ZigBee Wireless Soil Moisture Sensor Design for Vineyard ...

The superframe structure is only used in beacon mode. In non beacon mode
superframe structure is disabled and nodes compete for channel access via
CSMA/CA. The superframe is divided into 16 slots, the first slot contains the
transmitting beacon and he other 15 slots are used for node communication.
Coordinator node defines the structure of the superframe, with two sections:
Connection Access Period (CAP) and Connection Free Period (CFP). The
basic superframe structure is shown in Figure 1. In a larger network, when the
traffic volume is higher, most of the time slots are used for CAP, not for CFP
[6]. Therefore this mode is not suitable for a network which involves a larger
number of nodes.
Figure 1: IEEE 802.15.4 Superframe Structure [7]
A non beacon network is more useable than the beacon enabled network. The
Media Access Control (MAC) of the non-beacon mode is contention based
CSMA/CA. Therefore typically most of the receiver nodes are continuously
active. This requires a more robust power supply, but it allows for networks
where nodes can receive and transmit data continuously. For larger networks
like this vineyard monitoring system, the non beacon mode enabled network is
more suitable.
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