802.11ax

About the author

Michael Spalter

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Michael Spalter has been a networking technician for over 30 years and has been the CEO of DrayTek in the UK since the company’s formation in 1997. He has written and lectured extensively on networking topics. If you’ve an idea for a blog or a topic you’d like explored, please get in touch with us.

Usage of the 5Ghz Wi-Fi band is increasing. The 5Ghz band was used for 802.11a, introduced in 1999 but 802.11a wasn't widely adopted - later systems such as 802.11b through to 802.11n used the 2.4Ghz band. More recently, the 5Ghz band has been used for 802.11ac and again now for the latest 802.11ax standard.  In this article, I'll explain the benefits and downsides of the 5Ghz band compared to the more commonly used 2.4Ghz band.

Frequency & Wavelength

First, a little basic physics recap.  Radio signals exist as waves and can be drawn as a waveform. Wavelength (measured in cm or metres) is the distance from one point on a waveform to its next occurrence - literally the 'length of the wave' for example from one peak to the next. 

Frequency (measured in Hertz) is the number of times (or cycles) that a wavelength cycles per second.  If you have more waves per second, the distance between each peak is shorter, therefore wavelength and frequency are inversely proportional - increase one and the other reduces, and vice versa.

Waveforms are generally drawn as above - as a graph of amplitude over time but you could also draw it as a circle because a wave (more specifically, a sine wave) rotates from 0 to 360 degrees each cycle. A 1Hz signal would rotate 0-360° once a second. 


We draw waves as graphs as we can show frequency variations and time but it's still just a stretched out circle.  When the waveform crosses the X axis, it's at 0°, it rises to the peak (90°), back down to the X axis (now 180°), down to the bottom of the trough (270°) and then back to the X-axis (360 or 0°).

Advantages of Lower Frequencies

Lower radio frequencies have longer range than higher frequencies.  So, a 900Mhz signal would travel further than a 2.4Mhz signal, everything else being equal.

'Short Wave' radio is used by amateur radio (ham) operators, maritime users and long-distance radio stations (world services etc) and international propaganda broadcast. Short wave uses much lower frequencies compared to Wi-Fi, down to around 0.003Ghz (2 MHz) so the longer range is ideal for those applications and can travel thousands of Kilometres. Short wave can increase range further by tropospheric propagation (bouncing the signal off the Earth's troposphere).

Wi-Fi, on the other hand, uses the much higher frequencies, with 5Ghz having lower range than 2.4Ghz, assuming the same power input. There are several reasons why higher frequency has lower range:

1. A higher frequency (more cycles per second) uses more energy (power) than a lower frequency which means, given the same power input, there's less RF (Radio Frequency) energy output.
   
   
2. Frequencies in the microwave band (which includes 2.4Ghz and 5Ghz) are more readily absorbed by objects, rain and moisture in the air. As microwave photons have more energy than radio photons, they will excite molecules en-route more readily, causing friction and your WiFi signal is lost as heat. This is exactly how microwave ovens work (see my very old article on potatoes here). 
   
3. At lower frequencies, the longer wavelength means that the antenna can be more efficient because the effective surface area can be greater. At higher frequencies, the wavelength is narrower (2.4GHz=12.5cm. 5Ghz=6cm) so less of it would hit the same antenna.

This works with sound too.  A high-pitched sound will travel less far than a lower pitch sound because higher pitched sounds (a faster oscillation) will excite air molecules more as they travel, losing more energy as heat. So, if you're stuck up a snowy mountain, scream in a low pitch for a better chance of being heard. You won't cause an avalanche (citation).

Faraday Cages & Shields

Those wavelengths (12.5cm, 6cm) are real measurements - that's what you'd measure on a ruler if  you could see the microwave signals from your Wi-Fi device.  If you want to block radio waves you can build a Faraday Cage (or Faraday shield).  A Faraday shield blocks electromagnetic waves. It may be built into the walls and doors of a room and is commonly used for testing wireless equipment, operating MRI scanners or other sensitive measurements where external interference needs to be eliminated.

When you step into a Faraday Cage (room), instantly your mobile phone, your laptop, your pocket radio etc. will lose their wireless signal - dead.  This works because as radio or other electromagnetic radiation hits the cage, the charge is distributed around the conductive surface of the shield or cage, but does not penetrate inside; effectively it's a hollow conductor. In the case of a cage, the construction mesh needs to have holes only smaller than the smallest wavelength that you want to keep out.  So if you want to block WiFi from your kids bedrooms, you could embed the walls with a metal mesh with holes less than 6cm in size. 

You may be familiar with Faraday pouches which are used with keyless card entry fobs.  To prevent vehicle theft, the key/fob is placed into a pouch to block its signal from opening the car.   Some concert promoters are also insisting that audiences place their phones into faraday pouches, supposedly to engage people more into the moment and prevent recording/photos.

Advantages of Higher Frequencies

So, given that higher frequencies have lower range, why would we want to use them?

5Ghz still normally has sufficient range for a single office or modest house but if it is insufficient you can mitigate or  allow for by having more bases or a mesh system, which can also reduce local congestion.

Higher frequencies have the main advantage of providing higher traffic capacity which in a data environment means higher throughput:

1. A higher frequency, by definition, has more cycles (more waves) per second. Therefore if you are using each cycle to encode data, a 50Hz signal provides only 50 cycles per second whereas  a 5Ghz signal has 5,000,000,000 (five billion) cycles per second so you can see that a higher frequency enables you to encode more data per second.
   
   
2. Although 5Ghz usage is becoming more common, 2.4Ghz is still the most commonly used band so the 5Ghz band is still far less congested than the 2.4Ghz band.
   
   
3. The allocated band is larger at 5Ghz - there are more non-overlapping channels. In the 'A Band' (supported by all 5Ghz WiFi products) there are 8 non-overlapping 20Mhz channels and another 5 (in band 'C') were opened up in 2017 (link). In July 2020, Ofcom announced that the 6Ghz band would also be reallocated for Wi-Fi use, though it will take some time for vendors to produce hardware.
   
   
4. The shorter range of 5Ghz actually provides an advantage in that neighbours' Wi-Fi signals will not propagate as far, so are less likely to cause interference to your Wi-Fi. This is also assisted by the use of TPC which mandates that 5Ghz devices should reduce their transmission power to only that which is necessary to maintain a reliable signal.
   
   
5. As well as other nearby 2.4Ghz Wi-Fi networks, the 2.4Ghz band is also used and therefore may suffer interference from Bluetooth devices, home automation (e.g. Zigbee), garage door controllers, baby monitors, car alarms, smart meters and wireless speakers/mics. DECT (cordless) phones in Europe do not use 2.4Ghz, however microwave ovens do, so if your oven has been damaged or is poorly shielded, it may interfere with your Wi-Fi.
   
   
   

Okay, so which is better?

Hopefully you can see that each band offers advantages. If you want the highest speed, the 5Ghz protocols will provide those. If you want the best range or area coverage, 2.4Ghz would be better.   You will find that many devices such as home doorbells or security cameras will use 2.4Ghz - in those applications the link speed at 2.4Ghz is sufficient for the application so using 2.4Ghz is going to give the best coverage.  Most Wi-Fi routers and access points are now dual-band so if 5Ghz doesn't quite reach the furthest areas, you can switch to 2.4Ghz - which, if the signal is good, is still normally adequate for an HD video streaming service.

As always, I hope you find these blogs useful - please do share them using the links above, make comments below and let us know if you have any suggestions for new blog entries.

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