3G & LTE: How much spectrum do you really need?
Jan 15, 2013 by PolicyTracker


TagsBlog, Mobile, Wireless broadband

Everyone knows that mobile broadband traffic is going through the roof. So how much spectrum do you really need? While spectrum policy and regulation is constantly being developed, debated, and revised this simple question – oddly – seems to go unanswered most of the time. But the answer can certainly be determined.

Contrary to common belief it
is certainly possible to answer this question without having to resort to teams
of engineers and enormously complicated simulations models. As a technology
strategy consultant, I’ve worked on spectrum strategy questions like this for decades.
It turns out that there are only three parameters you really need to worry
about: The mobile or wireless technology that you want to apply, the distance
between base station sites (the inter-site distance), and the volume of
end-user traffic.

If know these three, you can
calculate your spectrum need using what amounts to kitchen math – but of course
you do need to know the right method. I’ve spent a number of years refining and
simplifying an Excel-based spectrum model that does exactly that. Since it is
remarkable simple, I’ve called it the SSM: The Simple Spectrum Model. I believe that any engineer or tech-savvy
economist can understand and apply this model without difficulty. It also
happens to represent the current de-facto industry standard for doing spectrum

Let’s look have a look at the
inputs: Any mobile technology can be defined in terms of its spectral
efficiency, i.e. how many bits you can transfer per unit spectrum. The values
for spectral efficiency are well-documented and easy to source (most of them). If
you know that you are working off an existing base station grid, the inter-site
distance is often known or at least it can be estimated. The traffic per user –
for example in GB per month – is also known from public sources, such as Cisco’s
VNI. In addition to this you need a value for the mobile broadband user density
per unit area but this is also quite easy to derive based on demographics.

If you’re looking to boost
your network capacity – and most network operators are these days – you can
essentially do three things: Increase your spectrum holdings, improve your
technology, or densify your grid. Many operators are doing all of the above at
the same time and continuously – which is the right approach. As spectrum
becomes more and more scarce, grid densifications are becoming more important
and thus the current hype surrounding small cells.

What about the technologies
available? Well, LTE will boost your capacity by a factor of at least two
compared to 3G (if the bandwidth stays the same) and up to 4 times if you also
double your bandwidth. You can also improve your technology by introducing
smart antenna techniques including MIMO. One very important new factor is how
unlicensed spectrum (e.g. for WiFi) will impact your business. I personally
believe that WiFi is a superb complement to 3G and LTE. 

But to make an informed
decision, you still need to calculate
what kind of traffic your spectrum can support. And I don’t know of any better
or more efficient way than the SSM. Find it here – and don’t hesitate to
contact me if you have questions.

 Claus Hetting