Strategies for improving performance of IEEE 802.15.4/ZigBee WSNs with path-constrained mobile sink(s) N. Vlajic ⇑ , D. Stevanovic, G. Spanogiannopoulos Department of Computer Science and Engineering, York University, Toronto, Canada article info Article history: Received 14 October 2009 Received in revised form 7 September 2010 Accepted 23 September 2010 Available online 29 September 2010 Keywords: Sensor networks Sink mobility ZigBee standard Performance evaluation Simulation abstract Most of the existing works on the topic of sink mobility in wireless sensor networks (WSNs) are of purely theoretical nature. The aim of this paper is to discuss the challenges as well as potential benefits associ- ated with the use of mobile sinks in WSNs that operate in space-constrained environments and employ real-world technology. Specifically, we examine the pros and cons of deploying path-constrained sink mobility in the framework of IEEE 802.15.4/ZigBee enabled sensor networks. The main contributions of this paper are as follows: First, we demonstrate that the advantages of deploying path-constrained sink mobility, as identified in one of our earlier works [4], are not fully appli- cable to ZigBee WSNs. Specifically, our OPNET-based simulation study shows that in ZigBee WSNs the findings from [4] hold only conceptually, at the highest level of user-data routing. However, once all of the mobility-related overhead is accounted for, no actual benefit of deploying a mobile-over deploying a static-sink can be observed. Subsequently, we propose the use of three mechanisms for control of mobility-related overhead in ZigBee WSNs: Suppressed Route Discover, Node Association Based on Residual Energy, and Footprint Chaining. The most complex of the three mechanisms (Footprint Chaining) is studied in detail, and conditions under which this technique achieves optimal performance are precisely identi- fied. The presented simulation results prove that with the three proposed mechanisms in place the ben- efits of mobile-over static-sink deployment can be regained, almost to the same extent as theoretically identified in [4]. To our knowledge, this paper is one of the first attempts to bring the topics of path-constrained sink mobility and ZigBee standard together. It is also the first published work to propose improvements to the current ZigBee standard specifically targeted for WSNs that involve the use of mobile sinks. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction In recent years, Wireless Sensor Network (WSN) technology has attracted increasing attention from both industry and academia thanks to its tremendous potential in various application fields, including: environment monitoring, security surveillance, disaster management and combat operations. To date, in most research studies on WSNs, the network is assumed to comprise a large num- ber of miniature battery-powered sensor devices scattered over an area of interest and forming a multi-hop 1 communication network, as shown in Fig. 1. The primary goal of the wireless sensors is to gather relevant data from their surrounding and, subsequently, to route the gathered data to a central processing node, commonly re- ferred to as sink. The sink is generally considered to have far superior capabilities than the ‘ordinary’ nodes (i.e. sensors), and it serves as a gateway point to the end user of the system. In the networking liter- ature, such systems consisting of multiple sending and one superior receiving station are known as many-to-one systems. In addition to employing a multi-hop many-to-one network model, another characteristic common to the majority of existing works on WSNs is the assumption that both the sensors as well as the sink are static. All static assumptions generally lead to sim- pler analysis and more tractable solutions. Nevertheless, in a num- ber of WSN application scenario, the presence of mobility is a fact of life, and thus cannot be ignored. For example: (a) In applications that involve the use of ‘wearable sensors’ [1], the sensor nodes are inherently mobile by the virtue of human mobility. (b) In applications where data collected by the sensors is intended for (e.g.) a user driving a car, such as in Smart Park- ing project [2] illustrated in Fig. 2, or for a ranger patrolling through a forest [3], the human user now plays the role of a data-sink and is inherently mobile. Another group of appli- 0140-3664/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2010.09.012 ⇑ Corresponding author. Tel.: +1 416 736 2100. E-mail addresses: vlajic@cse.yorku.ca (N. Vlajic), dusan@cse.yorku.ca (D. Steva- novic), spano@cse.yorku.ca (G. Spanogiannopoulos). 1 In a multi-hop WSN, data is passed from the source node to the destination by being relayed by intermediate nodes. Computer Communications 34 (2011) 743–757 Contents lists available at ScienceDirect Computer Communications journal homepage: www.elsevier.com/locate/comcom