Real-time performance of periodic data transmission in EPA industrial Ethernet

To evaluate and improve the real-time performance of Ethernet for plant automation（EPA） industrial Ethernet,the real-time performance of EPA periodic data transmission was theoretically and experimentally studied.By analyzing information transmission regularity and EPA deterministic scheduling mechanism,periodic messages were categorized as different modes according to their entering-queue time.The scheduling characteristics and delivery time of each mode and their interacting relations were studied,during which the models of real-time performance of periodic information transmission in EPA system were established.On this basis,an experimental platform is developed to test the delivery time of periodic messages transmission in EPA system.According to the analysis and the experiment,the main factors that limit the real-time performance of EPA periodic data transmission and the improvement methods were proposed.

Periodic Error Compensation for Quartz MEMS Gyroscope Drift of INS

In order to improve the navigation accuracy of an inertial navigation system （INS）, composed of quartz gyroscopes, the existing real-time compensation methods for periodic errors in quartz gyroscope drift and the periodic error term relationship between sampled original data and smoothed data are reviewed. On the base of the results, a new compensation method called using former period characteristics to compensate latter smoothness data （UFCL for short） method is proposed considering the INS working characteristics. This new method uses the original data without smoothing to work out an error conversion formula at the INS initial alignment time and then compensate the smoothed data errors by way of the formula at the navigation time. Both theoretical analysis and experimental results demonstrate that this method is able to cut down on computational time and raise the accuracy which makes it a better real-time compensation approach for periodic error terms of quartz micro electronic mechanical system （MEMS） gyroscope＇s zero drift.

Improvement Design for Distributed Real-Time Stream Processing Systems

In the era of Big Data, typical architecture of distributed real-time stream processing systems is the combination of Flume, Kafka, and Storm. As a kind of distributed message system, Kafka has the characteristics of horizontal scalability and high throughput, which is manly deployed in many areas in order to address the problem of speed mismatch between message producers and consumers. When using Kafka, we need to quickly receive data sent by producers. In addition, we need to send data to consumers quickly. Therefore, the performance of Kafka is of critical importance to the performance of the whole stream processing system. In this paper, we propose the improved design of real-time stream processing systems, and focus on improving the Kafka's data loading process.We use Kafka cat to transfer data from the source to Kafka topic directly, which can reduce the network transmission. We also utilize the memory file system to accelerate the process of data loading, which can address the bottleneck and performance problems caused by disk I/O. Extensive experiments are conducted to evaluate the performance, which show the superiority of our improved design.

An Efficient Real-Time Fault-Tolerant Scheduling Algorithm Based on Multiprocessor Systems

In the context of real-time fault-tolerant scheduling in multiprocessor systems, Primary-backup scheme plays an important role. A backup copy is always preferred to be executed as passive backup copy whenever possible because it can take the advantages of backup copy de-allocation technique and overloading technique to improve schedulability. In this paper, we propose a novel efficient fault-tolerant ratemonotonic best-fit algorithm efficient fault-tolerant rate-monotonic best-fit （ERMBF） based on multiprocessors systems to enhance the schedulability. Unlike existing scheduling algorithms that start scheduling tasks with only one processor. ERMBF pre-allocates a certain amount of processors before starting scheduling tasks, which enlarge the searching spaces for tasks. Besides, when a new processor is allocated, we reassign the task copies that have already been assigned to the existing processors in order to find a superior tasks assignment configuration. These two strategies are all aiming at making as many backup copies as possible to be executed as passive status. As a result, ERMBF can use fewer processors to schedule a set of tasks without losing real-time and fault-tolerant capabilities of the system. Simulation results reveal that ERMBF significantly improves the schedulability over existing, comparable algorithms in literature.

Joint Algorithm of Message Fragmentation and No-Wait Scheduling for Time-Sensitive Networks

Time-sensitive networks(TSNs)support not only traditional best-effort communications but also deterministic communications,which send each packet at a deterministic time so that the data transmissions of networked control systems can be precisely scheduled to guarantee hard real-time constraints.No-wait scheduling is suitable for such TSNs and generates the schedules of deterministic communications with the minimal network resources so that all of the remaining resources can be used to improve the throughput of best-effort communications.However,due to inappropriate message fragmentation,the realtime performance of no-wait scheduling algorithms is reduced.Therefore,in this paper,joint algorithms of message fragmentation and no-wait scheduling are proposed.First,a specification for the joint problem based on optimization modulo theories is proposed so that off-the-shelf solvers can be used to find optimal solutions.Second,to improve the scalability of our algorithm,the worst-case delay of messages is analyzed,and then,based on the analysis,a heuristic algorithm is proposed to construct low-delay schedules.Finally,we conduct extensive test cases to evaluate our proposed algorithms.The evaluation results indicate that,compared to existing algorithms,the proposed joint algorithm improves schedulability by up to 50%.

