DEEP: Density-based proactive data dissemination protocol for wireless sensor networks with uncontrolled sink mobility Massimo Vecchio a , Aline Carneiro Viana a , Artur Ziviani b, * , Roy Friedman c a INRIA-Saclay, 91893 Orsay, France b National Laboratory for Scientific Computing – LNCC, 25651-075 Petropolis, RJ, Brazil c Computer Science Department, Technion, Israel article info Article history: Received 11 August 2009 Received in revised form 23 October 2009 Accepted 6 January 2010 Available online 11 January 2010 Keywords: Mobile sink Probabilistic data dissemination Proactive data dissemination abstract This paper investigates proactive data dissemination and storage schemes for wireless sensor networks (WSNs) with mobile sinks. The focus is on schemes that do not impose any restrictions on the sink’s mobility pattern. The goal is to enable the sink to collect a representative view of the network’s sensed data by visiting any set of x out of n nodes, where x  n. The question is how to obtain this while main- taining a good trade-off between the communication overhead of the scheme, the storage space require- ments on the nodes, and the ratio between the number of visited nodes x and the representativeness of the gathered data. To answer this question, we propose density-based proactivE data dissEmination Pro- tocol (DEEP), which combines a probabilistic flooding with a probabilistic storing scheme. The DEEP pro- tocol is formally analyzed and its performance is studied under simulations using different network densities and compared with a scheme based on random walks, called RaWMS. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction A wireless sensor network (WSN) may consist of hundreds or even thousands of low cost nodes communicating among them- selves [1]. Classical application scenarios for WSNs include, e.g., environmental and structural monitoring, event detection, and tar- get tracking. In many of these applications, tiny sensor nodes are deployed in an area to be monitored. Each node is a small device able to collect information from the surrounding environment through one or more sensors, to process this information locally, and to exchange data through a wireless channel. Since nodes are typically powered by small batteries, which in general cannot be easily changed or recharged, one of the main concerns in deploying real and functional WSN applications is saving energy to extend the network lifetime. The data flows in WSNs are targeted towards special nodes called sinks (also referred to as base stations) using multi-hop com- munication among sensor nodes in the monitored area. A sink may link the WSN to another network (like a gateway) to propagate the sensed data for further processing. Sinks usually have enhanced computational, storage, and power capabilities over simple sensor nodes since they must do more complex data processing. Many WSN applications consider fixed sinks collecting data sent by the sensor nodes within the monitored area. Nevertheless, nodes close to the sink, acting as relays in a multi-hop scenario, typically con- sume more energy due to data forwarding than far away nodes and thus risk running out of battery earlier than the average node. Once these nodes nearby the sink die, the network becomes discon- nected, thus compromising the network lifetime. Additionally, fixed sinks can become vulnerability points of the network. To alleviate the problems of fixed sinks, a new paradigm has been promoted in several recent works: instead of the data flowing towards fixed sinks, mobile sinks traverse the network to collect the data from the sensor nodes. Here, we focus on such WSNs with mobile sinks. Data management proposals in WSNs with mobile sinks are characterized by their data dissemination strategy (how data is dis- tributed in the network) combined with the data collection strategy (how the mobile sink gathers the monitored data made available by the sensors in the network) [2]. Data dissemination may be per- formed in two ways: 1. Proactively, if the monitored data is proactively distributed and stored throughout the network for being later retrieved by the mobile sink [3–5]. 2. Reactively, if data is sent towards the mobile sink as a reaction for the detection of sink’s presence or queries [6–8]. Depending on how data is disseminated, the mobile sink may need to follow a predetermined trajectory in which it needs to visit specific nodes or locations in the network. Most previous work has 0140-3664/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2010.01.003 * Corresponding author. Tel.: +55 24 2233 6199 E-mail address: ziviani@Incc.br (A. Ziviani). Computer Communications 33 (2010) 929–939 Contents lists available at ScienceDirect Computer Communications journal homepage: www.elsevier.com/locate/comcom