GSM and UMTS - Excellent Past, Bright Future

Table of Contents

Abbreviations

List of Figures

1 Introduction

2 Evolution of Mobile Communications
2.1 First Generation (1G): Analog Cellular
2.2 Second Generation (2G): Multiple Digital Systems
2.3 Second to Third Generation (2G to 3G): GSM Evolution
2.4 Third Generation (3G) – IMT-2000

3 Technical Overview
3.1 Multiple Access Methods (Multiplexing) – the basis for economical use
3.1.1 Space Division Multiple Access (SDMA)
3.1.2 Time Division Multiple Access (TDMA)
3.1.3 Frequency Division Multiple Access (FDMA)
3.1.4 Code Division Multiple Access (CDMA)
3.1.4.1 Frequency Hopping Spread Spectrum (FH-SS)
3.1.4.2 Direct Sequence Spread Spectrum (DS-SS)
3.2 Structure of the GSM network
3.2.1 Radio Subsystem (RSS)
3.2.2 Network and Switching Subsystem (NSS)
3.2.3 Operation Subsystem (OSS)

4 UMTS – an international Standard
4.1 Domain Architecture of UMTS
4.1.1 User equipment (UE)
4.1.2 Utran
4.1.3 Core Network (Backbone)
4.2 Advantages of UMTS

5 Summary

Bibliography

Internet Resources

Appendix

Abbreviations

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List of Figures

Figure 2.1 Evolution of important mobile communication technologies

Figure 2.2 Transmission rates development from GSM to UMTS

Figure 2.3 Frequencies for IMT-2000

Figure 3.1 Cellular topology

Figure 3.2 TDMA-scheme

Figure 3.3 GSM-TDMA frame structure

Figure 3.4 FDMA-scheme

Figure 3.5 Characteristics of Spread Spectrum Systems

Figure 3.6 Characteristics of FH-SS

Figure 3.7 Principle of DS-SS

Figure 3.8 Orthogonal Variable Spreading Factor (OVSF) codes

Figure 3.9 Transmitted Signal before and after spreading

Figure 3.10 Functional Architecture of GSM

Figure 3.11 Example of the GSM network

Figure 4.1 UMTS architecture – R99 (Phase 2+)

Figure 4.2 The IMT-2000 Family

Figure 4.3 Basic architecture of an UTRA-network

Figure 4.4 Integrated core network

Figure 4.5 User interference in the neighbouring cell

Figure 4.6 Macrodiversity – communication through multiple channels

1 Introduction

Since the beginning of the 1990s the mobile telecommunication sector to mention the cellular communication services has continued to grow and evolved strongly. The reason for such an unprecedented level of development was possible with the existence of the so-called second generation digital technologies, with GSM (Global System for Mobile communication) being one of the most popular systems. In fact these second generation digital technologies, which are generally incompatible with each other, went eventually through standardization processes since the beginning of the 1980s reaching their limits of possibilities by now.^[1]

In order to be able to offer new services and to provide users with real mobility on a global scale, it has become essential to augment the technology and elevate the threshold to the so-called third generation technology. The following paper will first provide a short but more thorough historical overview of the developments in the cellular communication services. The second part will be exemplifying the technology behind GSM. In this part, the paper will first address the technologies used to provide wireless voice and data services to subscribers commonly referred to as multiplexing. Followed by examining the structure of the GSM network itself. The last main part will focus on the third generation technology by showcasing the widely used Universal Mobile Telecommunication System (UMTS). This part will not only introduce the technology by looking at the architecture in detail, but also determine some of the differences to the GSM technology and address the overall advantages. Finally, the paper will be summarized.

2 Evolution of Mobile Communications

Electric magnetic waves were firstly discovered as a communication medium at the end of the 19th century. Heinrich Hertz demonstrated practically the electromagnetic wave transmission in free space based on Maxwell’s theories of electromagnetic fields in 1886. Followed by the Italian Guglielmo Marconi, who developed the first useful wireless communication system in 1895.^[2] The first system that offered mobile telephone services was introduced in the late 1940s in the United States and was particularly used in cabs.^[3] The disadvantage of those early single cell systems, which were solely based on amplitude modulation, range from restricted mobility, low capacity, limited service to poor speech quality. Furthermore, the equipment itself was heavy, expensive and subject to interferences. A great step towards improved radio transmission was introduced with the invention of the frequency modulation technique by Edwin H. Armstrong in the year 1933.^[4]

2.1 First Generation (1G): Analog Cellular

The first analog cellular systems were introduced in the 1970s and 1980s to mention the B- and later the C-network initiated by the “Deutsche Bundespost” in 1986, which represented a quantum leap in mobile communication in regards to capacity and mobility.^[5] However, these cellular systems still transmitted only analog voice information (see Figure 2.1). The technical development of the C-network also called C 450 was solely in the hands of Siemens, which offered 222 pairs of radio channels anticipating within a 450-MHZ- band.^[6] The C-network used technical standards like AMPS (Advanced Mobile Phone System). Other countries incorporated standards, which were often based on AMPS, but the technology was incompatible with other standards like NMT (Nordic Mobile Telephone) in Scandinavia and TACS (Total Access Communication System). The mentioned standards exemplify the most prominent 1G ones accumulating new subscribers annually to reach nearly 20 million subscribers by 1990.^[7]

