RE: Channel/physical interference at nRF52840

user114127 — Wed, 06 Apr 2022 13:53:21 GMT

Okay. So it's a random error.

Got it. Thanks.

Best :-)

Ethan

RE: Channel/physical interference at nRF52840

ketiljo — Wed, 06 Apr 2022 13:36:27 GMT

Probably just a coincidence. Interference should have the opposite effect.

RE: Channel/physical interference at nRF52840

user114127 — Wed, 06 Apr 2022 13:22:20 GMT

Hi there!

I have a question about the data of WiFi off case and 2417MHz case.

Why is the average receive rate lower when WiFi is off?

I suppose this is quite counter-intuitive, since there will be less interference when WiFi is off.

Best :-)

Ethan

RE: Channel/physical interference at nRF52840

ketiljo — Tue, 25 Jan 2022 14:17:34 GMT

Hi,

I am using nRF52840 and channel 20, 21.

I want to know whether there is any channel interference issue using nFR52840 in BLE.

I did some test about that and I am going to explain it.

There are two transmitters and two receivers. (one is ch20, other is ch21)

I tested how many data can actually get in below two different conditions

Put them far away (50cm) from each of them (transmitter & receiver set)
Put close to all transmitters and receivers

With three different interference conditions (Without Wi-Fi / set Wi-Fi channel on 2417MHz / set Wi-Fi channel on 2422MHz)

And there are the average receive rate of each cases.

	Condition 1	Condition 2
Wi-Fi off	96.02%	83.27%
2417MHz	99.95%	78.47%
2422MHz	92.27%	79.70%
Average	96.08%	80.48%

It seems like there are some interference depends on the distance of transmitter & receiver set and Wi-Fi.

So I want to know is that right? Or is that just a coincidence?

I attached the file about that test result just in case.

If I did not explain enough, feel free to ask about it.

3884.Channel interference on nRF52840.xlsx

I hope to get the answer about that.

This is expected as the difference in frequency is low. When the TX of one pair is near the RX of the other pair, the power of the TX will partly block the RX. The problem is worst at the adjacent or neighbor channel. Remember that the adjacent channel is 2 MHz away in 2 Mbps mode. If you increase the distance in frequency between the pairs, the packet loss will be better.

This called selectivity and describes the ratio between the wanted and unwanted signal at different frequencies: https://infocenter.nordicsemi.com/topic/ps_nrf52840/radio.html#unique_595666871

You can see the same if the receiver is close to a wifi transmitter. But as the bandwidth is much higher for the Wifi transmitter, you must increase the frequency distance more to get "out" of the wifi-transmitter bandwidth.

You can repeat the test on channels 18 and 22 for instance if you are using 2 Mbps and 20 and 22 for 1 Mbps and see how the packet loss looks like then.