The Spreading Factor (SF) is linked to the mechanism that adapts the emission power and transmission speed to the network conditions around the device. The SF enables better radio resource management and optimisation of energy consumption. Speed and radio performance vary according to the spreading factor used. The biggest factor (SF12) gives the longest signal range (highest sensitivity of the technology), and so potentially the best. This also helps with improved geolocation of the device by the network, because the signal emitted will reach the most gateways. Not all LPWAN technologies have this flexibility.
LoRa® is a radio technology based on spread spectrum modulation, which can demodulate messages with very low signal levels, below the noise threshold: levels identified by the SNR (Signal Noise Ratio). The Spreading Factor varies between 128 = 2^7 (SF7) and 4096 = 2^12 (SF12). Message size depends on the SF: with SF7, 242 bytes are sent in 399 ms, while with SF12, 51 bytes are sent in 2793 ms. The Spreading Factor used also has an impact on the object’s electrical consumption; the higher the SF, the longer it takes to send a message of a given size. Repeating a message (retry), on different radio channels, and at different moments, is an effective way of improving service quality, using redundancy to work around possible one-off or more sustained radio disruptions. Orange recommends “retrying” three times.
Speeds depending on the SF:
|
Spreading Factor |
Speed |
|
12 |
293 bps |
|
11 |
537 bps |
|
10 |
977 bps |
|
9 |
1.8 kbps |
|
8 |
3.1 kbps |
|
7 |
5.5 kbps |