Ofcom today published its final rules for the 4G spectrum auction in the UK. Key points:
The UK’s first 4G service has just gone live with others set to follow next spring, but some people are asking whether anyone really needs faster 4G speeds yet.
In addition, the amount of spectrum that can be used for mobile services is more than doubling with the 4G spectrum auctions that have or will soon take place in Europe. So the future’s bright … our mobile and wireless networks should have the capacity to meet the future demands of consumers and businesses for using our smart phones and wireless broadband services?
However, the amount of data we consume through our mobile devices has been growing frenetically and many expect that growth to continue, particularly as smart phones and tablets become more widespread.
The chart below shows a series of market forecasts that vary widely but all show rapid growth – the Mid forecast shows roughly a 100 times increase in demand for mobile data over the next 10 years. NOTE – it’s plotted on a logarithmic scale which gives a compressed view of how fast demand for data is predicted to increase. Going up one notch on the vertical axis represents an ten-fold increase in demand (not a doubling). So is there perhaps a question to answer despite the imminent arrival of 4G and so much new spectrum. And what could we do if there were a risk of a mobile network capacity crunch in the future?
Source: Real Wireless
Does or can government help industry meet soaring demand?
One reason to consider this now is because, if we do need to bring more spectrum on stream in the future, the process is cumbersome to say the least – potentially years of international negotiations and heaps of technical work. In order to get more spectrum in 10 years’ time, we might need to set the wheels in motion quite soon.
The key things to consider are:
My associates, Real Wireless, experts in mobile technologies mapped out the potential future technology enhancements that could increase the capacity of mobile networks in a study for Ofcom. Generally we can identify quite a few techniques now which could be introduced over the next 10 years (despite the uncertainty inherent in technology forecasts):
Real Wireless worked out a number of plausible combinations of these techniques and looked at how much additional spectrum Ofcom is currently predicted to make available for mobile use over the next 20 years – up to 350MHz (which compares well to the 200MHz of 4G spectrum currently being released in Europe). This enabled them to make a good forecast (using information on real geographic areas) of how mobile network capacity is likely to increase in the future.
This allowed mobile data demand to be matched against mobile network capacity (once the fluctuations of mobile data demand during the day were taken into account to get a measure of the peak demand).
Spectrum currently earmarked for mobile could be exhausted in just over a decade
The result is that that there may well be a network capacity crunch, in as little as 10 to 12 years’ time in some areas, even given the likely technological improvements and increased spectrum we currently expect to come on stream.
By capacity crunch we mean that the mobile operators will have exhausted all the techniques for increasing capacity we can currently forecast, and the only way to increase capacity would be a significant expansion in base station sites. This would not only be costly, but physical and planning limitation could mean that a major expansion was unlikely to be feasible, particularly in urban areas.
The result was derived by evaluating the costs of the alternatives for increasing mobile network capacity, i.e. using more of the spectrum available for mobile vs. new technologies vs. deploying more base stations. The most cost effective way to increase capacity to meet demand was calculated on a rolling 2-3 year basis. The result is shown in the graph below.
Source: Real Wireless
What could be done to provide more capacity?
The option that is most in the control of governments and regulators is to try to allocate more spectrum for mobile. It’s likely that any suitable candidates are already being used for something else, hence there would be a cost to society in switching over such spectrum to mobile.
The 700MHz band is one possibility. Although currently used for terrestrial TV broadcasting, moves are afoot in Europe and in other regions to consider possible future mobile use. The 700MHz band is attractive because it may gain broad international support. This would make it more likely that leading handsets would work on it. Also, its physical characteristics mean that it can provide more reliable coverage, and hence capacity, compared to the majority of existing mobile spectrum.
700MHz could alleviate the potential capacity crunch
Our research shows that mobile operators could save substantial sums of money by deploying 700MHz spectrum at the key point in the future, instead of deploying more base stations. Consumers should benefit as well through lower prices and more consistent service quality.
However the timing of when 700MHz is available is important, particularly the closer we are to the worst case scenario of when mobile broadband demand is high and the government cannot release as much spectrum for mobile as it currently expects over the next 10 years.
If 700MHz spectrum were available in 2020, the benefits for mobile operators (and consumers) would be much greater than if it were only available when current 700MHz licences expire in 2026.
If 700MHz is not available until 2026, mobile operators would have to start deploying new base station sites when the capacity crunch hit in 2022 to 2024. Deploying new sites would lock the operators into a certain course of action (to exploit the new sites to the full). The potential cost savings from using 700MHz would be much lower than if 700MHz had been available before the new sites were deployed. In other words, there is a risk that the industry could get locked into the wrong technology path.
