16, security systems based on wireless camera networks, and online collaboration using camera phones. Meeting image transmission deadlines is a key challenge in such systems due to unpredictable network conditions. In this paper, we present CAMRIT, a Control-based Adaptive Middleware framework for Real-time Image Transmission in distributed real-time embedded systems. CAMRIT features a distributed feedback control loop that meets image transmission deadlines by dynamically adjusting the quality of image tiles. We derive an analytic model that captures the dynamics of a distributed middleware architecture. A control-theoretic methodology is applied to systematically design a control algorithm with analytic assurance of system stability and performance, despite uncertainties in network bandwidth. Experimental results demonstrate that CAMRIT can provide robust real-time guarantees for a representative application scenario.     

Designing and Rightsizing the Information System Architecture

Information system design and sizing constitute a complex, top-down process that tailors the technology architecture to application requirements. Practitioners usually tackle this top-down process by focusing on individual design aspects, such as data or specific applications, and by relying on their previous experiences to compare alternative architectural solutions. Acquisition costs are usually accounted for, but related operating and maintenance costs are often neglected or underestimated. The complexity of optimizing individual design problems leads researchers to avoid a global optimization perspective and, thus, the IS architecture is usually a result of the juxtaposition of multiple local optima.This paper takes an overall perspective on the cost minimization problem of information system design to achieve a better trade-off between cost and performance over the whole expected life of the technology architecture. A comprehensive design methodology is discussed as an integrating framework that accounts for all categories of costs, including design, implementation, maintenance, and operation, to achieve a globally cost-minimizing solution.     

分布、实时、容错一体化设计方法研究

针对分布式航天器系统的运行环境和特点，对嵌入式系统在空间环境、实时、容错、分布上的需求进行了分析，提出了分布、实时、容错一体化的嵌入式系统设计方法，从满足实时要求下的实时容错能力、免疫与自愈相结合的综合容错能力、单节点的容错与节点间容错相结合的分布容错能力和多种容错方法集成等4个方面，对设计方法进行了阐述。     

Achieving jitter-free and predictable real-time control by accurately timed computer peripherals

Contemporary real-time computers are unable to manipulate external parallel processes simultaneously, and their response times are generally unpredictable, resulting in jitter of the corresponding sampled data systems. It is shown that these problems can be easily solved by endowing process control computers with input/output facilities, working fully in parallel, and making use of exact time specifications. The required system functions are compiled, the design of the additional hardware components is given, and the real-time operating system support is discussed. As a by-product, the exact timing feature of input/output operations opens a new way of synchronising the access of multiple tasks to shared peripherals, which is based on the dimension time.     

Design of a real-time knowledge-based controller with applications in hydraulic turbine generator systems

Issues in the design and implementation of a real-time Knowledge-Based Controller (KBC) have been investigated. The design objective of such a controller is to maintain overall system stability and performance not only during normal, but also contingency, conditions. A general structure for such controllers is proposed. It consists of four major components: a knowledge base, a real-time inference engine, information processing algorithms, and a distributed controller. The functions of each individual component, as well as the relationship among them, are considered. The proposed design methodology is applied to synthesize a real-time knowledge-based controller for a hydraulic turbine governor.     

分布式实时操作系统消息机制的设计与实现

随着数字信号处理技术的迅猛发展,针对并行数字信号处理(DSP)应用自主开发了一个满足用户需要的高性能分布式实时操作系统--腾飞分布式实时操作系统(TF-RTOS).消息机制用于线程间的通信,是操作系统中的重要部分.在开发TF-RTOS过程中,从消息命令包、消息队列、消息传递过程和消息原语这4个方面设计并实现了一种直接消息传递的消息机制,该消息机制具有简化线程间通信、增强系统功能、提高系统性能的特点.     

Feedback utilization control in distributed real-time systems with end-to-end tasks

An increasing number of distributed real-time systems face the critical challenge of providing quality of service guarantees in open and unpredictable environments. In particular, such systems often need to enforce utilization bounds on multiple processors in order to avoid overload and meet end-to-end deadlines even when task execution times are unpredictable. While recent feedback control real-time scheduling algorithms have shown promise, they cannot handle the common end-to-end task model where each task is comprised of a chain of subtasks distributed on multiple processors. This paper presents the end-to-end utilization control (EUCON) algorithm that adaptively maintains desired CPU utilization through performance feedbacks loops. EUCON is based on a model predictive control approach that models utilization control on a distributed platform as a multivariable constrained optimization problem. A multi-input-multi-output model predictive controller is designed based on a difference equation model that describes the dynamic behavior of distributed real-time systems. Both control theoretic analysis and simulations demonstrate that EUCON can provide robust utilization guarantees when task execution times deviate from estimation or vary significantly at runtime.     

Modular abstractions for verifying real-time distributed systems

In this work we present a verification methodology for real-time distributed systems, based on their modular decomposition into processes. Given a distributed system, each of its components is reduced by abstracting away from details that are irrelevant for the required specification. The abstract components are then composed to form an abstract system to which a model checking procedure is applied. The abstraction relation and the specification language guarantee that if the abstract system satisfies a specification, then the original system satisfies it as well.The specification languageRTL is a branching-time version of the real-time temporal logicTPTL presented in Alur and Henzinger [1]. Its model checking is linear in the size of the system and exponential in the size of the formula. Two notions of abstraction for real-time systems are introduced, each preserving a sublanguage ofRTL.     

Experimental evaluation of linear time-invariant models for feedback performance control in real-time systems

In recent years a new class of soft real-time applications operating in unpredictable environments has emerged. Typical for these applications is that neither the resource requirements nor the arrival rates of service requests are known or available a priori. It has been shown that feedback control is very effective to support the specified performance of dynamic systems that are both resource insufficient and exhibit unpredictable workloads. To efficiently use feedback control scheduling it is necessary to have a model that adequately describes the behavior of the system. In this paper we experimentally evaluate the accuracy of four linear time-invariant models used in the design of feedback controllers. We introduce a model (DYN) that captures additional system dynamics, which a previously published model (STA) fails to include. The accuracy of the models are evaluated by validating the models with regard to measured data from the controlled system and through a set of experiments where we evaluate the performance of a set of feedback control schedulers tuned using these models. From our evaluations we conclude that second order models (e.g., DYN) are more accurate than first order models (e.g. STA). Further we show that controllers tuned using second order models perform better than controllers tuned using first order models.     

The COMPLEX methodology for UML/MARTE Modeling and design space exploration of embedded systems

The design of embedded systems is being challenged by their growing complexity and tight performance requirements. This paper presents the COMPLEX UML/MARTE Design Space Exploration methodology, an approach based on a novel combination of Model Driven Engineering (MDE), Electronic System Level (ESL) and design exploration technologies. The proposed framework enables capturing the set of possible design solutions, that is, the design space, in an abstract, standard and graphical way by relying on UML and the standard MARTE profile. From that UML/MARTE based model, the automated generation framework proposed produces an executable, configurable and fast performance model which includes functional code of the application components. This generated model integrates an XML-based interface for communication with the tool which steers the exploration. This way, the DSE loop iterations are efficiently performed, without user intervention, avoiding slow manual editions, or regeneration of the performance model. The novel DSE suited modelling features of the methodology are shown in detail. The paper also presents the performance model generation framework, including the enhancements with regard the previous simulation and estimation technology, and the exploration technology. The paper uses an EFR vocoder system example for showing the methodology and for demonstrative results.