Context

Wireless testbeds enable to effectively test the wireless protocols or applications in a real-life environment. In such an environment, the spectrum is not 'clean', and the locations of the nodes are fairly random. Current testbeds generally offer very limited flexibility in terms of application scenarios, node failure and the like, and are therefore not the ideal validation tools for real-life wireless network operation. Further, one of the major research issues in wireless networks is the development of energy efficient protocols in order to enlarge the lifetime of the nodes and thus the network. However, in existing testbeds it is not possible to measure the energy consumption of each individual node efficiently.

w.iLab.t testbed

The w-iLab.t testbed includes both a wireless mesh and sensor network infrastructure. These networks can interact with each other, making it possible to test advanced scenarios such as using the mesh network as a backbone for the sensor network. Further, interference between both networks can be studied. In order to facilitate the emulation of realistic sensor scenarios and to measure the energy consumption, the testbed is equipped with a custom designed hardware solutions, called the Environment Emulator (EE). Using the EE, it is possible to emulate the behavior of any type of sensor or actuator without the need for real sensor/actuator hardware or the development of a full-blown sensor application. It is possible to emulate the battery depletion, depending on the real life power consumption of the sensor node. When the node's battery is depleted or the node is destroyed (e.g., in an explosion), the node can be switched off. The EE can be programmed to emulate a sensor event (e.g., temperature rise, motion detection), an actuator event or to support voice streams. Further, the EE can be used to monitor the energy consumption of each individual sensor. Altogether, this means that it is possible to assess the complete usability of a certain wireless sensor and actuator network application or protocol in a real-life environment. The initial core of w-iLab.t was based on the widely used MoteLab testbed from Harvard University.

The w-iLab.t testbed is deployed in an office building of 18x90m and is spread out over three floors. It consists out of 200 node locations(see further) at fixed locations at the iMinds office premises, including meeting rooms, class rooms, offices and corridors.

Node locations of the w-iLab.t testbed

Map of the second floor.

Additionally, w-iLab.t is equipped with a shielded wireless environment. This environment is built up by 4 shielded boxes in which an iNode is installed. The iNodes are interconnected between the boxes by coax cables via a variable attenuator. By varying the signal attenuation, node mobility can be simulated in a repeatable way.

Left: RF shielded boxes. Right: iNode inside the box.

iNodes:

Every w-iLab.t node is generic and is equipped with one or more sensor nodes, an intermediate node with 2 WiFi 802.11 radios, the environment emulator and a Bluetooth interface.

The sensor nodes are Tmote Sky motes that use a Tiny OS development environment. They consist of a TI MSP430 processor running at 8MHz, 10KB of RAM, 1Mbit of Flash memory and an IEEE 802.15.4 compliant Chipcon CC2420 radio operating at 2.4GHz with a maximum indoor range of approximately 100 meters. Each node includes sensors for light, temperature, and humidity. The hardware setup is extendable with a large variety of other radios (e.g Software Defined Radio, sensing engine), as long as the radio has a USB or RS232 serial interface.

The intermediate nodes (called iNodes) are Alix 3C3 devices running Linux. These are mini PC's equipped with Ethernet, USB, serial, vga, audio and two IEEE 802.11 a/b/g interfaces. All the iNodes are connected to the management backbone using Power-over-Ethernet switches, making it possible to power up/down the iNodes as needed without physical interaction with the iNodes. The iNodes can become an active member of the experiment as it is possible to adjust the kernel, the driver, to add click router code or to add java-based applications.

Finally, the Environment Emulator is located in between the iNode and the sensor node.

iNode mounted to the ceiling.

Accessing the testbed

The w-iLab.t testbed is centrally managed for control and monitoring purposes. It supports easy configuration and deployment, including installation of new software, protocols and middleware components via an intuitive web-based interface. Registered users can upload executables, associate those executables with the nodes (both sensor nodes and iNodes) to create a job, and schedule the job to be run on W-iLab.t. During the job all messages and other data are logged to a database, which is presented to the user upon job completion and then can be used for processing and visualization.

All the possibilities of the complete testbed, the environment emulator scenarios and events, a visualization and a graphical analysis tool, are accessible through a web interface. The visualization tool can visualize any type of node status and/or link information on a map of the building, while the graphical analyzer plots out the data. The information for both tools is gathered from the database through the use of user customizable MySQL statements, making it extremely flexible.

External users can access the testbed over a secured OpenVPN connection.

Contribution to CREW

The w-iLab.t testbed as well as new cognitive radio extensions will be made available in the federated testbed.