Article - Issue 30, March 2007
Wireless Communications Reach Maturity
Professor William Webb FREng
Mobile phone technology has developed at a rapid rate over the last few decades. Anticipating future developments in wireless communications is crucial for manufacturers when they decide on new product lines and for operators when they buy licences and deploy networks. Professor William Webb FREng gives an overview of the likely progress in this field and takes a snapshot of future mobiles’ capabilities in 2020.
Many will recall that in 2000, the UK Government held an auction of licenses to use radio spectrum suitable for ‘3G’ (‘third generation’) mobile communications. This was particularly memorable because of the very large sums that the mobile operators bid in order to win such a licence – over £22bn. In fact, this third generation marked a steady evolution for mobile phone systems which had progressed from analogue ‘first generation’ phones in the 1980s, to digital ‘second generation’ phones in the 1990s, and hence logically to the third generation in the 2000s.
This evolutionary process suggests a fourth generation of mobiles in the 2010s. But extrapolation is sometimes dangerous and in this case it would be wrong. For a range of reasons that I will explore in this article, there will not be much more evolution in the wireless networks that surround us. However, perversely, it will be this stability that allows a dramatic growth in applications and hence the value of the mobile phone to us all.
From analogue to digital
The concept of generations of cellular technology only really makes sense for the first two generations. These were distinctly different, because the first generation was based on an analogue technology which, in the UK,was called the Total Access Communications System (TACS) and the second was based on digital technology called the Global System for Mobile communications (GSM).
In the analogue system, speech was transmitted as a continuously variable waveform whereas in the digital system it was coded into binary digits which were then transmitted. This is exactly the same difference as between analogue radio (FM and AM) and digital radio (DAB), or between analogue and digital TV. Digital transmission brought many advantages including better quality of speech, much enhanced security, greater capacity and the ability to carry data and text messages readily. These advantages were clear to both consumers and operators and the transition from one generation to the next proceeded smoothly in the early 1990s.
Having already moved from analogue to digital, there was no such distinguishing feature to separate the next ‘generation’ of mobile communications from those that had gone before. However, industry and the standards bodies decided that a phone system capable of much higher data rates was needed and therefore designed a new standard to achieve this, calling it ‘3G’.
In Europe, the distinctions were reasonably clear in that 3G was based on a different method of dividing up the radio resources (by giving out non-interfering ‘codes’ rather than by dividing the resource up into discrete time slots) and each radio channel had a much greater bandwidth to enable higher data rates (5 MHz as compared to 200 kHz). In the US, many 2G systems were already based on code division multiple access (CDMA) and were already using relatively wide bandwidth channels (1.25 MHz). These were just evolved slightly and termed 3G, but this is merely a matter of semantics, or marketing – there was no material change in the underlying technology.
The 3G systems were supposed to provide markedly higher data rates than their predecessors. Initially, they were designed for data rates similar to home broadband connections (around 2Mbit/s) compared to 2G systems with, at the time, data rates closer to home dial-up connection speeds (around 20kbit/s) – a hundred-fold improvement.
As 3G was deployed, it became clear that whilst theoretically possible, these high data rates were not economically practical. It seemed that data rates of perhaps 15% of most broadband connections (300kbit/s) were more realistic, supporting mobile TV and reasonably fast download of music files, but insufficient for higher quality TV or very large file download.
At the same time, 2G systems evolved to become capable of at least 100kbit/s – sufficient for many mobile applications. The differences were no longer so stark. Perhaps this explains why 3G has not been embraced as enthusiastically by consumers as 2G. To most users, it represents a relatively minor evolution.
In the last few years there has been much discussion in the industry around the development of a 4G system. Given that such systems often take a decade to research, standardise, develop and deploy, if we expect another generation some time in the 2010s, then clearly there is a need to work on it now.
