In Europe LoRa uses unlicensed frequency spectrum in 868 MHz band (ISM). Devided in sub-bands between 863 and 870 Mhz. Everyone is allowed to use this spectrum, but has to obey restrictions determined and enforced by the government per ISM (sub)-band. Generally speaking:
- Devices are not allowed to exceed a maximum power output of 14 dBm (25 mW)
- Devices are only allowed a limited time-on-air (time it is sending). This duty-cycle is maximum 1% of an hour for that sub-band.
LoRaWAN specifies that each time a message is send in one ISM subband, the device must wait the remaining time of the duty cycle in that band before resending (For time on air of 0.5s and 1% duty-cycle, this means waiting 49,5s).
To enforce regulations, KPN requires all devices to be certified for LoRa, see Certification of LoRa devices. Or use standard certified LoRa chips. These chips know how to handle the different channels and duty cycle and will respond with an error when a user tries to send a message too soon.
Downlink & Duty-Cycle
Within ISM bands, gateways are also seen as one device, so duty cycle applies to the gateways as well. For receiving uplink messages from devices, no regulatory limit applies, but for downlink messages the gateway has to obey the Duty Cycle. Downlink capacity is increased by sending on a low SF, changing sub-bands and setting up gateways in area’s with many LoRa Devices. Nevertheless, the downlink capacity stays limited. Developers should design their solution with a minimum number of downlink messages. LoRa Acknowledgements are also downlink messages.
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