Friday, 27 May 2011


GSM is a technology that has been widely acclaimed a huge success with large number of networks, services and subscriber base around the world, contributing to Rapid explosion in mobile subscribers in recent times. This trend has made the technology a focus to a large number of analysts and commentators World over. It has therefore been considered appropriate and timely, to present this topic “GSM
The topic will look at the technology upon which GSM is built, the historical development of the standardization process. It will present an overview of the architecture, signaling, security, roaming and the various roaming arrangements employed to support local and global mobility.
It will further discuss supported services, features, evolution process towards achieving 3G broadband requirements and recent advances in the technology. To fully appreciate the impact globally, African and Nigerian scenarios as well as the some global statistics will be presented.
Global system of Mobile Communication (GSM) is based on a digital wireless Time division multiple Access technology. One of the key attributes of this technology is a standardized digital radio carrier channel that allows multiple users to simultaneously share the channel. It uses time division multiplexing to share one radio carrier frequency waveform among 8 to 16 conversations. It originally operated in the
900MHz band, but has found application in the 1800 MHz and 1900MHz, while recent developments have extended consideration for its application to the 800Mhz band. The 400 MHz band is specified for GSM rural application because of extension of coverage range it offers. 
GSM works on comprehensive set of open standards established by European telecommunications standards institute (ETSI) for ensuring interoperability of terminals and infrastructure. These standards allow operators to select network equipment, base stations and other equipments offered by a number of network operators. As an open standard technology, GSM also ensures more reliable roaming performance and the smooth compatibility of elements across network and geographic region. 
GSM which today stands for Global System for Mobile Communications, started in the early 1980`s as Group Special Mobile. At that time Europe experienced a rapid expansion of analog cellular telephone system. Nations such as France, Germany,
United Kingdom and Scandinavia etc. each developed unique standards and equipment, which were incompatible with the networks of other countries. Numerous difficulties were presented by this situation including:
v System incompatibility which prevented roaming outside each respective country
v Economies of scale and subsequent consumer savings could not be realized since the market for each country was limited.
In 1982, the Conference of European Posts and Telegraphs (CEPT) formed an alliance called the Grouped Special Mobile (GSM). The aim of this group was to study and specify requirements for a common and open technical standard for a public mobile system that will be adopted by participating countries.
The chosen standard was required to meet the following criteria:
v High speech quality
v Low terminal and service cost
v Support for International roaming
v Ability to support handheld terminals
v Support for range of new services and facilities
v Spectral efficiency, and
v ISDN compatibility
GSM technology was chosen as fulfilling the set out requirements. This incidentally was not among the then standard analog options (e.g. AMPS in the U.S. and TACS in the U.K.), based on Frequency Division Multiple Access (FDMA.), instead, it was digital Time Division Multiple Access (TDMA), becoming the first commercially operated digital cellular technology.
By 1987 all the basic architectural features were decided. In 1989, the European telecommunications Standards Institute (ETSI) took over the development of GSM standards. With the phase 1 specification completed in 1990 the initial GSM recommendations and guidelines were presented in a document of nearly 6000 pages.
Phase 2 specifications were completed in 1992. Work however continued in developing further phases of the standards, to incorporate new services and features.
In summary, GSM technology was born out of a pan-European political initiative backed by the European Commission together with telecommunication operators and equipment manufacturers to promote regional harmonization of cellular networks.
European Telecommunication Standards Institute has been responsible for GSM standardization.
The first GSM network was launched in 1991 by the Finnish mobile operator,
Radiolinja, followed by several more in the following year. As countries outside Europe adopted the technology; it became apparent that the system would be a global success, thus, the name Global system for Mobile communications.

