LLCC68 datasheet(33/106 Pages) SEMTECH

33 / 106 page

LLCC68

Data Sheet

Rev. 1.0

DS.LLCC68.W.APP

July 2019

33 of 106

Semtech

www.semtech.com

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, the user is invited to 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.

It is the capability to receive signals with negative SNR that increases the sensitivity as well as link budget and range of the

LoRa® receiver.

A higher spreading factor provides better receiver sensitivity at the expense of longer transmission times (time-on-air). With

a knowledge of the key parameters that can be selected by the user, the LoRa® symbol rate is defined as:

where BW is the programmed bandwidth and SF is the spreading factor. The transmitted signal is a constant envelope

signal. Equivalently, one chip is sent per second per Hz of bandwidth.

6.1.1.2 Bandwidth

An increase in signal bandwidth permits the use of a higher effective data rate, thus reducing transmission time at the

expense of reduced sensitivity improvement.

LoRa® modem operates at a programmable bandwidth (BW_L) around a programmable central frequency fRF

Figure 6-1: LoRa® Signal Bandwidth

An increase in LoRa® signal bandwidth (BW_L) permits the use of a higher effective data rate, thus reducing transmission

time at the expense of reduced sensitivity improvement. There are regulatory constraints in most countries on the

Table 6-1: Range of Spreading Factors (SF)

Spreading Factor (SF)1

1. Not all SF are available for any bandwidth with the LLCC68

2^SF (Chips / Symbol)

128

256

512

1024

2048

Typical LoRa® Demodulator SNR [dB]

-2.5

-5

-7.5

-10

-12.5

-15

-17.5

2SF

---------

BWL

------------

BWL

------------

–

BW_L

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