From SensorScope Wireless Distributed Sensing System for Environmental Monitoring
The measurement system we propose consists in multiple measuring stations capable of communicating between each other constituting a wireless sensor network. These individual measuring stations have been designed to meet the following requirements: low energy consumption, long communication range, low cost, simple installation, energy autonomy, high-quality data, water resistant, and to retrieve data in real-time.
The Sensing Stations
The measuring stations consist mainly in three modules: processing and communication, energy management, and data acquisition. All electronic components are housed in a watertight package which is placed, together with all the sensors, on an aluminium skeleton.
Vidicam
Besides meteorological and hydrological parameters, we provide a real-time image of the deployment:
The Wireless Sensor Network
SensorScope makes use of a wireless sensor network to gather environmental data, such kind of network being very close to the so-called ad hoc networks. Such networks are formed by autonomous devices, which operate in a self-organized manner and communicate together using radio interfaces. As communication ranges are limited due to physical properties of radio waves, only close hosts can directly communicate to each other. This means that multi-hop routing must be used, in which data packets are forwarded along a chain of network nodes from the source to the destination. Ad hoc and sensor networks have been have been extensively studied in the past few years due to the difficulty to provide features such as auto-organization or robust multi-hop routing.
Using a multi-hop WSN makes it possible for SensorScope to gather data over a wide area with only one sink and to arbitrarily modify that monitored area by moving/adding/removing stations whenever needed. Since the stations are always monitoring their network neighborhood, these changes are quickly and automatically taken into account without the need to reconfigure the network. A station may also fail, for instance due to lack of energy, without impacting on data gathering. If that station was indeed part of a route to the sink, a new route will automatically be created and used to replace the deprecated one.
Besides delivering gathered data to the base station, the WSN is also responsible for quite a few duties, such as time synchronization. To allow for useful exploitation of data, each measure must indeed be tagged with a timestamp, and since the stations are subject to a substantial time drift (crystals have a correct but not very high precision), it is often needed to resynchronize the stations. In SensorScope, the current time is simply regularly propagated from the sink to the network by mean of multi-hopping. The WSN used is also very energy-efficient and is able to turn off the radio (which is the biggest energy consumer in the system) most of the time, without impacting on data gathering. Thanks to this mechanism and the solar energy system, stations should theoretically never undergo a power outage.