Andreas Köpke

Simulating wireless and mobile networks in OMNeT++ the MiXiM vision

Wireless communication has attracted considerable interest in the research community, and many wireless networks are evaluated using discrete event simulators like OMNeT++. Although OMNeT++ provides a powerful and clear simulation framework, it lacks of direct support and a concise modeling chain for wireless communication. Both is provided by MiXiM. MiXiM joins and extends several existing simulation frameworks developed for wireless and mobile simulations in OMNeT++. It provides detailed models of the wireless channel (fading, etc.), wireless connectivity, mobility models, models for obstacles and many communication protocols especially at the Medium Access Control (MAC) level. Further, it provides a user-friendly graphical representation of wireless and mobile networks in OMNeT++, supporting debugging and defining even complex wireless scenarios. Though still in development, MiXiM already is a powerful tool for performance analysis of wireless networks. Its extensive functionality and clear concept may motivate researches to contribute to this open-source project [4].

Chaotic maps as parsimonious bit error models of wireless channels

The error patterns of a wireless digital communication channel can be described by looking at consecutively correct or erroneous bits (runs and bursts) and at the distribution function of these run and burst lengths. A number of stochastic models exist that can be used to describe these distributions for wireless channels, e.g., the Gilbert-Elliot model. When attempting to apply these models to actually measured error sequences, they fail: measured data gives raise to two essentially different types of error patterns which can not be described using simple error models like Gilbert-Elliot. These two types are distinguished by their run length distribution; one type in particular is characterized by a heavy-tailed run length distribution. This paper shows how the chaotic map model can be used to describe these error types and how to parameterize this model on the basis of measurement data. We show that the chaotic map model is a superior stochastic bit error model for such channels by comparing it with both simple and complex error models. Chaotic maps achieve a modeling accuracy that is far superior to that of simple models and competitive with that of much more complex models, despite needing only six parameters. Furthermore, these parameters have a clear intuitive meaning and are amenable to direct manipulation. In addition, we show how the second type of channels can be well described by a semiMarkov model using a quantized lognormal state holding time distribution.

Improving the Energy Efficiency of Directed Diffusion Using Passive Clustering

Directed diffusion is a prominent example of data-centric routing based on application layer data and purely local interactions. In its functioning it relies heavily on network-wide flooding which is an expensive operation, specifically with respect to the scarce energy resources of nodes in wireless sensor networks (WSNs). One well-researched way to curb the flooding overhead is by clustering. Passive clustering is a recent proposal for on-demand creation and main- tenance of the clustered structure, making it very attractive for WSNs and directed diffusion in particular. The contribution of this paper is the investigation of this combination: Is it feasible to execute directed diffusion on top of a sensor network where the topology is implicitly constructed by passive clustering? A simulation-based comparison between plain directed diffusion and one based on passive clustering shows that, depending on the scenario, pas- sive clustering can significantly reduce the required energy while main- taining and even improving the delay and the delivery rate. This study also provides insights into the behavior of directed diffusion with respect to its long-term periodic behavior, contributing to a better understand- ing of this novel class of communication protocols.

MiXiM: the physical layer an architecture overview

Simulating the physical layer of wireless communication remains a challenge. Communication standards like OFDM or MIMO systems go beyond the simple single narrow frequency band, single antenna model used in popular simulators. Yet, these technologies gain popularity, since they provide researchers with a plethora of possibilities that can be explored to invent new protocols or improve existing ones. However, building a detailed and sufficiently accurate model for such complex systems is a tremendous task that takes a lot of time. In this paper we present the physical layer model of MiXiM, which tackles this task. It provides the researcher with an easy to use interface to the wireless transmission medium. It models the wireless medium in all three dimensions (time, space and frequency) supporting the implementation of future wireless communication standards, but at the same time also supports easy modeling and simulation of traditional single frequency systems.