Confidentiality-aware message scheduling for security-critical wireless networks

Without considering security, existing message scheduling mechanisms may expose critical messages to malicious threats like confidentiality attacks. Incorporating confidentiality improvement into message scheduling, this paper investigates the problem of scheduling aperiodc messages with time-critical and security-critical requirements. A risk-based security profit model is built to quantify the security quality of messages; and a dynamic programming based approximation algorithm is proposed to schedule aperiodic messages with guaranteed security performance. Experimental results illustrate the efficiency and effectiveness of the proposed algorithm.

IPC Mechanisms in Satellite Real-Time Microkernel Operating System

One of the most important features of modem minor satellites is to realize autonomous moving. The perfomance of the satellite autonomous computer operating system acting as the control center is of utrnost importance. The recent trend in operating system development is adopting microkernel architecture that holds such advantages as microminiaturization, modularity, portability and extendibility. IPC is the key of microkernel design. Message-based IPC mechanism is generally used in existing microkernel Operating system. It is of consistency, safety and reliability.However, it can not provide efficient support for real-time applications in satellite systems and it only applies to loose coupling multi-processor architecture. In this paper, an improvement solution for existing message-based IPC is proposed at first to obtain real-time performance. Then a new IPC mechanism is designed. It particulary applies to shared memory tight coupling multi-processor architecture.

An On-Line Scheduler over Hard Real-Time Communication System

By thorough research on the prominent periodic and aperiodic scheduling algorithms,anon-line hard real-time scheduler is presented,which is applicable to the scheduling of packets over a link.This scheduler,based on both Rate Monotonic,pinwheel scheduling algorithm Sr and Polling Serverscheduling algorithms,can rapidly judge the schedulability and then automatically generate a bus tablefor the scheduling algorithm to schedule the packets as the periodic packets.The implementation of thescheduler is simple and easy to use,and it is effective for the utilization of bus link.The orderly executionof the bus table can not only guarantee the performance of the hard real time but also avoid the blockageand interruption of the message transmission.So the scheduler perfectly meets the demand of hard real-time communication system on the field bus domain.

Optimal Checkpoint Placement on Real-Time Tasks with Harmonic Periods

This paper presents an optimal checkpoint strategy for fault-tolerance in real-time systems where transient faults occur in Poisson distribution. In our environment, multiple real-time tasks with different deadlines and harmonic periods are scheduled in the system by rate-monotonic algorithm, and checkpoints are inserted at a constant interval in each task. When a fault is detected, the system carries out rollback to the latest checkpoint and re-executes tasks. The maximum number of re-executable checkpoints and an equation to check schedulability are derived, and the optimal number of checkpoints is selected to maximize the probability of completing all the tasks within their deadlines.

1553B总线上消息的实时调度

为了优化1553B总线传输性能,降低总线上消息传输的延迟时间,讨论了周期消息和非周期消息混合传输情况下总线上的消息调度策略。首先,借鉴周期任务的调度模型对周期消息进行建模,提出了改进的速率单调消息调度算法。然后,利用排队论建立非周期消息的M/M/1排队模型,定量分析了1553B总线的平均响应时间和总线利用率等时间性能参数,并对非周期消息的延迟时间进行优化,推导出总线最优服务率和最小平均延迟时间的计算公式,给出了非周期消息的调度算法。最后,对上述算法在消息混合传输下的可调度性进行了验证。实验结果表明,在总线利用率达96%时,混合消息的平均响应时间为0.713ms。在消息混合传输的情况下,非周期消息的平均响应时间和M/M/1排队模型下理想的非周期响应时间偏差不超过10%。上述算法时间响应特性良好,能够保证周期消息和非周期消息的实时调度。

PTS领域中的Agent体系结构设计与实现

目前大部分的多Agent系统协作理论没有对实时、动态和通信不可靠环境下的Agent体系结构给出合适的解决方案。该文首先给出了对动态、实时和通信不可靠环境下的多Agent协作问题的一种典型描述──PTS领域的定义，并分析了PTS领域的消息处理及动作执行的循环机制。在此基础上，给出了适合于PTS领域的Agent体系结构，最后在微机平台上用面向对象的方法以机器人足球仿真比赛为背景实现了这种体系结构。

基于手机短信的水电站施工期水情自动报汛系统研发

设计了水电站施工期专用短信报汛方案,基于GSM网络的短信业务开发了水电站施工期自动报汛系统。系统按照用户预先配置的手机短信方案,将水情测报系统中的流域水情信息自动编制成定时、振铃回复、预警、预报等报汛短信,通过GSM Modem设备直接发送至最终用户的手机。该系统已经在锅浪跷水电站施工期水情服务工作中投入应用,运行稳定、可靠,能满足水电站施工期水情报汛工作的需要。

