RFM92 Datasheet, PDF (23/126 Pages) List of Unclassifed Manufacturers – Low Power Long Range Transceiver Module

RFM92W/93W V3.0
4. RFM92W/93W 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 settings are summarised in the table below. 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. In the table below a coding rate of 4/5 is used.
Table 12 Example LoRa^TM Modem Performances
Bandwidth
(kHz)
125
125
250
250
500
500
Spreading Factor
6
12
6
12
6
12
Nominal Rb
(bps)
9380
293
18750
586
3750
1172
Sensitivity
(dBm)
-122
-137
-119
-134
-116
-131
Typically such performance gains require high stability frequency references, with LoRa^TM this is not the case. Low crystal
tolerances are easily accommodated reducing the overall BoM cost for a given increase in link budget.
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.
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