Michael Mock

Continuous clock synchronization in wireless real-time applications

Continuous clock synchronization avoids unpredictable instantaneous corrections of clock values. This is usually achieved by spreading the clock correction over the synchronization interval. In the context of wireless real time applications, a protocol achieving continuous clock synchronization must tolerate message losses and should have a low overhead in terms of the number of messages. The paper presents a clock synchronization protocol for continuous clock synchronization in wireless real time applications. It extends the IEEE 802.11 standard for wireless local area networks. It provides continuous clock synchronization, improves the precision by exploiting the tightness of the communication medium, and tolerates message losses. Continuous clock synchronization is achieved with an advanced algorithm adjusting the clock rates. We present the design of the protocol, its mathematical analysis, and measurements of a driver level implementation of the protocol on Windows NT.

Implementing the real-time publisher/subscriber model on the controller area network (CAN)

Designing distributed real-time systems as being composed of communicating objects offers many advantages with respect to modularity and extensibility of these systems. However, distributed real-time applications exhibit communication patterns that significantly differ from the traditional object invocation style. The publisher/subscriber model for inter-object communication matches well with these patterns. Any implementation of that model must address the problems of binding subscribers to publishers, of routing and filtering of messages, as well as reliability, efficiency and latency of message delivery. In the context of real-time applications, all these issues must be subject to a rigid inspection with respect to meeting real-time requirements. We argue that for embedded control systems built around smart microcontroller-powered devices these requirements can only be met when exploiting the properties of the underlying network. The CAN-Bus (CAN: Controller Area Network) which is an emerging standard in the field of real-time embedded systems is particularly suited to implement a publisher/subscriber model of communication. We present an implementation of the real-time publisher/subscriber model that exploits the underlying facilities of the CAN-Bus. In particular, we introduce a novel addressing scheme for publisher/subscriber communication that makes efficient use of the CAN-Bus addressing method. We provide a detailed design and implementation details along with some preliminary performance estimations.

A step counter service for Java-enabled devices using a built-in accelerometer

The presence of 3D acceleration sensors in mobile devices has already raised a new range of context-aware applications, in particular in the sports and wellness sector. In this paper, we present an accelerometer-based step counter middleware for J2ME-enabled smartphones to simplify the development of activity aware applications, creating an abstraction layer between the client and the signal processing algorithms and raw sensor access. The service provides information about the step count, stop detection and changes in the phones orientation, independently of the phones location on the human body. The software package runs natively on Symbian S60 phones, providing an interface to J2ME applications and has been validated experimentally on a Nokias N95 smartphone.

Clock synchronization for wireless local area networks

High-precision clock synchronization is one of the most basic requirements in distributed real-time systems. This paper presents an enhanced clock synchronization protocol for wireless local area networks based on the IEEE 802.11 standard. Reducing the time-critical path of the protocol enhances the synchronization precision. As wireless communication links are inherently unreliable, special emphasis is put on fault tolerance. The protocol guarantees high precision even in the presence of message losses. The protocol is implemented in a Windows NT NDIS driver for Lucent WaveLAN cards. For this driver-level implementation, our measurements have shown that a precision of 150 /spl mu/s is achieved.

Toolkit-Based High-Performance Data Mining of Large Data on MapReduce Clusters

The enormous growth of data in a variety of applications has increased the need for high performance data mining based on distributed environments. However, standard data mining toolkits per se do not allow the usage of computing clusters. The success of MapReduce for analyzing large data has raised a general interest in applying this model to other, data intensive applications. Unfortunately current research has not lead to an integration of GUI based data mining toolkits with distributed file system based MapReduce systems. This paper defines novel principles for modeling and design of the user interface, the storage model and the computational model necessary for the integration of such systems. Additionally, it introduces a novel system architecture for interactive GUI based data mining of large data on clusters based on MapReduce that overcomes the limitations of data mining toolkits. As an empirical demonstration we show an implementation based on Weka and Hadoop.