The technology was originally intended for the 900MHz frequency band, but subsequently has been adapted for newly allocated 1800MHz (PCN) band, in Europe and the 1900MHz (PCS) band in the North America. The variants of the standards are known as DCS 1800 and PCS 1900 respectively. The core technical parameters specified are presented in table below. 
       GSM                      900
Mobile frequency Range
        Rx:                   925-960
        Tx:                   880-915        
Multiple Access Method
Duplex Method
Number of Channels
        124 (8 Users Per Channel)
Channel Spacing
        200 KHz
        GMSK (0.3 Gaussian Filter
Channel Bit Rate
         270.833 KB/S
Maximum Base Station
e.r.p. (W)

Cell radius. Minimum & Maximum
         0.5 & 35 (km)
Traffic Channels / RF Carrier; initial & Design Capability

         8 & 16
Source: ITU-R REC. M.1073-1

The basic architecture of the GSM is not different from other cellular systems. It comprises of Base transceiver station (BTS), Base station controller (BSC), Mobile switching center (MSC), Home location register (HLR), Visitor Location register (VLR), Equipment identity register (EIR) network management system, and the mobile station which is made up of the mobile equipment and the Subscriber identity module (SIM). GSM defines several standard interfaces; the radio interfaces (Um), the interface between the MSC and BSC (A interface) and the signaling interface, which allows roaming between networks. This is based on the ITU-T No. 7 signaling standard and is defined as a mobile application part (MAP)
The BTS and BSC together for m the base station subsystem (BSS) and carry out all the functions related to the radio channel management. This includes the management of the radio channel configurations, allocating radio channel for speech, data and signaling purposes, and controlling frequency hopping and power control. The BSS also includes, as does the MS, the speech encoding and decoding and channel coding and decoding.
The MSC, VLR and HLR are concerned with mobility management functions. These include authentication and registration of mobile customer, location updating, and call set up and release. The HLR is the master subscriber database and carries information about individual subscribers numbers, subscription levels, call restrictions, supplementary services, and the current location (or more recent locations) of subscribers. The VLR acts as a temporary subscriber database for all subscribers between its coverage areas, and contains similar information to that in the HLR. The provision of VLR means that the MSC does not need to access the HLR for every transaction.
The air interface (Um) uses LAPDm layer 2 signaling protocol, which is also used for the BTS to BSC (A-bis), interface. The layer 3 protocols consist of three sub layers, dealing with radio resource management (RR), Mobility management (MM), and connection management (CM).
RR management is concerned with managing the logical channels, including paging, channel assignments, handover, measurement reporting, and other functions. The mobility management layer support functions necessary to support the mobility of the user, which includes Authentication, location updating, attach and detach of
International mobile subscriber identity (IMSI), and registration. The connection management layer is concerned with call control, establishing and clearing circuits, management of supplementary services and the short message service.
The BSC to MSC (A interface), and the various MSC to Register interfaces, employ
ITU-T No.7 signaling using the message transfer part (MTP), signaling connection control part (MCCP), transaction capabilities part (TCAP) and mobile application part (MAP).
The information on the air interface needs to be protected, to provide user data (including speech) confidentiality and to prevent fraudulent use of subscriber and mobile identities. The basic mechanisms employed are user authentication and user data encryption. Each mobile user is provided with a subscriber identity module
(SIM), which contains the IMSI, the individual subscriber authentication key (Ki), and The authentication algorithm (A3). After the mobile user has made an access and service request, the network checks the identity of the user by sending a random number RRAND to the mobile. The mobile uses the RAND, the K1 and A3 to produce a signed response (SRES), which is compared with a similar response produced by the network, and access only continues if the two responses match.
Roaming is defined as the ability for a cellular customer to automatically make and receive calls, send and receive data, or access other services when traveling outside the geographical coverage area of the home network, using a visited network. It is performed in accordance with recommendation ITU-R M.624.
If the visited network is in the same country as the home network, this is known as National Roaming. If the visited network is outside the home country, it is known as
International Roaming (some times also called Global Roaming). If the visited network operates on a different technical standard than the home network, it is known as Inter-standard roaming

