A comparative introduction to major global wireless standards, technologies and their applications
From GSM to LTE-Advanced Pro and 5G: An Introduction to Mobile Networks and Mobile Broadband, 3rd Edition provides technical descriptions of the various wireless technologies currently in use. It explains the rationales behind their differing mechanisms and implementations while exploring the advantages and limitations of each technology.
This edition has been fully updated and substantially expanded to reflect the significant evolution in mobile network technology occurring over the past several years. The chapter on LTE has been extensively enhanced with new coverage of current implementations of LTE carrier aggregation, mobility management, cell reselection and handover procedures, as well as the latest developments in 5G radio and core networks in 3GPP. It now features additional information on the TD-LTE air interface, IPv6 in mobile networks, Network Function Virtualization (NFV) and Narrowband Internet of Things (NB-IOT). Voice-over-LTE (VoLTE) is now treated extensively in a separate chapter featuring coverage of the VoLTE call establishment process, dedicated bearer setup, header compression, speech codec and bandwidth negotiation, supplementary service configuration and VoLTE emergency calls. In addition, extensive coverage of Voice-over-Wifi and mission critical communication for public safety organizations over LTE has been added. The WLAN chapter now provides coverage of WPA2-Professional with certificates for authentication in large deployments, such as the global Eduroam network and the new WLAN 60 GHz air interface. Bluetooth evolution has been addressed by including a detailed description of Bluetooth Low Energy (BLE) in the chapter devoted to Bluetooth.
* Describes the different systems based on the standards, their practical implementation and design assumptions, and the performance and capacity of each system in practice is analyzed and explained
* Questions at the end of each chapter and answers on the accompanying website make this book ideal for self-study or as course material.
Martin Sauter works in the telecommunication industry as a thought leader, researcher, book author and blogger and is based in Cologne. His interests are focused on mobile communication networks, multimedia applications and especially the wireless Internet.
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 only by a few, GSM is used worldwide by billions of people today. This has mostly been achieved by steady improvements in all areas of telecommunication technology and the resulting steady price reductions for both infrastructure 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 Service (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.
Although the first standardization activities for GSM date back to the middle of the 1980s, GSM is still the most widely used wireless technology worldwide. In recent years, however, 4G LTE networks have become tremendously popular and a new service was standardized to support voice calls via the LTE radio network. This service is referred to as Voice over LTE (VoLTE) and is discussed separately in Chapter 5. Although efforts to roll out VoLTE are significant, a large percentage of mobile voice calls are still handled by GSM and UMTS networks to which devices without VoLTE support fall back for this service. In addition, even if a device and a network support VoLTE, a transfer to GSM or UMTS is still required when the user leaves the LTE-coverage area. As a consequence, knowledge of GSM is still required for a thorough understanding of how mobile networks are deployed and used in practice today.
1.1 Circuit-Switched Data Transmission
Initially, GSM was designed as a circuit-switched system that establishes a direct and exclusive connection between two users on every interface between all network nodes of the system. Section 1.1.1 gives a first overview of this traditional architecture. Over time, this physical circuit switching has been virtualized and many network nodes are connected over IP-based broadband connections today. The reasons for this and further details on virtual circuit switching can be found in Section 1.1.2.
1.1.1 Classic Circuit Switching
The GSM mobile telecommunication network has been designed as a circuit-switched network in a similar way to fixed-line phone networks. At the beginning of a call, the network establishes a direct connection between two parties, which is then used exclusively for this conversation. As shown in Figure 1.1, the switching center uses a switching matrix to connect any originating party to any destination party. Once the connection has been established, the conversation is then transparently transmitted via the switching matrix between the two parties. The switching center only becomes active again to clear the connection in the switching matrix if one of the parties wants to end the call. This approach is identical in both mobile and fixed-line networks. Early fixed-line telecommunication networks were designed only for voice communication, for which an analog connection between the parties was established. In the mid-1980s, analog technology was superseded by digital technology in the switching center. This meant that calls were no longer sent over an analog line from the originator to the terminator. Instead, the switching center digitized the analog signal that it received from the subscribers, which were directly attached to it, and forwarded the digitized signal to the terminating switching center. There, the digital signal was again converted back to an analog 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 to an analog audio signal was done directly in the phone.
Figure 1.1 Switching matrix in a switching center.
GSM reused much of the fixed-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 fixed-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 fixed-line networks.
Figure 1.2 Necessary software changes to adapt a fixed-line switching center for a wireless network.
As a mobile network consists of many switching centers, with each covering a certain geographical 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 management and routing of calls of fixed-line networks cannot be used for GSM. Instead of a static call-routing mechanism, a flexible mobility management architecture in the core network became necessary, which needed to be aware of the current location of the subscriber and thus able to route calls to them at any time.
It was also necessary to be able to flexibly change the routing of an ongoing call as a subscriber 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 between the software of a fixed switching center 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 fixed-line and mobile networks. Only the software in the switching center determined whether the hardware was used in a fixed 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 significantly changed today with the rise of the Internet. While voice calls remain important, other forms of communication such as e-mail, instant messaging (IM), social 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 inefficient and costly, most network operators have, in the meantime, replaced the switching matrix in the MSC with a device referred to as a media gateway. This allows them to virtualize circuit switching and to transfer voice calls over IP packets. The physical presence of a circuit-switched infrastructure 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 especially when a radio base station site supports GSM, UMTS and LTE simultaneously. Typically, connectivity is then established over a single IP-based link.
The air interface between the mobile devices and the network is not affected by the transition from circuit to packet switching. For mobile devices, whether the network uses classic or virtual circuit switching is therefore completely transparent.
As many network infrastructure manufacturers compete globally for orders from telecommunication network operators, standardization of interfaces and procedures is necessary. Without standards, which are defined 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,...