5

so the BLE advertising channels are located at 2402Mhz, 2426Mhz and 2480Mhz. That is so it does not interfere with the 3 wifi channels in the 2.4Ghz band.

My question is especially about the 2426Mhz advertising channel. Wifi channel 6 ranges from 2426Mhz to 2448Mhz.

My understanding is that the 2426Mhz advertising channel of BLE ranges from 2425Mhz to 2427Mhz. Is this correct?

Then it does overlap with a wifi channel and interfere? Where is my falacy in the logic? I dont get it and cant find any information about this.

Execuse my probably bad english, its not my native language.

Regards

  • 1
    Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 17 '17 at 4:46
5

Wifi Channel 6 is centered at 2437Mhz and is 22Mhz large, so ranging from 2426 to 2448 as you stated (well that would rather be 23Mhz large, so not sure if it is 2427-2448 or 2426-2447).

But data is actually transmitted along a 20 MHz bandwidth, the remaining 2Mhz are used as a guard band so there's enough attenuation along the edge channel.

So there's no data transmitted at 2426 Mhz when using Wifi Channels 1 or 6 (1, 6 and 11 are the most used since they are non-overlapping)

From Argenox

LE uses 40 1MHz wide channels, numbered 0 to 39. Each is separated by 2MHz.

Channels 37, 38, and 39 are used only for sending advertisement packets. The rest are used for data exchange during a connection. We’re interested in what’s happening in these 3 channels, and that’s what we’ll cover here.

During BLE advertisement, a BLE Peripheral device transmits packets on the 3 advertising channels one after the other. A Central device scanning for devices or beacons will listen to those channels for the advertising packets, which helps it discover devices nearby.

Channels 37, 38 and 39 are spread across the 2.4GHz spectrum on purpose. 37 and 39 are the first and last channels in the band, while 38 is in the middle. If any single advertising channel is blocked, the other channels are likely to be free since they’re separated by quite a few MHz of bandwidth.

This is especially true since most other devices that interfer with BLE are narrow band. Channel 38 in particular was placed between Wi-Fi channels 1 and 6 so it avoids the Wi-Fi signal. The wide spacing of the advertisement channels helps BLE better manage the interference from Wi-Fi, Classic Bluetooth, Microwaves, Baby Monitors, etc to ensure that advertisements succeed.

You may find this study relevant to your question:

Coexistence and Interference Tests on a Bluetooth Low Energy Front-End

Here are some parts:

On other hand Wi-Fi signals will see Bluetooth as narrow band interference and only in the cases that the Bluetooth interference is not more than 10 dB below the Wi-Fi signal can occasionally cause interference. In most cases Wi-Fi transmits 20 dBm and Bluetooth transmits 0 dBm so if we take into account the path loss Friis equation of the transmitted Wi-Fi signal

Lpath= −27.55dB +20 log (2.4MHz ) +20×log[dist(m)]

and the Link Budget equation

Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB) − Lpath

We get to the theoretically conclusion that only if the Wi-Fi Router is more than 3 meters away from the connecting equipment and the Bluetooth equipment is on a 3 meters area around the Wi-Fi equipment, that occasionally the Bluetooth signal can cause interference over the Wi-Fi

The study conclude that:

C. Coexistence with Wi-Fi Due to their dependence on the same band, the potential for interference exists. Therefore it is important to see if there is interference from Wi-Fi on the BLE transmissions. The results show no effect on the Bit Error Rate or RSSI readout, in fact the RSSI readout shows that the value increases. The results obtained show that BLE hopping is effectively avoiding the Wi-Fi occupy channels, therefore there is very good coexistence between BLE and Wi-Fi.

| improve this answer | |
  • That clears it up thank you! Working on my bachelors thesis and its not that easy to find any information about this subject. I will take a look at the study! – User Name Mar 9 '17 at 17:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.