Table 30. Spreading Factor, Chips/Symbol And Lora Snr; Table 31. Lora Bandwidth Setting - ST STM32WL55JC Reference Manual

RM0453
The LoRa packet frames are illustrated in the figure below.
Explicit packet frame
n preamble symbols
Implicit packet frame
n preamble symbols
The LoRa packet frames start with a preamble that is used to synchronize the receiver with
the received signal. By default, the packet is configured with a 12-symbol-long preamble
sequence. The preamble length is programmable by Set_PacketParams() command.
This allows the transmission of near arbitrarily long preamble sequences.
The receiver undertakes a preamble detection process that periodically restarts. For this
reason, the preamble length at receiving side must be configured identical to the one at
transmitting side. When the preamble length is not known at receiving side or when it varies,
the maximum preamble length must be programmed at receiving side.
In the explicit packet format, the preamble is followed by a header with CRC, then followed
by the payload and payload CRC.
In the implicit packet format, the preamble is directly followed by the payload and payload
CRC.
The payload is a variable length field that contains the user data coded at the coding rate,
either as specified in the explicit header or in the sub-GHz configuration when using implicit
mode, by Set_PacketParams() and Set_ModulationParams() commands.
The payload can be followed by an optional payload CRC.
Explicit header mode
The default operation mode is the explicit header mode, where the header provides
information on the payload. The header is transmitted using maximum forward error
correction coding rate 4/8. It is protected by its own header CRC to allow the receiver to
discard a packet up on receiving an invalid header.
Figure 12. LoRa packet frames format
n header symbols
Preamble Header + CRC
Preamble
SF defined by spreading factor
CR = 4/8
SF defined by spreading factor
Payload
CR defined by coding rate
RM0453 Rev 2
Sub-GHz radio (SUBGHZ)
Payload
CR defined by coding rate
CRC
CRC
MSv62618V1
163/1454
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