移动通信之旅：从GSM到LTE-Advanced

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"From GSM to LTE-Advanced: An Introduction to Mobile Networks and Mobile Broadband" 是一本由 Martin Sauter 编著的书籍，专注于无线通信技术的发展，从2G的GSM（全球系统移动通信）到3G的UMTS（通用移动通信系统），再到4G的LTE-Advanced（长期演进增强版）。这本书旨在为初学者提供一个全面而易懂的介绍，弥补了现有技术文献在深度和简明性之间的空白。在无线通信领域，GSM是一种第二代（2G）移动通信标准，它引入了数字信号处理和分组交换，使得语音通话和短信服务变得普遍且可靠。UMTS是3G技术的一部分，它进一步提升了数据传输速率，支持多媒体服务和互联网接入，使用户能够在移动设备上浏览网页和下载内容。随着对高速数据需求的增长，LTE（Long Term Evolution）应运而生，作为4G技术的先驱，提供了比UMTS更快的数据传输速度和更低的延迟。LTE-Advanced是LTE的升级版，通过载波聚合等技术实现了更高效的数据传输，为用户提供接近宽带的移动体验。本书不仅涵盖了这些技术的基本原理，如无线传输、网络架构和频谱效率，还讨论了移动通信系统的核心组件，如基站、移动设备、核心网络和空中接口协议。作者深入浅出地解释了从GSM演进到LTE-Advanced的过程中，如何逐步提升网络性能和用户体验。书中可能包括了信号编码、多址接入技术（如TDMA、CDMA和OFDMA）、无线资源管理、移动性管理和服务质量保证等方面的内容。此外，书中可能还探讨了无线通信与互联网的融合，以及这些技术对社会和经济的影响。对于那些希望快速了解移动通信发展历程和工作原理的学生或专业人士来说，这是一本理想的入门读物。然而，由于本书未提供具体内容，我们无法详细介绍每个章节的具体细节，但可以确信它将为读者提供一个全面的视角，让他们能够理解和跟踪无线通信技术的最新发展。 "From GSM to LTE-Advanced" 是一本旨在填补现有文献空白的书籍，通过简洁易懂的方式，引领读者穿越移动通信技术的演变历程，从2G的GSM到4G的LTE-Advanced，为理解现代移动通信网络和移动宽带服务打下坚实的基础。

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xiv Preface

Readers familiar with previous editions of this book will nd many updates in this revi-

sion. In Chapter 1, additional information has been included on the 3GPP Release 4 Mobile

Switching Center architecture that is now used in most networks. In Chapter 2, only few

updates were necessary because the deployed feature sets of GPRS and EDGE networks have

remained stable in recent years. Chapter 3 was signicantly enhanced as High-Speed Packet

Access (HSPA) features such as higher order modulation, dual carrier operation and enhanced

mobility management states are now in widespread use. While only a few LTE networks were

in operation at the publication of the previous edition, the technology has since spread and sig-

nicantly matured. Chapter 4 was therefore extended to describe Circuit-Switched Fallback

(CSFB) for voice telephony in more detail. In addition, a section on Voice over LTE (VoLTE)

was added to give a solid introduction to standardized voice over IP telephony in LTE networks.

Furthermore, a description of LTE-Advanced features was added at the end of the chapter. As

the global success of LTE has signicantly reduced the importance of WiMAX, the chapter on

this technology was removed from this revised edition. In Chapter 5, on Wi-Fi, a new section

was added on the new 802.11ac air interface. Also, a new section was added to describe the

Wi-Fi-Protected Setup (WPS) mechanism that is part of commercial products today. Finally,

the chapter on Bluetooth has also seen some changes as some applications such as dial-up

networking have been replaced by other technologies such as Wi-Fi tethering. Bluetooth has

become popular for other uses, however, such as for connecting keyboards to smartphones and

tablets. This chapter has therefore been extended to cover these developments.

Martin Sauter

Cologne

January 2014

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Global System for Mobile

Communications (GSM)

At the beginning of the 1990s, GSM, the Global System for Mobile Communications triggered

an unprecedented change in the way people communicate with each other. While earlier analog

wireless systems were used by only a few people, GSM is used by over 5 billion subscribers

worldwide in 2014. This has mostly been achieved by the steady improvements in all areas

of telecommunication technology and the resulting steady price reductions for both infra-

structure equipment and mobile devices. This chapter discusses the architecture of this system,

which also forms the basis for the packet-switched extension called General Packet Radio Ser-

vice (GPRS), discussed in Chapter 2, for the Universal Mobile Telecommunications System

(UMTS), which is described in Chapter 3 and Long-Term Evolution (LTE), which is discussed

in Chapter 4. While the rst designs of GSM date back to the middle of the 1980s, GSM is still

the most widely used wireless technology worldwide and it is not expected to change any time

soon. Despite its age and the evolution toward UMTS and LTE, GSM itself continues to be

developed. As shown in this chapter, GSM has been enhanced with many new features in recent

years. Therefore, many operators continue to invest in their GSM networks in addition to their

UMTS and LTE activities to introduce new functionality and to lower their operational cost.

In addition, it should be mentioned at this point that the industry has standardized on a

new solution for voice telephony for LTE that has only little in common with GSM anymore.

Although standardization is complete, efforts to roll out the new system are signicant, and at

the time of writing, there were only few voice-over LTE systems to be found in practice. Cur-

rent LTE-capable devices thus continue using GSM and UMTS networks for voice telephony

with a fallback mechanism.

