BusNet – A Sensor Network Built Over a Public Transport System

BusNet is a sensor network to be built on a public transport system to monitor environmental pollution. BusNet uses only a few sensors mounted on public transport buses to gather data on air pollution levels in a large geographical area in contrast to a large number of sensors required in a conventional sensor network deployed for such a purpose. The public transport network also acts as the communication network in BusNet. Because only a few sensors are needed for the BusNet it is less costly to build and easy to manage. Even though we present BusNet with respect to one particular application the idea is generic enough to be used in other systems in which a large number of sensors can be replaced by a few moving sensors mounted on public transport vehicles.

Air pollution changes considerably in different areas of a city and even from building to building. Data gathered from a single point are not representative of air pollution levels in different parts of the city and therefore a large number of data gathering points spread over the city is needed. While for a small city it may be feasible to deploy such a system; it would be prohibitively expensive to deploy a system over a larger geographical area such as a large city or a country.

We observe that most countries have a public transport system that spans the country. Buses and train networks have central points (such as regional bus/train stations) from which regional transport networks span out. There are bus and train routes inter-connecting these regional stations as well as central hubs in capital cities. This forms a large public transport network. We propose to use several sensors mounted on the vehicles of the public transport system as a replacement for a network consisting of large number of sensors. These vehicle mounted moving sensors would be able to gather data that covers a large geographical area. When the buses arrive at bus stations, which also function as data collection centers, gathered data are transferred over a wireless link to the collection point. Data gathered in regional collection points are transferred to buses traveling between the regional centers and the main collection center. In this scenario the public transport system functions as a data delivery network as well as the data collection network. Therefore, it is quite different from vehicle assisted data delivery networks, where vehicles form an ad hoc network to deliver data.

In our system data travel in vehicles and also vehicles facilitate data gathering by hosting sensors. We assume that the gathered data are not required in real time in this particular application. We name this network BusNet and we have commenced building a prototype to be deployed using the public transport system in Sri Lanka.