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8.2 LoRa® Modem
8.2.1 LoRa Modulation Principle
The LoRa modem uses a proprietary spread spectrum modulation, which permits an increased link budget and increased
immunity to in-band interference compared to legacy modulation techniques. It has the capability to receive signals with
negative SNR that increases sensitivity as well as link budget and range of the LoRa receiver.
8.2.1.1 Spreading Factor (SF)
The spread spectrum LoRa modulation is performed by representing each bit of payload information by multiple chips of
information. The rate at which a spread symbol (containing 2
between the nominal symbol rate and chip rate is the Spreading Factor and it defines the number of bits sent per symbol.
Note that 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.
8.2.1.2 LoRa Bandwidth (BWL)
The LoRa modem operates at a programmable bandwidth (BWL) around a programmable central frequency fRF. The LoRa
modem bandwidth always refers to the double side band (DSB), as shown in
An increase in signal bandwidth permits the use of a higher effective data rate, thus reducing transmission time at the
expense of reduced sensitivity.
Note: There are regulatory constraints in most countries on the permissible occupied bandwidth, therefore allowing usage
of only a subset of BWL.
8.2.1.3 Coding Rate (CR)
To further improve the robustness of the link, the LoRa modem employs cyclic error coding to perform forward error
detection and correction. Such error coding incurs a transmission overhead.
LR1121
User Manual
Rev 1.1
UM.LR1121.W.APP
Mar 2023
SF
chips) is sent is referred to as the symbol rate (Rs). The ratio
Figure 8-2: LoRa Signal Bandwidth
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Figure 8-2: LoRa Signal
Bandwidth.
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