Strategies for improving performance of IEEE 802.15.4/ZigBee WSNs with path-constrained mobile sink(s)

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 associated 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 applicable 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 identified. The presented simulation results prove that with the three proposed mechanisms in place the benefits 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.