**8. References**

[1] I. Akyildiz, W. Su, Y. Sankarasubramaniam and E. Cayirci, "Wireless sensor networks: A survey," *Computer Networks Journal,* vol. 38, no. 4, pp. 393-422, 2002.

[2] P. Rentala, R. Musunuri, S. Gandham and U. Saxena, "Survey of Sensor Networks.," 2002.

68 Wireless Sensor Networks – Technology and Protocols

seconds.

**7. Conclusion** 

is further reduced.

increase node lifetime.

**Author details** 

G. P. Hancke

**8. References** 

S. Chinnappen-Rimer

*Department of Electrical and Electronic Engineering Science, University of Johannesburg, Johannesburg, South Africa,* 

*University of Pretoria, Pretoria, South Africa* 

*Information Security Group, Royal Holloway, University of London, Egham,* 

*United Kingdom and Department of Electrical, Electronic and Computer Engineering,* 

A survey," *Computer Networks Journal,* vol. 38, no. 4, pp. 393-422, 2002.

[1] I. Akyildiz, W. Su, Y. Sankarasubramaniam and E. Cayirci, "Wireless sensor networks:

and hence increased node lifetime.

The time it takes for an event message to reach node 14 and node 24 using the mobile algorithm with re-transmissions of event messages restricted to nodes with four or more neighbours is shown in Figure 10. If the mobile node has just passed out of range of node 24 and node 14, then these nodes must wait for approximately 72 seconds before the mobile node is within range again. Alternatively, depending on the real-time requirement of the application, the perimeter nodes can retransmit the event message as electromagnetic waves travel faster than the mobile sink and the message should reach the sink in less than 72

An optimum path for a mobile sink is calculated so that the number of hops that the message has to be re-transmitted is small. Because all neighbouring nodes can pass an event message to the sink, no specific set of nodes is overloaded with the task of routing event messages to the sink. This ensures more equitable usage of all sensor nodes in the network

It has been shown that the number of messages received per node can be reduced by using a specific path for the mobile node/sink to move along. All neighbouring nodes can store messages when an event occurs, and if the sensor detecting the event is not an immediate neighbouring node along the path of the mobile sink, the number of hops that the message has to be re-propagated is small. By restricting the nodes that re-transmit a message to nodes with four or more neighbours, the number of messages received per individual node

Thus the use of a mobile sink moving along a calculated path around the application area can significantly reduce the number of messages received per individual node and hence

	- [18] L. Ben Saad and B. Tourancheau, "Towards an Efficient Positioning of Mobile Sinks in Wireless Sensor Networks inside Buildings," in *3rd International Conference on New Technologies, Mobility and Security (NTMS)*, 2009.
