Mobility Support in IEEE 802.15.4 Based Mobile Sensor Network

Providing diverse Quality of Service (QoS) with ultra-low power consumption and support of mobility is the most important and challenging issue in wireless body area networks (WBANs). The IEEE 802.15.4 standard exhibits a desirable feature for WBAN, but its inability of mobility support makes it insufficient. In this paper, we show what is required for node mobility support and propose two strategies for the support. We observed that the amount of time required for the association process is the key reason IEEE 802.15.4 is unable to handle mobility. In this paper, we present a new fast association technique, which prevents nodes from scanning multiple channels. In the proposed scheme, by scanning just a single channel, a node can learn about all the coordinators working in different channels. The single channel scanning scheme is able to decrease the association time of IEEE 802.15.4 operating in 2.4 GHz by 32 times. Furthermore, in this paper, a method to increase the node connectivity time with its coordinator in IEEE 802.15.4 beacon-enabled mode is introduced. The method tries to anticipate whether the node is moving towards or away from the coordinator by analyzing the signal strength of multiple beacons received from the same coordinator. Thus, the connectivity time is increased by choosing the coordinator with good signal strength, but located both furthest from the node and toward the direction which mobile node is moving. Our approach results in significant improvement by reducing the number of times the moving node switches coordinators. Experimental results have verified that our schemes work well in the mobile sensor network environment.