Conclusion

The development trend in telecommunications is driven by user service requirements asking for access to a diversified range of personalised set of services to anyone, anywhere, anytime but not at any price. Borders between telecommunications, information technology and entertainment services are disappearing and users can combine service offerings from various operators. Deregulated world-wide market and rapid introduction of mobile services of the second generation, specifically GSM, has lead to the conclusion that one "ultimate mobile solution ", one radio access network and one single core network standardised to a very detailed level is not realistic. Flexibility and opportunities of choice within mobile communications are avaiIable to a large extent already today. The choice is available for users, service operators, network operators and manufacturers. Consequently UMTS development takes into account the opportunity of the choice and the multiplicity of futed and mobile telecommunication networks and services. Several of these systems can evolve towards UMTS with their own targets and pace. Such facts are influencing the current standardisation process at both national, regional.

The evolution path of 3G/UMTS as well as its some aspects give us an overall general picture of 3G really is a necessary step after all. Technically speaking, 3G is an advancement over present GSM services, able to offer much in terms of quality multimedia services. However, for users of mobile telephony, it is not so important to them what sort of technology makes communication possible. It is the type of service and the quality of the service that they obtain that is of more importance to them. What users want are services that make things more convenient and accessible. GSM is predominantly a voice service technology and this was the most important service to offer at the time when GSM was introduced because mobile telephones should offer just that: Telephone services but with mobility. However, it has since evolved to encompass some data services such as SMS and some internet access capability. Further enhancements allowed even faster access to the Internet and to other services. With 3G and UMTS, even more services can be introduced to the public.


In my country, Vietnam, we have six mobile service providers, yet none of them offer 3G services. Two mobile technologies have been using there. A half of providers uses GSM technology. And the rest uses cdma-1x. The quality service of cdma-1x in my country is not good. The calls sometimes drop or speech is delayed. Even the strategists of cdma-1x companies created a lot of advertisement campaigns or sale promotion, they can not attract the customers who had used GSM services. GSM providers gain over 70 percent of mobile market. 3G technology has just been setting up the fundamental platform in Vietnam mobile service market. For example, ZTE Corporation, China's largest listed telecommunications manufactures and leading wireless solutions provider, is to install Vietnam's first 3G network in Ho Chi Minh city. ZTE will provide a network based on the Corporation's 450 MHz EV-DO (EVolution - Data Optimized or EVolution - Data Only) technology, which will bring 3G technology to the seven million inhabitants of Vietnam's largest city. I hope that Vietnames will soon have chance to use the 3G services in the near future.

The role of standards

3GPP held its first meetings in December 1998 after agreements between the regional standards bodies (ETSI, AFUB, and others) were made to focus the development of UMTS and WCDMA technologies under a single global project. The 3GPP Release '99 physical layer interface is now becoming stable and work is proceeding on the subsequent annual releases of the specifications, known as Releases 4 and 5.

The need for industry concensus on certain design and implementation issues calls for the need for standardisation on agreed areas. For example, the UTRA air interface is standardised clearly in 3GPP; this allows multiple vendor equipments to be introduced into the market, thus driving competition. Thus standardisation is needed in cases where interfaces between vendor equipments exist. In such cases, resources expended constitute overhead and visibility of the standards process enables competitor intelligence gathering. However, more crucially, standardisation can be used to enforce technology leadership and thus competive advantage.

On the other hand, evolution can remain vendor specific; for instance, it may not be necessary to standardise a particular receiver algorithm which functions within a terminal or basestation; in these cases, equipment is not prevented from multi-vendor functioning where no standardisation exists, but the performance or cost to market may differ from one vendor to another.

3GPP Road map

The 3rd Generation Partnership Project (3GPP) is a collaboration agreement that was established in December 1998. The collaboration agreement brings together a number of telecommunications standards bodies which are known as "Organizational partners". The current Organizational Partners are ARIB/TTC (Japan), CCSA (China), ETSI (Europe), ATIS (North America), and TTA (South Korea).

