Technical features that characterise mobile communications

Questions regarding mobile communications are grouped separately from those on fixed network communications due to a number of technical and regulatory considerations. Since the need for regulation stems from the use of radio frequency in the access portion of the network, we will begin with the technical aspects.
Technical feature 1) Use of radio frequency
Radio spectrum is a limited resource that has traditionally been shared between, for example, television and radio broadcasters, government, military and private users (such as taxi operators) and mobile phone network operators. In a technical sense, a mobile phone user is a two-way broadcaster, requiring two radio channels, one from and the other to the other user/s.
Hence, the basic challenge to mobile phone technology is how to provide services to as many users and at as high a data rate as possible using a limited resource, i.e. the radio spectrum allocated to mobile communications. Since each radio channel requires a frequency to be allocated to it, the conventional way of solving the problem is to divide the frequency as much as the technology allows and allocate separate channels to each active (talking) mobile user. The technology in question is called Frequency Division Multiple Access (FDMA).
In FDMA technology, the way to increase capacity, namely the number of simultaneously active users, is to divide the frequencies further, thus reducing the bandwidth assigned to each user. This results in poorer voice quality and, in any case, a technological limit exists on the number of radio channels that can be used for mobile communications.
Instead of dividing up frequencies, the cellular system divides up geographical areas into separate cells. The size of a cell varies depending on the user density in the area which is typically 2-5 km in radius. Each cell is covered by a two-way antenna; one for transmission to and the other for reception from the mobile users in the cell. This is normally called the (radio) base station. The way to increase capacity is to allow the same frequency to be used by different cells as long as they are not adjacent. If the same frequency is used by adjacent cells, interference or jamming will occur, especially at the periphery. This geographical reallocation of the same radio frequency in non-adjacent cells is called 'frequency reuse'.
Another important technology that permits the use of the cellular mobile network is the automatic 'hand-over' (or 'hand-off'). This enables a mobile user to keep talking even when they move from one cell to an adjacent cell, by handing over the radio channel from one cell to the next one.
Technical feature 2) Implications for regulation
Since the available radio spectrum is limited, there is also a limit to the maximum number of mobile operators. However, the actual number of operators to be given licences is more dependent on regulatory and business considerations than technical limitations. Technology is flexible in this sense. For example, depending on the density of users, the cell size can be varied; the higher the density, the smaller the cell size. When users increase, extra capacity can be added by breaking the cell up into smaller components or by adding more, overlapping cells.
It seems that the regulators decide the number of operators on the principle of 'small enough for each operator to have sufficient customers to be profitable but large enough to stimulate competition'. Therefore, the number of operators to be given licences varies from country to country and even from time to time.
For example, in the UK, when 2nd generation (GSM) services were started in 1991, there were only two operators, Cellnet and Vodafone, but in 1993 two more licences were awarded to Orange and One2One. For 3rd generation services, applications for which closed in January 2000, the government announced that five licences would be given in March of that year, with a view to starting operations in 2002. In Hong Kong, as many as seven operators were given licences, although later one was acquired by another.
There are basically two methods of selection. One is through auction, adopted, for example, by the US and the UK. The other is the so-called 'beauty contest', where selection is made by the regulator on the basis of the contents of applications. Each system has its own merits and demerits.
Technical feature 3) Small screen, low power consumption
Mobile terminals must be portable in terms of size and weight, i.e.easily carried in a pocket or handbag. Furthermore, their power consumption must be low so that once their batteries are charged, they can last at least a few hours in active use and a few days in waiting mode. Although for voice calls these problems are almost solved, for access to the internet they still pose a significant challenge and require new solutions. For example, because of the smaller size screens of mobile terminals, web pages must be of a different design from those for PC access. The current Windows operating system consumes too much power even in waiting mode, requiring a new low energy operating system designed for the smaller screen of mobile terminals.
These new challenges led to a range of technical initiatives geared to mobile communications, such as Wireless Application Protocol (WAP) and EPOC. WAP was first developed by Ericsson, Motorola, Nokia and Unwired Planet (now Phone.com) and is a mobile equivalent of the Hyper Text Transfer Protocol (HTTP), which enables mobile terminals to access web pages over the radio channel.
EPOC is the name of an operating system developed by Symbian, a venture led by Psion and involving Ericsson, Nokia, Motorola, NTT DoCoMo and others, but with the notable exception of Microsoft. Microsoft, for its part, is improving its Windows CE for mobile use. Recently, Ericsson also decided to co-operate with Microsoft in this endeavour.
As far as mobile data terminals are concerned, Personal Digital Assistants (PDAs) are designed with a focus on data applications. Meanwhile NTT DoCoMo's 'i-mode' terminal is basically a mobile phone with a slightly bigger screen. The 'i-mode' and its associated web services with some 3000 web sites has been a great success. It was launched in February 1999 and by December of that year had 2.5 million users, increasing to 6 million by April 2000.
Technical feature 4) Generation of systems
Mobile systems evolved from first generation analogue (1G) systems in the 1980s to second generation digital (2G) systems in the1990s. The first version of the third generation (3G) multimedia standards was completed in 1999, waiting for official approval by the ITU in mid-2000. Japanese operators plan to start services in 2001, as the current radio spectrum allocated to the 2G system is quickly running out due to unexpected growth in demand.
The European Union (EU) has recommended that all its members finalise the licensing of the Universal Mobile Telecommunication System (UMTS), the European version of 3G standards, and that services are launched by 1st January 2002 - a challenging timetable to meet.
Finland was the first country to licence 3G operators, assigning four licences in March 1999. The UK closed applications for five licences in January 2000 and the results will be announced later in the year. In addition to the current four mobile network companies (BT Cellnet, Vodafone AirTouch, Orange and One2One), the following operators also submitted applications:

1. 3G - part of Eircom, the Irish telecoms group
2. Crescent Wireless - organised by shareholders of Global Crossing
3. Epsilon Tele.Com - a subsidiary of the Japanese finance house, Nomura
4. NTL Mobile - a joint venture between the US-based cable group NTL and France Telecom
5. One.Tel Global Wireless - a subsidiary of One.Tel, the Australian telecoms group
6. SpectrumCo - a consortium led by Virgin and partners Tesco, EMI, Sonera and others
7. TIW UMTS - a subsidiary of TIW, the telecoms company listed in Montreal and Atlanta
8. Telefonica UK - a subsidiary of the Spanish and Latin American telecoms company
9. WorldCom Wireless (UK) - part of the US-based global telecoms company.

In the US, the ITU's document World Telecommunication Development Report - Mobile Cellular World Telecommunication Indicators (1999) states that:

"Since the United States only introduced digital wireless systems a couple of years ago, it is not forecast to have 3G systems until 2003-2005. A problem in the US market has been that no single digital standard has been agreed, and carriers use different digital technologies that are often not interoperable. However, it is a market with a potentially high demand for professional mobile data services. The relative lack of success of second-generation digital mobile systems in the United States leaves the field open for 3G."

If you would like to add to the debate on technical aspects of mobile communications go to the Mobile Workshop.