LLCC68 datasheet(32/106 Pages) SEMTECH

32 / 106 page

LLCC68

Data Sheet

Rev. 1.0

DS.LLCC68.W.APP

July 2019

32 of 106

Semtech

www.semtech.com

6. Modems

The LLCC68 contains different modems capable of handling LoRa® and FSK modulations. LoRa® and FSK are associated with

their own frame and modem.

•

LoRa® modem  LoRa

® Frame

•

FSK modem  FSK Frame

The user specifies the modem and frame type by using the command SetPacketType(...). This command specifies the frame

used and consequently the modem implemented.

This function is the first one to be called before going to Rx or Tx and before defining frequency, modulation and packet

parameters. The command GetPacketType() returns the current protocol of the radio.

6.1 LoRa® Modem

The LoRa® modem uses spread spectrum modulation and forward error correction techniques to increase the range and

robustness of radio communication links compared to traditional FSK based modulation.

An important facet of the LoRa® modem is its increased immunity to interference. The LoRa® modem is capable of

co-channel GMSK rejection of up to 16 dB. This immunity to interference permits the simple coexistence of LoRa®

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

range when legacy modulation schemes fail.

6.1.1 Modulation Parameter

It is possible to optimize the LoRa® modulation for a given application, access is given to the designer to four critical design

parameters, each one permitting a trade-off between the link budget, immunity to interference, spectral occupancy and

nominal data rate. These parameters are:

•

Modulation BandWidth (BW_L)

•

Spreading Factor (SF)

•

Coding Rate (CR)

•

Low Data Rate Optimization (LDRO)

These parameters are set using the command SetModulationParams(...) which must be called after SetPacketType(...).

6.1.1.1 Spreading Factor

The spread spectrum LoRa® modulation is performed by representing each bit of payload information 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 symbol rate and chip rate is the spreading factor and it represents the number of symbols sent per bit of

information.

Consideration on SF5 and SF6

In the LLCC68, two spreading factors have been added compared to the previous device family, SF5 and SF6. These two

spreading factors have been modified slightly and will now be able to operate in both implicit and explicit mode. However,

these modification have made the new spreading factor incompatible with previous device generations. Especially, SF6 on

the LLCC68 will not be backward compatible with the SF6 used on the SX1276. Furthermore, due to the higher symbol rate,

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