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Evolution of Cellular to UMTS Concept

Mirza Shahidul Islam
Director, BTTB (May 2000)

It is 100 years since a system for communicating using electromagnetic waves was first demonstrated by Marconi and Papov, although the actual beginning of radio go back much further. Over the intervening decades, radio technology has developed with incredible rapidity, until today it is one of the primary means of global communications. It is impossible to imagine a world without radio, a world where there was no communication via satelites, where no-one had a personal mobile phone, where the airwaves were not filled with an enormous variety of music and entertainment.

Radio is already competing with wired links as the main means of communications for the home and office. By the beginning of the 21st century it will prevade communications in every area of activity in every part of the world.

Into the cellular age:

Once considered as a prerogative of the elitist class, Mobile Communication has now been recognized as the main technology for making one telephone available to each person in the world. The last decade of the twentieth century and full range of twenty-first century will witness significant developments in the field of Mobile communications. However, it is necessary to provide proper infra-structural, institutional and policy support for the proper absorption and utilization of the technology in the region.

The concept of a cell based radio communication system had been developed as early as 1947

in the Bell Laboratories in the USA. However the concept was to remain purely theoretical until the technology was available to implement such a system. In a cellular network, radio transmitters operating at frequencies approaching microwave, send and receive voice and data traffic from users within their coverage area or ‘cell’. The cells within the system are contiguous, usually covering entire country, and user can move from cell to cell, maintaining communications by cells ‘handing off’ the subscriber to the adjacent cell. Calls are switched through the cellular network, which in turn is linked to the national and international telephone system.

Although simple in concept, there were man’ hurdles to be overcome before the first cellular networks could be established. Government had to be persuaded to allocate scarce frequency spectrum for such a service, manufacturers ha to develop the technology and the service had to be designed in such a way as to be affordable b the public at large, despite the enormous investment required to set up the network.

These difficulties were resolved and the firs public cellular networks went live in Nordi countries of Sweden, Denmark, Norway an Finland in 1980. Networks soon sprang up in

North America, Europe, Asia-Pacific and Australasian. From its original concept as a essentially vehicular service, cellular move towards providing personal communication with low-cost, user-friendly hand portable terminals. Cellular radio has proved to be one of the most successful technological innovations of the late 20th century. At the end of 1994 there were almost 50 million cellular subscribers worldwide, and the industry estimates that this figure will approach 200 million by the beginning of the new millennium. The initial cellular networks used analogue technology but new digital systems have been developed, notably Europe’s GSM (Global System for Mobiles) which has already established itself as the world’s leading digital cellular solution. Over 70 GSM networks are in operation in Europe, Africa, the Middle East, Asia-Pacific and Australasia and many more will be introduced over the next few years.

Perhaps the most remarkable fact concerning the impact of cellular telephony is that it is becoming the standard method of communication for many millions of people around the world.

The nature of the cellular subscriber has also changed. Ordinary consumers are now turning to cellular radio in ever increasing numbers and this trend is accelerating as network operators produce new and innovative tariff packages aimed at the mass market.

One of the main driving forces behind the development of the worldwide cellular market has been competition. As more and more governments deregulate their telecommunication regimes, the mobile sectors invariably the first area into which they introduce competition. Second (and even third and fourth) mobile operators are being licensed, creating an atmosphere of intense competition and forcing rapid growth in the market. This competition is extremely beneficial to the customer, bringing low prices for services and terminals; as well as new features and facilities.

An Unruly family of Cellular Standards:

Incompatible cellular standards would not matter if cellular phone owners never left home. But using your cellular phone while traveling abroad - known as roaming - is futile unless your home network’s spectrum and standard is compatible with the cellular standard where you are visiting. The existence of roaming agreements between cellular networks may allow calls to be billed back to the customer’s home network. If spectrum and standards are incompatible, however, don’t bother to unpack your cellular phone. Your only choice is to rent a phone built to a compatible standard.

Until recently cellular networks were based on one of several competing analogue technologies. A number of factors - including cost and availability of frequency spectrum - determined the selection of a specific analogue standard. By the early 1990s, a map showing analogue cellular standards, in use around the world, resembled a patchwork quilt. The Americas were served by AMPS - based networks. Europe, the Middle East, and Asia were served primarily by the NMT format. Other parts of Asia and the Middle East were also served by TACS systems. And Japan was served by the JTAC and NTAC standards, which Motorola helped to develop.

Going Digital

New cellular standards have recently been introduced that rely on digital - rather than analogue - technologies, largely because digital technologies can serve many more cellular subscribers. Digital standards also permit the introduction of such value-added services as call forwarding, voice mail, and data transmission. Many developing nations seeking to provide basic telephone service are leap-frogging analogue technology entirely, in favour of the latest digital cellular technologies.

The first digital standard, GSM, was introduced in Western Europe in 1992. Designed to provide a roaming capability through the continent, GSM allows a subscriber to easily use his or her cellular telephone on any GSM network. A credit card-sized SIM (subscriber identity module) card-bearing pertinent subscriber information on a microchip - inserted into a borrowed or rented phone allows it to function as the subscriber’s own phone. providing access to subscriber’s services, as well as direct billing of charges to the subscriber’s home-network account. International roaming between GSM networks has became a relatively simple matter for the subscriber.

