Development of Mobile Communications

Abstract

This article describes the development of GSM and 3G cellular-based mobile communication systems from the early days, where only the privileged few could communicate on the move, to the emergence of the mass market systems of today where, it seems, everyone has a mobile phone. The technology changes that have brought this about are described and the various “buzz-words” such as GPRS, EDGE, i-Mode & UMTS are explained. The story of the development of the different generations of mobile system is told and the key features of each of these generations are described. This covers an appreciation of the technology and describes some of the services and products that can be provided to customers. Finally, the article takes a brief look beyond the present day and describes some future trends and how the world of mobile communications will change.

Cellular radio operation

The key to the success of cellular radio communications systems is its efficient use of the radio spectrum and its ability to manage the mobility of a large number of connected mobile terminals. This allows a large number of users to be accommodated in a small number of frequencies.

The basis of cellular radio is that the same radio channels (frequencies) can be used over and over again thus allowing much greater capacity than the simple mobile communications systems that preceded it. This is done by limiting the range of each channel so that it does not interfere with the same frequencies used in a nearby area. The coverage area is divided into discrete cells each capable of serving a number of users who can pass seamlessly from cell to cell as they move through the network. Coverage can therefore be provided over large areas in which customers can move freely while maintaining service.

Early cellular mobile systems

1st Generation Systems

The 1st Generation cellular radio systems used analogue radio technology (usually frequency modulation). Different countries had different frequency allocations and there was little industry collaboration on the development of the systems. As a result, many different systems, that were mostly incompatible, arose in different parts of the world.

The system used in the UK was called TACS (Total Access Communications System). It was based on, but was not compatible with, the US system known as AMPS (Advanced Mobile Phone System). Cellular mobile service in the UK using TACS technology was opened by Cellnet and Vodafone in January 1985.

One of the main problems with the analogue systems is that, generally, because of the incompatible standards, it was not possible to take phones to other countries and use them (i.e. roaming was not generally possible). Also, these systems primarily provided voice communications and could not easily accommodate the increasing requirement for data communications.

The TACS service in the UK had closed down by 2001 and was superseded by the next generation system.

2nd Generation Systems

New cellular radio systems were developed to overcome the limitations of the first generation systems. In Europe, a new system based on digital techniques was proposed and developed. This is known as GSM (Global System for Mobile communications).

The Early Development of GSM
In 1982, a new body - Groupe Spécial Mobile (the original meaning of GSM) - was set up under the European body the CEPT (European Conference of Postal and Telecommunication Administrations). Its task was to specify a new mobile radio system operating at 900MHz. The first meeting was held in Sweden in December 1982 with representatives from 11 countries present. The GSM standard was conceived.

The main work started in 1987 following extensive prototyping. It was decided to adopt a digital radio interface using TDMA (Time Division Multiple Access) operating in the 900MHz frequency band. The GSM TDMA system uses 8 timeslots in a basic 200kHz carrier. GSM was designed to offer a standard set of services & features. This allows inter-operator roaming.
In 1989 the work was transferred to the European body ETSI (European Telecommunications Standards Institute). By 1990 the Phase 1 specifications were frozen. Work then started on adapting the specifications to work in the 1800MHz frequency band.

GSM Becomes a Global Standard

In 1987 a group of future GSM operators (15 operators from 13 countries) signed a Memorandum of Understanding (MoU) intending to promote the use of the GSM standard world-wide. With the change of emphasis to a world-wide standard, GSM was renamed "Global System for Mobile communications". Other countries outside Europe began to adopt the standard in particular the UAE, Hong Kong, Australia & New Zealand.
The first commercial GSM networks started service in 1991; 13 networks went live in 7 countries
The first roaming agreements were signed in 1992 and roaming started soon after. GSM was born!

General Features of the GSM Standard

The GSM standard was designed to be very flexible to allow the easy provision of services. Because there is a common standard, all GSM networks work the same way and, generally, every network can offer service to users from any other network. As a result, there is a large amount of roaming traffic and users have become used to receiving service when they travel abroad.
Another important feature of GSM is the high level of security provided. Powerful algorithms are used to authenticate users. Also, the radio interface is encrypted to a high degree of security which makes it very difficult to eavesdrop.

GSM uses a removable SIM (Subscriber Identity Module) card that holds the identity of the user. Because the SIM card can be plugged into any compatible mobile phone, users can change mobile terminals easily and take their identity with them. Also, a user’s list of names and telephone numbers can be stored on the SIM card so personal information can be transferred easily also. The SIM card has been further developed to add more processing power and memory. This allows new types of applications and operating systems to be run on the SIM that could be used by the network operator to offer customised services.