On entering a foreign country, The GSM handset automatically detects and displays the names of the available networks. The user can then check and select any of the networks for which it is permitted access (Permitted network). A permitted network is one with which the user’s home operator has a roaming agreement. The user at this point is able to use his phone just like any other local subscribers to the visited network. Typically, the user experience is not totally transparent: some services such as SMS may be available exactly as they would in the home network, while others like voicemail and helpdesk hotlines may be available but require a different access method and identification. The level of service transparency very often varies depending on the roaming agreement between the home operator and the visited network. 
GSM, in addition to speech was standardized to offer a wide range of data bearer services of data rate up to 9.6kbps capable for connection to circuit switch or packet switched data networks. It also offers group 3 facsimiles as a data service by use of an appropriate converter
Some of the important GSM features are: SMS, WAP, Circuit Switched Data, Packet data, Location based services, SIM card, Supplementary services, Integration with terminals etc.
Among the myriads of supplementary services supported by GSM technology are:
Voice mail services, short messaging services, mobile office (data, fax & Internet), voicemail service while roaming, multi party conferencing, mail box transfers, call Hold / Waiting, Call forwarding, wireless application protocol based services, SIM toolkit based services, e-banking, e-commerce, SMS roaming, Unified messaging services (e-mail to SMS, SMS to e-mail, e-mail to fax, SMS to WWW), Calling line identification presentation (CLIP), calling line identification restriction (CLIR) etc,
Short Message Service (SMS) is the ability to send and receive text messages to and from mobile telephones. The text can be words, numbers or an alphanumeric combination. SMS was created as part of the GSM Phase 1 standard. Each short message is a maximum of 160 characters in length when Latin alphabets are used, and 70 characters in length when non-Latin alphabets such as Arabic and Chinese are used. The first short message was sent in December 1992 from a Personal Computer (PC) to a mobile phone on the Vodafone GSM network in the UK.
A major area of growth in the cellular market worldwide has been the massive rise in the use of short messaging services (SMS) allowing customers telecommunications contact at the fraction of the cost of a voice call. SMS is particularly popular in the young market segment.
The growth of the Internet applications and mobile communications led to many early proprietary solutions providing Internet services for mobile, wireless devices. Some of the problems these partial solutions faced includes: Bandwidth and delay: These were not considered in HTTP design Catching: This is though useful in many cases but quite often disabled by content providers, POSTting: Sending content from a client to a server can cause additional problems if the client is currently disconnected. To avoid many islands of incompatible solutions, e.g. special solutions for GSM, IS-136, or certain manufacturers, the wireless application protocol forum (WAP forum) was founded in June 1997 by Ericsson, Motorola, Nokia, and Unwired planet. The basic objectives of the WAP forum are to bring diverse Internet content (e.g. web pages, push services) and other data services (e.g. stock quotes) to digital cellular phones and other wireless mobile terminals (e.g. laptops). Moreover, a protocol suit should enable global wireless communications across different wireless technologies e.g. GSM, CDPD, UMTS.
Looking beyond “voice handsets” an important feature is the ability to synchronize between different devices and services. One development that enables this synchronization process is the Bluetooth technology
Bluetooth is the key to enabling wireless personal area networks (WPA) connect devices in close proximity or short-range radio devices by way of transmission of signals between radio circuits thus enabling a wireless connection of a GSM mobile phone to portable PC’s and handheld computers, scanners, printers, cameras, etc.
Bluetooth encompasses both a standard communications interface and a low-cost computer chip, which are already available. As a technology, Ericsson conceived it in 1994, and in 1998 Nokia, Ericsson, IBM, Intel and Toshiba founded the trade association.
Bluetooth operates as a 79 channel frequency hopping system in the frequency range 2.4000-2.4835GHz with a channel spacing of 1MHz and provides low -cost, low power, robust, secure, efficient, high capacity, multiple simultaneous links, ad-hoc voice and data networking of up to 1MB/sec in a range of 10meters. It does not require line of sight, therefore allowing devices to communicate with each other from pockets, bags and around corners and hence its support in GSM mobile phone technology.
