Millimeter or Centimeter waves for 5G?

Attending the Globecom 2014 workshop on “Emerging Technologies for 5G” makes it clear to me that there are quite different views on where to go regarding spectrum. In particular this was evident from the concluding panel in the workshop. On one side is the millimeter wave camp, that are attracted by the fact that at 30 GHz and above (Gerhardt Fettwies thinks we should we even go above 100GHz since attenuation is less and antennas can be integrated on chips) here are large spectrum regions where exclusive licensen is possible. Exclusive licensing of course preferred by the operators, since it removes uncertainty about the availability of spectrum. If you invest billions of dollars in infrastucture you do not want to compete for spectrum every day. However, the very high frequencies represents a technology uncertainty – will it actually work ? When will the decvices be available? What will they cost ? Will the coverage be sufficient? Ted Rappaport at NYU says it will.

In the other camp we have proponents for centimeter wavelengths (say 6-12GHz). Here there is little uncertainty about the technology. It works at 5GHz, and it will work at sligthly higher frequencies as well. However, the spectrum is already assigned to other services and has to be shared. This something the WiFi community has been living with this for quite some time. We have a fairly good idea that this will work fine for indoor use, it is likely to promote low-power, low-cost hardware, but it will take some time to get the regulation in place. Instead of a technology uncertainty, we have a regulatory uncertainty. The incumbents seem to prefer the technology uncertainty to the “political”, despite the obvious.

As usually, in the discussion the distinction between where the technology is going to be used is not made. Is it the outdoor “coverage/mobility”-world that is discussed or the indoor “capacity”-world.  In the outdoor environment the charge for exclusive licensing can be motivated, in the indoor world where very little interference leak out to other buildings at higher frequencies nationwide licensing make little sense – sharing, however, seems to be the way to go.

60 GHz for indoor seems OK, although there are problems. As Robert Heath, UT Austin, points out, various blocking/shadowing phenomena, e.g. body shadowing, device orientation as well as “hand blocking” from the user holding the device, are problems to be dealt with. The billion dollar question  remain: Do we need to go through the ordeal of 60GHz for outdoor “macro-cellular”? 1Gbit/s would be fine while driving in the street –  I am sure it can be done -but can we afford the solution ? The new promising technology (e.g. beamforming) is actually going to be needed at 60 GHz just to overcome the high propagation loss. 1 Gbit/s is a lot so will the number of required base stations (and the associate cost) be managable ?

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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