An adaptive approach to object-oriented real-time computing

Real time computing is becoming an enabling technology for many important distributed applications such as flexible manufacturing, multimedia, robotics and process control. Traditionally, real time systems have been realized as isolated embedded systems. Unfortunately, this approach no longer suffices for future complex systems in the application scenarios mentioned above. In this situation, the use of an object oriented design paradigm greatly reduces the complexity of the system while improving reusability and manageability. Furthermore, the surrounding IT infrastructure is more and more accessible through object oriented interfaces (e.g. CORBA). In addition, object oriented modeling allows reflection of the dynamic characteristics of the applications mentioned above by instantiating objects dynamically. In order to meet the real time requirements in such an environment, static scheduling is not sufficient since many non predictable resource conflicts influence execution times. Therefore, the most distinguishing requirement of these complex heterogeneous systems is the need of the computing system to dynamically adapt to dynamically changing conditions. Little work has been done on integrating object oriented system design with resource allocation algorithms that are flexible enough to cope with this new requirement. The paper presents an approach for an adaptive object oriented system with integrated monitoring, dynamic execution time prediction and scheduling. It explains how this approach is applied to CORBA and C++.

Efficient Reliable Real-Time Group Communication for Wireless Local Area Networks

We consider teams of mobile autonomous robot systems that coordinate their work via communication over a wireless local area network. In such a scenario, timely delivery and group support are the predominant requirements on the communication protocol. As the mobile robot systems are communicating via standard hardware, we base our work on the IEEE 802.11 standard for wireless local area networks. In this paper, we present a reliable real-time group communication protocol that enhances the IEEE 802.11 standard. The reliability and real-time properties of the protocol are based on time-bounded dynamic time redundancy. By this, network bandwidth is used much more efficiently than in a message diffusion approach based on static redundancy. The fault detection mechanism needed to implement the time-bounded dynamic redundancy concept is achieved by an implicit acknowledgement scheme that consumes no additional bandwidth for acknowledgement messages.

Discovering bits of place histories from people's activity traces

Events that happened in the past are important for understanding the ongoing processes, predicting future developments, and making informed decisions. Significant and/or interesting events tend to attract many people. Some people leave traces of their attendance in the form of computer-processable data, such as records in the databases of mobile phone operators or photos on photo sharing web sites. We developed a suite of visual analytics methods for reconstructing past events from these activity traces. Our tools combine geocomputations, interactive geovisualizations and statistical methods to enable integrated analysis of the spatial, temporal, and thematic components of the data, including numeric attributes and texts. We demonstrate the utility of our approach on two large real data sets, mobile phone calls in Milano during 9 days and flickr photos made on British Isles during 5 years.

Real-time communication in autonomous robot systems

Designing control and robotic systems as autonomous decentralized systems introduces a new degree of flexibility in the manufacturing and in the application of such systems. This flexibility is required for the systems to work in environments that are not totally predictable and that can change dynamically. In this paper, we present a new concept for real-time communication that supports this flexibility while still preserving real-time guarantees for hard real-time communication. The concept is designed to work on multiple-access busses. In particular we consider its application on wireless local area networks and field-busses. The concept addresses requirements of hard-real time, soft real-time and non real-time communication. For this, we extend the TDMA (time-division multiple-access) approach for time-triggered hard-real time communication by the concept of shared channels that support event-triggered communication and coexist with hard real-time channels. A first implementation of concept has been carried out in the context of the CAN-bus.

Reliable real-time cooperation of mobile autonomous systems

Autonomous systems are expected to provide increasingly complex and safety-critical services that will, sooner or later, require the cooperation of several autonomous systems for their fulfillment. In particular, coordinating the access to shared physical and information technological resources will become a general problem. Scheduling these resources is subject to strong real-time and reliability requirements. In this paper, we present an architecture that allows autonomous mobile systems to schedule shared resources in real-time using their own wireless distributed infrastructure. In our architecture, there is a clear separation between the application-specific scheduling part that is modeled as a function of the global state and the communication part that is used to provide the global state. By isolating the more error-prone communication part within a communication hardcore, the reliability of the overall system is increased and the locally executed scheduling function can be designed with primary focus on the application-specific real-time requirements.