nRF91 coexistence support - Can LTE radio be gated by an external radio?

RE: nRF91 coexistence support - Can LTE radio be gated by an external radio?

droberson — Mon, 23 Mar 2026 18:09:04 GMT

Hey Simon,

That is what I discovered as well (Ticket 324716). Sounds good, I think I have my answer regarding this.

Thanks,

Derek

RE: nRF91 coexistence support - Can LTE radio be gated by an external radio?

Simon D-M — Mon, 23 Mar 2026 13:35:39 GMT

Hi,

I don't know nRF5 SDK too much, but I wasn't able to find anything about having COEX on nRF5 SDK.

I even found another DevZone ticket (324716) where a colleague said that we didn't have it for Wi-Fi. I assume this is the same for cellular COEX.

Best regards,

Simon D-M

RE: nRF91 coexistence support - Can LTE radio be gated by an external radio?

droberson — Fri, 20 Mar 2026 17:30:33 GMT

Hey Simon,

Thanks for confirming, that was my suspicion. The reason I am looking into this is for a project where the host MCU is still running the legacy nRF5 SDK, and not the nRF Connect SDK. To my knowledge, the legacy SDK SoftDevice doesn't have coexistence support. Please correct me if I am wrong.

Thus, I thought I could be clever and perhaps reverse the logic since the nRF9151 obviously uses the new nRF Connect SDK. Alas, this doesn't seem possible.

Question: Can you confirm that the legacy nRF5 SDK doesn't have 1-wire coexistence support?

It looks like I will have to devise a handshaking / grant protocol over our modem communication interface.

Thanks,

Derek

RE: nRF91 coexistence support - Can LTE radio be gated by an external radio?

Simon D-M — Fri, 20 Mar 2026 12:34:00 GMT

Hi Derek,

[quote user=""]Can the reverse be done? Ie, can the nRF9151 modem stack be tightly coupled with the MPSL layer that receives a grant from another MCU to allow LTE transmissions? For example, could you could wire a PA (Power Amplifier) signal from a nRF52840 to a gpio on the nRF9151 and configure this GPIO as a LTE grant? In this scenario, the nRF52840 BLE stack would have priority.[/quote]

Unfortunately, the AI was right this time, it can't be done the other way around.

I believe the reason behind this "host-only" solution is that LTE communication require some very strict timing and regulations, so it needs to act as the host.

Also, if you are OK sharing that (keep in mind that this is a public ticket), can you tell me a bit more about the reason behind that requirement ?

Best regards,

Simon D-M