The original scope of 3GPP was to produce globally applicable Technical Specifications and Technical Reports for a 3rd Generation Mobile System based on evolved GSM core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access (UTRA) both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). The scope was subsequently amended to include the maintenance and development of the Global System for Mobile communication (GSM) Technical Specifications and Technical Reports including evolved radio access technologies (e.g. General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)).

3GPP releases:

• Release 99: Complete. Include enhancements to GSM/GPRS (EDGE). Support for GSM/EDGE/GPRS/WCDMA radio-access network. Most deployment today uses R99.
• Release 4: Complete. MMS support. Efficient interconnection of CN infrastructure over IP networks.
• Release 5: Complete. Delivered HSDPA and first phase of IMS. Half of WCDMA network
  deployments now include the HSDPA evolution.
• Release 6: Complete. Includes HSUPA, enhanced multimedia support using Multimedia Broadcast/Multicast Services (MBMS), performance specifications for advanced receivers, WLAN integration, and evolution of the IP Multimedia System IMS.
• Release 7: On-going (expected mid-2007). Enhanced GSM data functionality. Optimisation/fine tuning of earlier releases for performance enhancements, improved spectral efficiency, increased capacity, and better resistance to interference. Also provides optimisations for VoIP over HSPA.
• Release 8: In progress (expected 2009). Constitutes a refactoring of UMTS as an intirely IP based fourth generation network.
  

UMTS Market aspects

The wireless communications business has experienced an exceptional growth during the last 10 years. This growth has been particularly remarkable in those markets in which GSM was the dominant standard, Europe and Asia Pacific. GSM economies of scale and its fundamental characteristics such as global roaming and competitive short message services (SMS) helped this boost. Current global volumes were not expected in any existing forecast. Figure 5 displays the evolution of the cellular subscribers worldwide from 1991 and shows several forecasts for the coming years, which indicate that the cellular subscriber growth rate is expected to continue growing during this decade.


During the 1990s, with the introduction of second-generation (digital) standards, voice telephony went wireless. The 1990s was also the decade of the Internet take off, with Internet-based multimedia services (MMSs) becoming increasingly popular and the web becoming the ‘de facto’ world information database. Second-generation (2G) cellular standards were, however, not designed to support these new Internet-based services and applications. Third-generation (3G) standards are meant to become the vehicle for Internet based multimedia and other data services to go wireless as well.

Key drivers of UMTS market:

• Growth in the market for fixed networked multimedia services.
• Increasing demand for rapid and remote access to information.
• eCommerce and transaction based applications.

Key enablers of UMTS market:

• Appropriate regulatory framework.
• Advances in spectrum efficient radio technologies and data compression techniques.
• Development of open UMTS standards.
• Improvement in user interface design and display technologies.
• Reduced size, power, and cost of mobile devices.
• Early of exploitation of GPRS and GSM services.

However, UMTS market also has to face with some barriers such as:

• Security and fraud issues.
• High cost and limited availability of spectrum.
• High cost of UMTS technology.
• Poor coverage and incomplete roaming.

A lot of mobile operators have had to pay large sums of money for 3rd Generation operating licences. In Europe, some of the highest amounts paid came from German and British Mobile operators. In Germany, the cost per licence was approximately US$ 7.6 billion and in the UK, it ranged from US$ 6.3 to US$ 9.4 billion. This has led to many operators having less resource for putting in place of 3G infrastructure and has caused delays in the commercial launch of the services. While some operators had to pay billions for the licences, there were others, such as Finland and Sweden that were awarded licences for much smaller sums of money. The disadvantage that these operators had was that rollout had to happen at a much faster rate as compared to operators who paid high sums of money.

There are operators who did not obtain licences to operate a 3rd Generation network, either due to not having been selected or having decided not to bid for the licences. A good alternative technology to UMTS is that of EDGE, which allows users to have reasonable quality of multimedia services over the GSM network.

