Happy Birthday to the 1940’s Sex Symbol Who Co-Invented Wi-Fi

Last week on November 9th, it would have been Hedy Lamarr’s 108th Birthday. Better known for her leading roles in Hollywood, this bombshell was actually the brains behind the technology we have used for Wi-Fi and Bluetooth. 

Despite being a famous actress and arguably one of the most beautiful women in the world, her passion was science and she spent all her free time between filming tinkering with ideas and inventions. 

Without her innovative mind and natural affinity for scientific problem solving, we may not be using the Wi-Fi, Bluetooth and other RF technologies we rely upon each and every day. 

Along with composer George Antheil, Hedy Lamarr patented FHSS (Frequency Hopping Spread Spectrum) back in August of 1942. The inspiration for their idea was to prevent signal jamming on RF-controlled torpedoes. 

Hedy Lemarr heard about the possibility of United States Navy torpedoes being veered off-course from enemy signal jamming – Leading her to the idea of a frequency-hopping RF guidance system that would be much more difficult to jam and interfere with. 

Despite the brilliance of the idea, it was unfortunately never used for its intended purpose, with senior officials taking the view that Hedy would be more helpful in the war effort selling kisses as a pin-up. 

Despite Hedy and George attempting to patent their RF transmitter device that emulated player-piano capabilities, their ingenious frequency hopping idea was immediately classified by the US government and was not used in time to help with World War II. 

15 years later, the idea of spread spectrum and FHSS was further developed and used for the first time during the Cuban Missile Crisis between US ships blockading Cuba. 

In the 1970’s, FHSS was declassified but with their original patent now expired, neither Hedy or George made any money from their technology or the subsequent developments.

What does FHSS have to do with Wi-Fi?

Most of the early Wi-Fi deployments used frequency-hopping technology, with FHSS being one of the original technologies used for RF communication. Legacy Wi-Fi radios using RF communications used the 2.5GHz ISM band. Most frequency-hopping legacy Wi-Fi radios were made between 1997 and 1999. 

How does FHSS work? 

In simple terms, Frequency Hopping Spread Spectrum works by using a small frequency carrier space to transmit data, then hopping to another small frequency carrier space and transmits data, then to another frequency, and another and so on. 

In more specific terms, the frequency and period of time used for each data transmission is precise and determined by the dwell time. FHSS will transmit data for a set period of time (dwell time) on a certain frequency. After that time, it will move to another frequency and again transmit for only the dwell time before moving on again. 

The hopping used by FHSS radios is predetermined with a set hopping sequence. Rather than transmitting on one set channel of frequency space, a pattern of hops (or subchannels) is predefined so that it is hopping through a series of small carrier frequencies. Once a series of hops has been completed, it then repeats. 

The Institute of Electrical and Electronics Engineers (the IEEE) is the largest technical professional association, nurturing, developing and advancing global technologies. The standard of 802.11 from the IEEE specified that each hop must be 1 MHz in size, and then arranged in a predefined sequence. 

These sequences consisted of at least 75 hops but no more than 79 (in North America and the majority of Europe). Some other countries used much less hops, e.g. France had a sequence of 35 and Japan used 23. 

In order for a transmission to be successful, both the FHSS transmitters and receivers had to be synchronised on the same carrier hop at the same time. An FHSS access point could be used to configure a hopping sequence, with the information then being delivered via 802.11 beacon management frame to a client station. 

The dwell time is also specified by the local regulatory body. A maximum dwell time of 400 milliseconds per carrier frequency during any 30 second time period was set by the Federal Communications Commission. They regulate international communications through cable, radio, television, satellite and wire to promote connectivity. However, typical dwell times are usually between 100 and 200 milliseconds. 

The IEEE 802.11 standard also specified a maximum bandwidth of 79 MHz. This means that the maximum number of hops possible for a hop sequence would be 79. Based on a hop sequence of 75 hops, with a dwell time of 400 ms, it would take approximately 30 seconds to complete one FHSS hop sequence. As we mentioned above, once completed, the sequence is then repeated. 

