NODE DENSITY

If the total number of sensor nodes increases, the node density in the framework raises too. Figure 4.10 shows the relationships between node density and the number of layers in the framework. Note that D represents the number of nodes in a Voronoi

Fig. 4.10: Total number of node vs layers.

region. Obviously, the total number of sensor nodes raises as the layer and D increase.

Chapter 5 Conclusions

Adopting data aggregation techniques and hierarchical structure in a WSN for tracking moving objects are effective to prolong the lifetime of the WSNs. However, delay constraints on update and query operations for tracking critical objects should be considered in the WSN that adopts data aggregation and hierarchical structure. So, object tracking applications on WSNs, which meet the QoS constraints, can provide accurate object location and real-time response.

In this paper, we proposed a hierarchical framework that is based on the concept of Voronoi diagram. All of the sensor nodes in the WSN are organized into Voronoi regions hierarchically. Each Voronoi region is associated with a cluster head, which collects the sensory data. Then, the cluster head delivers the collected data upward its cluster head at the higher layer. Moreover, we proposed the anchor nodes approach.

The anchor nodes are located at some layer in the framework. Each anchor node is responsible for storing and aggregating the sensory data. Thus, the proposed hierarchical framework with anchor nodes can support critical object tracking and meet QoS constraints, such as query and update delays. Moreover, we conducted simulations to validate and evaluate the proposed framework. Our simulation results show that the hierarchical framework can achieve better performance (i.e., smaller update delay, lower collision probability, and shorter transmission path) than the flat structure. Besides, the simulation study explores the relationships between anchor layer and the query/update delay constraints. Generally speaking, selecting proper layer in the hierarchical framework to deploy anchor nodes can facilitate the

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