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.

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 softwarebased 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.

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.