LLCC68 datasheet(34/111 Pages) SEMTECH

34 / 111 page

LLCC68

Data Sheet

Rev. 1.1

DS.LLCC68.W.APP

Dec 2024

34 of 111

Semtech

LLCC68

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.

The LLCC68 does not have a packet handler dedicated to LR-FHSS modulation. It provides the relevant modulation and frequency hopping

capability.

GMSK is supported by the modems. and is treated as a special case of (G)FSK where fdev=br/4.

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 16dB. 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 set using command SetModulationParams(...) which must be called after SetPacketType(...):

• Modulation BandWidth (BW_L)

• Spreading Factor (SF)

• Coding Rate (CR)

• Low Data Rate Optimization (LDRO)

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.

SF5 and SF6 Considerations

Two spreading factors, SF5 and SF6, have been modified slightly in the LLCC68 and can now operate in both implicit and explicit mode.

However, these new spreading factors are incompatible with previous generation devices, in particular SF6 on the LLCC68 is

not backward

compatible with SF6 on the SX1276. Furthermore, due to the higher symbol rate, the minimum recommended preamble length needed to

ensure correct detection and demodulation from the receiver is increased compared to other Spreading Factors. For SF5 and SF6, you

should use 12 symbols of preamble to have optimal performances over the dynamic range or the receiver.

Note: The spreading factor must be known in advance on both transmit and receive sides of the link as different spreading factors

are orthogonal to each other. Note also the resulting Signal to Noise Ratio (SNR) required at the receiver input.

LLCC68 Datasheet(PDF) 34 Page - Semtech Corporation

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