Chapter 4 Medium Access Control Protocols for Wireless Sensor Networks
Fig. 7. SMAC without adaptive listening.
Fig. 8. SMAC with adaptive listening.
become aware of its transmission due to various wireless communication propagation
modes (paths).
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Fig. 9. Data forwarding is not interrupted.
4.4 An Adaptive Energy-E?±cient and Low-Latency MAC for Data
Gathering in WSNs (DMAC) Protocol
Within one cycle, adaptive listening in SMAC only forwards packets two hops
away from the sending node (as shown in Figure 8) assuming the CTS packet
is only overheard by the next hop from the receiver. Packet forwarding will
be interrupted, and the packet must wait until the next scheduled wakeup
time in order to be forwarded to the next hop. DMAC protocol [6] suggests
continuous data forwarding as shown in Figure 9. In order to accomplish this,
nodes on the chain path from source to the sink must wake up sequentially,
by having staggered schedules.
The schedule of every node is shifted. It shares half of its wakeup period
with its downstream node (child) and the other half with its upper stream node
(parent) as shown in Figure 9. RTS/CTS control packets are not necessary.
Only ACK packet and data retransmission are implemented to ensure packet
delivery. DMAC adapts itself to the network tra?±c through three schemes: (1)
First, if a node has more than one packet to transmit, it will set the more data
flag in the MAC header to request its parent node to extend its wakeup time
(e.
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