In summary, the advantage of 3G to mobile operators is the new revenue generation that would steam from services offered to users. With data services becoming more important day by day and mobility becoming an essential part of life, it is most likely that these new mobile data and internet services will draw many users. The reason why many operators were willing to pay such large sums of money for 3G licences speaks for itself. They predict that revenue that will be obtained from 3G services and applications will sometime down the road, make their investments worthwhile and reap profits for them.

In addition, if a technology offers high performance differential with low incremental complexity and it is available quickly, it is likely that the sales effort needed will be low. Conversely, if the technology offers a more limited performance-complexityavailability combination, the technology could still be marketed, but a more intensive sales and marketing effort will be needed. Often, technologies that do offer significant incremental performance but also demand high complexity implementation do not achieve market success. Optimisation of the four parameters: sales and marketing effort, performance, complexity and availability will contribute to success.

UMTS Technical aspects

The technical advantages of 3G are far more than that of 2G and its enhancements such as GPRS and EDGE. GSM was originally deployed as a circuit switched network for voice services. However, when it was deduced that data services will bring in more revenue, it led to operators upgrading their circuit switched networks with a packet switched data network on top of it. Although 3G was already conceived, the enhanced GSM network would provide data and voice services in the meantime. Circuit switched networks have always been used for voice services in organizations and the most obvious advantage is that of higher access speeds. When networks introduce UMTS, users will be able to experience a maximum speed of 2Mbps indoors and 384Kbps outdoors. Although these numbers are only theoretical maximums achievable, practically, the average should be around 300Kbps, and this would allow users to experience multimedia type services.

The big advantage of 3G is that it introduces entirely packet based networks. As compared to early GSM which was a circuit switched based network. Enhancement to GSM had introduced packet switching with GPRS and EDGE. However, with a fully IP based network such as UMTS, a lot more advantages are possible.

Quality of service, which was not fully addressed by GSM and its enhancements, is another advantage of UMTS. With UMTS, quality of service measures has been incorporated in to the technology to make sure that spectrum allocation is optimized. This means that for a particular type of data service, e.g. multimedia video streaming, the appropriate amount of bandwidth will be allocated by the network for that particular service to ensure that the user experience is maximized.

Because of the employment of WCDMA and direct sequence spread spectrum techniques, spectral efficiency is also increased for UMTS, as compared to GSM. Because of the nature of WCDMA, the spectrum available is translated into high data rates and this is ideal for high bandwidth data requirements.

The security aspects of UMTS are also an improvement over that of GSM, although what security functions found in UMTS are generally improved versions of GSM security functions. In GSM, security for users was found in the SIM and the radio interface was encrypted. In UMTS, encryption in the air interface is now broadened to include the base stations and radio network controller connections as well. Other security features have also been included in the base stations and in data authentication. 6 Therefore, in terms of security, UMTS does show and improvement over GSM. However, like every other system, it is not a fully secure one and is vulnerable to misuse and abuse.

UMTS Services aspects

UMTS services are based on common capabilities throughout all UMTS user and radio environment. The purposes of UMTS are:

• Enabling users to access a wide range of telecommunications services, including many that are today undefined as well as multimedia and high data rates.
• Allowing the difference between service offering of various serving networks and home environments.
• Providing support for interfaces which allow the use of terminals normally connected to fixed networks.
  
• Facilitating the provision of small, easy to use, low cost terminal with long talk time and long standby operation.
• Providing an efficient means of using networks (specially spectrum).

