1.3 Structure of the Book
Wireless networks are very complex multidisciplinary systems; to describe these networks, we need to divide the details into several categories to create a logical organization for presentation of important material. This book is organized in five sections: one introduction chapter and four parts. The introductory material presented in Chapter 1 defines the meaning and sketches the path of evolution of the wireless networks. This chapter also provides an overview of the important wireless systems and outlines the details of the rest of the book. The material presented in Chapter 1 identifies different sectors of the wireless market, familiarizes the reader with the forces behind the growth of these sectors, and provides an overview of the standards developed to address them. The material presented in Chapter 1 should motivate the reader to study the details provided in the remainder of the book.
Each of the four parts of the book consists of several chapters directed toward the description of certain aspects of wireless networks. Parts One and Two are devoted to the principles of wireless network operations. These parts provide the technical background needed for understanding wireless networks. The technical aspects are either related to the design of the air-interface or issues related to deployment and operation of the infrastructure. Part One consists of three chapters describing technical aspects of the air-interface. Part Two has two chapters devoted to the technical aspects of the wireless network infrastructure. Parts Three and Four are devoted to describing the details of typical wireless networks in a comparative manner. Part Three consists of three chapters describing both voice- and data-oriented wireless WANs. Part Four consists of four chapters on local broadband and ad hoc wireless networks, including WLAN, WPAN, and indoor positioning.
1.3.1 Part One: Principles of Air-Interface Design
Wired terminals connect to power lines, and wired access to information networks is reliable, fixed, and relatively simple. Wireless mobile terminals are battery operated, and wireless access is through the air, unreliable, and band limited. The design of the physical connection and access method and understanding of the behavior of the medium for wireless operation is far more complicated than wired operation scenarios. The design of air-interface for wireless connections needs a far deeper understanding of the behavior of the channel and a more complex physical and medium access control mechanism. The behavior of the wireless medium is more complex than the wired medium because in wireless channels the received signal strength suffers from extensive power fluctuations caused by temporal and spatial movements. Wireless transmission and access techniques are more complex because they have to be power and bandwidth efficient, and they need to employ techniques to mitigate the fluctuations caused by the medium. Part One of the book is devoted to the analysis of the behavior of the channel in Chapter 2, an overview of the applied wireless transmission techniques in Chapter 3, and a description of the medium access control techniques used in voice- and data-oriented networks in Chapter 4.
Chapter 2 describes modeling of the path-loss, fluctuation of the channel, and the multipath arrivals of the signal. Path-loss models describe the relation between the average received power in a mobile station and its distance with the base station. These models are used in deployment of the networks to determine the coverage of a base station. The received power at the receiver is not fixed, and it changes in time as the mobile moves or the environment changes. Models for the variations of the channel are used to design the adaptive elements of the receiver, such as synchronization circuits or equalizers, to cope with the variation of the channel. Models for multipath characteristics allow the design of a receiver that can handle the interference of the signals arriving from different paths to the receiver.
The second chapter related to air-interface is Chapter 3, which describes transmission techniques that are used for the physical (PHY) layer of wireless networks. The diversity and complexity of transmission techniques in wireless systems are far more complex than those in wired networks. This chapter provides a comprehensive coverage of all transmission techniques that are employed in voice- oriented cellular and PCS systems, as well as data-oriented mobile data and WLAN and WPAN systems. The transmission techniques are divided into pulse transmission techniques used in infrared (IR) networks and UWB systems, traditional modulation techniques mostly used in digital cellular and mobile data networks, and spread spectrum technologies used in CDMA cellular, as well as WLANs and WPANs. More advanced techniques such as CCK used in 802.11b and OFDM used in 802.11a and HIPERLAN-2 are also described in this chapter.
The third chapter related to air-interface is Chapter 4, which is devoted to multiple access alternatives applied to wireless networks. This chapter starts with a description and comparison of the voice-oriented FDMA, TDMA, and CDMA access methods. The second part of this chapter is devoted to CSMA- and ALOHA-based random access techniques used in data-oriented wireless networks. The last part analyzes the applied access methods for integration of the voice and data that has evolved to operate in the voice- and data-oriented networks.
