Advantages and disadvantages of 5GHz Wi-Fi bridging

8th December 2016 – Written by Peter Cronshaw

As a part of the wireless bridging team at DigitalAir Wireless I’m always asked what the advantages and disadvantages are when using 5GHz. A few years back I would say pros would out way the cons however, these lines are becoming blurred and the opposite is now coming into focus.

Cast your memory back to 1999 and to the dawn of the new millennium. Myself, I was 21 years of age without a care in the world. The Y2K bug was looming, some saying it would be the collapse of the world economy. The Matrix, one of the most iconic films ever made, was released to critical acclaim. Also released was Star Wars Episode One and for some, ruined an entire childhood. One other important event happened in 1999 that would’ve slipped through some nets is the release of IEEE’s latest standard 802.11a. This added the 5GHz space as well as 2.4GHz which gave potential data rates of up to a whopping 54Mbps. 2.4GHz was becoming more and more saturated, 5GHz gave badly needed airspace offering multiple non-overlapping channels as opposed to only the three within 2.4GHz. 5GHz was now free to be used for wireless bridging.

Too much of a good thing.

In 2007 the Granddaddy of the smartphone, Apple’s iPhone swaggered onto the scene which changed everything, for the first time a phone driven by an operating system and the smartphone as we know it today was born. By 2009 IEEE’s 802.11n was released, faster, more reliable and giving us features like MIMO (multi input, multi output) using multiple antennas and planes to give increased performance to enhance transmit and receive communication. The demand for 5GHz in mobile devices was huge, by 2012 Samsung’s Galaxy 3 handset gave us dual antennas in a mobile phone for the first time. Mobile phone sales for the 2012 fell a little from the previous year however, we’re still talking an estimated 1.75 billion units sold. The next few years up to 2015 saw another 3.5 billion sold. 

I know what you thinking, what relevance has a mobile phone sales got with wireless bridging? When any population increases within a finite space to house them you’re either going to need to expand or go somewhere else. It wasn’t hard to see that 5GHz was going the way of 2.4GHz and fast. 

5GHz was expanded further in 2014 with the arrival of 802.11ac and gave us the use of 80 and 160MHz wide channels. This gave the capability of achieving speeds of up to 700Mbps however, also opened up a can of worms as to potentially achieve these speeds you would need to use 160MHz channels, of which there is only one within Band B, and two in the whole of the 5GHz range. 

End of an error…era

And that my friends is my point and I’ll get straight to it. No sane person could specify a 5GHz solution for a primary, mission critical link especially in a heavily built up area. DigitalAir take the consultative approach to any project and we’re not happy until we’ve done our due diligence and put all options on the table. I strongly advise that if you need a wireless bridge and it’s critical to your business please consider your business and sanity and give us a call. We’re vendor agnostic and our advice…. is free.

On that note…

A little Knowledge...

The 5GHz space is split a few bands:

Band A Lower - UNII-1: 5180MHz – 5240MHz 

Band A Middle - UNII-2: 5260MHz – 5320MHz 

Band B Extended - UNII-2e: 5500MHz – 5720MHz 

Band C Upper - UNII-3: 5745MHz – 5805MHz 

Band A is typically set aside for indoor wireless. For wireless bridging Band B is where it’s at. Within this space are split into 20, 40, 80 and 160MHz wide channels. Below is a little table that may prove useful.

Band B Extended - UNII-2e:

11 x 20MHz Wide Channels.

6 x 40MHz Wide Channels.

3 x 80Mhz Wide Channels.

1 x 160Mhz Wide Channel.

 

Centre Freq (Mhz)

802.11a
(20Mhz)

802.11n
(40Mhz)

802.11ac
(80Mhz)

802.11ac
(160Mhz)

1

5500

100

102(60-64)

 

 

2

5520

104

 

 

3

5540

108

110(108-112)

106(100-112)

 

4

5560

112

 

 

5

5580

116

118(106-120)

 

114(100-128)

6

5600

120

 

 

7

5620

124

126(124-128)

122(116-128)

 

8

5640

128

 

 

9

5660

132

134(124-128)

 

 

10

5680

136

 

 

11

5700

140

142(140-144)

138(132-144)

 

12

5720

144

 

 

Band C - UNII-3

There are four channels at the end of the line within 5GHz in Band C. Now, these channels could be used but be aware the power required to transmit at these frequencies will take you into illegal limits and will then require a light license from OFCOM. Limit to operate legally in the UK is 1Watt. Having said that it may not cure your ills if you’re experiencing cochannel interference. The truth being not enough education is out there. Anyone and their dog can buy a reasonably well specified cost effective bridge these days for as little as £250 and it doesn’t require much experience to get it up and running. There will be a lot of people out there using Band C that simply don't know about the restrictions and could land themselves a hefty fine if caught out.

 

Centre Freq (Mhz)

802.11a
(20Mhz)

802.11n
(40Mhz)

802.11ac
(80Mhz)

802.11ac
(160Mhz)

1

5745

149

151 (149-153)

 

 

2

5765

153

 

3

5785

157

159 (157-161)

155 (149-161)

4

5805

161

 

DFS.

You may also come across Dynamic Frequency Selection (DFS) This means if an access point detects weather radar and other government radio systems then that access point must, by law, vacate that channel for an hour minimum. If that access point is near, then the channel will need to be permanently avoided.

Pretty fly for a Wifi

I hope there has been some useful information found here. I wanted to illiterate my primary reason for this is blog and that is we are getting increasing amounts of people calling in asking for health checks on links experiencing issues and It’s alarming how many are caused by interference. Some of these issues can be cured with a simple channel change although we have the feeling of postponing the inevitable but, some we’ve seen are being drowned in a maelstrom of 5GHz and there’s no choice but to look at swapping the link out.

Right I'm off, I think I’ve taken enough of your time. If you are experiencing issues, you've tinkered around and are still

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