On the Relationship between Network Congestion and Local Contention in IEEE 802.15.4 Based Networks

Due to the specific operation of wireless sensor networks (WSN) and especially to the multi-hop nature of many WSNs, local contention can lead to network-wide congestion and reduce both the efficiency and the lifetime of the network. In this paper we study the interdependence between end-to-end congestion and local contention including different mobility patterns using three different application scenarios. In each of the scenarios discussed, all nodes send information to a sink which is the PAN coordinator. In the first one, all the nodes are static, in the second one the sink is static while the nodes are moving and in the third one the sink is static while the rest of the nodes are mobile. The work is based on the slotted CSMA/CA MAC adopted in IEEE 802.15.4 protocol specification for LR-WPAN. Results show the effects of changing local contention regulating parameters like activity periods, number of MAC layer retransmissions and transmission buffer size on the overall network congestion.