Ubiquitous computing is increasingly introduced in our daily life. An emerging application is environmental monitoring in urban areas. Data gathering in such wireless sensor networks can be performed by using uncontrolled mobile sinks besides the fixed sinks in order to reduce the transmission energy. This method can be highly inefficient as the notification of presence by the mobile sink is not guaranteed. An efficient hybrid method for message relaying and load balancing is proposed in low mobility wireless sensor networks. The system uses either a single hop transmission to a nearby mobile sink or a multi-hop transmission to a far-away fixed node depending on the predicted sink mobility pattern. Taking a mathematical approach, the system parameters are adjusted so that all the sensor nodes dissipate the same amount of energy. Consequently, the problem of losing connectivity due to the fast power drainage of the closest node to the fixed sink is resolved. Numerical results showed that the system lifetime outperforms classical methods of message gathering.
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