Mirko Caspar

Wake-Up-Receiver Concepts - Capabilities and Limitations

A promising idea for optimising the power consumption of mobile communication devices represents the usage of an additional ultra-low-power receiver unit, which is able to control the main transceiver in order to reduce the standby power consumption of the overall system. Such a Wake-Up-Receiver (WuRx) unit senses the medium and switches on the communication interfaces in case of an external request. Otherwise, all system components for the network communication are completely switched off. Especially in the domain of resource-limited and embedded devices, WuRx technologies enable novel communication paradigms. But on the application layer, not all scenarios allow the efficient usage of such WuRx technologies. Dependent on environmental parameters, technological limitations and conceptual requirements, different strategies are necessary to ensure energy-efficient system operation. In this article, we present a critical analysis of the capabilities and the conceptual limitations of WuRx approaches. Therefore, we identify critical parameters for WuRx concepts, which limit the efficiency in real world scenarios. Our goal is to classify sufficient fields of application. Furthermore we evaluate the influences of these parameters on the system behaviour. In addition, we introduce heterogeneous energy harvesting approaches as an efficient way for the system optimisation. The proposed technologies are capable to be integrated into small-sized wireless sensor platforms and prolong the system uptime significantly. The presented simulation results are focusing on actual smart metering scenarios and wireless sensor networks. Based on these measurements, we were able to apply further optimisation steps within the system configuration on the application layer. In this context, we focus on application-specific key issues, like the trade-off between measurement quality and quantity, the usage of data buffering approaches and QoS capabilities.

SimANet – A Large Scalable, Distributed Simulation Framework for Ambient Networks

In this paper, we present a new simulation platform for complex, radio standard spanning mobile Ad Hoc networks. SimANet - Simulation Platform for Ambient Networks - allows the coexistence of multiple radio modules with different communication technologies and protocol stacks within one node, which can be used concurrently. By the usage of efficient data structures like Randomised Skip Quadtrees, SimANet allows the analysis and evaluation of large scale, heterogeneous network topologies in both static and dynamic simulation scenarios based on different movement models. The software design enables a modular extension with additional models for power consumption, communication complexity or barrier simulation. Furthermore, an integrated MPI library provides the possibility to run distributed test cycles on parallel computing systems. Thereby, special sliding time window algorithms avoid the typical disadvantage of a slow network interconnection structure and allow a dynamic load balancing on the available hardware resources during the runtime. With the main focus on the evaluation of abstract multi-interface, multi-standard communication concepts, we compare the functionality and the complexity of SimANet with well-known simulation tools like ns2-MIRACLE, ns2-NW-Node, OMNet++ and TeNS. Simulation results for different application scenarios estimate features like versatility, practicality or usability in large scale network topologies with up to 105 nodes.

Performance analysis of radio standard spanning communication in mobile Ad Hoc networks

In this paper, the feasibility and necessity of a new concept for radio standard spanning communication in mobile Ad Hoc networks (MANET) has been analysed. Past research approaches limited their solutions to the usage in a homogeneous topology on basis of a unique radio standard. The proposed concept offers the possibility to connect standardised radio modules on a hardware near layer by the usage of a dedicated Interface Block. Such an IFB allows the interoperability between tasks with incompatible protocols. For evaluating the conceptual advantages of this approach, different network topologies have been tested in a dedicated simulation environment. The scenario-based performance analysis includes the behaviour of the nodes both in static and in high-dynamic network topologies. Thereby, the main objective of verification is a qualitative evaluation of the power consumption in each node and in the entire topology. Furthermore, improvements of route paths and the connectivity level have been analysed. The degree of improvements in the analysed scenarios averages 15% and rises up to 35% in a random distributed, heterogeneous network topology with a high node density.

A capable, high-level scheduling concept for application-specific wireless sensor networks

The primary objective of wireless sensor networks is the monitoring of a system or area by measuring different kinds of sensor data. Dependent on the application scenario, a specific measurement scheduling scheme is preferred. Based on this scheduling, an optimisation of the available energy resources in each sensor node and accordingly in the whole network topology is possible. At the same time, an application-specific synchronisation of the measurement points ensures a maximum quality for the merged sensor information. One essential requirement for any kind of scheduling scheme is a synchronised time base in the entire network topology. In order to define capable measurement schemes for any kind of available sensor node hardware, lightweight synchronisation concepts are necessary. In this paper we present a scheduling concept for distributed, resource-limited sensor networks based on a capable time synchronisation approach. The concepts operate on the application layer and enable application-specific, energy-efficient sensor measurement schemes. For proof of concept, the approaches were implemented on a sensor node hardware platform. Several test scenarios evaluate the feasibility and clarify an excellent usability in wireless sensor network environments.

