Coordinated
wake-ups are inserted on the path from source to sink such that
each node wakes up when its downstream node is ready to send its data. This
technique is very close to the work done in DMAC. Fast Path Algorithm is,
however, more general than DMAC which only works under the assumption of
having one sink in the network. Additionally, Fast Path Algorithm is verified
using UCB Motes.
4.7 Mobile Sensor MAC (MS-MAC) Protocol
SMAC was originally designed for staticWSNs.MS-MAC [8] protocol provides
a mechanism for mobile nodes to quickly follow the schedule of the cluster it
is moving to. SMAC neighbor discovery mechanism enables nodes to discover
newly added nodes to the network. This mechanism will also help discover
nodes moving from one cluster to another. During neighbor discovery, nodes
keep listening to the medium for 10 seconds every 2 minutes. Thus, it could
103
Virtual Cluster 1 Virtual Cluster 2
Border Nodes
take 2 minutes for a mobile node to get connected to the new cluster where
it has relocated.
Border nodes can help solve this problem since they are aware of their
cluster schedule and their neighbors schedule on di?®erent clusters. If a mobile
node starts crossing the border of two adjacent clusters, border nodes will
detect its mobility due to the variations in the received signal level at the
border nodes??™ antenna. Once the mobility is detected, border nodes in one
cluster will inform adjacent border nodes that a node is moving towards their
cluster.
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