In the never-ending quest for more spectrum to support rising data usage, and now the exploding numbers of devices promised for the IoT, capacity in the sub-6 GHz bands – always considered optimal for mobile and wireless
access – is at a premium. Like any other famine, this will create two responses:
• migration into new areas which previously looked less attractive, such as high frequency bands, or those with incumbent users like broadcasters
• more efficient use of the resources already available
Both will be important in the run-up to 5G. More spectrum is being released round the world, both licensed and unlicensed. In 2014, the FCC opened up 100 MHz of additional spectrum in the 5 GHz band for Wi-Fi and other usage and other regions are also expanding the available capacity in this key band.
The centimeter and millimeter wave bands have created high excitement because of their large capacity and at the World Radio Conference in 2019, several bands above 24 GHz will be considered for 5G. Ahead of that, the
FCC recently agreed to open up four bands above 24 GHz, with a view to laying foundations for 5G – these will initially be used to trial fixed wireless applications, but are mainly arousing interest as an enabler of hyper-dense HetNets in future.
“It was once thought that frequencies above 28 GHz could not support mobile services because their wavelengths were too short and the signal propagation losses were too high,” FCC Commissioner Mignon Clyburn said. “But industry engineers have now turned these weaknesses into strengths by finding ways to use short wavelengths to build dynamic beamforming antennas to support high capacity networks that are small enough to fit into handsets.”
The US bands in question are 28 GHz (27.5 to 28.35 GHz); 37 GHz (37 to 38.6 GHz); 39 GHz (38.6 to 40 GHz); and 64-71 GHz. But more interesting than the frequencies themselves are the licensing regimes which will accompany these plentiful sources of spectrum around the globe. Some, like 60 GHz and 80 GHz, have been licence-exempt in most areas where they are available; others, like LMDS, have been subject to licence.
Many stakeholders believe these high capacity bands will only deliver their full benefits if they are flexibly licensed. Newly emerging regulatory frameworks have interesting potential for the HetNet and 5G, supporting shared access. Initially, schemes like Europe’s licensed shared access (LSA) and the US’s authorized spectrum access (SAS) were developed to allow for sharing between incumbent and new users, while preserving the former from interference.
Examples include the TV white spaces spectrum (for which there is a Wi-Fi variant called 802.11af) and the newly opened US CBRS band in 3.5 GHz, which has three tiers of access with different levels of openness. The top level is for incumbent federal users with full protection, the bottom level is for general access, and the middle layer supports light licences which provide some interference protection, but need not be confined to MNOs.
As virgin spectrum runs out in many areas, such schemes will become more and more important to wireless providers.
But some of the techniques designed to preserve the incumbents from harmful interference, such as cognitive radios and geolocation databases, will also be adapted for even more dynamic access systems, some of them in spectrum bands with no incumbents, but where different users want access with varying degrees of protection.
The WBA announced a partnership with the Dynamic Spectrum Alliance (DSA) last year to develop technologies that operate in TVWS. The two organizations will co-develop guidelines for interoperability and for “promoting the usage of unlicensed wireless technologies at both technical and regulatory level”.
Such initiatives could lead, in time, to dynamic spectrum trading and flexible on-demand allocation – a central pool of spectrum being assigned to any service provider as required was considered the stuff of dreams only a few years ago, but is now looking achievable. There are already Wi-Fi trading systems such as BandwidthX, which launched in 2013. Such approaches are sure to be applied to licensed and shared access bands in future too.
The 2016 WBA Annual Industry Report is available to download here.