**1. Introduction**

98 Wireless Sensor Networks – Technology and Protocols

Vol. 17, No. 5 pp. 1494 - 1507

HongKong, March 2004

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Yu Y., Krishnamachari B. & Prasanna V. (2004). Energy-Latency Tradeoffs for Data Gathering in Wireless Sensor Networks. IEEE INFOCOM 2004. Twenty-third AnnualJoint Conference of the IEEE Computer and Communications Societies,

> There are many techniques used to conserve WSN energy, in order to prevent its premature dead. Longer distance transmission, involving a number of relaying nodes, increases energy consumption very fast. It is striven to receive a messages from nodes located as close as possible to a Base Station (BS). The nodes are deployed and we have no possibility to change its location. In order to achieve energy saver effect, more rational seems to be having mobile BS, especially that in real life there is usually only one. Typically, in WSN there are a lot of sources of messages. BS should be moved to the location where messages are flow evenly from all directions. If this condition is met, it prevents unnecessary BS movements in other directions. Furthermore, such BS location reduces consumption of energy spending for communication but, as a drawback, it reduces the WSN lifespan.

> So, as it was assumed that in order to obtain the longer WSN lifespan, Base Station (BS) position can't be fixed, and it needs to be mobile. Having BS fixed to one position one agrees for quick nodes' energy depletion, since the messages routed along the same paths will drain energy to zero quite fast and render these nodes not operational, which ultimately would lead to network death.

> There are advantages and disadvantages of moving BS closer to the origin of messages sent. The closer to the source of messages BS is, than less consumption of energy spending for communication in WSN is. However, if we move BS to close to a potential threat (e.g. source of fire, in case we monitor fire hazard in some area), this vital WSN element may be too exposed and ultimately damaged or even completely destroyed (which would render entire WSN no longer operational). Therefore special attention shall be brought to the idea how far BS shall be moved.

© 2012 Nikodem et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Nikodem et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Another issue to consider is; how often BS should change its position? To minimize BS movement once the intensity of messages is neither changing rapidly nor area of these changes migrating too far, what would the threshold (or any other factor) that has influence on decision that BS won't be moved.

Since it is the common knowledge that migrating BS could help extend WSN lifespan, it is just a question; how this migration should be organized. There are several aspects to be investigated, among others: whether BS should change its position every time a message is received or not (if not how often should it be?), how far BS should move from its previous (original position), how the BS movement affects behavior of all nodes and the BS neighborhood. Another crucial aspect is how to notify the nodes from BS neighborhood that will soon become out of communication range with BS, when it is moving away from these nodes.

BS movement just a fracture of relay radio link range, seems to be energetically unreasonable, since just this kind of movement involves new distribution of nodes calculation and new relays designation, that consumes a lot of valuable energy resources.
