Wireless Sensor Networks

The academic year 2010-2011 saw major improvements to the Embedded Systems module (see previous post). One of such improvements was aimed to reflect the increasing importance and widespread use of wireless sensor networks (WSNs). Such networks are a specific type of distributed embedded system, and have been applied to application domains such as habitat monitoring, earthquake prediction and smart homes. WSN nodes (also known as motes) are thumb-sized computers that operate on batteries and sense the environment around them. Motes can cost between £50-£250 each (depending on their wireless radio standard, processing/storage capabilities and packaging), plus additional costs for specific sensors (temperature, light, sound, etc.)

To provide students with practical experience on the development of such systems, I submitted a request to the university's Rapid Response Fund to finance the purchase of a set of wireless sensor nodes (with matching funds from the CS department). I was really happy to see that both the university and the department have such mechanisms to enable small but high-impact initiatives that can improve student experience. It was very lightweight, no bureaucracy, and in a few weeks I've got the notification that the request was granted.

I had decided to purchase a IRIS Classroom Kit, which includes 30 motes, 20 light/temperature sensors and 10 USB data acquisition boards (for programming and debugging on lab PCs), respective software and documentation. After the delivery of the kit, I tested the motes and started to prepare my laboratory activities and experiments. To simplify the programming of the motes by the students, I chose Mote Runner, a new software package that had been recently released by IBM within their alphaworks. In an agreement with IBM's research center in Zurich, York became one of the first universities worldwide that could use that software package for teaching and research purposes (alongside ETH Zurich). I will probably write more about Mote Runner in another post, but here's some information coming directly from the source:

I've prepared six 2-hour lab sessions covering different aspects of WSN design, including system specification, embedded software programming, networking protocols, energy efficiency, system simulation and deployment. Some of the lab sessions included simple exercises to familiarise students with the hardware and software infrastructure, while others followed a problem-based learning approach.

In one of the problem-based sessions, students were divided in two groups that were given 10 motes each, and were asked to create a simple packet forwarding protocol to transmit a message over the Computer Science building, from the Crossrail Lab (where the lab sessions took place) to my office. Once both groups had the protocol implemented and the motes deployed, they should call my office from the CrossRail lab and ask for the message to be transmitted (actually a sequence of colors that should be displayed by blinking LEDs on a mote). The message would then be loaded to a base station mote, which in turn should forward it to other nodes, successively towards the destination. The first group to complete the mission was awarded a box of chocolates.


Part of the assessment of the students (their exam!) was also based on Mote Runner and the IRIS motes. This time, the problem involved indoor localisation of a mobile mote using radio signal strenght obtained from six stationary motes. Students were evaluated on the accuracy of the localisation algorithms they implemented, as well as the memory footprint and energy efficiency of their solutions. They actually did well!


At the moment I am thinking about some new problems that I can use to assess the students taking the Embedded Systems module in the next academic year. But I can't give you any details now... my students would be really sad if I ruin the surprise :-)