Wireless and Mobile Data Networks - Hardcover

Ahmad, Aftab

Hardcover

ISBN 10: 0471670758 ISBN 13: 9780471670759

Verlag: Wiley-Interscience, 2005

Inhaltsangabe

Wireless and Mobile Data Networks provides a single point of knowledge about wireless data technologies, including:
* Comprehensive easy-to understand resource on wireless data technologies
* Includes wireless media, data transmission via cellular networks, and network security
* Provides a single point of knowledge about wireless data
* Focuses on wireless data networks, wireless channels, wireless local networks, wide area cellular networks and wireless network security

An Instructor Support FTP site is available from the Wiley editorial department.

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Über die Autorin bzw. den Autor

AFTAB AHMAD received his DSc in communications from The George Washington University. Currently, he is Associate Professor of Computer Science at Norfolk State University. He has published a number of research papers and a book, Data Communication Principles: For Fixed and Wireless Networks. His current research involves ad hoc network routing, wireless network planning, Quality of Service (QoS)–based call control in IP radio access networks (IP-RAN), and QoS routing with IP.

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Connecting to the Future of Wireless Data Technologies

Presenting complex subjects without getting into advanced mathematics, Wireless and Mobile Data Networks gives students and professionals a comprehensive overview of major wireless network architectures and standards.

The opening chapters introduce wireless data network types, architectures, and wireless local area network (WLAN) components. The author follows with physical and medium access control layers of WLANs, mobile IP, and session initiation protocol (SIP); then expands on other relevant topics, such as wide area wireless data networks, security in wireless data networks, routing in ad hoc network, and wireless personal area networks (WPAN); followed by the wireless metropolitan area networks (MANs).

This up-to-the-minute and in-depth coverage of how key standards and protocols work includes:

• Wireless LAN architectures, such as IEEE 802.11
• Wireless PAN architectures, such as Bluetooth (IEEE 802.15.1), IEEE 802.15.3/3a (high data rate and UWB-based PANs), and IEEE 802.15.4 (low power, low data rate PANs)
• Wireless broadband access, such as IEEE 802.16/16a
• Comparisons between architectures, such as IEEE Wireless MANs (IEEE 802.16 and 802.16a) compared to the European Union approaches (HIPERACCESS and HIPERMAN)
• 3G cellular standards, including CDMA2000® and W-CDMA
• Ad hoc networks
• Security in wireless data networks

Wireless and Mobile Data Networks is both an up-to-date reference for IT professionals and a comprehensive textbook for advanced communications and computer science students.

Presenting complex subjects without getting into advanced mathematics, Wireless and Mobile Data Networks gives students and professionals a comprehensive overview of major wireless network architectures and standards.

The opening chapters introduce wireless data network types, architectures, and wireless local area network (WLAN) components. The author follows with physical and medium access control layers of WLANs, mobile IP, and session initiation protocol (SIP); then expands on other relevant topics, such as wide area wireless data networks, security in wireless data networks, routing in ad hoc network, and wireless personal area networks (WPAN); followed by the wireless metropolitan area networks (MANs).

This up-to-the-minute and in-depth coverage of how key standards and protocols work includes:

• Wireless LAN architectures, such as IEEE 802.11
• Wireless PAN architectures, such as Bluetooth (IEEE 802.15.1), IEEE 802.15.3/3a (high data rate and UWB-based PANs), and IEEE 802.15.4 (low power, low data rate PANs)
• Wireless broadband access, such as IEEE 802.16/16a
• Comparisons between architectures, such as IEEE Wireless MANs (IEEE 802.16 and 802.16a) compared to the European Union approaches (HIPERACCESS and HIPERMAN)
• 3G cellular standards, including CDMA2000® and W-CDMA
• Ad hoc networks
• Security in wireless data networks

Wireless and Mobile Data Networks is both an up-to-date reference for IT professionals and a comprehensive textbook for advanced communications and computer science students.

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Wireless and Mobile Data Networks

By Aftab Ahmad

John Wiley & Sons

Copyright © 2005 Aftab Ahmad
All right reserved.
ISBN: 978-0-471-67075-9

Chapter One

WIRELESS DATA-INTRODUCTION

In studying the principles of data communications, the wireless spectrum is generally treated as part of communications media only. This may give the impression that the remaining components of a wireless data network were the same as those of a fixed, wired network. The reality, however, is quite different, thanks to a number of factors with varying degree of roles in wireless and fixed, wired networks. There are network components that exist in only one network type and not the other. There are also network components existing in both types, but playing a less significant role in one or the other. There are many sub-systems, such as antenna radiation and mobility management that do not surface in the fixed, wired networks. Wall connectors are not usually part of transmission systems in wireless networks. There are systems that do make an essential part of both network types, but with much less significance in one than the other. Examples of such systems are power consumption systems, data security, and privacy, by containing signal, signal-detection techniques and error-control techniques. Lastly, there are certainly many components that play equally important roles in both types of networks, such as switching and routing techniques, flow and congestion control mechanisms and call-control procedures. Thus a study of wireless data networks has its own scope, different from networking systems in general.

