Thus, each node
transmits during its allocated time slot and enters the sleep mode otherwise.
While TDMA prevents collisions within each cluster, it does not prevent
collisions between clusters. Nodes in neighbor clusters might transmit at the
same time, resulting in collisions. In order to prevent collisions, LEACH uses
the CDMA mechanism and assigns to each cluster a unique CDMA code.
LEACH is a distributed and localized protocol. It achieves energy savings
by having inactive nodes enter the sleep state, by using cluster head rotations,
and by using data aggregation at the cluster head. The main disadvantage of
this protocol is that it uses CDMA to resolve interferences between adjacent
clusters. This may not be always feasible and may result in poor bandwidth
utilization.
3.2 Bluetooth
Bluetooth (IEEE 802.15.1) [19] is a wireless technology intended to connect
di?®erent wireless devices such as telephones, notebooks, PDAs, printers, computers
and so on to form a Piconet as shown in Figure 1. Piconets can be
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present two schedule-based MAC protocols, LEACH and Bluetooth.
Ali Abu-el Humos et al.
Chapter 4 Medium Access Control Protocols for Wireless Sensor Networks
Fig. 1. Bluetooth Piconet.
combined together to form a Scatternet, where the slave node in one Piconet
may act as the master for the adjacent Piconet. Bluetooth devices are low
power devices with a transmission range of approximately 10 m.
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