Based on above objectives, specific requirement related to services are outlined in the ETSI specifications. Data rates offered for bearer services are:

• 144 kbits/s for satellite and rural outdoor
• 384 kbits/s for urban outdoor
• 2048 kbits/s for indoor and low range outdoor
  

UMTS network services have different QoS classes for four types of traffic:

• Conversational (voice, video telephony, video gaming) This is characterized by low delay tolerance, low jitter (delay variation) and low error tolerance. The data rate requirement may be high or low, but is generally symmetrical.
• Streaming (multimedia, video on demand, webcast) This concerns one-way services, using low- to high-bit rates. Streaming services have a low-error tolerance, but generally have a high tolerance for delay and jitter. That is because the receiving application usually buffers data so that it can be played to the user in a synchronized manner.
• Interactive (web browsing, network gaming, database access) This consists of typically request/response-type transactions. Interactive traffic is characterized by low tolerance for errors, but with a larger tolerance for delays than conversational services. Jitter (delay variation) is not a major impediment to interactive services, provided that the overall delay does not become excessive.
• Background (email, SMS, downloading) This is characterized by little, if any, delay constraint.
  

Implementation and Integration aspects in UMTS

Research studies aiming to improve the overall performance of multiple access techniques such as WCDMA or TDCDMA have provided interesting and applicable methods. However, these results may not necessarily be part of the first UTRA commercial systems in the next 2 years. Thus, it will be some time before techniques such as Software Radio, Adaptive Antennas, and Multi-user Detection enhance capacity, coverage and increase system stability.

Implementation and integration appear as key limitations to bring these advanced techniques into operating systems or near future11 exploitable networks. Processing power demands for example, do not allow rapid implementation of the above methods. Furthermore, integrating such techniques into smaller components is a great challenge. This means, that while less optimum supporting techniques like system on a chip, maximizing power consumption, or operating at very low power come into place; the aforementioned improvements will remain academic.

At present, while UMTS frequency licensing becomes big business for governments, operators seem to have fall into the spin of supremacy and consolidation for market share and have somehow forgotten the timeliness of technology. Manufacturers are finding themselves in a race to supply plain vanilla solutions and are incapable of implementing true breakthroughs in multiple access or radio-access techniques.

Thus, it seems reasonable to think that it may be to the benefit of industry as a whole and governments themselves to concentrate on putting more resources into the realization of new communications technologies than just coping with spectrum allocation and acquisition to offer services with higher transmission rates. Such an approach will make UMTS a clear platform for advanced technology from the start and not just one more alternative to provide new mobile applications.

Some enhancing technologies are used in UMTS

Capacity Increasing Antenna

By increasing the number of base station (BS) antennas we can resolve the uplink limitation of WCDMA. However, this approach does not allow a single step solution because many factors intervene before completing the process. These factors include: propagation environment, BS configuration, environmental issues as a result of power levels, and network integration in terms of the radio network controller (RNC). However, here we consider first the BS configuration by looking at the antenna design. We need low correlation between the antennas achievable by adequate separation between the antennas. The beam forming technique may exploit a uniform linear array, where the inter-antenna spacing falls near 1/2 of a carrier wavelength. Then sectors using narrow beams will have an increased antenna gain when compared to typical sector antenna.

While pico and micro environments have higher angular diversity, the macro environment has lower angular diversity, but higher multi-path diversity. Thus, the macro environment can benefit from beam forming techniques, because the latter applies more to lower angular diversity conditions.

Multi users detection technique

Multi-user Detection (MUD) techniques may apply to both the uplink (UL) and downlink (DL). However, initially due to processing power constraints in the MS, MUD may be exploited first in the BS. Thus, here we look at performance enhancement primarily in the UL while implementing MUD in the BS. The two UTRAN registration area (UTRA) modes, i.e. Frequency division duplex (FDD) and time division duplex (TDD) can benefit from MUD techniques. In fact, the joint detection algorithm is already an inherent part of the TDD mode. Capacity within interference-limited WCDMA can improve through the use of efficient receivers. This implies that the structured multiple access interference can be dealt with at the receiver through multi-user detectors.

Software radio applications

This solution appears more realistic today through Software Radio (SR), the application of flexible and programmable transceivers. Thus, SR sets itself as a key technology to drive the realization of global standards in 3G systems. The evolution of GSM to UMTS alone will benefit multi-band multi-mode (GSM 900, 1800, 1900, GPRS, UMTS (FDD and TDD) terminals. On the other hand, SR not only applies to terminals or Mobile Stations (MS) but also the to the Base Stations (BS).

