Does passive wifi and bluetooth scanning cause interferance with GPS and LTE

[Michael Zeng]

Hi, conceptual question here:

I'm developing a product that will use all three of the nRF5340 ,nRF7002, and nRF9160. The nRF5340 and nRF7002 will be constantly in "scanning mode"--literally, they will be running code that is fundamentally the same as the bluetooth and wifi scanning samples. My application is to constantly scan for devices and, periodically, send any data the wifi and bluetooth scanners found (along with GPS data) up to the cloud.

Does this scanning interfere with the nRF9160's activity? I believe the scans are passive, so they don't broadcast any data, but I'm unsure if this should still impact the GPS and LTE performance or not.

If they do interfere, is there a way to limit the LTE and GPS to bands that minimize interference? 

Thanks,

Michael

[Øyvind]

Hello Michael, 

I will forward this to our developers to find an answer. I hope to have an answer by Monday. 

Kind regards,
Øyvind

[Øyvind]

Hi Michael, 

I've gotten some response, waiting for final feedback from our nRF91 team. 

Kind regards,
Øyvind

[Michael Zeng]

got it, thank you. eagerly awaiting an answer!

Thanks,

Michael

[Øyvind]

From the WiFi team I get the following response. 

Scans are a combination of active and passive, depending on the regulatory rules in place (see https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/working_with_nrf/nrf70/developing/regulatory_support.html ). Generally, they are active in the 2.4 GHz band, and passive in the 5 GHz band. The default scan regulatory zone is "World", i.e. the first table entry on the page above. Channels marked as "DFS" or "Passive only" employ passive scan, all others are active. We will support an option to force scans to be fully passive in NCS 2.5.0. 

The nRF91 team are asking what device will be the host device in your system. Could you please provide some input?

I will be out of office the next 3 weeks for summer break. One of my colleagues will provide an answer from the nRF91 team if there are any updates.

[Michael Zeng]

Hi,

Thanks for the response, I see.. I'm unsure if the scanning is active or passive then, but what I do know is that we are simply using the code from the wifi scan sample and the central heart rate coded sample. Would these scans interfere with LTE (just sending MQTT requests periodically) and GPS?

You could say the nRF5340 is the host in the system; but both the nRF5340 and nRF9160 will be running their own firmware, and communicate via I2C. 

Thanks,

Michael

[Øyvind]

Hi MIcharl, I've got some more feedback from our team (not based on your last comment):

2.4GHz and 5GHz ISM bands are not overlapping in freq. domain with cellular bands so from that angle they are not interfering fundamentally. Secondly, if ISM radio is scanning passive (no transmitting, only receiving?) interference to cellular should be negligible. Off course as WiFi passive scanning requires WiFi chip to be “on”/active and potentially does even some flash writings what not “second order activity” during the scan, all EMI coming from that activity may couple/radiate to cellular receiver/antenna (whole PCB is antenna unless known otherwise) and cause some cellular receiver performance deterioration. Whether such deterioration would be visible in “field conditions” taken into account with all other ~1000 inaccuracies involved, maybe not dominating one.

Another scenario is that active cellular transmitter power (fundamental or harmonic) leaks into scanning ISM band receiver and jams it somewhat. Unlikely it causes damage but may cause some noise level increase and/or fail results.