Does Bluetooth interfere with WiFi?
I’ve read that WiFi b/g/n is using 2.3995 to 2.4845 GHz. Bluetooth is in between: 2.4000 to 2.4835 GHz. So what will happen when I put a Bluetooth sending device next to a WiFi sending device? Will the two devices be aware of each other (like two WiFi devices do)? Or will they send their data as if they were alone (means interference)?
\$\begingroup\$ If you are experiencing the problem, it could be due to USB 3: USB 3.0* Radio Frequency Interference Impact on 2.4GHz Wireless Devices — White Paper. \$\endgroup\$
\$\begingroup\$ The search term is «wifi and Bluetooth coexistence» one resource ti.com/pdfs/vf/bband/coexistence.pdf \$\endgroup\$
2 Answers 2
Yes, WiFi and Bluetooth can disturb each other.
But both are equipped to handle that. A standard that is not capable to handle disturbance and/or interference will simply be unusable under many circumstances.
The 2.5 GHz ISM band is also used by Microwave ovens and other wireless standards like Zigbee.
Wifi transceivers are able to detect when certain data has been lost and can ask for a re transmission. It is also possible to lower the datarate which makes the link more «robust» in the sense that it is less sensitive to disturbances.
Bluetooth uses frequency hopping, it changes channel (frequency) 1600 times per second. That way if one channel is disturbed only part of the data is lost. Also a re-transmit of data is possible.
So yes, interference happens, it is a fact that the standards simply have to deal with.
\$\begingroup\$ So Bluetooth and WiFi don’t have a common CA/CD (collision avoidance/collision detection) system. They simply don’t know each other and it’s just noise for the other party. That’s what I wanted to know. Is that right? \$\endgroup\$
\$\begingroup\$ When I do large wifi transfers from my laptop TO an external device, suddenly my mouse becomes jerky. I think that when the laptop is transmitting a lot, it disturbs significantly the mouse. The same thing doesn’t happen when receiving. \$\endgroup\$
\$\begingroup\$ @slebetman and wifi uses frequency hopping. No it doesn’t, it is not part of the standard. For WiFi a channel is selected and then that is used, see en.wikipedia.org/wiki/IEEE_802.11 The channel is not changed dynamically so there is no «hopping». But feel free to prove me wrong. \$\endgroup\$
\$\begingroup\$ @Thomas the explanation is simple: when sending a file, your laptop transmits a signal which is strong at your laptop (and then disturbs the mouse) but weaker at your WiFi access point. When receiving, the situation is reversed, the signal is strong at the access point but weaker at your laptop. Such a weak signal does not disturb the mouse. \$\endgroup\$
\$\begingroup\$ @Bimpelrekkie correct, WiFi doesn’t frequency-hop, but in the early days of 802.11b, many people confused DSSS with FHSS and I think that is how this confusion was born. \$\endgroup\$
Wifi uses a listen before transmit system. If the channel is busy, it holds off transmitting. Eventually it gets through. Each channel is fixed. If it tries to use a channel that is busy, from bluetooth, then it will wait. This may reduce the data speed for wifi if it has to wait too much.
Bluetooth for over a decade now uses adaptive frequency hopping (Bluetooth 1.2) so it will actively check each of it’s channels to see if they are good or bad, and blacklists them for a while. This is on top of it’s normal frequency hopping. If it tries to use a channel(s) that is busy, from say wifi, then it will move on to the next and won’t use those wifi channels, essentially not interfering.
So both try to actively prevent interfering with others and suffer data loss or speed loss for it. But because of these techniques, they can coexist. In a quiet environment, the wifi and the bluetooth networks won’t even bother each other. In a noisy environment, there goes your bandwidth.
Why is Bluetooth so slow if it uses the same frequency as WiFi?
Bluetooth and WiFi share the same frequency. Both wireless standards operate in the 2.4 GHz band , although WiFi also operates in the 5 GHz and soon 6 GHz bands. However, WiFi reaches speeds of tens and even hundreds of Mbps in 2.4 GHz, but Bluetooth doesn’t. Why?
There are two important factors that make WiFi and Bluetooth differ in range and speed. The first aspect to take into account is the power used to broadcast each signal, and the second is the bandwidth used in each broadcast to send content.
Bluetooth power is usually less than WiFi
Starting with the power, the higher the power with which a signal is emitted, the greater its range. In the case of WiFi, the maximum power is 0.1 W (or 100 mW) for 2.4 GHz networks, and up to 0.2 W (or 200 mW) for 5 GHz networks. in the case of Bluetooth, the speed varies depending on the class. The Bluetooth classes are:
- Class 1: range of up to 100 meters, with an average power of 100 mW
- Class 2: range of up to 20 meters, with an average power of 2.5 mW
- Class 3: range of up to 1 meter, with an average power of 1 mW
- Class 4: range of up to 0.5 meters, with an average power of 0.5 mW
As we can see, a basic Class 1 Bluetooth signal has a range of 100 meters with a power of 100 mW . That distance is similar to what a 2.4 GHz WiFi signal can reach, since it operates using the same 100 mW power. 5 GHz WiFi, having a more limited range due to having a higher frequency, uses twice the power.
The problem for Bluetooth is that it does not always operate at 100 mW of power, since in those cases it would use up a lot of battery. Since Bluetooth 4.0, the Low Energy mode has been integrated, which allows Bluetooth to reduce the power used in the event that, for example, the device is close. In these cases, the power used drops considerably, and with it the range, as we see in the different classes. In return, the battery life increases.
Bandwidth, another Bluetooth problem
However, if at maximum power it consumes the same as WiFi and has the same range, why is it slower? This is where the bandwidth of the channels used comes into play. With WiFi 4, we find channels with 20 MHz of bandwidth, while with WiFi 5 there are channels of up to 80 and 160 MHz. With WiFi 6E, the option of having up to 320 MHz channels opens up. Thus, in addition to being much wider channels, in the future it will even be possible to use several at the same time.
In the case of Bluetooth, the bandwidth is quite limited by the use of 1 or 2 MHz channels . The latest standards have been improving the speed, where 4.0 reaches figures of up to 32 Mbps, and 5.0 and later reach figures of up to 50 Mbps . For this reason, Bluetooth has it very difficult to reach high transfer speeds like those of WiFi.