SOLAR PV CONTROL SYSTEM.pdf
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total number of 27 channels, where 16 is applied to the 2.4 GHz, 10 for 915 MHz and<br />
finally 1 for 868 MHz Devices that are constructed with IEEE 802.15.4 protocol stack<br />
implemented in it uses Direct Sequence Spread Spectrum (DSSS) to raise the<br />
bandwidth of the transmitted signal for a reliable communication. The physical<br />
specifications are given in the table 1 below.<br />
The IEEE 802.15.4 MAC Layer<br />
Table 2: Specification of IEEE 802.15.4<br />
Applications for IEEE 802.15.4 wireless sensor networks are target for home<br />
automation, home networking, PC peripherals, and home security and so on. Several<br />
of those application demands only low-to-medium bitrates around some few<br />
hundreds of kbps. The physical layer provides different bitrates depending on which<br />
frequency range is applied by the device. The frequency also decides how many<br />
channels are available within the frequency range. MAC protocol uses only one of<br />
these channels at a time. Since it is the MAC layer that is used to link communication<br />
between devices a general description of how device get associated and<br />
disassociated on the network follows below, which is according to the book:<br />
Protocols and Architectures for Wireless Sensor Networks.<br />
• A Full Function Device (FFD) can operate in three different roles: it can be a<br />
PAN coordinator, a simple coordinator or a device<br />
• A Reduced Function Device can operate only as a device A device must be<br />
associated to a coordinator node (which must be a FFD) and communicate<br />
only with this way forming a star network. Coordinator can operate in peer-<br />
to-peer fashion and multiple coordinators can form Personal Area Network<br />
Email: david.irungu@stu.kuct.ac.ke<br />
44<br />
2012
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