UMTS User equipment

The UMTS standard does not restrict the functionality of the User Equipment in any way. Terminals work as an air interface counter part for Node-B and have many different types of identities. Most of these UMTS identity types are taken directly from GSM specifications.

• International Mobile Subscriber Identity (IMSI)
• Temporary Mobile Subscriber Identity (TMSI)
• Packet Temporary Mobile Subscriber Identity (P-TMSI)
• Temporary Logical Link Identity (TLLI)
• Mobile station ISDN (MSISDN)
• International Mobile Station Equipment Identity (IMEI)
• International Mobile Station Equipment Identity and Software Number (IMEISV)
  

UMTS Radio access

Wide band CDMA (WCDMA) technology was selected to for UTRAN air interface. UMTS WCDMA is a Direct Sequence CDMA system where user data is multiplied with quasi-random bits derived from WCDMA spreading codes. In UMTS, in addition to channelisation, codes are used for synchronisation and scrambling. WCDMA has two basic modes of operation: Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

The functions of Node-B are:

Air interface Transmission / Reception Modulation / Demodulation CDMA Physical Channel coding Micro Diversity Error Handing Closed loop power control

The functions of RNC are:

Radio Resource Control Admission Control Channel Allocation Power Control Settings Handover Control Macro Diversity Ciphering Segmentation / Reassembly Broadcast Signalling Open Loop Power Control

UMTS Core network

The Core Network is divided in circuit switched and packet switched domains. Some of the circuit switched elements are Mobile Services switching Centre (MSC), Visitor Location Register (VLR) and gateway MSC. Packet Switched Elements are serving GPRS support node (SGSN) and Gateway GPRS Support Node (GGSN). Some network elements, like Equipment Identity Register (EIR), Home Location Register (HLR), VLR and Authentication Center (AUC) are shared by both domains.

The Asynchronous Transfer Mode (ATM) is defined for UMTS core transmission. ATM Adaptation Layer type 2 (AAL2) handles circuit switched connection and packet connection protocol AAL5 is designed for data delivery.

The architecture of the Core Network may change when new services and features are introduced.

Universal Mobile Telecommunications Service (UMTS) architecture

UMTS is the third generation system promoted by ETSI and provides vital link between today's multiple GSM systems and the ultimate single worldwide system for all mobile telecommunications, IMT-2000. It is one of the most significant advances to the evolution of telecommunications into 3G networks. It will address the the growing demands of the mobile and Internet applications in the overcrowded mobile communications sky. It will increase the network speeds to 2Mbps per mobile user and establishes a global roaming standard.

A UMTS network consist of three interacting domains; Core Network (CN), UMTS Terrestrial Radio Access Network (UTRAN) and User Equipment (UE). The main function of the core network is to provide switching, routing and transit for user traffic. Core network also contains the databases and network management functions. The basic Core Network architecture for UMTS is based on GSM network with GPRS. All equipment has to be modified for UMTS operation and services.

The UTRAN provides the air interface access method for User Equipment. Base Station is referred as Node-B and control equipment for Node-B is called Radio Network Controller (RNC).

It is necessary for a network to know the approximate location in order to be able to page user equipment. Here is the list of system areas from largest to smallest.

UMTS systems (including satellite) Public Land Mobile Network (PLMN) MSC/VLR or SGSN Location Area Routing Area (PS domain) UTRAN Registration Area (PS domain) Cell Sub cell

Licensed frequency bands of 3G technology

An important factor in the 3G-technology evolution path strategy is the support, in the spectrum licensed to operators, of the different radio technologies. Depending on the spectrum licensed for cellular use in a certain region, local operators may have a limited technology choice. Unfortunately, frequency licensing has not been historically uniform across different regions worldwide. Figure 3 shows the spectrum allocation in different regions of the ITU IMT-2000 recommended new bands. The recommended ITU spectrum for new bands for 3G deployment has been allocated in some regions for other purposes. Therefore, operators in different regions will have to try to accommodate in the specific licensed band.