A capable, lightweight communication concept by combining Ambient Network approaches with Cognitive Radio aspects

In this paper, we present a feasible communication concept within the field of cognitive radios and ambient networking. The approach deals with the integration of different radio modules into an embedded communication platform. Basic idea is the simultaneous coexistence of multiple independent network interfaces, which allows us to combine the advantages of different communication technologies. At the same time we bypass the disadvantages of one single radio standard with its application specific design limitations. The result is a lightweight, radio standard spanning communication system, specially in the field of mobile ad hoc networks. The approach enables interesting new ways to create a reliable, heterogeneous network infrastructure. To avoid the influences of interferences in the topology, a special Link Management Unit identifies an increasing interference behaviour based on parameters like the packet loss rate, packet transmission time or fluctuations of the signal quality. With this knowledge base, we are able to adapt the transmission technology dynamically. Thus, the system takes an active influence on the local interference level in the network. Unlike other related research projects, this concept requires no special hardware devices and no complex software architecture. Instead, our approach focuses on standardised, low cost hardware components to realise an embedded communication platform. The presented paper analyses the feasibility with application-specific simulations and evaluate the results based on real world measurements with a designed prototype platform.

Energy-efficient adaptive communication by preference-based routing and forecasting

Life simplifying fully automated factories are only feasible with a high accuracy and quality checking sensor density. In order to realize a huge amount of sensor nodes a single node must require minimal amount of energy for cost and uptime reasons. In this paper, a behavior adaptive routing protocol is presented which utilizes factory structures, resulting order relations, and application specific process data relevance to reduce energy requirements of nodes and increase their applicability. The reduction of data amount is realized by a parameter compressing data format and time-behavior adapted buffering. The reduction of number of transmissions is achieved by prevention of periodic updates and usage of echoes of other nodes. In order to react to dynamic environmental influences and energy fluctuations, sensor nodes improve their behavior. Change in behavior results from a compressed preference value. The accuracy of mapping of parameters to the preference is validated by several a priori rule checks and error adaptions.

Automated system testing using dynamic and resource restricted clients

Testing on system level using a static and homogeneous architecture of clients is common practice. This paper introduces a new approach to use a heterogeneous and dynamic set of resource restricted test clients for automated testing. Due to changing resources and availability of the clients, the test case distribution needs to be recalculated dynamically during the test execution. All necessary conditions and parameters are represented by a formal model. It is shown that the algorithmic problem of DYNAMIC TESTPARTITIONING can be solved in polynomial time by a heuristic recursive algorithm. A testbench architecture is introduced and by simulation it is shown that the testbench can execute the test requirements within a small variation using a number of several hundred clients. The system can react dynamically on changing resources and availability of the test clients within several seconds. The approach is generic and can be adapted to a huge number of systems.

A framework of virtual classroom model on the Internet

Currently, many E-Learning platforms of different qualities are available. Most of them lack in the direct interactivity between teacher and students and among students. In this paper, a framework of virtual classroom model on the Internet is proposed. It connects the advantages of existing offline approaches, like a white board, with the advantages of live streaming systems with many participants. The architecture of virtual classroom on the Internet is composed of three processes: functions and protocol classification process, client/server sequential process and collaborative functions for lecturer and student process. The model bases up on four main technologies: the flash media server architecture, the RTMP protocol, client-server connection flows and shared objects. The concept has been implemented and tested in some classes with international participants. The results show that the students can immediately interact with lecturers as though they are studying in real classroom. The lecturer and students can publish streaming audio, video and other data messages to present streaming media with interaction or navigation. The virtual classroom is interesting place for lecturers and students to join and become the most important feature of E-Learning web sites that makes more attractive and complete E-Learning system.

Web-based virtual classroom system model based on asynchronous and synchronous learning

In this paper, the web-based virtual classroom system model based on asynchronous and synchronous learning is proposed. The system model is provided tools for lecturers and learners to enhanced features for collaboration and interaction among participants in a web-based virtual classroom. The web-based virtual classroom system model is defined by combination of both asynchronous and synchronous learning functions. The asynchronous learning function consists of contents, upload and download documents, webboard, e-mail and video on demand (VoD). The synchronous learning function is composed of chat room, video conference room, whiteboard room, presentation room and people list. The results show that lecturers and learners are participated in a web-based virtual classroom. A proposed model is better support for personal participation and cognitive participation. This model can improve the convenience and flexibility of scheduling and learning time.

Embedded Ambient Networking - a Feasible, Lightweight Communication Concept

In this paper, we present a feasible communication concept within the field of ambient networks and cognitive radios. The approach deals with the integration of different radio modules into an embedded communication platform. Basic idea is the simultaneous coexistence of multiple independent network interfaces, which allows us to combine the advantages of different communication technologies. At the same time we bypass the disadvantages of one single radio standard with its application specific design limitations. The result is a lightweight, radio standard spanning communication system, specially in the field of mobile ad hoc networks. The approach enables interesting new ways to create a reliable, heterogeneous network infrastructure. To avoid the influences of interferences in the topology, an observer unit identifies an increasing interference behaviour based on parameters like the packet loss rate, packet transmission time or fluctuations of the signal quality. With this knowledge base, we are able to adapt the transmission technology dynamically. Thus, the system takes an active influence on the local interference level in the network. Unlike other related research projects, this concept requires no special hardware devices and no complex software architecture. Instead, our approach focuses on standardised, low cost hardware components to realise an embedded communication platform. The presented paper analyses the feasibility with application-specific simulations and evaluate the results based on real world measurements with a designed prototype platform.