How do Bluetooth and WiFi coexist?

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Bluetooth and WiFi share a frequency band.  So how do they peacefully coexist?  WiFi on the 5.0 GHz range avoid Bluetooth altogether.  However what strange magic allows them to operate side by side?

 Both Bluetooth (802.15) and WiFi (802.11) share an 87 MHz swath of the ISM band.  Bluetooth uses Frequency Hopping Spread Spectrum (FHSS) and jumps around 79 different 1 MHz channels.  WiFi uses Direct Sequence Spread Spectrum (DSSS) and uses a 22 MHz channel.  There are 11 channels in the ISM band but they overlap each other.  So properly implemented networks will be implemented on one of three non-overlapping channels (1,6, and 11).

So when a Bluetooth radiator hops to channels within the same 22 MHz channel the WiFi stations are communicating, there is interference.  How “loud” the signals are and how close the radiators determine how much interference occurs.  Typically the latest hardware of both WiFi and Bluetooth operate harmoniously.

When Bluetooth does experience significant interference it hops to the next channel in an attempt to avoid the interference.  Bluetooth is similar to the now extinct protocol Token Ring (802.5) which used collision detection.  Wifi, unlike Bluetooth and Token Ring acts more like Ethernet (802.3).  Both Ethernet and WiFi use Collision Detection to combat collisions.  The competing stations determine a random backoff time and retry communication.  In addition 802.11bg networks with rate shift to slower data rates in an attempt to lower the BER (Bit Error Rate).

There are situations where harmonious coexistence will not be possible.  I did work for a well-known  electronic gaming company.  There was a floor with scores of quality control analysts with 3-4 gaming consoles all of which necessarily use Bluetooth.  Designing a WiFi network to operate efficiently in this environment was certainly a challenge.  Depite copious contention both continued working quite well.  Kudos to the IEEE (who set he standards for both 802.15 and 802.11).

 To learn more check out the following videos…

geekyranjitexplains (Aug 8, 2013). Understand WiFi Routers Basics – Part 1 Geekyranjit Explains. Retrieved from

 

profgustin (Apr 9, 2012). Android – Intro to Bluetooth. Retrieved fromhttps://www.youtube.com/watch?v=M5_EJ27xjMU

 

 

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