7. THE DISTRIBUTED 3D SPACE COVERAGE SCHEMES FOR UNDERWATER WIRELESS SENSOR NETWORKS Hakan TEZCAN, 2004

Keywords: Wireless sensor networks, Underwater wireless sensor networks, Coverage, Placement, Distributed algorithm, Tactical surveillance.

Recent scientific advances in Micro Electro-Mechanical Systems (MEMS) and wireless network technologies have placed us at the doorstep of a new era where small wireless devices which are called sensor nodes will provide access to information anytime, anywhere. Contrary to more traditional computer networks, wireless sensor networks consist of a large number of these ultra-small autonomous sensor nodes. Each sensor node is battery powered and equipped with integrated sensors, data processing capabilities, and short range radio communications. In wireless sensor networks, sensor nodes gather data from their environment and convey these data to any end point using a wireless medium with a collaborated effort by using their limited power sources.

In this thesis, we propose a novel architecture for underwater wireless sensor networks that can be used to detect a target in the vicinity of the sensor nodes. According to our architecture, when sensor nodes first deployed randomly, sensors lie in surface buoys. After deployment, nodes adjust their depths via a cable which is also used for the communication link between the sensor and the surface buoy. Although the sensors are underwater, the nodes can collaborate through the wireless medium over sea surface by using the antenna at the surface buoys.

In wireless sensor networks, coverage represents how well an area is monitored and can be considered as the measure of Quality of Service (QoS) of the network. It is most desirable that each point in the sensor field should be within the sensing range of at least one sensor for achieving a good QoS. Therefore we also develop two distributed placement algorithms in order to maximize the coverage of the 3D underwater sensor space of our proposed architecture. One of these algorithms is developed for sensor networks consist of location aware nodes and the other one is for the sensor networks consist of non-location aware nodes. Our distributed placement algorithms that rely solely on local packet exchanges run on sensor nodes and calculate the depths of sensors according to the locations of neighboring nodes such that the maximum three dimensional coverage of the sensor space is maintained. Although our schemes are distributed and adaptive, they maintain a high coverage of the sensor space in the expense of acceptable control traffic overhead.