Remember that the original aim of this technology was to prevent signals getting jammed and US Navy torpedoes being veered off course by the enemy. Due to the Wi-Fi FHSS transmissions jumping inside a frequency range of 79 MHz, a narrowband signal or noise would only disrupt a small range of frequencies. This means that it would only cause a minimal amount of throughput loss.

The effects of interference can also be diminished through decreasing the dwell time. The longer the dwell time, the greater the throughput as the radio is transmitting data throughout the dwell time and the less often the transmitter has to waste time hopping to another frequency. The shorter the dwell time, the more frequent the transmitter has to hop, which decreases throughput. 

Do we still use FHSS for Wi-Fi?

For Wi-Fi we have moved on to other RF technologies like OFDMA (orthogonal frequency-division multiple access) rather than FHSS.

However, we do still use FHSS for devices using Bluetooth and other radio transmitters. 

If it wasn’t for the brains of Hedy Lamarr, we might have never seen the Wi-Fi and Bluetooth technology that we all know and love. If you’re interested to know more about Hedy Lamarr and the story of how her brains far exceeded her renowned beauty, have a look for the documentary ‘Bombshell – The Hedy Lamarr Story’ (2017). You can rent or buy it via Amazon Prime and other streaming platforms. 

As we all know with technological advances, there are many great and innovative minds out there. Perhaps even if Hedy and George hadn’t come up with their frequency-hopping idea, someone like-minded would have come up with a different path on the route to Wi-Fi and RF communication as we know it today. 

But the story of sex symbol and scientist Hedy Lamarr is always an interesting one for us Wi-Fi geeks. So Happy Birthday and Thank You to her! 

Image from https://en.wikipedia.org/wiki/Hedy_Lamarr

Is Bluetooth Interfering with my Wi-Fi?

Do you use Bluetooth and Wi-Fi at the same time? Whether you’re at work, home – Or working from home! – you might find that you’re connected to both Wi-Fi and Bluetooth via various devices. 

And if this is the case, it’s probably common for these connections to fight with each other and cause you to run into connectivity issues. Why, we hear you ask? Surely they are completely different from each other? Actually, they’re not. They have a lot more similarities that you might have thought. 

There are instances where Wi-Fi and Bluetooth can use the same radio frequency range for data transfer, meaning that Bluetooth could interfere with your Wi-Fi. 

If you’re experiencing wobbly Wi-Fi or a Bluetooth connection that keeps dropping out then we feel your pain – There is nothing more frustrating. Not only that, but it isn’t very productive, is it? If you’re having to continually reconnect your Bluetooth device to make it work then you could indeed be struggling with interference between that connection and the Wi-Fi. 

Why can Bluetooth interfere with my Wi-Fi?

When it comes to understanding how Bluetooth and Wi-Fi can transmit data and interact with each other, you need to know a bit about frequency bands. 

Telecommunication and other applications depend on a series of electromagnetic frequencies in the Radio Spectrum. Each range of frequencies, or bands, are used for specific purposes. Some of the main frequency bands that you may have heard of are:

  • Marine Band which is used for ships communicating outside of the range of the shore. 
  • Citizen’s Band which is public radio frequency, known as CB and most commonly used by truckers. 
  • Broadcasting Band like AM and FM, multiple bands that are used to broadbcast radio signals 

So which do Bluetooth and Wi-Fi come under? Well, they are on Industrial Scientific Medical bands, or ISM. The home of radio telecommunications. One of these, which you will likely have heard of, is the 2.4GHz frequency band and is commonly used for network connectivity.  

This spectrum is occupied by both Bluetooth and Wi-Fi 2.4GHz, which means that things on this band can get a bit over-crowded and thus cause electromagnetic interference. How do you know when this happens? Well, you might notice some of the following things on your connected devices:

  • Audio connections via Bluetooth cutting in and out
  • Pages that are slow to load, or don’t load at all
  • Your device telling you that there is an issue on your network

A connection as unreliable as this causes nothing but frustration – What you need is for your device to be able to communicate properly with the network. Unfortunately, these problems can be common when a frequency band is over-crowded and causing interference between devices and networks.

