RM0453 Rev 5 163/1450
RM0453 Sub-GHz radio (SUBGHZ)
227
A higher coding rate provides better immunity to interference at the expense of longer
transmission time. In normal conditions and factor of 4 / 5 provides the best trade off. In
case of strong interference, a higher coding rate may be used.
The coding rate and overhead ratio is given in the table below.
Low data rate optimization (LDRO)
For low data rates (typically high SF or low BW) and very long payloads (may last several
seconds), the low data rate optimization (LDRO) can be enabled. This reduces the number
of bits per symbol to the given SF minus 2, to allow the receiver to have a better tracking of
the LoRa receive signal. Depending on the payload length, the low data rate optimization is
usually recommended when the LoRa symbol time is equal or above 16.38 ms.
When using LoRa modulation, the total frequency drift over the packet time must be kept
lower than Freq_drift_max:
Freq_drift_max = BW / (3 x 2
SF
)
When possible, enabling the low data rate optimization (Set_ModulationParams()
command), relaxes the total frequency drift over the packet time by 16:
Freq_drift_optimise_max = 16 x Freq_drift_max
5.5.2 LoRa framing
The following types of LoRa packet formats are available:
• explicit header mode packet: includes a short header that contains information about
the number of payload bytes, coding rate and presence of CRC.
• implicit header mode packet (no header)
Table 32. Coding rate and overhead ratio
CR setting 0
(1)
1. No forward error correction.
12
(2)
2. Default value.
34
Coding rate (data bits/total coded bits) 4/4 4/5 4/6 4/7 4/8
Overhead ratio 1 1.25 1.5 1.75 2
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