Fredrik Österlind

Cross-Level Sensor Network Simulation with COOJA

Simulators for wireless sensor networks are a valuable tool for system development. However, current simulators can only simulate a single level of a system at once. This makes system development and evolution difficult since developers cannot use the same simulator for both high-level algorithm development and low-level development such as device-driver implementations. We propose cross-level simulation, a novel type of wireless sensor network simulation that enables holistic simultaneous simulation at different levels. We present an implementation of such a simulator, COOJA, a simulator for the Contiki sensor node operating system. COOJA allows for simultaneous simulation at the network level, the operating system level, and the machine code instruction set level. With COOJA, we show the feasibility of the cross-level simulation approach

Software-based on-line energy estimation for sensor nodes

Energy is of primary importance in wireless sensor networks. By being able to estimate the energy consumption of the sensor nodes, applications and routing protocols are able to make informed decisions that increase the lifetime of the sensor network. However, it is in general not possible to measure the energy consumption on popular sensor node platforms. In this paper, we present and evaluate a software-based on-line energy estimation mechanism that estimates the energy consumption of a sensor node. We evaluate the mechanism by comparing the estimated energy consumption with the lifetime of capacitor-powered sensor nodes. By implementing and evaluating the X-MAC protocol, we show how software-based on-line energy estimation can be used to empirically evaluate the energy efficiency of sensor network protocols.

An adaptive communication architecture for wireless sensor networks

As sensor networks move towards increasing heterogeneity, the number of link layers, MAC protocols, and underlying transportation mechanisms increases. System developers must adapt their applications and systems to accommodate a wide range of underlying protocols and mechanisms. However, existing communication architectures for sensor networks are not designed for this heterogeneity and therefore the system developer must redevelop their systems for each underlying communication protocol or mechanism. To remedy this situation, we present a communication architecture that adapts to a wide range of underlying communication mechanisms, from the MAC layer to the transport layer, without requiring any changes to applications or protocols. We show that the architecture is expressive enough to accommodate typical sensor network protocols. Measurements show that the increase in execution time over a non-adaptive architecture is small.

COOJA/MSPSim: interoperability testing for wireless sensor networks

Wireless sensor networks are moving towards emerging standards such as IP, ZigBee and WirelessHART which makes interoperability testing important. Interoperability testing is performed today through black-box testing with vendors physically meeting to test their equipment. Black-box testing can test interoperability but gives no detailed information of the internals in the nodes during the testing. Blackbox testing is required because existing simulators cannot simultaneously simulate sensor nodes with different firmware. For standards such as IP and WirelessHART, a white-box interoperability testing approach is desired, since it gives details on both performance and clues about why tests succeeded or failed. To allow white-box testing, we propose a simulation-based approach to interoperability testing, where the firmware from different vendors is run in the same simulator. We extend our MSPSim emulator and COOJA wireless sensor network simulator to support interoperable simulation of sensor nodes with firmware from different vendors. To demonstrate both cross-vendor interoperability and the benefits of white-box interoperability testing, we run the state-of-the-art Contiki and TinyOS operating systems in a single simulation. Because of the white-box testing, we can do performance measurement and power profiling over both operating systems.

The announcement layer: beacon coordination for the sensornet stack

Sensornet protocols periodically broadcast beacons for neighborhood information advertisement, but beacon transmissions are costly when power-saving radio duty cycling mechanisms are used. We show that piggybacking multiple beacons in a single transmission significantly reduces transmission costs and argue that this shows the need for a new layer in the sensornet stack--an announcement layer--that coordinates beacons across upper layer protocols. An announcement layer piggybacks beacons and coordinates their transmission so that the total number of transmissions is reduced. With an announcement layer, new or mobile nodes can quickly gather announcement information from all neighbors and all protocols by issuing an announcement pull operation. Likewise, protocols can quickly disseminate new announcement information to all neighbors by issuing an announcement push operation. We have implemented an announcement layer in the Contiki operating system and three data collection and dissemination protocols on top of the announcement layer. We show that beacon coordination both improves protocol performance and reduces power consumption.

Sensor Networking in Aquatic Environments - Experiences and New Challenges

In this paper we present the design and implemen tation of a small-scale marine sensor network. The network monitors the temperature in the Baltic Sea on different heights from the water surface down to the bottom. Unlike many other wireless sensor networks, this network contains both a wired and a wireless part. One of the major challenges is that the network is hard to access after its deployment and hence both hard- and software must be robust and reliable. We also present the design of an advanced buoy system featuring a diving unit that achieves a better vertical resolution and discuss remaining challenges of sensor networking in aquatic environments.

Integrating building automation systems and wireless sensor networks

Building automation systems (BAS) are used to control and improve indoor building climate at reduced costs. By integrating BAS with wireless sensor networks, the need for cabling can be removed, and both installation and operational costs significantly reduced. Furthermore, temporary BAS installations are made possible. By implementing and evaluating the open BAS standard BACnet on resource-constrained sensor nodes we show that integrating existing standard BAS protocols with wireless sensor networks is feasible.

Sensornet Checkpointing: Enabling Repeatability in Testbeds and Realism in Simulations

When developing sensor network applications, the shift from simulation to testbed causes application failures, resulting in additional time-consuming iterations between simulation and testbed. We propose transferring sensor network checkpoints between simulation and testbed to reduce the gap between simulation and testbed. Sensornet checkpointing combines the best of both simulation and testbeds: the non-intrusiveness and repeatability of simulation, and the realism of testbeds.

Accurate Network-Scale Power Profiling for Sensor Network Simulators

Power consumption is the most important metric in wireless sensor network research, but existing simulation tools for measuring or estimating power consumption are either impractical or have unclear accuracy. We present COOJA/MSPSim, a practical simulation-based tool for network-scale power estimation based on Contikis built-in power profiling mechanism, the COOJA sensor network simulator and the MSPSim sensor node emulator. We compare experimental results measured on real sensor nodes with simulation results for three different MAC protocols. The accuracy of our results indicates that COOJA/MSPSim enables accurate network-scale simulation of the power consumption of sensor networks.

Strawman: resolving collisions in bursty low-power wireless networks

Low-power wireless networks must leverage radio duty cycling to reduce energy consumption, but duty cycling drastically increases the risk of radio collisions, resulting in power-expensive retransmissions or data loss. We present Strawman, a contention resolution mechanism designed for low-power duty-cycled networks that experience traffic bursts. Strawman efficiently resolves network contention, mitigates the hidden terminal problem, and has zero overhead unless activated to resolve data collisions. Our testbed experiments show that Strawman instantaneously provides increased network capacity when needed, allocates the available bandwidth evenly among contenders, and increases energy efficiency in multihop collection networks compared to the traditionally used random backoff.