Non adaptative FHSS - Maximum output power

[Aurele]

Hello,

We intend to develop a new device. I found that nrf52 series can do non adaptative FHSS. Combined with a nRF21540 i would like to set the output to 20 dbm. 

According to the ETSI documentation (last version 2.2.2 : here is the link : etsi ) it seems it is possible to emits at 20 dbm but we need to stay in MU (medium utilization)

I read the MU is : 

MU = (Pout / 100 mW) × DC

where: MU is Medium Utilization factor in %. Pout is the RF output power as defined in clause 4.3.1.2.2 expressed in mW. DC is the Duty Cycle as defined in clause 4.3.1.3.2 expressed in %.

The maximum Medium Utilization factor for non-adaptive FHSS equipment shall be 10 %.

Does someone know what it implies ? Does it mean i cannot emits more than 10% of the time ?

I know that silicon labs has chips that can do adaptative FHSS but i would really like to stay with nordic devices if possible !!!

If you have any indication, don't hesitate to share ! ;)

Thank you in advance,

Aurélien

[ketiljo]

Whether it's adaptive or not is not what decides what output power you can use. I assume it's BLE you're planning to use. This is not adaptive by design and won't be unless the protocol is changed. When you're in connected mode, BLE will use all 37 channels so the limitation will be the MU factor as you say. This is the maximum transmission time on _one_ channel. 

But the problem is the advertisement channels. It's only three of them so it's not enough to satisfy the requirement of min 15 channels for adaptive FHSS and min 5 for non-adaptive FHSS. So the limitation will be the spectral density of 10 dBm / 1 MHz. 

You could advertise at 10 dBm and increase the power to 20 dBm when you're connected. But if you loose the link, you have to set it back to 10 dBm. So the practical use is limited. So the bottom line is that you're limited to 10 dBm in Europe unless the ETSI standard changes or the number of advertisement channels are is increased to 5. 

[Aurele]

Thank you very much for this detailed reply. It's clear enough now. So, i will stay at 10 dBm for now even if the hardware will be able to reach 20 dbm, it will allows me to test this feature. For the commercialization we will go with 10 dbm and hope that ETSI will change its rules in the future.

Thank you again