Abstract
Node mobility in multi-hop communication environments is an important feature of Wireless Sensor Network (WSN)-based monitoring systems. It allows nodes to have freedom of movement, without being restricted to a single-hop communication range. In IEEE 802.15.4 WSNs, nodes are only able to transfer data messages after completing a connection with a coordinator through an association mechanism. Within this context, a handover procedure needs to be executed by a mobile node whenever there is a disconnection from a coordinator and the establishment of a connection to another one. Many applications, such as those found in health monitoring systems, strongly need support for node mobility without loss of data during the handover. However, it has been observed that the time required to execute the handover procedure is one of the main reasons why IEEE 802.15.4 cannot fully support mobility. This paper proposes an improvement to this procedure using a set of combined strategies, such as anticipation of both the handover mechanism and the scan phase enhancement. Simulations show that it is possible to reduce latency during the association and re-association processes, making it feasible to develop WSN-based distributed monitoring systems with mobile nodes and stringent time constraints.
Highlights
A Wireless Sensor Network (WSN) may be composed of a large number of low-cost devices distributed within a particular area of interest
This proposal is based on a set of distinct approaches, and its main contributions can be summarized as follows: (1) we present a new handover mechanism compatible with the IEEE 802.15.4 standard where; (1.1) the handover decision is anticipated; (1.2) the orphan scan step is suppressed; (1.3) the number of channels used in the scan operation is minimized; (1.4) the message exchange sequence defined in the IEEE 802.15.4e optional FastA association mechanism is used; (1.5) the proposed handover mechanism has been assessed by simulation and the achieved results highlight significant improvements in the whole handover procedure; (2) a suitable setup of the IEEE 802.15.4
Simulations were performed comparing IEEE 802.15.4 standard association mechanisms (Std) with the improvements proposed in this paper, namely the anticipation of handover decision-making (Ant) and adequate setup of Media Access Control (MAC) parameters (MAC)
Summary
A Wireless Sensor Network (WSN) may be composed of a large number of low-cost devices distributed within a particular area of interest. Over the last few years, WSNs have been used for agriculture, environment, industry and health monitoring purposes [1]. IEEE 802.15.4 standard [2]. Defines one of the most widely used protocols for deploying WSNs, specifying the physical layer and medium access control sublayer for low-data-rate wireless connectivity. An IEEE 802.15.4 network operates either in one of two topologies, depending on application requirements: star topology or peer-to-peer topology. A cluster-tree topology is a special peer-to-peer topology that has been shown to be one of the most suitable for deploying wide-scale WSNs [3]. Regardless of the topology used, every node in an IEEE 802.15.4 network must be associated with the network, through an association procedure, before it can exchange messages (for more information about association and re-association process of the IEEE 802.15.4, please refer to [2])
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