In-building Wireless Video lecture and Books

See this recording of a lecture delivered on behalf of the IET Reading area, giving my views on the background, status and potential of in-building wireless. Warning – it’s over an hour long!

Lecture at (the lecture itself starts after 6 minutes – you can fast forward to this point)


For further reading on this subject, see chapter 13 of this book:

Antenans & Propagation Book

or this recently published text on in-building design with distributed antenna systems:

Tolstrup Indoor Radio Planning





The iPhone 3G is radical – but the business model is conventional

The new iPhone 3G, announced yesterday, looks like a very cool device.

But one of the more striking features from a business standpoint is that Apple appear to have reverted to a much more conventional business model than for previous versions.


iPhone 3G

When the original iPhone was launched, Apple managed to convince operators to enter into a revenue-sharing model, where they would take a proportion of the call revenues flowing to the operator. This required a very close relationship with the operator. The balancing factor in the deals was operator exclusivity for supplying the iPhone in a given territory. All of this ran counter to the prevailng industry trends, where the movement has been away from such approaches, with handset subsidies and operator locking gradually diminishing, and  revenue sharing almost unheard of, certainly in the case of handset manufacturers.

But with the release of the new device, reports suggest that Apple have reverted to a conventional hardware sale, leaving the operator to collect the revenues in the normal way. They also seem to be moving away from operator exclusivity. The technology may be revolutionary, but it seems that simple business deals work best for all concerned.

 Update: Interestingly, some reports have suggested that the net result is not necessarily favourable to operators, as the reduced retail price of the iPhone 3G requires operators to provide larger subsidies. I suspect operators ae smarter than that, and expect the device to drive take-up of data services and increased loyalty which which will provide a net positive effect.


A measurement device in your pocket

The recent news item that a US university had used mobiles to track the movement of thousands of individuals generated a lot of interest in the press. The study, reported in Nature, took anonymised data from a cellular operator as to the movements of their users and concluded from this that humans are creatures of habit, travelling the same routes to the same locations most of the time. This may not come as a great surprise to anyone who commutes to work each day and might not seem to be a significant advance for science but it does potentially give some indication of what more may be to come.


Nokia Eco-sensor concept

A Nokia Eco-Sensor Concept Phone (more)


Gathering data of most sorts – for example on the air quality throughout a country – can be very expensive. But costs can be much reduced, and the volume of data massively increased, by harnessing the daily movements of millions of mobile phones carried everywhere by most of us as part of our daily travels. The mobile is unique in being a device that either knows its own location, or which the network can locate, and which can input, process and transmit data. With our example of air quality measurements we could imagine clipping a small sensor onto the bottom of the mobile phones of volunteers. This might periodically sample the air quality and then the mobile might send a short data message back to the network. The network would then add the cell location to the message and pass this onto the agency conducting the trial. For very little cost, detailed information which was frequently being updated could be generated.


The list of possibilities is likely to be extensive. Ofcom is using around 50 mobile phones with Wi-Fi capabilities to test the Wi-Fi data rates available throughout London. Phones with microphones could test noise levels, deduce what TV programme their owner was watching to derive audience research data and much more. Phones docked in cars with vibration sensors could send back information on road quality and traffic speeds could be estimated from their position. The position of entrants out on a course for a cycling or running event could be tracked by the organisers to help them run the event smoothly. It seems likely that many specialists would like measurements of some sort in their specific areas of interest and many hobbies would benefit from more information.


This sort of application might raise privacy concerns and in some cases might require additional hardware or software to be added to the phone. But many users might be willing to agree to help if they thought that the information would benefit them – perhaps by leading to a better environment. In the near future you might leave your phone on for more reasons that just to receive incoming calls.

3G Femtocells Gain Clarity on Standardised Network Architecture

Following intensive work within Femto Forum, 3GPP has recently reached a
decision on an Iu-based interface between femtocells and femto gateways, meeting
the needs of operators who want an open, standardised approach to provide
interoperability amongst vendors. This is good news for vendors too, as it
provides the ability to provide a single interface for all of their customers.

News on the Femto Forum’s work in this area and the subsequent 3GPP work as

Femto cells get a surprise standard     

TechWorld  06/06/2008
3GPP Picks Femtocell
Unstrung  05/06/2008

Vital femtocell standards agreed

Fierce Wireless


Femto Forum approves interoperability principles

Telecom Paper


Femtocells gather steam after interoperability pact


Femto Forum Touts Progress



Femto Forum agrees on common standards

Total Telecom


Qualcomm Backs Femtocell Maker, ip.access



Qualcomm Invests in Femtocell Vendor Ip.access

PC World


Femto Forum lays down femtocell law



Femtocell market hotting up


Industry makes headway in femto harmonisation


Vendors Unite on Femtocell Architecture



Femtocell Trade Group Agrees on Single Interoperability



Big news for small cells

The Register


What use cognitive access?

Cognitive AccessThe logic seems compelling. Spectrum is scarce and expensive but much of it is unused in any given location at any particular time. Finding a way to make use of this spectrum must therefore unlock significant value and be worth pursuing. It is this logic that appears to have sparked interest in so-called “white space devices” in the US with many major players including Microsoft, Philips, Motorola, Google and others coming together to lobby regulators and develop prototypes. Such major backing surely indicates a major market and a rosy future?


But there may be a flaw in the logic. Finding a way to make use of the spectrum only generates value if the means to do so – the cognitive access – does not result in device costs or service restrictions that are greater than the value of the spectrum liberated. Quantifying any of this is almost impossible – not least because the value of spectrum is not clear – but there are significant device costs and service restrictions when cognitive access is used.


The device costs come from the need for cognitive devices to sense whether spectrum is unused. Explaining this in detail would be an article in its own right, suffice to say here that very sensitive detectors are needed which are currently proving difficult to implement in laboratory equipment, let alone consumer devices. Of course, technology improvements or novel approaches may change all this but in many cases the issues are down to fundamental limits rather than a lack of, say, processing power.


Even more problematic may be the service restrictions. There is no guaranteed access to white space. The owner of the spectrum may start using it more intensively (or even simply transmitting unwanted data just to stop other, potential competitors, using their spectrum) or many other white space users may also try to access the spectrum. So it will be difficult to offer services that require immediate and well-understood access such as voice traffic. Indeed, any services that require infrastructure might be difficult – the infrastructure would have to scan multiple channels and would be more expensive to deploy than systems such as cellular networks. Building such a network to access what is essentially unlicensed spectrum would be a risky business. Device-to-device communications might be feasible but this can already be accomplished in unlicensed spectrum at 2.4GHz, 5GHz and other smaller bands without all the added complexity of needed to scan carefully for unused channels.


The proponents of cognitive access do not appear to have clear plans for applications. They talk more about “wireless clouds” and “build it and they will come” type ideas. Grand schemes such as the interconnectivity of a wide range of consumer electronics items are mentioned. Maybe they will turn out to be right, but they have a lot of obstacles to overcome on route to such a vision.

Hexagons in 3D – Is it time to update the defining image of the cellular industry?

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 define frequency re-use in outdoor macrocellular 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.



Cubic Honeycomb

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

Mobile Broadband Data – in Finland!

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).

- 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:
Horsham, 28th May 2008 (via HSDPA!)