GSM technology also offers greater than twice the subscriber capacity of analogue systems, reducing the number of dropped and interrupted calls. The IRIDIUM system is based on the GSM technology standard including an IRIDIUM SIM card that will use both IRIDIUM - specific features and many services found on GSM systems.

Thanks to its regulation as a ready and reliable digital upgrade option, the GSM standard has also been adopted outside of Europe. GSM networks are now operational in Asia and the Pacific, the Middle East, and Africa. According to the GSM MoU Association 124 network operators in 75 nations have adopted GSM. One hundred GSM networks in 58 nations were known to be in operation as of September 1995.

Existing analogue cellular standards have also been enhanced with digital technology, which increases network carrying capacity while retaining much existing infrastructure. The AMPS standard, for instance, found throughout America as well as in Asia and Africa, has been upgraded to variants called N-AMPS and DAMPS. N-AMPS triples the number of voice channels within the operator’s existing spectrum allocation. A new, digital AMPS follow-on, dubbed IS- 136, has been selected by AT & T Wireless as an upgrade strategy for its extensive AMPS- based cellular network in the United States.

Another new digital standard, known as CDMA, has come on the scene. Based on the spread -

spectrum technology used by military radio works to code and simultaneously several transmission across a wide frequency spectrum CDMA has been under development for several years. CDMA’s technology is said to offer I an easy transition path for analogue AMP based networks and a dramatic increase in capacity over analogue technologies. How the more recent arrival of GSM (or digit enhanced analog standards) has led to its selection for first - generations digital networks some cellular operators. While CDMA continues to be tested in a number of countries, Hutchinson Telephone Company in Hong Kong is preparing a CDMA based network, and Korea deployed CDMA-based networks between 1996 and 1997 In the United States, several companies, including the Sprint Telecommunication Venture (STV), selected CDMA for their future PCS works.

Japan has continued to chart its own course cellular standards. The PDC and PHS digital standards recently developed for the home market have been a huge success. PHS networks were launched on July 1, 1995, by Iridium, investor DDI Corporation, the Astel Group Nippon Telephone and Telegraph, and qui signed up over 100,000 subscribers (DDI’s sidiary, DDI Pocket Phone, will be investing over 300 billion yen - more than US $ 3.5 billions- in its PHS network over the coming five years The PHS standard allows exended ‘cordl telephone conversation on a small cellular -handset. PHS call charges are generally lower than cellular charges, however - since PHS c not allow handoffs between its 200 - metre cells these system do not offer true mobile telephone service. Despite these limitations, the PHS s standard is being aggressively marketed to networks operators in other Asian nations.

New cellular networks are being introduced almost daily and existing networks continue to expand into regions with no existing telephone systems. Thanks to Japanese investors, even Mongolia will soon boast cellular coverage. Despite the development of new digital standards, analogue cellular is still holding its own in many parts of the world. Analogue - based equipment prices are generally lower than equivalent digital systems, and analogue networks provide quality service for subscribers needing basic wireless telephone service. Several analogue technologies have been upgraded in recent years to increase their carrying capacity and efficiency. These system enhancements allow network operators to offer improved service, without huge new investments in network infrastructure.

The end result - a continuing welter of competing, incompatible cellular standards, both analogue and digital.

A Global view of the UMTS concept:

The development of Third - generation mobile systems has been on going for several years. At the worldwide level, in the ITU, these systems are called IMT - 2000 (formerly FPLMTS -Future public land Mobile Telecommunication System). The European Third - generation system is known as the Universal Mobile Telecommunications System (UMTS). Europeans envisage UMTS to be a part of IMT -2000. By the end of 1998, the cellular market reached 300 million users worldwide, with subscribers of the first digital mobile cellular system

- GSM - counting for more than 140 million. In view of such dramatic growth, a long - term development of the mobile communications services market into Third - Generation services has to be secured.

The Universal Mobile Telecommunications

System (UMTS) is one of the systems selected by

International Telecommunications Union (LTU) as

part of the IMT 2000 process to define ‘Third Generation Mobile System’ (or 30) for use worldwide. The goal is to give a new focus to the development of mobile systems that will offer voice and mobile multi-media to the mass market.

A lot of people first heard about UMTS - and, more generally, IMT 2000 - on the occasion of an air interface debate aimed at reaching an agreement from among the many proposals for a third generation mobile system. However, these are other important third generation challenges that directly affect the commercial and operational aspects of a future UMTS standard. A universal system should offer a way to move towards a ‘unified’ network, new services for existing and new subscribers, and the ability to rapidly deploy a wide range of services.

Consequently, Alcatel is promoting a global view of the UMTS concept (Figure 1), including:

• New radio interface capable of providing high data rates for multimedia services.

• Means to implement a unified core network for fixed and mobile, as well as telecom and datacom applications.

