Wireless Networks: Where We Are, Where We're Headed

This chapter is from the book

Principles of Wireless Networks: A Unified Approach

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This chapter is from the book

This chapter is from the book 

Principles of Wireless Networks: A Unified Approach

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1.1 Introduction

Technological innovations of engineers during the 20th century have brought a deep change in our lifestyle. Today, when we fly over a modern city at night we see the earth full of footprints made by engineers. The glowing lights remind us of the impact made by electrical engineers; the planes we fly in and the moving cars below remind us of the contributions of mechanical engineers; and high-rise buildings and complex roads remind us of what civil engineers have accomplished. From the eyes of an engineer, the glow of light, the movement of cars, and the complexity of civil infrastructure relates to the challenges in implementation, size of the market, and the impact of the technology on human life. There is, however, one industry whose infrastructure is not seen from the plane because it is mostly buried under the ground, but it is the most complex, it owns the largest market size, and it has enabled us to change our lifestyle by entering the information technology age. This industry is the telecommunications networking industry.

To have an intuitive understanding of the size of the telecommunications industry, it is good to know that the size of the budget of AT&T in the early 1980s, before its divestiture, was nearly the budget of the fifth largest economy of the world. AT&T was the largest telecommunications company in the world, and its core revenue at that time was generated from plain old telephone service (POTS) that was first introduced in 1867.

During the past two decades, the cellular telephone industry augmented the income of the prosperous voice-oriented POTS with the subscriber fees of about 1 billion cellular telephone users worldwide [EMC01]. Today the income of the wireless industry has already surpassed the income of the wired telephone industry, and this income is by far dominated by the revenue of cellular phones. In the mid 1990s, the data-oriented Internet brought the computer communications industry from the office to the home, which soon generated an income comparable to that of the voice-oriented POTS and wireless industry. Figure 1.1 illustrates the growth of the fixed (POTS), wireless, and Internet industries in recent years. At the time of this writing, the information exchange industry that includes the fixed and wireless telephone as well as Internet access industries has an annual revenue of a few trillion dollars and is by far the largest industry in the world. The wireless networking industry makes up a third of the revenue of the information industry, and its share of the overall market is growing. Today this income is dominated by revenue from cellular telephone applications. The future of this industry relies on broadband wireless Internet access that is expected to develop a large market for emerging multimedia applications.

Figure 1.1 Worldwide growth of the fixed, wireless, and Internet communication industries in the past decade.

The purpose of this book is to provide the reader with a text for understanding the principles of wireless networks, which include the cellular telephone and wireless broadband access technologies. Wireless networking is a multidisciplinary technology. To understand this industry, we need to learn aspects of a number of disciplines to develop an intuitive feeling of how these disciplines interact with one another. To achieve this goal, we provide an overview of the important wireless standards and products, describe and classify their underlying technologies in a logical manner, give detailed examples of successful standards and products, and provide a vision of evolving technologies. In this first chapter, we provide an overview of the wireless industry and its path of evolution. The following five chapters describe principles of technologies that are used in wireless networks. The next three chapters discuss the details of wireless wide area networks (WANs), and the last four chapters describe short-range broadband and ad hoc wireless networks.

In this chapter we first provide an overview of the evolution of the wireless information network industry. We describe the meaning of a wireless network, and we give a summary of the important standards. Then we discuss the technical aspects and general structure of a wireless network. Finally we give an outline of the chapters of the book and how they relate to one another.

1.1.1 Information Network Infrastructure

An information network infrastructure interconnects telecommunication devices to provide them with means for exchanging information. Telecommunication devices are terminals allowing users to run applications that communicate with other terminals through the information network infrastructure. The basic elements of an information network infrastructure are a number of switches or routers that are connected via point-to-point links. Switches include fixed and variable rate voice-oriented circuit switches and routers that are low speed and high speed data-oriented packet switches. The point-to-point links include a variety of fiber, coaxial cable, twisted pair wires, and wireless connections.