A network of communicating Bluetooth devices is referred to as a ‘piconet’ The Bluetooth specification provides mechanisms for devices to discover each other, exchange identities and establishes communications with each other, all without prior knowledge of each other. This is referred to as Adhoc networking.
The needed broadband handling capability of Mobile data prompted work in developing standards for the third generation of mobiles. A total of 155MHz have been identified in the 1900MHz to 2170MHz band, and the ambition was to specify the system in such a way that it could be used worldwide. However, considering the
Page 11 of 16 massive investments already made in second generation systems, particularly in GSM, it was envisioned that many operators will prefer an evolutionary approach rather than reinvesting in totally new infrastructure. New technologies were considered to help solve the challenge of producing a standard from a variety of different starting points around the world, for instance the global pilot channel that indicates to a mobile what mobile standards and capabilities are available for use in any particular place. This was coupled with software radio technology where the operation of the mobile terminal is defined entirely in software, such that a single mobile will operate with many different network standards, possible even by downloading appropriate software over the air interface. These approaches were the focus for achieving the dream of a truly world wide mobile phone network.
The International telecommunication Union (ITU) made a request for proposals for radio transmission technologies (RTT) for the international mobile telecommunications (IMT- 2000) program. IMT 2000 formerly called future public land mobile telecommunication system (FPLMTS) tries to establish a worldwide communication system that allows for terminal and user mobility supporting the idea of universal personal telecommunication (UPT). Within this context, ITU has created several recommendations for FPLMTS systems e.g. network architectures (M.817), requirements for the radio interface, (M.1034), or framework for services supported
(M.816). IMT 2000 consideration includes different environments such as indoor, vehicles, satellites and pedestrians uses. The WRC 1992 identified 1885 to 2025MHz and 2110 to 2200MHz as the frequency band that should be available world wide for the new IMT-2000 systems (REC ITU-M.1036).
 Considering the existing investment in network infrastructures by operators standards were developed to supports a gradual transition from 2G to 3G. These include:
General Packet Radio Services (GPRS), Enhanced Data Rate For Global Evolution (EDGE), and Wideband Code Division Multiple Access (WCDMA). GPRS offers data rate of up to 115kbps in wide area, and always on connectivity, it uses existing GSM 900MHz, 1800MHz, 1900MHz, and standard GSM 200KHz carrier bandwidth, but requires GPRS core network. This a key technology for development and bridging the digital divide. Schools and small businesses in rural areas can benefit by having Internet access with ISDN like speed using GPRS. In the corporate market, this supports services like full mobile e-mail and intranet access to companies for their mobile workforce. GPRS equally supports all non-voice services like SMS and other information services. Because as people start using wireless data services, they will want faster speed which translates to higher network capacity demand. This high bandwidth demand led to the next step in the evolution to 3G capabilities which is EDGE.
 GSM, a technology developed for the European market has been widely adopted by the rest of the world including Africa. About 70% of African countries for instance have imbibed this technology. The ITU World telecommunications Indicator database
January 2000 records the world mobile cellular base as 488 million and population of 5,986 million out of which Africa accounts for 7.5 million mobile lines and a population of 769 million. This gives an indication that 1 out of every 6 world mobile subscriber lives in Africa. Two trends underscore the transformation of telecommunications taking place across the continent, as a result of privatization and deregulation there has been an explosion of mobile phone use and a burgeoning demand for reliable Internet service. Private companies have launched mobile phone networks and Internet service Providers in every African country.
Africa has the world’s least developed communication and information infrastructure with just 2% of the world’s telephones and fewer than 2 telephones per 100 inhabitants. With the introduction of Global System of Mobile Communications (GSM) in Nigeria in August 2001, Nigeria joined the number of African countries operating GSM technology. Below is a list of the African countries that operate GSM networks.