Delphi平台下的1553B总线卡通信应用技术研究

介绍一种基于Delphi平台的PCI-1553B总线卡接口通信应用技术,主要包括Delphi下1553B总线周期消息、非周期消息定义、消息传输故障重试、消息数据的中断采集、消息数据的动态更新以及总线消息的传输监控记录等编程技术。并基于1553B总线卡和Delphi平台设计了一套电控模拟器通信系统,验证了1553B总线的BC->RT通信和RT->BC通信以及BM总线监控功能。实践表明,利用Delphi开发1553B总线通信应用技术以及Delphi对数据库技术的完美支持,与其他开发语言相比,该技术可快速建立完善的1553B总线通信测试系统。

日志检查点回卷恢复策略的检查点周期求解模型

基于Markov链进程状态模型和拉普拉斯变换，提出了一种日志检查点回卷恢复容错策略的最佳检查点周期求解模型，该模型充分考虑了日志检查点回卷恢复策略中进程回卷恢复与正常运行期间执行速度存在的差别，同时允许进程检查点和回卷恢复期间发生故障事件。通过求解进程状态Markov链转移概率和权重，得到完成检查点间隔的期望执行用时，最后通过系统最小容错负载率得出进程的最佳检查点周期。该模型退化后与现有其它求解模型相一致，结果表明该模型能确保相对较低的容错开销。

面向车辆状态信息广播的功率控制算法

针对车载自组织网(VANET)中节点以固定功率发送信息导致的信道资源无法优化分配的问题,以车辆周期发送的状态信息的广播为研究对象,提出一种可自适应于车流密度变化的VANET功率控制算法。该算法通过定义功率控制周期构建并更新直接邻居列表,根据直接邻居车辆的位置来调整发射功率,进而控制节点的广播信息覆盖范围,实现信道资源的优化分配以及节点路由性能的优化。仿真结果验证了所提出算法的有效性,表明该算法能够有效根据车辆密度自适应调整发射功率、降低信道占用率并提高直接邻居数据包投递率,从而保证安全信息的有效传输。

交换以太网中实时消息截止期划分算法研究

为解决交换式以太网中实时消息在发送及接收链路上的截止期划分问题,首先给出了非抢占式EDF调度算法的可调度性分析方法,并分析了消息的提前释放对非抢占式EDF调度算法可调度性的影响,在此基础上提出了新的截止期划分算法(MDPS)。算法通过计算可满足调度条件时消息在发送链路及接收链路截止期应该划分的下限,并结合截止期的松驰量实现实时消息在发送及接收链路上的截止期划分。算法实验比较和分析表明,该算法在提高网络聚合带宽、减小消息的错失率方面明显优于现有的ADPS算法。

COTS Switch工业以太网实时调度算法

针对基于商用现成组件技术(Commercial Off-The-Shelf,COTS)的交换式以太网不能满足工业数据通信的实时性要求问题,给出了改进的FTT(Flexible Time-Triggered communication paradigm)网络调度模型,提出了新的周期性实时消息链路可调度性优化判定方法,在此基础上设计了一种基于EDF(Earliest Deadline First)的实时调度算法。算法通过对网络消息流量进行有效控制防止交换机缓冲区溢出,同时充分发挥网络在同一时间存在多个并行传输链路的优势,提高了网络实时性。仿真实验表明该算法在提高网络的聚合带宽、减小消息的平均等待延时和丢失率方面均有明显的优势。

多功能车辆总线非周期数据实时性分析与带宽分配的优化设计

在分析MVB数据传输机制的基础上,提出了非周期数据通信的优化带宽分配策略,推导出了相应的带宽分配策略的计算公式,并在实例中对优化后的策略进行了分析研究和性能比较。对带宽分配方法进行优化后,非周期数据通信的实时性有比较明显的提高。

CAN报文实时性提高分析及改进

随着汽车电子功能的增加,功能需求对报文实时性需求高与报文传输延时大的矛盾越来越突出。为了研究传输延时影响因素,本文建立了最大传输延时模型,并基于位填充(含报文间隙)、网络任务及其他调度周期等方面进行分析和测试。结果发现:网络负载越高,报文传输延时越大;新增报文优先级越高,对原整车网络报文传输延时越大。故在网络设计时,需降低网络负载,新增零件采用低优先级报文;在满足零件功能需求时,适当增大报文周期超出阈值。

主从结构交换式以太网中实时消息调度研究

为使交换式以太网能满足实时通信的要求,针对FTT-SE网络调度模型,提出了一种同时适用于周期性和非周期性实时消息的链路可调度性判定方法。在证明了消息链路调度优化问题MLSOP为NP-complete的同时,针对周期性实时消息的链路调度优化给出了启发式算法LSHA。最后,对于周期性和非周期性实时消息分别设计了基于EDF的调度算法。仿真实验表明,在提高网络链路带宽利用率和减小消息平均延时方面,该算法均较FTT-SE有明显的优势。