Sensors_**2011**, _11_, 11415-11446; doi:10.3390/s111211415  
_Sensors_  
**ISSN 1424-8220**  
www.mdpi.com/journal/sensors  
_Article_  
**On Mobility Management in Multi-Sink Sensor Networks for Geocasting of Queries**  
**[PERSON] \({}^{1,\star}\), [PERSON] \({}^{1}\), [PERSON] \({}^{2}\) and [PERSON] \({}^{1}\)**  
\({}^{1}\) Pervasive Systems Research Group, Department of Computer Science, University of Twente,  
P.O. Box 217, 7500 AE, Enschede, The Netherlands; E-Mails: [EMAIL_ADDRESS] (A.D.);  
[EMAIL_ADDRESS] (P.H.) \({}^{2}\) Ambient Systems B.V., Colosseum 15d, 7521 PV, Enschede, The Netherlands;  
E-Mail: [EMAIL_ADDRESS]  
\({}^{\star}\) Author to whom correspondence should be addressed; E-Mail: [EMAIL_ADDRESS];  
Tel. : +31-53-489-3633; Fax: +31-53-489-4590. _Received: 1 November 2011; in revised form: 21 November 2011 / Accepted: 28 November 2011 / Published: 1 December 2011_  
**Abstract:** In order to efficiently deal with location dependent messages in multi-sink wireless sensor networks (WSNs), it is key that the network informs sinks what geographical area is covered by which sink. The sinks are then able to efficiently route messages which are only valid in particular regions of the deployment. In our previous work (see the 5 th and 6 th cited documents), we proposed a combined coverage area reporting and geographical routing protocol for location dependent messages, for example, queries that are injected by sinks. In this paper, we study the case where we have static sinks and mobile sensor nodes in the network. To provide up-to-date coverage areas to sinks, we focus on handling node mobility in the network. We discuss what is a better method for updating the routing structure (_i.e._, routing trees and coverage areas) to handle mobility efficiently: periodic _global updates_ initiated from sinks or _local updates_ triggered by mobile sensors. Simulation results show that local updating perform very well in terms of query delivery ratio. Local updating has a better scalability to increasing network size. It is also more energy efficient than our previously proposed approach, where global updating in networks have medium mobility rate and speed. **Keywords:** geocasting; convex hull; local updating; mobile sensors; wireless sensor networksIntroduction  
Wireless Sensor Networks (WSNs) are a specific class of _ad hoc_ networks composed of many tiny devices called sensor nodes spread throughout a given area and capable of collecting information about the surrounding environment, of processing this information, and of circulating it through the network via a wireless communication channel. Applications of WSNs have emerged in many domains ranging from environmental monitoring to industrial automation as well as disaster management. In all these applications, one of the fundamental operations in a wireless sensor network is convergecast, which refers to the communication pattern where data is collected from a set of sensor nodes and forwarded towards a common end-point gateway, namely a _sink_ node, in the network. Initial deployments of wireless sensor networks had one sink, but many current WSN applications require multiple sinks. Having multiple sinks in the network gives advantages such as energy efficiency, reliability and alleviation of the uneven energy depletion problem of a single-sink deployment [1]. The work presented in this paper is mainly motivated by partly stationary, multi-sink deployments of WSNs such as real-time surveillance and city pollution monitoring applications. In these scenarios, the large majority of the deployed nodes are fixed and constitute the infrastructure of the network. In addition, the presence of a fraction of mobile nodes contributes to the overall information gathering process with local and often volatile knowledge [2]. For instance, in a firefighting scenario, firefighters and small helicopters (_i.e._, UAVs) can carry sensor nodes on board to collect data from the fire area.