Digi XBee SX 868 - Operation; Listen before Talk and Automatic Frequency Agility

Operation Operation
XBee® SX 868 RF Module User Guide
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Operation
The XBee SX 868 RF Module uses a multi-layered firmware base to order the flow of data, dependent
on the hardware and software configuration you choose. The following configuration block diagram
shows the host serial interface as the physical starting point and the antenna as the physical endpoint
for the transferred data. A block must be able to touch another block above or below it for the two
interfaces to interact. For example, if the device uses SPI mode, Transparent mode is not available as
shown in the following image:
The command handler code processes commands from AT Command Mode or API Mode; see API
serial exchanges. The command handler also processes commands from remote devices; see Remote
AT commands.
Listen Before Talk and Automatic Frequency Agility
This device implements Listen Before Talk (LBT) and Automatic Frequency Agility (AFA). The
advantage of LBT with AFA is that the device bypasses the Duty Cycle requirement imposed by
European standards. LBT+AFA requires that you use at least two frequencies for transmission. See
Regulatory conformity summary for a complete list of channels and frequencies.
This feature provides a level of fairness to the devices in a given area. Before this device transmits, it
senses a channel to determine if there is activity by taking an RSSI measurement for 5 ms. If the
measurement is below the threshold, the device transmits on that channel. If there is activity, that
channel is not used, and the device listens for at least 5 ms to allow transmissions to be received.