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184 From smart grid to internet of energy

FIG. 5.6 Superframe structure for IEEE 802.15.4 standard.

SD ¼ aBaseSuperframeDuration 2 SO symbols, for 0 SO BO 14 (5.2)

In the event of the value of SO is 15, the superframe will not carry on the
active mode after the beacon. When the value of the BO is 15, the value of SO
will be ignored.
The MAC layer responsibilities can be given as follows.
l Forming of Beacons for Coordinator: A coordinator can select its operating
mode as beacon-enabled mode or non-beacon mode. The coordinator runs
by using superframe structure in the beacon-enabled mode where the num-
ber of superframes is constrained by network beacons. Every active part of a
superframe contains 16 equally spaced slots (aNumSuperframeSlots). Fur-
thermore, coordinators periodically send network beacons in order to syn-
chronize devices connected to the network.
l Supplying Synchronization among PAN Coordinator and End-Device: The
synchronization is a critical process to determine status of devices in the net-
work and energy saving transactions. Therefore, an end-device operating in
beacon-enabled mode should follow beacons for presenting synchronization
to the PAN coordinator.
l Association and Disassociation: In star and mesh network types, automatic
setup and self-configuration features are enabled through association and
disassociation information provided by the MAC layer.
l Channel Access Process via CSMA/CA Technique: Channel access process
in the IEEE 802.15.4 standard is accomplished by employing CSMA/CA
method similar to other popular protocols developed for wireless networks.
However, request-to-send (RTS) and clear-to-send (CTS) mechanisms are
not utilized in this standard.
l GTS System: While the beacon-enabled mode is active, coordinator can com-
mit some parts of the efficient superframe into a device. These parts of the
superframe are called GTSs and they also include CFP of the superframe.