1.3.2 Part Two: Principles of Wireless Network Operation
In Part One of the book, technical issues related to design of the air-interface are presented. In Part Two we address technical aspects of fixed infrastructure of the wireless networks. This part consists of Chapters 5 and 6, addressing deployment and operation, respectively. Service providers often start with minimal infrastructure and antenna sites to keep the initial investment low. As the number of subscribers grows, service providers expand the wireless infrastructure to increase the capacity and improve the quality. The technology related to the deployment and expansion of the cellular infrastructure is discussed in Chapter 5, which is the first chapter related to technical aspects of the network infrastructure. This chapter discusses different topologies for wireless networks, describes cellular infrastructure deployment, and addresses issues related to the expansion of the size and migration to new technologies.
Chapter 6 is devoted to functionalities of the fixed network infrastructure to support the mobile operation. These functionalities include mobility management, radio resource and power management, and security management. These issues are addressed in three separate parts of Chapter 6. The mobility management part of Chapter 6 describes how a mobile terminal registers with the network at different locations and how the network tracks the mobile as it changes its access to the network from one antenna to another. The radio resource and power management part of Chapter 6 is devoted to the technologies used for controlling the transmitted power of the terminals. Voice-oriented networks control the transmitted power of the mobile station to minimize the interference with other terminals using the same frequency and to maximize the life of the battery. Data-oriented networks also use the sleep mode to avoid unnecessary consumption of power. Explanation of the methodologies and examples of how to implement power control and sleeping modes are provided in this part of Chapter 6. The last section of Chapter 6 is devoted to security in wireless networks. Wireless connections are inherently vulnerable to fraudulent connections and eavesdropping and need security features. The security of wireless networks is provided by authentication and ciphering. When a wireless terminal connects to a network, an authentication process between the network and the terminal checks the authenticity of the terminal. When the connection is established, the transmitted bits are scrambled with a ciphering mechanism to prevent eavesdropping. Algorithms used for these purposes are discussed in the last part of Chapter 6.
1.3.3 Part Three: Wireless Wide Area Networks
After completion of the overview of the standards in Chapter 1 and study of the technical aspects in Parts One and Two, we start detailed descriptions of specific wireless networks. These detailed descriptions are divided into two parts addressing WANs and LANs. The third part of the book is devoted to the description of important voice- and data-oriented wireless wide area networks. In Chapter 7 we describe GSM as an example for TDMA systems, and in Chapter 8 we describe IS-95 and IMT-2000 as examples of CDMA technology. The obvious reason for these selections is the current worldwide popularity of the GSM and emergence of the IMT-2000 and CDMA technologies as the choice of the emerging 3G systems. The last chapter in this part of the book is Chapter 9 which is devoted to mobile data networks.
Details of the architecture, mechanisms to support mobility, and layered protocols adopted by the GSM standard are described in Chapter 7. GSM is a complete standard that includes specification of the air-interface as well as fixed wired infrastructure to support the services. Other TDMA digital cellular standards, such as IS-136 or JDC, are very similar to GSM. Chapter 7 provides the most comprehensive coverage of a standard in this part of the book. First we describe all elements of the network architecture. Then we address mobility support mechanism with details of registration, call establishment, handoff, and security. The last part of this chapter provides details of how packets are formed and transmitted over the channel. The study of this chapter introduces the reader to the complexity and diversity of the issues involved in development of a wireless standard.
Chapter 8 is devoted to the CDMA and IMT-2000 technology that is the direction of the immediate future of 3G cellular systems. After a brief description of IS-41 and IS-634, which are the standards for communication between cellular switches and base stations in North America, details of the air-interface, IS-95, for cmdaONE that was developed by Qualcomm will be described. Then the 3G systems and how they differ from IS-95 are described. This chapter is completed with a summary of ITU's IMT-2000 standard. Because the wired backbone of the TDMA and CDMA systems are very similar, most of our attention is paid to the air-interface that is completely different from TDMA systems such as GSM. The details of GSM, IS-95, and IMT-2000 conclude our description of popular voice-oriented wide area systems.