This is why we use ISM bands for telecommunication – The traditional radio frequencies were too populated. What you might not know, however, is that ISM bands were originally to transfer heat, not data! Hence why your microwave can cause interference issues with your Wi-Fi and Bluetooth. They use the same technology, but radio waves at a different frequency. That’s why you are always told to not put your router or devices anywhere near your microwave! In fact, any device that gives off electromagnetic frequency could cause interference with your home network and lead to Wi-Fi issues. 

If you’re struggling with slow signal strength, an unreliable signal that cuts in and out, Bluetooth audio problems or a lag between Bluetooth devices (e.g. keyboards or mouse) then you could be experiencing interference issues. 

But is there anything you can do about the interference between Bluetooth and Wi-Fi?

Ways to Reduce Interference Between Bluetooth and Wi-Fi

If you think that your Wi-Fi or Bluetooth problems are down to interference then you’ll be pleased to know that there are a few straightforward things you can do to try and resolve the issues. One simple tweak could make a big difference! 

  1. Try connecting to a Lower Traffic Router Network

    If you have a modern router, then it should have the option to operate on different channels, for example 2.4GHx and 5GHz. If you have this option, then try changing the channel on the router that you’re connected to. This should hopefully help to relieve any network congestion.

    There’s unfortunately not an awful lot you can do if the interference is coming from outside your home, which is more common in densely populated areas like blocks of flats. You can see how dense your area is by looking at how many networks there are in the list when you try to connect.

    Thankfully, as we said above, modern routers are trying to combat this problem by having the option to use a higher frequency band. Dual band routers are particularly useful for this.
  2. Keep up-to-date with software updates

    Modern devices compatible with Bluetooth will mostly have the ability to hop along the channels in the 2.4GHz bands, known as frequency hopping. This helps to alleviate any issues caused by interference. In order for your Bluetooth device to be able to do this, you need to make sure you have stayed up to date with software updates.

On the 2.4Ghz band, some routers can transmit on multiple channels. Couple this with the ability for newer Bluetooth devices to frequency hop and you’re unlikely to struggle with interference between Bluetooth and Wi-Fi. Any interference issues could then be down to physical barriers rather than frequency interference.

  1. Can you remove any physical barriers?

    You may or may not be aware that different materials can affect your signal differently; some will completely block it. If you have lots of glass, concrete, brick or walls in general then this can cause the signal to get weaker, thus affecting your connectivity. Keep this in mind when you place your router somewhere – Behind a concrete wall or in a solid wooden cabinet are not ideal places! You’ll be surprised where our Wi-Fi experts have found routers…

    If you are using the 5GHz frequency band, then you need to be as close to your router as possible, with little physical barriers. Operating on a higher frequency means you are more susceptible to material interference.
  2. Can you get closer to the router?

    If certain materials are weakening your connection and you can’t easily remove that barriers, perhaps you can move either your router so it’s better located, or you and your device so you are closer to the router.
  3. Forget all your networks

    If the above solutions haven’t worked, then you might need to try forgetting all your networks on all your Wi-Fi and Bluetooth devices, unpair everything and then re-connect and re-pair. Yes, it’s a bit of a faff, but it can help remove old connections that are no longer needed that are crowding the network and causing interference problems. 

Still having problems? Call the Experts

If you’ve tried the above ideas and you’re still struggling with an unreliable connection, dodgy audio and/or slow internet then it could be time to call in the experts and get the fault diagnosed. 

Our Wi-Fi experts work out of Hampshire, London and Cardiff and can help solve your Wi-Fi woes and get you a more reliable connection. You can contact us here. You don’t have to put up with rubbish Wi-Fi! 

You can also read more about Wi-Fi interference on our previous blogs.