Spreading Factor (SF)

What is it? 

A spreading factor is a parameter that controls data transmission speed and chirp rate. It also influences range, congestion, time-on-air, battery life, and receiver sensitivity. There are 6 spreading factors overall: SF7, SF8, SF9, SF10, SF11, and SF12. 

How does it work? 

In the context of the Chirp Spread Spectrum (CSS), which underlies LoRa technology, chirps (or symbols) serve as carriers of data. Lower spreading factors result in faster chirps and a higher data transmission rate. On the other hand, every increase in spreading factors makes the chirp rate and data transmission rate shrink by half. 

Additionally, lower spreading factors cut the range of LoRa transmissions, decreasing processing gain and raising the bit rate. This way, changes in spreading factors enable the network to raise or reduce the data rate for each end device at the expense of the range. 

Another application of spreading factors is suggestion control. It means that signals modulated with different spreading factors and transferred simultaneously on the same frequency channel do not interfere with each other. At the same time, using spreading factors allows for higher receiver sensitivity. 

Higher spreading factors prolong time-on-air, as sending data before the receiver gets it requires more time in this case. Accordingly, it extends active times and shortens battery life.

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