RM0453 Rev 1 161/1461
RM0453 Sub-GHz radio (SUBGHZ)
218
Spreading factor (SF)
The LoRa spread spectrum modulation is performed by representing each data bit of the
packet payload by multiple chips of information. The rate at which the spread information is
sent, is referred to as the symbol rate (Rs). The ratio between the nominal data rate and the
chip rate is the spreading factor (SF). It represents the number of symbols per data bit.
The spreading factor must be known in advance on both transmit and receive side of the
link.
The resulting signal to noise ratio (SNR) required at the receiver input, is influenced by the
spreading factor. This allows the increase of the receiver sensitivity, and so increase the link
budget and range.
A higher spreading factor provides a better receiver sensitivity, more link budget and longer
range at the expense of a longer transmission time (see the table below).
For SF5 and SF6, due to the higher symbol rate, the minimum preamble length needed to
ensure correct detection and demodulation of the received signal is 12 symbols.
Bandwidth (BW)
An increase in signal bandwidth allows the use of a higher effective data rate and reduces
the transmission time at the expense of a reduced sensitivity, less link budget and shorter
range. The LoRa modem operates at a programmable bandwidth (BW) around a
programmable RF frequency (f
rf
).
There are country dependent regulatory constraints on the permitted occupied bandwidth.
The LoRa signal bandwidth refers to the double side bandwidth (DSB). The bandwidth
selection range is given in the table below.
Forward error correction coding rate (CR)
The sub-GHz radio communication reliability can be improved by performing forward error
correction. This is particularly efficient in the presence of interference. The coding rate can
be changed in response to channel condition. The coding rate information is included in the
packet header for use by the receiver.
Table 30. Spreading factor, chips/symbol and LoRa SNR
Spreading factor (SF) 5 6
(1)
1. The SF6 is not backward compatible with earlier LoRa devices.
7
(2)
2. Default value.
8 9 10 11 12
2
SF
(chips/symbol) 32 64 128 256 512 1024 2048 4096
LoRa demodulator SNR (dB) –2.5 –5 –7 –9.5 –12 –14.5 –17 - 19
Table 31. LoRa bandwidth setting
LoRa BW setting012345678
(1)
1. Bandwidth 250 kHz and 500 kHz are not available below a 400 MHz RF frequency.
9
(1)
Bandwidth (kHz) 7.81 10.42 15.63 20.83 31.25 41.67 62.5 125 250 500
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