Category Archives: Bluetooth

What does FHSS have to do with the $10 bill?



The US Treasury department thinks that we need a woman on the $10 bill.  I don’t know why they want to take Old Hamilton off because he was for the central bank in the first place, but this is a tech blog not a political one.

So I nominate Hedley Lamarr! Sorry that’s Hedy Lamarr…

Hedy Lamarr was born in eastern Europe and fled to America during the rise of the Nazis and Facists.  She became a leading woman in Hollywood and is known as one of Hollywood’s most beautiful.  However few know that her intellect rivalled her beauty.

With the help of her Hollywood composer neighbor, George Antheil, she developed Spread Spectrum and Frequency Hopping technologies to thwart the jamming of Allied radio communications by the Axis.  Wifi, CDMA, and Bluetooth are all based on the work he initiated.

Differences between FHSS and DHSS:

  • DHSS has higher throughput than FHSS (as much as ten times)
  • FHSS resists jamming nlike DHSS
  • DHSS is much more efficient in an outdoor environment.
  • FHSS does well indoors as it reacts more efficiently multipath
  • FHSS is more suceptible to narrowband noise than DHSS
  • DHSS combats microwave oven interference  better than FHSS
  • The synchronization of FHSS is a fraction of that used by DHSS
  • DHSS suffers more from the challenges of Near-Far than FHSS




Using WiFi to overcome a weak cellular coverage

credit: Ankit Tuteja
credit: Ankit Tuteja

So we have all had issues with our cell phone.  So says Ankit Tuteja in an article which gives some ideas on boosting performance which you can find here:   But wait “…you are  WiFi Superman, not SmartPhone Superman” you say.  This is true but there is much overlap in the RF/Wireless world not to mention within devices like SmartPhones.  This leads me to my next point.  If you have a bad cell signal for voice or data you can sometimes fix this by establishing a good WiFi connection.

In addition to Mr. Tuteja’s tips on boosting your cell phones performanceI recommend the following workarounds:

  1. For voice Issues use Skype, Google Voice, or others listed here:
  2. For Data Issues tether your device to a friend who has stronger coverage from a different provider.  To find out more about tethering / mobile hotspots check out this article:
  3. To help your signal for both voice and data use BlueTooth or even better an ear bud as it will reduce attenuation of the device while reducing your brain’s exposure to LTE, WiFi, and BlueTooth (if you choose the ear bud option)

I hope between the info in this blog and in Ankit’s article your mobile experience will be a little better each day!

How do Bluetooth and WiFi coexist?


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 from