Data Sheet

Page 22
RFM95/96/97/98(W)
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WIRELESS & SENSING PRELIMINARY DATASHEET
4. RFM95/96/97/98(W) Digital Electronics
4.1. The LoRa
TM
Modem
The LoRa
TM
modem uses spread spectrum modulation and forward error correction techniques to increase the range and
robustness of radio communication links compared to traditional FSK or OOK based modulation. Examples of the
performance improvement possible, for several possible settings, are summarised in the table below. Here the spreading
factor and error correction rate are design variables that allow the designer to optimise the trade-off between occupied
bandwidth, data rate, link budget improvement and immunity to interference.
Table 58 Example LoRa
TM
Modem Performances
Bandwidth
(kHz)
Spreading Factor Coding rate
Nominal Rb
(bps)
Sensitivity
indication
(dBm)
Frequency
Reference
6 4/5 782 TBC 10.4
12 4/5 24 TBC
6 4/5 1562 TBC 20.8
12 4/5 49 TBC
TCXO
6 4/5 4688 -121 62.5
12 4/5 146 -139
6 4/5 9380 -118 125
12 4/5 293 -136
XTAL
For European operation the range of crystal tolerances acceptable for each sub-band (of the ERC 70-03) is given in the
specifications table. For US based operation a frequency hopping mode is available that automates both the LoRa
TM
spread
spectrum and frequency hopping spread spectrum processes.
Another important facet of the LoRa
TM
modem is its increased immunity to interference. The LoRa
TM
modem is capable of
co-channel GMSK rejection of up to 25 dB. This immunity to interference permits the simple coexistence of LoRa
TM
modulated systems either in bands of heavy spectral usage or in hybrid communication networks that use LoRa
TM
to extend
range when legacy modulation schemes fail.