LoRa / CSS (Chirp Spread Spectrum)
LoRa is a spread spectrum modulation that uses chirp pulses whose frequency is swept over time. It can decode a signal even below the noise floor; on a common sub-GHz receiver chip, sensitivity down to -148 dBm is reported at the lowest data rate. The cost is a very low data rate and long air time.
A chirp is a pulse that sweeps its frequency linearly within a given band. Because the receiver knows this sweep, it can integrate the signal along the time axis; the collected energy grows while random noise does not. The result is decodability at extraordinarily low levels.
- Spreading factor: as it grows, sensitivity increases, the data rate drops and the time the packet stays on air gets longer.
- Duty cycle effect: long air time consumes the hourly transmission budget quickly; it is limiting in applications that need a continuous stream of commands.
- Latency: at a high spreading factor the packet duration can rise to hundreds of milliseconds.
On a crane or hydraulic lever remote control you expect motion to stop immediately when the operator releases the button; this is why LoRa is typically suited to telemetry and sensor applications that report infrequently, while narrowband FSK or frequency-hopping protocols are suited to remote control requiring a fast response.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety