g., node 9 in Figure 10), (2) Second, if two or more nodes have the same
parent node (e.g., nodes 3 and 4 in Figure 10), the parent node will extend its
wakeup time to allow all its child nodes to transmit their data to it. This is
called a data prediction scheme in DMAC, and (3). Third, if two interfering
nodes at the same tree level have di?®erent parent nodes (e.g., nodes 7 and 8
in Figure 10), then one of them can use the More-To-Send packet to request
its parent node to extend its wakeup time.
100 Ali Abu-el Humos et al.
Chapter 4 Medium Access Control Protocols for Wireless Sensor Networks
Fig. 10. DMAC wakeup times in data gathering tree.
DMAC is only e?±cient in data gathering tree scenario where tra?±c is
unidirectional from source node to sink node. SMAC is a more general and
more e?±cient protocol under di?®erent communication scenarios.
4.5 Wireless Sensor MAC (WiseMAC) Protocol
In WiseMAC protocol [2], all the nodes in the network wake up periodically
(with period Tw) to check for any activity of the medium, as shown in Figure
11. Nodes are not synchronized to wake up simultaneously and this reduces
the synchronization overhead. On the other hand, since a receiving node turns
its radio on for a short period of time(?‰? Tw) when it samples the medium,
the transmitting node should transmit along a preamble signal of size equal
to Tw, in order to ensure that the receiving node will be awake to receive
the data packet which follows the preamble.
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