How to evaluate a channel if is clear in property in NRF528 serials

[LeoXie]

Dear,

    How to evaluate a channel if is clear in property in NRF528 serials? e.g. there are ED and CCA in 802.15.4 standard, how to implement CSMA in NRF52810?

[Kenneth]

I believe this is explained here;
https://infocenter.nordicsemi.com/topic/ps_nrf52833/radio.html#ieee802154_ed

Best regards,
Kenneth

[LeoXie]

Dear Kenneth,

    the platform that I am using is NRF52810, so there are no ED module inside

[Kenneth]

Ah, then the only option is to trigger the RSSI_START task while in receive mode:
https://infocenter.nordicsemi.com/topic/ps_nrf52810/radio.html#rssi

Best regards,
Kenneth

[LeoXie]

Dear Kenneth,

    thank you, does RSSI detection can detect all kind of protocol carrier? e.g. there ara wifi, bt, zigbee and others share the one channel, how can I estimate if it could send packages? 

   what is NRF52810 RSSI detection theory? does it can get RSSI value after received a packge or just sensed carrier in the air?

   if it's trying to estimate if is the channel clean enough for a while, should I triggle RSSI_START continuously?

[Kenneth]

It detects signal strength on channel (the actual modulation should not matter). You can in any case download nRF Connect for Desktop and run RSSI Viewer there if you want to test with wifi, bt, microwave oven or other sources.

You can sample RSSI at any time while in receive mode using the start RSSI task, and you can sample as many times as you want.

I personally don't think using CSMA is very efficient in the 2.4GHz band, since all packet transmissions are typically very short (in the 100-200us) range, I think it is more efficient to use frequency hopping to reduce risk of collisions.

[LeoXie]

thank you Kenneth,

there are many Zigbee devices at 2405MHZ, about 200 pieces, but the RSSI seems lower than something at 2454 ~ 2474mhz

do you know any good articles for frequency hopping?  if there are more than 100 devices whthin personal erea mesh network, frequency-hop arithmetic will face a big challenge

[Kenneth]

RSSI is affected by distance and antenna, so even if you have 100 devices, they may be so far away that they will not interfere (even if you are using the same frequency).

Also have in mind that the time on-air is typically so short, that even if you have multiple devices using the same frequency, you will be able to communicate. Typical example can be BLE and advertising. Even they all use the same advertising frequencies (up to 3), you are able to see and connect to a device that is advertising.

I don't have any good article on frequency hopping, typically you can choose a protocol that use frequency hopping and then you don't need to consider what actually happen in the lower layers of the protocol (frequency hopping and retransmissions).

Best regards,
Kenneth

[LeoXie]

Dear Kenneth,

   thank you a lot, Gotcha.