3G technology evolution paths- UMTS and cdma2000

Analogue technologies were dominant in the cellular market up to 1997, when their global market share was exceeded by that of 2G digital technologies. The last 10 years have seen a phenomenal growth of the cellular penetration worldwide, which has defined the shape of the 2G technologies global market share as displayed in figure 1.


Today, the convergence of 2G technologies towards the 3G evolution path is relatively clear. The entities that are representing and driving the evolution of 2G technologies have endorsed the 3G/UMTS evolution path:

• The GSM Association, representative of the GSM operators worldwide, is a market representative of the 3rd Generation Partnership Project (3GPP) and fully supports 3G/UMTS evolution path.
• 3G Americas, a wireless industry association dedicated to the Americas, supports the seamless deployment of GSM, GPRS, EDGE and UMTS throughout the Americas and fully endorses the migration of TDMA operators to the GSM family of technologies. The transition from TDMA to GSM technologies for operators is helped by the GAIT standard functionality (GSM, ANSI-136, Interoperability Team) that enables interoperability between TDMA and GSM technologies.
• In Japan, the two most important PDC operators (NTT DoCoMo and J-Phone), which on October 1st, 2001 covered 75.7% of the Japanese subscriber base, have selected UMTS WCDMA technology for their 3G evolution.

The alternative 3G evolution path to UMTS is the one endorsed by the CDMA Development Group (CDG), which supports an evolution to 3G based on cdmaOne technology. cdmaOne was initially developed in the United States and soon adopted in other regions. Figure 2 shows the market share cdmaOne technology holds in different global regions. Although cdmaOne has been introduced in most of the regions worldwide, only in America, especially in the United States, and to some extent in Asia Pacific, fundamentally in Korea, has it developed an important momentum.

Additionally, many current cdmaOne operators are analysing the possible migration paths to UMTS. Such migration can be done through the migration to GERAN (GSM/EDGE) with the later integration of UTRAN (WCDMA) or it can be done through the direct introduction of UTRAN. This last option is however dependent on the cellular operator licensed bandwidth, since WCDMA technology is currently not supported in the 800 MHz band, the future availability of dual mode cdmaOne/WCDMA terminals and the integration effectiveness of the technologies.

Third - Generation (3G) evolution paths

The International Telecommunications Union (ITU) launched the International Mobile Telecommunications-2000 (IMT-2000) program, which, together with the main industry and standardisation bodies worldwide, targets to provide the framework for the definition of the third-generation (3G) mobile systems. Several radio access technologies have been accepted by ITU as part of the IMT-2000 framework. IMT-2000 is a radio and network access specification defining several methods or technology platforms that meet the overall goals of the specification. The IMT-2000 specification is meant to be a unifying specification, enabling mobile and some fixed high speed data services to use one or several radio channels with fixed network platforms for delivering the services envisioned:

■ Global standard
■ Compatibility of service within IMT-2000 and other fixed networks
■ High quality
■ Worldwide common frequency band
■ Small terminals for worldwide use
■ Worldwide roaming capability
■ Multimedia application services and terminals
■ Improved spectrum efficiency
■ Flexibility for evolution to the next generation of wireless systems
■ High-speed packet data rates

• 2 Mbps for fixed environment
• 384 Kbps for pedestrian
• 144 Kbps for vehicular traffic

From the existing IMT-2000-accepted standards, two main differentiated 3G evolution paths are available for current cellular operators. Such paths are the UMTS and the cdma2000.