Because key interfaces are standardised, equipment from different manufacturers work together in the same network. Because all equipment works to the same specification, it is mass produced from many competing manufacturers thus lowering the cost. This also gives GSM network providers a wide choice of equipment vendors as well as the ability to “mix and match” equipment from different vendors.

Main Services Provided by the Original GSM Standard are:

Speech - Speech is digitised and good speech quality is possible in GSM's relatively low bit rate.
Data & Fax - A range of data rates up to 9600 bit/sec was standardised initially. The capability of sending and receiving Group 3 Fax was also provided. A data rate of 14.4kbit/s was later standardised.
Supplementary Services - These include Call Forwarding; Call Barring; Call Waiting, Multi-party calls; CLI (Calling Line Identification).

Short Message Service (SMS) - Text messages of up to 160 characters in length can be sent between mobile phones. Longer messages can be sent by concatenating SMS texts.

Cell Broadcast - Broadcast messages that can be customised for specific areas and for specific topics (eg weather) can be sent to all mobiles in the service area of a cell or group of cells.
Improvements to the GSM Standard in Later Standardisation Phases Included:

Better Speech Quality - New voice coders (codecs) were developed that improved speech quality and made better use of the radio capacity. These included the EFR (Enhanced Full Rate) and AMR (Adaptive Multi-Rate) codecs.
HSCSD (High Speed Circuit Switched Data) – A number of developments improved on the basic 9600bit/sec data rate provided: The HSCSD standard was developed to provide data rates greater than 64kbit/sec although in practice the rate is limited by the radio capacity and the capabilities of the mobile terminals. HSCSD gives the user dedicated multiple time slots to provide the higher rates. However, this technique is very hungry on radio resource and because multiple time slots are allocated to each user, the capacity of each radio carrier is greatly reduced. An advantage of HSCSD is that it can be used to provide “real time” services like live video because each user has dedicated resource.

GPRS (General Packet Radio Service) – This is another development intended to provide higher data rates. Like HSCSD, GPRS uses multiple time slots to increase the data throughput. Unlike HSCSD, GPRS does not allocate these slots just to one user – many users share the slots using them to send and receive data only when they need to. As a result, GPRS uses the radio resource much more efficiently than HSCSD and the capacity of the radio carrier is much higher. The way GPRS works, however, means that it cannot (currently) support “real time” services (like live video) as the user’s application cannot be guaranteed a time slot immediately when requested. The result is that variable delay is introduced to the data transmission. This makes GPRS much more suitable for “packet based” types of services such as Web browsing or downloading of data files. Practically, at present, typical rates of around 40kbit/sec (peak) can be achieved. There is scope for these rates to increase with further development of the mobile terminals and the introduction of more advanced channel coding schemes. Another feature of GPRS is that the user can set up an “always on” connection. Because the time slots are not used unless there is data to transmit, there is no overhead and the user can be permanently connected to a service such as an email server or an intranet.

EDGE (Enhanced Data for GSM Evolution) – EDGE is a modulation technique that allows each time slot on the GSM radio access to carry more data. As a result, the data rates provided by HSCSD and GPRS can be further increased. The take up of EDGE technology has been relatively small and many operators have chosen 3rd Generation systems as the route to higher data rates.

New Network Services – Some of the new services that were specified are: Multiple Subscriber Profile; Call Transfer, Calling Name Presentation and pre-pay control. Some of the new services are provided by Intelligent Network (IN) platforms (such as CAMEL) that have been introduced in the GSM core network.

Location Technologies – Basic location of the mobile can be provided by the identification of the cell and sector in use. More accurate location methods have also been developed using a variety of technologies including GPS (Global Positioning System). In some cases, it is a regulatory requirement to identify the location of the mobile for emergency calls (eg in North America).

Development of Mobile Terminals
Mobile terminals have also undergone rapid development. The early "brick-like" mobile terminals were soon superseded by more elegant models with superior performance. Battery life improved, multiple frequency bands introduced and new capabilities such as data downloading and web browsing incorporated.

More recently, many more new features have been incorporated into mobile terminals including high resolution cameras, music players, PDA (Personal Digital Assistant) and email functions and even radio and TV reception. The mobile device has become an essential "life tool" for many people.

In summary, the mobile terminal has undergone a remarkable transformation in a very short time. This has been driven by improvements in technology and manufacturing and also customer demand

A terminal that performs well and is easy to use is key to giving the user a good experience of the mobile network.