• A flexible service architecture to allow operators to meet subscribers needs.

Figure-1 Alcatel's UMIT Concept

IMT 2000 and the UMTS concept:

ITU defined, via IMT 2000 (and its predecessor the Future Public Land mobile System or FPLMTS), the requirements to be met by a standard third generation mobile communications system. Europe’s response was UMTS, which was just one of more than ten proposals from around the world. The Japanese promoted Wideband Code Division Multiple Access (WCDMA), while the US proposed two major technologies CDMA 2000, an evolution of IS-95 (known commercially as CDMA One) and UWC-136, which is an evolution of 15-136.

Figure 2 shows the main IMT 2000 proposals together with the corresponding second generation technologies (currently deployed and widely used) issued by the same standardization body.

Figure-2-Third Generation IMT2000 Technology

The 2G/3G link shown in Figure 2 indicates that both standards are released by the same standardization body, but does not imply that the third generation proposal is an evolution of the second generation standard. For example, there is a clear difference between the Global System for Mobile communication (GSM) and UMTS air interfaces, as well as between W-CDMA and Personal Digital Cellular (PDC). Nevertheless, when a third generation proposal is a development of the second generation standard, strong inter-working links exist that make it possible to deploy ‘30 islands’.

Once the air interface has been defined, the domain to be studied is the network as relating to interoperability of the new station with the existing mobile networks. Se issues then have to be resolved to ensure g harmonization, in addition to the definite the physical part of the air interface. This taken into account when specifying a con UMTS standard between Japan and Europe especially in the definition of the Radio A Core Network interface, as discussed below;

UMTS, as an evolution of GSM, is from GSM Mobile Application Part (MAP) ‘~ while CDMA 2000 is from the IS-41 ‘~ UWC 136 uses both as a complete overlay the radio and network aspects of the General Packet Radio Service (GPRS) solution bas IS-l36. Further more, studies are being c. out to implement complete inter working between the GSM MAP and IS-41.

Today IMT 2000 encompasses the following third generation systems :

• UMTS as defined by the Third Gene Partnership Project (3GPP), including European Telecommunications Stan Institute Special Mobile Group (ETSI Japan’s Association of Radio Industrial Businesses (ARIB) and Telecommunication Technology Committee (TTC) committees Korea’s Telecommunication Technology Association (TTA) and the North Am

T1P1 committee (with T1 Tr46).

• CDMA 2000 defined by the 3GPP2, including ARIB. Tl. TTA and TTC. CDMA is an evolution of the CDMA One star

• UWC- 136, which is based on the GPRS Enhanced Data rate for GSM Evolution (EDGE) technologies defined by ET carrying data on an overlay network to classical’ IS-136 voice networks. The result of the process is the definition of three technologies for the air interface that can co-exist with the two main core networks standards. Possible interworking between the air modes and the Core networks is shown in Figure 3

Even though the list of third generation standards is shorter than the second generation list, two main technologies still exist: CDMA (UMTS and CDMA 2000) and Time Division Multiple Access (TDMA) UWC-136). It should be noted that no complete agreement (which would have led to a single standard) has been found between the CDMA proposals. Of course, there is some degree of hannonization between UMTS and CDMA 2000, and some radio parameters are identical. However, the network mobile signaling aspects still need to be studied to achieve full interworking.

Driving UMTS and Co-ordination of Activities:

The definition of UMTS - its vision, its evolutionary way from second generation systems into the future, all its dimensions will be a result of co-operation between many organization representing all interest. The telecommunication industry agreed that UMTS must have an effective decision process to achieve broad consensus on policy and strategy matters. The result is the creation of the ‘UMTS Forum’ which started its work in early 1996 focusing on four main issues;

• Regulatory, • Spectrum,
• Market and Society, and • Technology Impact.

The first Mission statement was that UMTS would use the present IMT-2000-spectrum as a core band. The UMTS Forum claims that additional spectrum is required for broad band services in

the order of 187 MHz for terrestrial and 30 MHz for satelite services. The UMTS Forum has started to support the preparations for getting more spectrum for mobile multimedia services in future. The world Radio Conference WRC2000 will discuss this under Agenda Item 1.6.1 A positive decision is expected in the interest of the mobile community. In Figure 4 shows the present spectrum allocations for GSM, DECT, PCS and IMT-2000.

Conclusion:

The motivation for UMTS results from recognizing the future developments towards multimedia combined with personal mobility. In addition to the technical innovations in the existing networks, only near broadband radio technologies can completely reflect such requirements. This needs to be combined with the achieved level of worldwide mobility in GSM using network intelligence. Covergence between fixed and mobile networks will arise together with the upcoming demand for mobility independent from user location and user needs to be developed in an evolutionary way.

The 21st century customer will demand services independent from the access method. IJMTS will find its way to satisfy this customer by providing ‘Universal Mobile Telecommunications Service.’

References

I. Celebration 130 years of ITO (1865.1995).

2. Electronics for you . November 1996.

3. Alcatel Telecommunication Review 3rd Oct. 1999.

  1. Global Communication (wireless) Millennium Issue.