Investigation of Wireless Sensor Networks for Structural Health Monitoring

Table 2

Comparison of three kinds of topology for WSN.

	Networking features	Advantage	Disadvantage
Star	Supporting point-to-multipoint and multipoint-to-point communication.; Need for a concentrator or hub (coordinator for ZigBee network). All data are transited by hub.; Suited for networking in which the distance between equipments is small and scattered in a circular fashion.; Suitable for massive, low-speed, and non-real-time applications, such as distortion monitoring.	Brief structure. Protocol is simple by using a polling mode.	The entire spatial span of the transmission network is equal to the span of the physical layer.; Concentrator can carry out the role of data fusion. Its reliability has the decisive effect regarding the performance of the entire network.
Cluster tree	Network is composed of many star topologies, using a star to connect the concentrator.; Suitable for situations where data needs to be converged, such as in a structure monitoring network that has an intelligent analysis ability.	A leveled and clear structure.; Transmission distance is greater than the star topology.; Protocol is relatively simple and clearer than with mesh networks.	All the root nodes of the cluster tree (concentrator or the convergent point) are essential nodes, upon which there is also the demand of a high ability in terms of data fusion. Energy consumption and reliability as well as the influence on the entire network are a major issue.
Mesh	All entities can communicate with each other as long as they are within the scope of the network and if there is no direct path; they also can communicate in “multihop” fashion.; They can form highly complex and large capacity networks. The network can cover a large physical space so it is suitable for installation on scattered structures.; The network also has self-organisation and self-healing capabilities.	The behaviour of the single node is relatively consistent.; The capacity of the network is large.; Generally it does not have any essential node. There are many available communication routes and the success ratio of the transmission is increased in comparison to those gained with other networks.	The behaviour of the entire network is not easily controlled.; With an increasing number of nodes, the complexity of the network behaviour increases greatly and the efficiency is reduced.