2.2 Second Generation (2G): Multiple Digital Systems

The further developments of 2G cellular systems were driven by the need to improve transmission quality, system capacity, coverage and standardization. Continuous improvement in the semiconductor technology and microwave devices brought digital transmission to mobile communications.^[8] While speech transmission prevails to be dominant, other services provided by 2G systems like short message services (SMS) or fax fortified increasingly higher demands. The current most propagated 2G standard GSM was specified by the European Telecommunication Standards Institute (ETSI) in two phases to name D1 and D2 as being the first cellular mobile networks in Germany starting in 1992 (see Figure 2.1).^[9] GSM could support 10000 people per square km, which is particularly necessary in major cities with multiple business facilities, and is used in over 110 countries around the world.^[10] In fact there are 400 cellular mobile network providers worldwide offering different GSM-variances to “some 250 million of the world’s 450 million cellular subscribers”^[11] which are all compatible regarding their architecture, but not in terms of frequencies.^[12]

It became evident that the analog AMPS used mainly in the United States and the digital GSM at 900 MHZ (abbreviated GSM-900 by the ETSI while completing Phase 1 of the standardization process in 1990) in Europe were not able to accommodate such a huge subscriber base especially in cities. In the beginning of this development, the United States did not provide any additional frequency band, whereas Europe opened up a new frequency band named DCS (Digital Cellular System) at 1800 MHZ, nowadays better known as GSM-1800. These fundamentally different decisions lead to two different developments in Europe and in the United States. New efficient technologies were researched and developed in the United States that could all function on the frequencies of AMPS.^[13]

The result was a narrow band version of AMPS, a digital CDMA (Code Division Multiple Access) system and a digital TDMA (Time Division Multiplexing), which are all incompatible with each other.^[14] GSM is one a few examples that showcases that striving for a common standard determines the better alternative, if you consider that Europe has one standard, however, subscribers of the system can also use their phone in Australia, Singapore or the United States.

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Figure 2.1 Evolution of important mobile communication technologies^[15]

2.3 Second to Third Generation (2G to 3G): GSM Evolution

Since Phase 1 of the standardization process of GSM-900, multiple tele-services and bearer services have been specified (including data transmission up to 9 kbps), but only a few very basic supplementary services were offered.^[16] The result included that the GSM standard was enhanced in Phase 2 to incorporate a huge variety of supplementary services and improved speech compression/decompression called CODEC and enhanced full rate (EFR) in 1996.^[17] In the same year ETSI decided to add Phase 2+ to integrate 3G capabilities like high-data rate services and new transmission principles with High-speed circuit-switched data (HSCSD) providing a theoretical maximum of 8 x 14.4 Kbps = 115.2 Kbps (see Figure 2.2).^[18] The most revolutionary services were added with the ability to support packet switched data (e.g. for internet based applications) to introduce the general packet radio service (GPRS – with 8 x 21.4 Kbps = 171.2 Kbps^[19]) and later the enhanced data rates for GSM evolution (EDGE). The Edge standard uses a different modulation technique than the previous services to achieve a peak rate of 48 Kbps per GSM timeslot.^[20]

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Figure 2.2 Transmission rates development from GSM to UMTS^[21]

2.4 Third Generation (3G) – IMT-2000

In order to come up with a standard of the 3G network an independent body, representing the multitude of different technologies of the second generation in the role of the ITU (International Telecommunication Union), defined the IMT-2000 concept, also referred to as the UMTS (Universal Mobile Telecommunication System).^[22] The 3rd generation of mobile technologies started in Europe with field tests of UMTS in Japan with the so called FOMA service and in Korea with cdma2000.^[23] The most important network access technology that was proposed is a special case of a wideband CDMA (W-CDMA) with the two modes TDD (Time Division Duplex) and FDD (Frequency Division Duplex), which will be examined in chapter 4. Figure 2.3 illustrates that some of the provided frequency range for UMTS in Europe is already reserved for Digital Enhanced Cordless Telecommunications (DECT). The rest of the frequency range is reserved for UTRA FDD 1920-1980 MHz (uplink path) and 2110-2170 MHz (downlink path) as well as for UTRA TDD 1900-1920 MHz and 2010-2025 MHz (uplink and downlink path).^[24] The characteristics of IMT-2000 can be described as a single family of compatible standards sharing the following facts:

- Used Worldwide
- Used for all mobile applications
- Allow both packet-switched (PS) and circuit switched (CS) data transmission
- Providing high data rates up to 2 Mbps (depending on mobility and velocity)
- Providing high spectrum efficiency^[25]

[...]

^[1] Compare [UMTS Origins, 2004], p. 1.

^[2] Compare [Mobilkommunikation, 2003], p. 26.

^[3] Compare [UMTS, 2001], p. 26.

^[4] Compare [Mobilkommunikation, 2003], p. 27.

^[5] Compare [UMTS, 2001], p. 38.

^[6] Compare [C-Netz].

^[7] Compare [UMTS, 2001], p. 38.

^[8] Compare [UMTS Protocols, 2005].

^[9] Compare [Nachrichtentechnik, 2003], p. 206.

^[10] Compare [Mobilkommunikation, 2003], p. 28.

^[11] [UMTS Evolution, 2005].

^[12] Compare [Mobilkommunikation, 2003], p. 28.

^[13] Compare [Mobilkommunikation, 2003], p. 29.

^[14] Compare [UMTS, 2001], p. 45-49.

^[15] [UMTS, 2001], p. 34.

^[16] Compare [UMTS Evolution, 2005].

^[17] Compare [Nachrichtentechnik, 2003], p. 206-207.

^[18] Compare [UMTS Origins, 2004], p. 22.

^[19] Compare [Mobilkommunikation, 2003], p. 161.

^[20] Compare [Mobilkommunikation, 2003], p. 177.

^[21] [UMTS Network, 2005].

^[22] Compare [UMTS Origins, 2004], p. 4-8.

^[23] Compare [Mobilkommunikation, 2003], p. 31.

^[24] Compare [UMTS Origins, 2004], p. 4-8.

^[25] Compare [UMTS Evolution, 2005].