Datasheet
Table Of Contents
- 1. General Description
- 2. Electrical Characteristics
- 3. SX1272/73 Features
- 4. SX1272/73 Digital Electronics
- 4.1. The LoRaTM Modem
- 4.2. FSK/OOK Modem
- 4.2.1. Bit Rate Setting
- 4.2.2. FSK/OOK Transmission
- 4.2.3. FSK/OOK Reception
- 4.2.4. Operating Modes in FSK/OOK Mode
- 4.2.5. General Overview
- 4.2.6. Startup Times
- 4.2.7. Receiver Startup Options
- 4.2.8. Receiver Restart Methods
- 4.2.9. Top Level Sequencer
- 4.2.10. Data Processing in FSK/OOK Mode
- 4.2.11. FIFO
- 4.2.12. Digital IO Pins Mapping
- 4.2.13. Continuous Mode
- 4.2.14. Packet Mode
- 4.2.15. io-homecontrol® Compatibility Mode
- 4.3. SPI Interface
- 5. SX1272/73 Analog & RF Frontend Electronics
- 6. Description of the Registers
- 7. Application Information
- 8. Packaging Information
- 9. Revision History
www.semtech.comPage 25
SX1272/73
WIRELESS, SENSING & TIMING DATASHEET
Rev. 2 - July 2014
©2014 Semtech Corporation
4.1.1.2. Spreading Factor
The spread spectrum LoRa
TM
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 represents the number of symbols sent per bit of information.
The range of values accessible with the LoRa
TM
modem are shown in the following table.
Table 13 Range of Spreading Factors
Note that the spreading factor, SpreadingFactor, 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, so link budget and
range, of the LoRa receiver.
Spreading Factor 6
SF = 6 Is a special use case for the highest data rate transmission possible with the LoRa modem. To this end several
settings must be activated in the SX1272/73 registers when it is in use. These settings are only valid for SF6 and should be
set back to their default values for other spreading factors:
Set SpreadingFactor = 6 in RegModemConfig2
The header must be set to Implicit mode.
Set the bit field DetectionOptimize of register RegLoRaDetectOptimize to value "0b101".
Write 0x0C in the register RegDetectionThreshold.
4.1.1.3. Coding Rate
To further improve the robustness of the link the LoRa
TM
modem employs cyclic error coding to perform forward error
detection and correction. Such error coding incurs a transmission overhead - the resultant additional data overhead per
transmission is shown in the table below.
Table 14 Cyclic Coding Overhead
SpreadingFactor
(RegModemConfig2)
Spreading Factor
(Chips / symbol)
LoRa Demodulator
SNR
6 64 -5 dB
7 128 -7.5 dB
8 256 -10 dB
9 512 -12.5 dB
10 1024 -15 dB
11 2048 -17.5 dB
12 4096 -20 dB
CodingRate
(RegModemConfig1)
Cyclic Coding
Rate
Overhead Ratio
1 4/5 1.25
2 4/6 1.5
3 4/7 1.75
4 4/8 2