1.1 Circuit-Switched Data Transmission

Initially, GSM was designed as a circuit-switched system that establishes a direct and exclu-

sive connection between two users on every interface between all network nodes of the system.

Section 1.1.1 gives a rst overview of this traditional architecture. Over time, this physical

From GSM to LTE-Advanced: An Introduction to Mobile Networks and Mobile Broadband,

Revised Second Edition. Martin Sauter.

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Global System for Mobile Communications (GSM) 3

Operating system of the

switching center

Switching and signaling

software

Fixed line subscriber and

call control

Mobile subscriber management

Mobility management

Call control

Operating system of the

switching center

Switching and signaling

software

Figure 1.2 Necessary software changes to adapt a xed-line switching center for a wireless network

signal, which was then sent over the copper cable to the terminating party. In some countries,

ISDN (Integrated Services Digital Network) lines were quite popular. With this system, the

transmission became fully digital and the conversion back into an analog audio signal was

done directly in the phone.

GSM reuses much of the xed-line technology that was already available at the time

the standards were created. Thus, existing technologies such as switching centers and

long-distance communication equipment were used. The main development for GSM, as

shown in Figure 1.2, was the means to wirelessly connect the subscribers to the network. In

xed-line networks, subscriber connectivity is very simple as only two dedicated wires are

necessary per user. In a GSM network, however, the subscribers are mobile and can change

their location at any time. Thus, it is not possible to use the same input and output in the

switching matrix for a user for each call as is the case in xed-line networks.

As a mobile network consists of many switching centers, with each covering a certain geo-

graphical area, it is not even possible to predict in advance which switching center a call should

be forwarded to for a certain subscriber. This means that the software for subscriber manage-

ment and routing of calls of xed-line networks cannot be used for GSM. Instead of a static

call-routing mechanism, a exible mobility management architecture became necessary in the

core network, which needed to be aware of the current location of the subscriber and was thus

able to route calls to the subscriber at any time.

It was also necessary to be able to exibly change the routing of an ongoing call as a sub-

scriber can roam freely and thus might leave the coverage area of the radio transmitter of the

network over which the call was established. While there was a big difference in the software

of a xed and a Mobile Switching Center (MSC), the hardware as well as the lower layers of

the software which are responsible, for example, for the handling of the switching matrix were

mostly identical. Therefore, most telecommunication equipment vendors like Ericsson, Nokia

Solutions and Networks, Huawei and Alcatel-Lucent offered their switching center hardware

both for xed-line and mobile networks. Only the software in the switching center decided if

the hardware was used in a xed or mobile network (see Figure 1.2).

1.1.2 Virtual Circuit Switching over IP

While in the 1990s voice calls were the dominating form of communication, this has

signicantly changed today with the rise of the Internet. While voice calls still remain

important, other forms of communication such as e-mail, instant messaging (IM), social

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4 From GSM to LTE-Advanced

networks (e.g. Facebook), blogs, wikis and many more play an even bigger role. All these

services share the Internet Protocol (IP) as a transport protocol and globally connect people

via the Internet.

While circuit switching establishes an exclusive channel between two parties, the Internet is

based on transferring individual data packets. A link with a high bandwidth is used to transfer

the packets of many users. By using the destination address contained in each packet, each

network node that the packet traverses decides over which outgoing link to forward the packet.

Further details can be found in Chapter 2.

Owing to the rise of the Internet and IP-based applications, network operators thus

had to maintain two separate networks: a circuit-switched network for voice calls and a

packet-switched network for Internet-based services.

As the simultaneous operation of two different networks is very inefcient and costly, most

network operators have, in the meantime, replaced the switching matrix in the MSC with a

device referred to as media gateway. This allows them to virtualize circuit switching and to

transfer voice calls over IP packets. The physical presence of a circuit-switched infrastruc-

ture is thus no longer necessary and the network operator can concentrate on maintaining and

expanding a single IP-based network. This approach has been standardized under the name

‘Bearer-Independent Core Network’ (BICN).

The basic operation of GSM is not changed by this virtualization. The main differences can

be found in the lower protocol levels for call signaling and voice call transmission. This will

be looked at in more detail in the remainder of this chapter.

The trend toward IP-based communication can also be observed in the GSM radio network,

even though it is still dominated today by classic circuit-switched technology. This is due to the

wide distribution of the network that makes it difcult to change transport technology quickly

and because the datarates required for GSM are low.

The air interface between the mobile devices and the network is not affected by the transition

from circuit to packet switching. For mobile devices, it is therefore completely transparent if

the network uses classic or virtual circuit switching.

1.2 Standards

As many telecom companies compete globally for orders of telecommunication network oper-

ators, standardization of interfaces and procedures is necessary. Without standards, which are

dened by the International Telecommunication Union (ITU), it would not be possible to make

phone calls internationally and network operators would be bound to the supplier they initially

select for the delivery of their network components. One of the most important ITU standards

discussed in Section 1.4 is the Signaling System Number 7 (SS-7), which is used for call

routing. Many ITU standards, however, only represent the smallest common denominator as

most countries have specied their own national extensions. In practice, this incurs a high cost

for software development for each country as a different set of extensions needs to be imple-

mented in order for a vendor to be able to sell its equipment. Furthermore, the interconnection

of networks of different countries is complicated by this.

GSM, for the rst time, set a common standard for Europe for wireless networks, which has

also been adopted by many countries outside Europe. This is the main reason why subscribers

can roam in GSM networks across the world that have roaming agreements with each other.

The common standard also substantially reduces research and development costs as hardware

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