Channel Activity Detection (Cad) - Semtech LR1121 User Manual

8.2.2.2 Header (explicit packets only)
The header provides payload information:
• The payload length in bytes
• The forward error correction coding rate
• An optional 16-bit CRC for the payload
The header is transmitted with maximum error correction code (4/8). It also has its own CRC to allow the receiver to discard
invalid headers.
8.2.2.3 Payload
The packet payload is a variable-length field that contains the actual data coded at a rate specified in the header in explicit
mode or in the register settings in implicit mode. An optional CRC may be appended.
8.2.2.4 LoRa Packet Time On Air
The Time On Air of the LoRa packet is shown in the LR1121 drivers.

8.2.3 Channel Activity Detection (CAD)

Used only in LoRa packets, the Channel Activity Detection (CAD) is a LoRa specific mode of operation where the device
searches for the presence of a LoRa preamble signal.
At the end of the search period, the device triggers the IRQ CADdone. If a valid signal has been detected it also generates
the IRQ CadDetected. A minimum of 2 symbols is recommended to perform a CAD.
After the search has completed, the device returns to STDBY_RC mode. The length of the search is configured via command
SetCadParams(...).
LR1121
User Manual Rev 1.1
UM.LR1121.W.APP Mar 2023
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