Cote d'Ivoire
South Africa
Burkina Faso

Equatorial Guinea


Sao Tome And Principe

Central African Republic
Sierra Leone


 In Nigeria, until late 2000, only NITEL was sole cellular service provider. However, between 1990 and 1999, several licences, were issued for GSM operations, which never took off. In January 2001, three operators succeeded in the licensing exercise for GSM operation in Nigeria including NITEL, MTN and ECONET. The licensing conditions required each of the operators, within one year of operation, to connect a minimum of one hundred thousand (100,000) subscribers. On the 8th of August 2001, the operators launched commercial services and have so far spread their networks across major cities in the country. Between launch and now the operators have cumulatively connected over a million lines, exceeding the obligation by over 233%. 
The Nigerian Government, who moved for and adopted the GSM cellular technology in 1999, recognized telecommunications as a strategic and effective means of interaction and exchange of information among individuals as well as between and across cultures and saw GSM as an effective means to the end. Below is an outline of some areas in which Nigeria has profited from the initiative.
v  Introduction of GSM in Nigeria in August 2001, improved the countries teledensity. Before this time, the teledensity of the country was way below the
ITU minimum recommended of 1%, with the number of mobile lines at an appropriate of 35,000 provided by NITEL Analogue (ETACS). Within one year of GSM in Nigeria, the number of mobile lines has grown well beyond 1 million making Nigeria beat the minimum ITU recommended teledensity.
v  GSM services have created thousands of jobs in many Nigerian cities and suburbs directly or indirectly. Apart from Nigeria employed by the GSM operators direct business, there are franchise holders, dealers, distributors and retailers making a living selling GSM handsets; subscription pacts and airtime recharge cards. This has substantially reduced the menace of crime resulting from joblessness.
v GSM network enhanced feasibility of on-line banking and e-commerce initiatives. Some banks now practice GSM banking, which enable customer’s access to their account from their GSM handsets using the short message services with some others using the platform for electronic money transfers.
v GSM brought an improved access of Nigerians to telephones. Artisans, drivers,
Okada operators, Upholstery makers, Mechanics etc. are now easily connected.
GSM has broken myths about who a mobile phone user has to be. The ordinary man in the street now is not only just admiring those who use mobile phones as a sign of affluence because he too can afford one. Nigeria can proudly be said to have joined the league of major telecommunications players around the
World, with telephone and value added facilities being made available to those who may ordinarily not have gotten access to such.
v The incursion of GSM into Nigeria has to a large extent become a compass for the international financial and investor community into viability of investing in
v Economic activities of majority of Nigerians changed as they now appreciate the worth of communication, the cost of doing business is coming down, frustrations are disappearing, the stress is lessening and the sad tale of having to drive through the inexplicable traffic of major Nigerian cities especially
Lagos and Port Harcourt is now a thing of the past. In the same vein, GSM brought about improvement in operational efficiencies of corporate organizations. Businesses reduced operational cost by decreasing transportation overhead, with business decisions reached through conference calling or one to one call.
v GSM has become potent tool of economic growth and development in Nigeria and would continue to positively impact Nigeria economic growth through manpower and infrastructure development by the operating companies.
The acceptance level for GSM globally can be seen through from statistics presented below.

v  120 operators in 50 countries / Areas in Europe
v  320 million subscribers in Europe over a ten -year period
v 2-5 competing operators in every country; 4 -6 with UMTS
v 61% average penetration in Western Europe in yr. 2000, reaching 74% in some countries
v Euro70 billion cumulative investment in GSM

v COMBINED TURNOVER:                      Euro 240 billion
v CUMMULATIVE INVESMENT:          170 billion in UMTS            license plus  Additional 132 billion in infrastructure

v Direct employment:                                        470,000 employees
v Indirect employment:                                    2 million.


v GSM is in more than 174 countries of the world.
v There are over 400 second and third generation GSM wireless network operators.
v GSM is the most rapidly growing wireless technology today reporting over 646.5million subscribers or 71% of the total digital cellular wireless market as at January 2002.
v GSM represents 67% of the world’s wireless market.
v The other technologies (ANALOG, TDMA, CDMA, PDC) are at an average of 8%, with cumulative of 33%
v Year 2000 growth rates equaled 75%
v GSM grew by 40% in 2001, (191.4Million subscribers)

In America, GSM is the least deployed technology with 17 million subscribers
v TDMA has the highest subscriber base of 90 million subscribers
v CDMA has 69.2 million subscriber base.
(Source: EMC World Cellular database).