The RF 868MHz is a public bandwidth European Low Power Networks (LPWAN) as Sigfox and LoRaWan are using for communicating.
This bandwidth is regulated by different norms like ERC-REC-70-3E in Europe and have national norms in relation. In France ARCEP 2014-1263 seems to be the last one validated in the JO on the 30th of January 2015. The following video is a second episode of my VLOG on LPWan technologies. As usual, the video is in French but this post will give you a overview in english.
Basically, the 868Mhz band is going, from 865MHz to 870MHz and split in 6 different sub-bands where different rules applies.
The rules are based on 2 restrictions:
- Transmission power – it is the maximum power an emitter can use on the channel when it is communicating. 25mW (eq 14dB) is the usual power the lpwan uses for communicating.
- The duty cycle – it is defined as the maximum ratio of time on the air per hour. Basically, 1% means you can speak 36s per hour, not more. Duty Cycle is applicable for the sub-band.
The six channels are defined as the following picture :
The more interesting channel is the second one, from 868.0 to 868.6 – on these 600kHz we have the 2000 Sigfox channels and the 3 standard LoRaWan channels.
The first channel 865-688 is a 25mW / 1% channel, it is a large area to add LoRa channels but it is also a zone used by RFIDs.
The 868,7 to 869,2 sub-band is a 25mW area but the duty cycle is 0.1%, this zone can be interesting to communicate when an object is emitting once a day : the risk of collision is really lower and the number of time you will have to re-emit is, as a consequence, lower, so in this sub band you can expect to preserve your energy.
The 869,3 to 869,4 sub-band is not usable for LPWAN as the maximum power is 10mW but you have no duty-cycle so it can be a good area for local object communication.
The 869,4 to 869,65 zone is particularly interesting because you can communicate with 500mW with a 10% duty cycle. An object would ne be able to use a such power when running on battery but in a central network point of view it is a really good channel for downlink communications. The gateway can communicate far away and be listen over the local noise of the object ; the larger duty cycle allows the gateway to communicate with many objects.
The last zone 869,7 to 870 is the last 25mW / 1% zone where you can deploy extra LoRaWan channels.
Actually the area where the magic appends this the 868.0 to 868.6, it is the area where both Sigfox and LoRaWan deployed the network.
In this zone we have 200kHz used by Sigfox to deploy the 2000 channels offered by the technology ( 2000 x 100Hz = 200kHz ). On the same location we have the first 125kHz channel of LoRaWan (what a bad idea) centered on 868.1, then the two other default channels on 868.3 and 868.5. This band of frequencies is globally fully used by these LPWan solutions.
In this area the duty-cycle for any communication between 868.0 to 868.6 is 1%, so even if the technologies propose different channels, the duty cycle is applicable on the global band. It means for Sigfox a maximum of transmission of 36s per hour. As a 12 bytes transmission is 6s we have a maximum of 10 communications per hour.
The device is allowed to transmit its 6 communications one after one all over the first 36s of the hour or at any other frequency like one every 10 minutes. The regulation don’t care until you respect the 1 hour global duty-cycle.
For LoRaWan, the situation is differing : the duty-cycle is managed by channel and the device get channels one after the other. As a consequence the duty-cycle have to be divided by the number of channels in the same band. As the standard configuration have 3 channels in the same sub-band the duty-cycle of each of the channel is 0,33%. But, if you allocate some channels on other band ( like 869,7 – 870) you can set a 1% duty cycle more on this one. So your device can be able to communicate 3×0,33% on a band + 1% on the other band. Basically you can communicate 2% (up-to 3%) with this mechanism.
Useful links :