History of 2.5G systems

Once the second-generation systems became established it soon became apparent that the limited data capabilities of some of the 2G systems were a significant disadvantage. Many applications for data transfer with the increased use of the Internet and laptop computers were seen. Even though the third generation systems were on the horizon, developments were needed to provide a service before they entered the market. One of the first was the General Packet Radio Service (GPRS) development for the GSM system. Its approach centred on the use of packet data. Up until this time all circuits had been dedicated to a given user in an approach known as circuit switched, i.e. where a complete circuit is switched for a given user. This was inefficient when a channel was only carrying data for a small percentage of the time. The new packet switched approach routed individual packets of data from the transmitter to the receiver allowing the same circuit to be used by different users. This enabled circuits to be used more efficiently and charges to be metered according to the data transferred.

Further data rate improvements were made using a system known as EDGE (Enhanced data Rates for GSM Evolution). This basically took the GPRS system and added a new modulation scheme, 8PSK, to enable a much higher data rate to be achieved. Whilst the symbol rate remained the same at 270.833 samples per second, each symbol carried three bits instead of one.

Whilst GPRS and EDGE were applied to GSM networks, enhancements were also applied to the CDMA system that originated in the USA. Here an evolutionary path from 2G through 2.5G to 3G was created.

History of Second - Generation (2G) systems (continued)

GSM

During the early 1980s, analog cellular telephone systems were experiencing rapid growth in Europe, particularly in Scandinavia and the United Kingdom, but also in France and Germany. Each country developed its own system, which was incompatible with everyone else's in equipment and operation. This was an undesirable situation, because not only was the mobile equipment limited to operation within national boundaries, which in a unified Europe were increasingly unimportant, but there was also a very limited market for each type of equipment, so economies of scale and the subsequent savings could not be realized.

The Europeans realized this early on, and in 1982 the Conference of European Posts and Telegraphs (CEPT) formed a study group called the Groupe Spécial Mobile (GSM) to study and develop a pan-European public land mobile system. The proposed system had to meet certain criteria:

• Good subjective speech quality

• Low terminal and service cost

• Support for international roaming

• Ability to support handheld terminals

• Support for range of new services and facilities

• Spectral efficiency

• ISDN compatibility
  

In 1989, GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI), and phase I of the GSM specifications were published in 1990. Commercial service was started in mid-1991, and by 1993 there were 36 GSM networks in 22 countries. Although standardized in Europe, GSM is not only a European standard. Over 200 GSM networks (including DCS1800 and PCS1900) are operational in 110 countries around the world. In the beginning of 1994, there were 1.3 million subscribers worldwide , which had grown to more than 55 million by October 1997. With North America making a delayed entry into the GSM field with a derivative of GSM called PCS1900, GSM systems exist on every continent, and the acronym GSM now aptly stands for Global System for Mobile communications.

Initially, GSM was specified to operate only in the 900-MHz band, and most of the GSM networks in service use this band. There are, however, other frequency bands used by GSM technology. The first implementation of GSM at a different frequency happened in the United Kingdom in 1993. That service was initially known as DCS1800 since it operates in the 1800-MHz band. These days, however, it is known as GSM1800. After all, it really is just GSM operating at 1800 MHz.

History of Second - Generation (2G) systems

Unlike first-generation systems, which are analog, second-generation systems are digital. The use of digital technology has a number of advantages, including increased capacity, greater security against fraud, and more advanced services. Like first-generation systems, various types of second-generation technology have been developed. The three most successful variants of secondgeneration technology are Interim Standard 136 (IS-136) TDMA, IS-95CDMA, and the Global System for Mobile communications (GSM). Each of these came about in very different ways.

IS-136 and IS-54

IS-136 came about through a two-stage evolution from analog AMPS. As described in more detail later, AMPS is a frequency division multiple access (FDMA) system, with each channel
occupying 30 KHz. Some of the channels, known as control channels, are dedicated to control signaling and some, known as voice channels, are dedicated to carrying the actual voice conversation. The first step in digitizing this system was the introduction of digital voice channels. This step involved the application of time division multiplexing (TDM) to the voice channels such that each voice channel was divided into time slots, enabling up to three simultaneous conversations on the same RF channel. This stage in the evolution was known as IS-54 B (also known as Digital AMPS or D-AMPS) and it obviously gives a significant capacity boost compared to analog AMPS. IS-54 B was introduced in 1990.