Conclusions
Despite the exciting changes that 4G is likely to make to our smartphone and tablet experiences, regulators and mobile operators have to keep an eye on the future needs of the mobile networks. Our technological inventiveness may not be enough to avoid a capacity crunch 10 years down the line, hence the mobile sector is likely to need even more spectrum, preferably harmonised on a European or wider basis.
The 700MHz spectrum is potentially a good prospect, but the cost savings it could bring need to be offset against the costs of clearing out the existing broadcasting users.
Full details of the work, including an illustrative video, download of the full report and a link to Ofcom’s use of analysis in their UHF strategy consultation are available at:
http://www.realwireless.biz/mobile-capacity-in-the-uk-major-study-published/
If you had to pick a single iconic image to represent the world of the mobile operator , it would have to be the hexagon. Much used in the early marketing literature of operators, the hexagon provided a simple representation of the area covered by a base station, and helped to illustrate how a limited set of frequencies could be reused in order to serve an unlimited number of users. This is the central ‘magic’ of cellular networks.
Hexagons defining outdoor cellular coverage areas
More formally, a hexagon defines the region which contains points which are closer to one base station site than to any other if the base stations are arranged in a regular grid. Assuming uniform wave propagation conditions, it therefore shows the coverage area of the base station in the centre of the hexagon, i.e. locations where a mobile would receive and deliver a stronger signal to this base station than to any other. The hexagon is a special case of a Voronoi polygon, which contains the closest locations to any random selection of points.
Voronoi Polygons for Random Points (Base Station Sites)
Real-world propagation conditions are never like that, of course; in practice the coverage area of a given base station is very irregular indeed. Nevertheless, the hexagon provides a useful idealisation – its six sides give an indication of the number of sources of interference which need to be considered when working out the total capacity of a basic cellular system.
So what’s new? Today, cellular systems are undergoing a period of renewal. Well over two-thirds of voice traffic occurs inside buildings and it’s likely that data services will occur even more inside buildings. This means that mobile networks need to do more than provide coverage to a 2D plane – they need to consider the third dimension. Re-use of radio resources vertically is inevitable, whether using Wi-Fi access points or femtocells. A 2D map can be coloured without reusing colours in adjacent shapes using just four colours, so 4 frequencies can be reused without limit to avoid interference between adjacent cells. In 3D, the number rises greatly adding to the complexity. [Note: I haven't yet been able to find the 3D equivalent of the four-colour theorem - I'd be fascinated to hear if anyone knows the answer]
So the question arises: what is the equivalent of the hexagon in three dimensions? In the jargon, we are seeking a space-filling polyhedron. There exist various exotic candidate shapes (anyone for rhombo-hexagonal dodecahedra?). However, we don’t simply want a polyhedron which fills the space, but one which corresponds to a 3D version of the Voronoi polygon, enclosing the points closest to the antennas.
If the antennas in a building are on a regular grid across each floor of the building, with antennas directly above and below each other on successive floors, then the Voronoi polygon is simply the humble cube.
Inside a cubic lattice
If the antennas on successive floors are offset between floors, so that an antenna is at the midpoint of its four nearest neighbours on the floor above, then a rather more interesting shape results. This arrangement is known to crystallographers as a body-centred cubic arrangement, for which the Voronoi polygon is the truncated octahedron. This has 8 regular hexagonal faces, 6 regular square faces, 24 vertices and 36 edges.
The Truncated Octahedron
So there are 14 adjacent interference-creating cells surrounding each antenna:
A Lattice of Truncated Octahedra
Finally, we can contemplate arranging the antennas in a face-centred cubic pattern. The Voronoi polygon in this case is the rhombic dodecahedron, with 12 rhombic faces.
Rhombic Dodecahedron
The lattice in this case looks like this:
Lattice of rhombic dodecahedra
Of course, these patterns don’t relate closely to the reality of in-building propagation any more closely than the real world of outdoor macrocell planning. In particular, the high propagation losses involved in penetration through walls and floors will distort the relevant shapes hugely.
Nevertheless, doesn’t an industry which has changed so much deserve a new defining image? Perhaps the truncated octahedron could fit the bill !
The Truncated Octahedron
In case anyone doubted the staggeringly high growth of mobile data over the last year or so, I came across some fascinating (and very detailed) statistics on mobile data in Finland (thanks to Dean Bubley for pointing these out).
Stunningly:
- Total data traffic in ‘07 was 13 x larger in volume than the previous year
- 92% of data traffic was from computers rather than phones
- This share of traffic was from just 2.1% of devices
Full details at:
http://www.netlab.tkk.fi/~jakivi/publications/Kivi_Mobile_Data_Service_Usage_2005_2007.pdf
Simon
Horsham, 28th May 2008 (via HSDPA!)
