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Posted by Tom Cheesewright on

There can be only one… network: Why we need to make better use of spectrum in the future

There can be only one… network: Why we need to make better use of spectrum in the future

What does this sentence mean to you?

‘This year the UK government will auction off 250MHz of radio spectrum to be used for 4G mobile phone services’.

If the answer is ‘Nothing’ then let me try to explain, because this stuff is important.

Think of a child’s drawing of the world. Land at the bottom, sky at the top, people and houses in the middle.

Now imagine that the sky is divided into 300 million very, very thin horizontal layers stacking up into space. These layers are grouped together into bands — imagine them as different colours like a rainbow. Some are thinner, some thicker.

This rainbow of colours represents the radio wave spectrum. Each colour represents a group of radio frequencies (a ‘band’) we have allocated to different uses. Some bands carry AM or FM radio, some the signals for 3G mobile phones, and some your Wi-Fi network.

Frequencies are measured in Hertz (Hz for short) which represents the number of times the wave oscillates (goes up and down) every second. The frequency has a huge impact on how useful a band may be for different things. High frequencies can carry lots of information but need lots of energy and don’t travel very far. Low frequencies aren’t so good at carrying information but will amble on endlessly over very great distances.

Most modern digital services exist in a sweet spot between 10 Megahertz (10,000 oscillations per second) and 10 Gigahertz (10 million oscillations per second). Here you get a reasonable balance between range, energy consumption and information capacity. Though there’s still a marked difference between the characteristics at the top and bottom of this range.

Each band is a different size, depending on how many layers (Hertz) the relevant governing body has decided to allocate to each use. Bands are typically allocated by the Megahertz (thousand Hertz). Some might have just a few tens of thousands (e.g. Wi-Fi), some might have a few hundred thousand (3G).

My suggested visualisation is by no means scientifically accurate but it does get across one important thing: the amount of useful spectrum available is finite — so we need to make good use of it. Just as we do any other resource.

Back to the beginning

So back to my opening: the UK government plans to auction off 250MHz of spectrum next year to be shared between up to four different operators — e.g. Vodafone, 02, EE or Three.

Now let’s do some maths.

Take your 250MHz and multiply it by the amount of data that can be carried on each single layer/Hertz. This is measured in bits per Hertz per second, and the ideal world figure for LTE — the 4G standard to be used in the UK — is around 8 bits per second per Hertz. That means that in any one place at any one time, the total data capacity of 4G is around 2 million bits per second or 2 Gigabits per second.

Let’s put that into real world terms. Netflix reckons you need the following in order to stream its content:

  • 1 Megabit per second to watch standard definition TV on a laptop-sized screen
  • 2 Megabits per second to watch standard definition video on a large TV
  • 4 Megabits per second to watch HD video

On this basis 500 people in Oxford Circus or Exchange Square in Manchester could all watch Strictly in high definition at the same time over 4G. That doesn’t sound too bad.

But the real world and the ideal world are very different. According to studies by Ofcom and others a more realistic figure is 1.3 bits per second per Hertz. That means instead of 500 people happily streaming Strictly, you’re down to 80.

Some people are more pessimistic still. That number could be significantly smaller once you take into account the impact of handling different types of traffic and real, real world conditions. Suddenly you’re down to just fifteen people on each network being able to watch Strictly in all its HD glory.*

But I don’t care about watching Strictly in HD!?

Strictly is just a useful metaphor. 4 Megabits per second is not, in the grand scheme, a lot of bandwidth to demand.

The first portable devices with 4K or Ultra High Definition screens are already starting to appear. These will devour four times the bandwidth of full HD. Every time more bandwidth has become available, we have created services to fill it. Trust me: 4Mbps will feel like dial-up in a few years (and if you don’t know what that feels like, and you really want to experience the web the way it used to be, check this out.

So what’s the answer?

Check out this chart showing how the available spectrum is chopped up in the UK.

Now think: how many of the services on here could not be delivered over an internet connection? For a start, all broadcast services, and all mobile services could be. This doesn’t determine what you use to carry that internet connection (e.g. 3G), but it does mean you don’t need to allocate chunks of spectrum to specific services. Rather you just allocate spectrum to different means of delivering an internet service.

Because technology will move forward constantly you don’t want to keep reallocating the same spectrum every time a new standard comes along. But maybe break it into two or three blocks with a rolling programme of upgrades, each time a significant new milestone is reached. This way we can ensure there is always enough bandwidth for us all to watch Strictly — and do a lot more valuable (and enjoyable) things, whenever we want to and wherever we are.


*Can I just point out at this point that I am not a particular fan of Strictly Come Dancing — it just happened to be the first programme that popped into my head.

Tom Cheesewright