Stephen Temple

One of the hardest things to do is to reverse the habits of a lifetime. The mobile industry, with the support of governments and national regulators, has spent almost its entire lifetime looking upwards to the next higher band in the spectrum to continue its success story. But that path is no longer sustainable. The spectrum capacity for the next big national mobile network upgrading will have to come by making considerably more efficient use of the mid and low mobile bands.

First a brief recap. 1G started its life around 450 MHz in some countries and then 900 MHz became the norm. 2G began its life at 900 MHz and was extended to 1800 MHz. 3G was focussed in 2.1 GHz. It all started to go wobbly with 4G with a schism between going up to 2.6 GHz and down to 800 MHz. It all went horribly wrong in the formative period of 5G when the consensus view, following the habits of a lifetime,  was that 28 GHz was the future of 5G. It turned out to be a costly error. The University of Surrey 5GIC was among the fastest to realise that 28 GHz was going to be a mobile coverage disaster. In 2016 they recommended pivoting downwards to mid-band 3.4-3.8 GHz with 700 MHz delivering national coverage of much reduced data speeds and 26 GHz providing huge capacity relief for traffic hot spots. Ofcom played a leading role, having the RSPG chair at the time, in delivering this re-think across Europe in record time (and some might say “just in time”).

This brings us onto 6G. Already, for some, the old habits of a lifetime have kicked-in. Terahertz is held up as the next “inevitable” destination for 6G mobile networks. It is not. It is very likely uses will be found for Terahertz spectrum somewhere on the 6G canvass but providing national coverage of high performing mobile networks will not be one of them. A stunning data rate over a pitifully tiny geographic area is not remotely a “mobile” service proposition.

There is a growing consensus that widespread coverage needs to be put at the heart of the 6G initiative so as to prevent a “digital divide” and to contribute to  improved health and social care outcomes and future transport ambitions. This has profound spectrum policy implications as the spectrum capacity for a significant upgrading of the performance of  our national “mobile” infrastructure will have to be found by looking downwards to the mid and low bands that have the propagation characteristics that make national coverage economically viable. This may need re-enforcing with satellite technologies but that will need far better integration with terrestrial mobile services and spectrum if it is to ever break out of being an expensive niche.

But how can that be possible? All the mobile spectrum at mid and low bands has already been allocated and in use?

There will not be a single all encompassing solution. Growing the low and mid band  “spectrum cake” bigger for everyone will need a multi-pronged approach:

1. Band de-fragmenting –  Mobile operators have finished with a legacy of fragments of bands across the low and mid band ranges.  There is a significant efficiency gain to be had from de-fragmenting these spectrum holdings. This is within the gift of the MNO’s to solve among themselves. More complicated to bring about but potentially more fruitful is to look at the pattern of TV digital terrestrial viewing on 600 MHz DTT versus on-demand viewing over time and think of a 6G scenario where spectrum resources can follow the viewers in the most spectrum efficient way, noting that DTT is very spectrally efficient for mass concurrent viewing but many DTT channels, even today, only attract micro audiences.
2. Leap in spectrum efficiency – This has to be the main thrust. Ofcom’s recent consultation on spectrum management strategy for the 2020s has an outstanding piece of analysis in their ‘good neighbours’ vision. A lot of research will be needed to deliver on that vision and more so as energy efficiency now has to be a concurrent consideration.
3. Satellite-terrestrial mobile spectrum sharing – What will be needed here will be moving the game on from satellite and terrestrial mobile interests seeing themselves as competitors for new spectrum to becoming partners in spectrum sharing arrangements within the same band.
4. AI and in-flight spectrum refarming –  Very large efficiency gains could be delivered if it were  possible to transform long lead spectrum changes into real time changes. This will require real time intelligence. Huge world wide investments is being made in research into AI applied telecommunications networks. AI will almost certainly feature strongly in 6G and that is likely to include spectrum usage. This will lead to having to think through a whole new spectrum regulatory framework that looks nothing like the one we have today.

None the above modernisation is likely to happen or, if it does happens, it will happen badly if everybody remains in their silos grimly defending the old spectrum habits of a lifetime. No single company or entity could deliver the above alone. Only a cooperative voluntary effort on an immense scale offers the guarantee of a successful outcome.   How is that even possible in practice? Well, that is what a mobile technology generation change has proven to do particularly well. An entire industrial eco system all agrees to make a change at the same time right across the globe every ten years. It deals with the complex interdependencies at a stroke and create almost instant economies of scale. There is no reason why all the hooks for more efficient use of mid to low band spectrum, including AI applied to spectrum sharing, cannot come built into the next generation of mobile technology. But timing is critical.

That is the significance of the DCMS and the UK Spectrum Policy Forum supported  6G research initiative. It’s prime purpose is to bring spectrum policy makers alongside the UK University research base right from the start of the 6G initiative.  In this way spectrum policy makers can influence the direction of spectrum related research towards their vision of more intensive spectrum sharing and far more efficient use of the spectrum. But spectrum efficiency cannot be considered in a vacuum. There are complex trade offs with maximising coverage and  connectivity and minimising costs and the carbon footprint.

The benefits of closer links between our University research base and spectrum policy makers flow both ways. Researchers can be more confident that their ideas will be wanted by industry and regulators. Later international collaborations will be needed and routes found into the global standards body for the best ideas. But we need to get our own ideas sorted out first. The prize is for public money going into long term research to be far more productively spent and successful research outcomes emerge that can deliver an enlarged national “spectrum cake” to support a larger higher performing wireless based economy. That is a new habit with a lot going for it.