RFM95 datasheet(22/121 Pages) HOPERF

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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

LoRaTM Modem

The LoRaTM 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

LoRaTM Modem Performances

Bandwidth

(kHz)

Spreading Factor

Coding rate

Nominal Rb

(bps)

Sensitivity

indication

(dBm)

Frequency

Reference

4/5

782

TBC

10.4

4/5

TBC

4/5

1562

TBC

20.8

4/5

TBC

TCXO

4/5

4688

-121

62.5

4/5

146

-139

4/5

9380

-118

125

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 LoRaTM spread

spectrum and frequency hopping spread spectrum processes.

Another important facet of the LoRaTM modem is its increased immunity to interference. The LoRaTM modem is capable of

co-channel GMSK rejection of up to 25 dB. This immunity to interference permits the simple coexistence of LoRaTM

modulated systems either in bands of heavy spectral usage or in hybrid communication networks that use LoRaTM to extend

range when legacy modulation schemes fail.

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