A component framework for content-based publish/subscribe in sensor networks

Component-based architectures are the traditional approach to reconcile application specific optimization with reusable abstractions in sensor networks. However, they frequently overwhelm the application designer with the range of choices in component selection and composition. We introduce a component framework that reduces this complexity. It provides a well-defined content-based publish/subscribe service, but allows the application designer to adapt the service by making orthogonal choices about: (1) the communication protocol components for subscription and notification delivery, (2) the supported data attributes and (3) a set of service extension components. We present TinyCOPS, our implementation of the framework in TinyOS 2.0, and demonstrate its advantages by showing experimental results for different application configurations on two sensor node platforms in a large-scale indoor testbed.

Towards comparable simulations of cooperating objects and wireless sensor networks

Simulators are indispensable tools to support the development and testing of cooperating objects such as wireless sensor networks (WSN). However, it is often not possible to compare the results of different simulation tools. Thus, the goal of this paper is the specification of a generic simulation platform for cooperating objects. We propose a platform that consists of a set of simulators that together fulfill desired simulator properties. We show that to achieve comparable results the use of a common specification language for the software-under-test is not feasible. Instead, we argue that using common input formats for the simulated environment and common output formats for the results is useful. This again motivates that a simulation tool consisting of a set of existing simulators that are able to use common scenario-input and can produce common output which will bring us a step closer to the vision of achieving comparable simulation results.

The adaptive-intervals MAC protocol for a wireless PROFIBUS

For the PROFIBUS, a standardized and wellknown fieldbus; system, it is attractive to use wireless media. A natural approach in creating such a system is to re-use as much existing technology as possible. In the area of wireless local area networks (WLANs) clearly the IEEE 802.11 standard is the leading technology. Hence, the question comes up, how this technology can be used in the creation of a wireless PROFIBUS. The PROFIBUS is used for its abilities in matching realtime requirements even under harsh environmental conditions. On the other hand, wireless links are error-prone and show time-variable behavior. Hence, an important question is, how good the so-called realtime performance, a set of measures taking reliability and timeliness into account, of the PROFIBUS protocol over wireless links is. This paper presents corresponding results and compares them with those of a new, polling-based class of protocols, called adaptive intervals. It shows up, that the adaptive intervals protocols achieve up to an order of magnitude better realtime performance than the PROFIBUS protocol. We conclude from this that it is a promising approach to replace the existing PROFIBUS MAC protocol by another protocol for creation of a wireless PROFIBUS.

Measuring the Node Energy Consumption in USB Based WSN Testbeds

Energy consumption is one of the critical concerns in sensor networks. In particular, there is substantial interest to investigate the distribution of the energy consumption among different nodes depending on the protocol stack applied for specific traffic characteristics. Unfortunately, experimental investigations to this point are rather difficult, as means for cheap, easy to deploy, while precise estimation of actual energy consumption are not really available. As a solution we developed an affordable and precise circuit that measures the energy consumption in situ. It delivers the result to the sensor node, enabling nodes to take their remaining energy into account. Furthermore, it is to some extent independent from the node type and the testbed type.

Adam A Testbed for Distributed Virtual Environments

In distributed virtual environments (DVEs) the data on which the hosts operate is not consistent at all times. To restore data consistency, the DVE has to employ a consistency algorithm. Unfortunately, all existing DVEs have been built for specific application scenarios, which makes it impossible to compare the consistency algorithms and to choose a suitable candidate for a new scenario. To overcome this, we have created a modular simulator-based DVE testbed named Adam with the ability to plug in different application scenarios as well as different consistency algorithms and network constraints. The testbed also contains a large set of measurement tools. Our testbed currently supports two application scenarios and several of the most common consistency algorithms found in the literature. We can compare the solutions on an objective scale and confirm that optimistic consistency typically outperforms loose consistency.

What’s new? Message reduction in sensor networks using events

Observing the environment is the raison dpsilaetre of sensor networks, but the precise reconstruction of the measured process requires too many messages for a low power sensor network. The number of messages can be reduced by focussing on events relevant for the application. This paper examines three event definitions for a home automation example and compares the message reduction. In the extreme case, the number of transmitted messages drops from more than 3000 messages per node and hour to a maximum of about two messages per node and hour.