Today AMPS, IS-54B, and IS-136 are all in service. AMPS and IS-54 operate only in the 800-MHz band, whereas IS-136 can be found both in the 800-MHz band and in the 1900-MHz band, at least in North America. The 1900-MHz band in North America is allocated to Personal Communications Service (PCS), which can be described as a family of second-generation mobile communications services.

History of First-Generation (1G) systems

Mobile communications really started in the late 1970s, with the implementation of a trial system in Chicago in 1978. The system used a technology known as Advanced Mobile Phone Service (AMPS), operating in the 800-MHz band. For numerous reasons, however, including the break-up of AT&T, it took a few years before a commercial system was launched in the United States. That launch occurred in Chicago in 1983, with other cities following rapidly.

Meanwhile, however, other countries were making progress, and a commercial AMPS system was launched in Japan in 1979. The Europeans also were active in mobile communications technology, and the first European system was launched in 1981 in Sweden, Norway, Denmark, and Finland. The European system used a technology known as Nordic Mobile Telephony (NMT), operating in the 450-MHz band. Later, a version of NMT was developed to operate in the 900-MHz band and was known (not surprisingly) as NMT900. Not to be left out, the British introduced yet another technology in 1985. This technology is known as the Total Access Communications System (TACS) and operates in the 900-MHz band. TACS is basically a modified version of AMPS.

Many other countries followed along, and soon mobile communications services spread across the globe. Although several other technologies were developed, particularly in Europe, AMPS, NMT (both variants), and TACS were certainly the most successful technologies. These are the main firstgeneration systems and they are still in service today.

First-generation systems experienced success far greater than anyone had expected. In fact, this success exposed one of the weaknesses in the technologies—limited capacity. Of course, the systems were able to handle large numbers of subscribers, but when the subscribers started to number in the millions, cracks started to appear, particularly since subscribers tend to be densely clustered in metropolitan areas. Limited capacity was not the only problem, however, and other problems such as fraud became a major concern. Consequently, significant effort was dedicated to the development of second-generation systems.

The amazing growth of wireless communications

The wireless market has experienced a phenomenal growth since the second-generation (2G) digital cellular network based on global system for mobile communication technology (GSM) were introduced in 1990s. Since then, GSM has become the dominant global 2G radio access standard. This growth has taken place simultaneously with the large experienced expansion of access to the Internet and its related multimedia services.
Cellular operators now face the challenge to evolve their networks to efficiently support the predicted demand of wireless Internet-based multimedia services. In order to do this, they need to perform a new rapid radio access technologies, capable of delivering such services in a competitive and cost effective way. It is called the Third-Generation (3G) wireless. When the full promise of 3G is realized, wireless users will have global access to a variety of voice, data and video services. Users will be able to access all their communications services easily from anywhere using any terminal. Users will simply choose the most convenient means to communicate, while network operators will choose the most efficient way to transport communications.

Though 3G wireless will change the way people think about communications, the path for carriers to reach 3G is more evolutionary than the previous two generations of wireless have been. First-generation wireless, analog cellular, was an entirely new form of communications that required a system-wide deployment of infrastructure for a market that didn't yet exist. Second-generation wireless was in some ways a more gradual transition. Established companies had the luxury of deploying digital service as an overlay to the analog network. New carriers had to deploy entirely new digital networks, but they had the benefit of a market that was already aware of wireless telephony and an existing demand for the advanced services that digital technology offered. Still, the transition had to happen fairly quickly for established carriers to compete with all-new digital carriers.

Now, just a few years after the transition to digital wireless, another generation of wireless communications is approaching, but it doesn't mean existing systems will become obsolete. Instead, carriers will find new ways to use existing systems more efficiently while adding network elements that provide new services. The key to 3G is convergence - not only a technological convergence of different kinds of communications but, more importantly, a convergence for business reasons.