The last topic in this part is the description of mobile data networks provided in Chapter 9. This is a comprehensive coverage of all mobile data services including short messaging and application programming for wireless data networks. Although a number of technologies have been examined for mobile data services, the market for this industry has not yet reached the market size of the popular cellular telephone industry. The delay in formation of the market has created a fragmented industry. To cover the details of this fragmented industry, we first provide an overview of all technologies and classify them into logical groups. Then we provide details of CDPD, a data-oriented network overlaid on AMPS infrastructure, and GPRS, which is embedded in the voice-oriented GSM system. In spite of small growth of the mobile data industry, recently short messaging systems (SMS) and application protocols for mobile data networks have attracted considerable market attention. As a result, we have devoted the last two sections of this chapter to SMS and application protocols, respectively.
1.3.4 Part Four: Local Broadband and Ad Hoc Networks
As we discussed earlier, 3G systems integrated cellular telephone, PCS, and mobile data services into one standard system operating in licensed bands. However, WLAN and WPAN have their own standards for broadband and ad hoc networking in unlicensed bands. At the time of this writing, most visionaries in wireless technology developments believe that the future is shaping with the merger of the broadband and ad hoc networking and 3G systems. In addition, there is a trend for integration of geolocation features into the next generation wireless networks. These networks support broadband wireless access to the backbone infrastructure, as well as ad hoc wireless networking. The last part of the book is devoted to these short-range local wireless networks. This part consists of five chapters, three of them devoted to WLAN, one to WPAN, and one to wireless geolocation principles.
The first of the three chapters on WLAN is Chapter 10 which provides an overview of the WLAN industry. This chapter analyzes the evolutionary path of the WLAN and explains how it started for office and manufacturing environments and is currently heading toward home area networking (HAN). Chapter 11, which describes details of the IEEE 802.11 standard for WLAN, follows the introduction to WLAN. Chapter 11 plays the same role as Chapter 7 on GSM was playing in Part Three; it provides details of the IEEE 802.11 to demonstrate all aspects of a data-oriented wireless standard operating in unlicensed bands. The medium access technology for the IEEE 802.11 is CSMA/CA which sets this standard as a connectionless, data-oriented standard. This feature eases the Internet access either by direct connection or connection through an existing wired LAN. The contents of this chapter describe the objective of the standard, explain specifications of the physical (PHY) and medium access control (MAC) layer alternatives supported by this standard, and provide the details of mobility support mechanisms such as registration, handoff, power management, and security. The next chapter, Chapter 12, is devoted to wireless ATM activities and the HIPERLAN standard. HIPERLAN-1 and IEEE 802.11 are considered data-oriented WLANs. Wireless ATM and HIPERLAN-2 are considering integration of voice and data from the point of view of the voice-oriented networks. The medium access for these standards is keen on supporting QoS for voice applications, which makes them suitable for integration into the existing prosperous cellular telephone networks. This chapter starts with an overview of the technical aspect of wireless ATM, then provides a short description of HIPERLAN-1, and at last describes the necessary details of HIPERLAN-2.
Chapter 13 describes WPANs with particular emphasis on details of Bluetooth technology. As discussed earlier, WPANs are ad hoc networks designed to connect personal equipment to one another. However, today's personal devices need to be connected to both voice- and data-oriented networks. The access method for these systems are designed to accommodate that need. Beyond that, WPANs are perceived to have lower power consumption which makes them compromise on the highest supportable data rate as compared with WLANs. This chapter starts by describing the IEEE 802.15 standards committee on WPAN and HomeRF activities under this standard. Then details of Bluetooth technology are described in some depth. The last part of this chapter analyzes the interference between IEEE 802.11 and Bluetooth, both operating in the 2.4 GHz ISM bands.
Chapter 14 is devoted to indoor geolocation and cellular positioning as emerging technologies to complement the local and wide local area wireless services. This chapter provides a generic architecture for the wireless geolocation services, describes alternative technologies for implementation of these systems, and gives examples of evolving location-based services. Location-based services provide a fertile environment for the emergence of E- and M-commerce applications.