Frequencyhopping
spread spectrum is used to avoid interference with other devices or
other networks. Bluetooth operates in the 2.4 GHz ISM band which is divided
into 79 channels of 1 MHz each, with a bit rate of 1 Mbps. A Bluetooth network
can have at most eight nodes, one master and seven slaves. This small
number of nodes disqualifies Bluetooth technology from being used in WSNs.
4 Contention-based Protocols
based MAC protocol used in Mobile Ad hoc Networks (MANETs). This protocol
was intended for single-hop networks. Energy waste due to idle listening is
not a serious problem in MANETs. However, IEEE 802.11 provides an option
where nodes can switch to Power Save (PS) mode and turn o?® their radios to
conserve energy. Even if this option is enabled, the IEEE 802.11 may still not
be able to properly maintain node synchronization in the network [17]. However,
the IEEE 802.11 PS mode was further exploited in the design of MAC
layer protocols for WSNs and is usually considered as a point of comparison
in simulations.
There is a rich literature addressing contention-based MAC protocols in
sensor nodes. We describe next several of the most representative such protocols.
4.1 Sensor-MAC (SMAC) Protocol
SMAC protocol [16] considers energy e?±ciency as the most important factor,
while latency and fairness are regarded as secondary criteria. Since most of
the time a wireless node will be in idle listening, SMAC turns o?® the node??™s
transceiver periodically.
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