Have we reached “peak-spectrum”?

After reading the FCC report “MOBILE BROADBAND:THE BENEFITS OF
ADDITIONAL SPECTRUM
” one can easily get the impression that we have passed “peak spectrum” and that we are running out of the stuff at a rapid rate. You may contest that,  unlike oil, the electromagnetic spectrum is an infinitely reusable resource and we can thus never be out of spectrum. Even if there is no more additional spectrum, we can still make wireless capacity go up. The problem is, however, building high capacity wireless systems is much cheaper if there is an abundance of free spectrum. Limited spectrum means that we need to

  • limit the transmission range and therefore invest in more infrastructure, that is a denser networks of basestations and/or
  • use more power as we go to more and more spectrally efficient modulation with lower energy efficiency  as consequence

The first factor is well known to the operators and also dealt with in the report. They can simply calculate what there alternative cost is if the do not get the next chunk of spectrum in the next auction and can bid accordingly.  The latter (energy)  factor is not so much discussed. We can not do very much about in the short term, since such properties are given by standardized air-interfaces (e.g. LTE).  In the long run, to save energy (cost),  additional spectrum may play an important role here as well. Like for oil, the price for spectrum will go up – although  for different reasons. This makes it very clear that efficient use of spectrum is a key factor to in constructing affordable systems.

A point that the report, I think, misses is that many of the simple capacity/cost/spectrum calculations work for classic cellular deployment, but do not scale to very high capacity systems. For these scenarios we leave the “blanket coverage paradigm” and cover only specific places with extreme bandwidths. These are the places were the customers are, i.e. primarily indoor locations. Here the spectrum picture looks much more favorable and there is plenty of existing, licensed spectrum for secondary use.

Jens Zander

About Jens Zander

Professor Jens Zander is professor in Radio Communication Systems at the Royal Institute of Technology, Stockholm, Sweden. He has been among the few in Swedens Ny Teknik magazine's annual list of influential people in ICT that have been given the epithet “Mobile Guru”. He is one of the leading researchers in mobile communication and is the Scientific director of the industry/academia collaboration center Wireless@KTH. His research group focuses on three main areas – the efficient and scalable use of the radio frequency spectrum, economic aspects of mobile systems and application and energy efficiency in future wireless infrastructures.
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