Wireless, however, does not imply mobility. There are wireless networks in which both ends of communications are fixed, such as in wireless local loops. In satellite communication systems, even though the satellite is always mobile, the mobility profile of the satellite is designed so as to provide a constant signal level to the connected terminals, thus emulating a fixed end. Wireless networks with mobility, however, provide the biggest challenge to the network designer.

We will devote this chapter to various types of wireless data networks that network engineers have to design and deal with. We will start the discussion with wireless voice communication, as the bulk of data in cellular networks is still voice. Also, most of the telecommunications developments have been in telephony.

1.1. WIRELESS VOICE

Before beginning a discussion on wireless data networks, a few words about the voice signal might be advisable. Even though the wireless data systems were the precursor of all electronic communications systems, most of the progress in telecommunications is a result of voice networks. In fact, most of the developments in cellular systems to date owe their existence to the voice signal. Wireless voice poses somewhat relaxed requirements to system designers, which make it easier to make engineering decisions. Here are some examples of the characteristics of wireless voice.

1.1.1. Fixed Minimum Bandwidth

The voice signal has most of its energy within 300 Hz to 3400Hz, giving a bandwidth of 3.1kHz, such as shown in Figure 1-1. For typical digital transmissions, a nominal value of 4 kHz is assumed. Consequently, all channels with a bandwidth of 4 kHz or higher could ideally provide the same quality of transmitted voice if all other factors are kept constant. Digital speech is transmitted in one of the several standard coding forms, such as ITU G.711, G.721, G.722, G.723, G.728 and G.729. These standards are based on different mechanisms of speech digitization and compression, and produce a digital bit stream of either fixed (G.711, 721,) or variable but a known average rate (G.728, 729). PSTN uses G.711, which is based on 8-bit per sample PCM transceiver using one of the two quantization techniques (A-Law in Europe and m-Law in North America and Japan), both resulting in a 64 kbps encoded voice bit stream. PCM is a waveform coding technique that deals directly with the speech signal for digitization and transmission purposes.

Other standards use model-based coding, which extracts certain parameters from the speech signals and transmits these parameters instead of the speech signal. These later systems, called Vocoders, result in bit streams anywhere from 16 kbps to less than 4kbps. However, due to the inflexible nature of the PSTN, the 64 kbps standard is the one most used for voice transmission. For bandwidth-constrained systems, such as wireless networks, lower bit rate coding techniques have been considered as better alternatives. For example, the European GSM systems typically employ regular pulse excited hybrid voice coding (RPE), resulting in 13 kbps bit stream and the U.S. Department of Defense (DoD) uses 4.8 kbps code excited linear predictive (CELP) technique in federal standard FS 1016. In either case, once a network is designed to support a certain type of voice coding, the required minimum bandwidth is fixed. Such is not the case in data communications. Numerical, textual, or graphical data could be transmitted using any bandwidth without impairing its quality, as long as error-control mechanisms are employed to remove errors or retransmit lost packets and packets with errors. The channel bandwidth can only limit the speed of data transmission.

1.1.2. Vague Definition of Service Quality

A second characteristic of voice signal is a lack of a strict scientific definition of the quality of transmitted speech. The quality of voice transmitted is perception-driven and can't be adequately measured. Even though the International Telecommunications Union (ITU) standards based on scientific definition of quality perception allow for an automated measurement of voice quality, the most commonly used metric is still the mean opinion score (MOS), a subjective quality-determining mechanism in which listeners allocate a number between 1 and 5, where 5 is for excellent quality. The procedure for MOS is defined in ITU recommendation ITU-TP.800. A standard introduced for automated quality assessment was introduced in the early part of 2001. Called Perceptual Evaluation of Speech Quality (PESQ), it takes into account factors such as packet loss, delay and jitter. PESQ is defined in the ITU standard ITU-T862. Though its usability for Internet is agreeable, its validation, too, is done by comparing it to MOS.

In circuit-switched wireline networks, a fixed voice coding mechanism is employed, usually based on waveform coding. However, in connectionless Internet, neither fixed coding scheme must be employed, nor do the network characteristics remain constant. In wireless networks, the wireless channel is highly unstable, enhancing the vagueness of quality. In fact, despite strides in speech coding mechanisms, there is a discernable degradation in the quality of transmitted speech in cellular networks as compared with PSTN voice quality.

1.1.3. Delay Requirements

A third and perhaps the strictest characteristic of conversational speech is the stringent requirement on maximum delay. Due to its highly interactive nature, the conversational speech signal is required not to have more than a fraction of a second delay (250msec maximum recommended by ITU). The variation in delay is expected to be even smaller by at least an order of magnitude. These requirements make the flexibility of packet switching somewhat less than ideal for voice communications. Therefore, the voice networks have traditionally been circuit switched. This applies to cellular wireless networks as well. Consequently, a voice network consists of a...

Details zur Ausgabe

• Verlag: Wiley-Interscience
• Erscheinungsdatum: 2005
• Sprache: Englisch
• ISBN 10: 0471670758
• ISBN 13: 9780471670759
• Einband: Gebundene Ausgabe
• Auflage: 1
• Anzahl der Seiten: 376
• Kontakt zum Hersteller: Wiley-VCH GmbH; product_safety@wiley.com; ; Boschstrasse 12; Weinheim; 69469; Deutschland