The Japanese Government announced a research programme some years ago aimed at producing a system capable of delivering 100Mbit/s to end users, following the trend that each generation should deliver a large increase in data rates (at least in principle, even if practice often differs). In some cases, those with technologies that differ from 3G, claim that they are 4G. Given there is no longer any clear difference between generations, there is little reason why they should not do so, but equally little to be gained. So when can we expect a true 4G and what will it look like?
Figure 1 suggests why 4G is unlikely to be different from 3G, and indeed perhaps may not even emerge. It illustrates that there is always a trade-off between range and data rate. Broadly speaking, higher data rates require more spectrum. More spectrum can only be found higher in the frequency band, but higher frequency signals have a lower propagation range. Each generation has accepted a shorter range in return for a higher data rate. But, as Figure 1 shows, the next ‘step’ in the process, where 4G might logically fit, is already taken by a mix of 3G enhancements and Wi-Fi.
Only if we discovered a new technology might we break out of this trade-off. There are many contenders. Cognitive radios, based on handsets where most processing is done in software, might spot unused pieces of spectrum and momentarily transmit on them, but they cannot currently do this with sufficient accuracy and are overly expensive.
Perhaps the most promising are advanced antenna systems which can either steer signals towards phones or make use of multiple antennae to send many different messages simultaneously. But, as the areas covered by each base station get smaller, the radio propagation environment makes these less effective while their costs per user increase and they are already considered overly costly and complex for most situations. So pragmatically, there is little under consideration that is likely to change the dynamics that govern wireless communications. We might instead see enhancements to all the different standards making up the complete communications network, with perhaps some new niche standards emerging in areas such as ultrashort range communications.
Fulfilling its potential
However, all this does not mean that there will be no new developments in wireless communications. The next 10-20 years might see some of the most dramatic changes for the end user. This is because as networks become stable and ubiquitous it becomes easier to write applications to run on top of them – in much the same way that internet applications are rapidly emerging, now that the underlying hardware has stabilised and standardised. So, based on these predictions, how will the world look 20 years from now?
It is 2020. Your mobile is now much more than just a communication device – more like a remote control on your life. You still call it a ‘mobile’ from habit – but it is an organiser, entertainment device, payment device, security centre and so much more. On a typical day it will start work even before you wake. Because it knows your travel schedule it can check for problems on the roads or with the trains, and adjust the time it wakes you up accordingly, presenting you with the best route into work.
It can control your home, re-programming the central heating if you need to get up earlier and providing remote alerts if the home security system is triggered. It is your payment system – just by placing the phone near a sensor on a barrier you can automatically pay for tickets for journeys, or buy items in shops.
It is your entertainment centre when away from home. As well as holding all your music files, as some phones today are able to do, it will work with your home entertainment system while you sleep to find programming that will interest you and download it as a podcast so that you can watch it on the train or in other spare moments.
It will intelligently work out what to do with incoming phone calls and messages. Because it knows your diary, it will know, for example, to direct voice calls to voicemail when you are in a meeting, perhaps providing a discrete text summary of the caller and the nature of their call.
Leaving home without your mobile, bad enough already, will become rather like leaving home without a wallet, keys, music player and mobile all at once – quite unthinkable!
All these services can be provided with the wireless networks that we have today – hence the reason why even without an evolution to 4G, the role of the mobile phone can grow dramatically. Advances are needed in the phone itself in terms of better screens, voice recognition, increased storage and longer battery life, but these are all areas of constant evolution where further enhancements can be confidently predicted. A lack of a new generation will actually provide the stability we need for services to be widely developed and for the mobile phone to become a remote control for our lives.
Biography – William Webb FREng
William joined Ofcom as Head of Research and Development and Senior Technologist in 2003. He worked previously for a range of communications consultancies in the UK and spent three years providing strategic management across Motorola’s entire communications portfolio. William has published ten books, is a Visiting Professor at Surrey University and a Trustee and Fellow of the IET.
‘Wireless Communications: The Future’William Webb – 2007