To support transmission of voice, data, and video, several wired information network infrastructures have evolved throughout the past century. Wireless networks allow a mobile telecommunications terminal to access these wired information network infrastructures. At first glance it may appear that a wireless network is only an antenna site connected to one of the switches in the wired information infrastructure which enables a mobile terminal to be connected to the backbone network. In reality, in addition to the antenna site, a wireless network may also need to add its own mobility-aware switches and base station control devices to be able to support mobility when a mobile terminal changes its connection point to the network. Therefore, a wireless network has a fixed infrastructure with mobility-aware switches and point-to-point connections, similar to other wired infrastructures, as well as antenna sites and mobile terminals.

In the same way a telephone service provider needs to add its own infrastructure to allow a mobile telephone to connect to the PSTN, a wireless data network provider needs its own infrastructure to support wireless Internet access.

The difference between Examples 1 and 2 is that the wireless network in Figure 1.2 is a connection-based, voice-oriented network, and the wireless network in Figure 1.3 is a connectionless data-oriented network. A voice-oriented network needs a dialing process, and after the dialing, a certain quality of service (QoS) is guaranteed to the user during the communication session. In data-oriented networks there is no dialing, and terminals are always connected to the network, but a definite QoS is not guaranteed.

1.1.2 Overview of Existing Network Infrastructure

Because the existence of the wireless networks heavily depends on the wired infrastructure that they connect to, in this section we provide an overview of the important types of wired infrastructure. More details on the evolution of these wired backbone infrastructures are provided in Appendix 1A. The most commonly used wired infrastructures for wireless networks are the PSTN, the Internet, and hybrid fiber coax (HFC), originally designed for voice, data, and cable TV distribution applications, respectively. Figure 1.4 provides an overall picture of these three networks and how they relate to other wired and wireless networks.

Figure 1.4 Backbone infrastructures: PSTN, Internet, and HFC.

The main sources of information transmitted through telecommunications devices are voice, data, and video. Voice and video are analog in nature, and data is digital. The dominant voice application is telephony, which is a bidirectional, symmetric, real-time conversation. To support telephony, telephone service providers have developed a network infrastructure that establishes a connection for a telephone call during the dialing process and disconnects it after completion of the conversation. As we saw in Example 1, this network is referred to as the PSTN. As shown in the top of Figure 1.4, the cellular telephone infrastructure provides a wireless access to the PSTN. Another network attached to the PSTN is the private branch exchange (PBX), which is a local telephone switch privately owned by companies. This private switch allows privacy and flexibility in providing additional services in an office environment. The PSTN physical connection to homes is a twisted-pair analog telephone wiring that is also used for broadband digital services. The core of the PSTN is a huge digital transmission system that allocates 64 kbps channels for each direction of a telephone conversation. Other network providers often lease the PSTN transmission facilities to interconnect their nodes.

The infrastructure developed for video applications is cable television, shown in the lower part of Figure 1.4. This network broadcasts wideband video signals to residential buildings. A cable goes from an end office to residential areas, and all users are provided service that is tapped from the same cable. The set-top boxes leased out by cable companies provide selectivity of channels depending on the charged rates. The end offices, where a group of distribution cables arrive, are connected to one another with fiber. For this reason, the cable TV network is also called hybrid fiber coax (HFC). More recently cable distribution has also been used for broadband home access to the Internet.

The data network infrastructure was developed for bursty applications and evolved into the Internet that supports Web access, email, file transfer, and telnet applications, as well as multimedia (voice, video, and data) sessions with a wide variety of session characteristics. The middle part of Figure 1.4 shows the Internet and its relation to other data networks. From the user's, point of view, the data-oriented networks are always connected, but they only use the transmission resources when a burst of information needs it. Sessions of popular data communications applications, such as Web browsing or file transfer protocol (FTP) are often asymmetric, and a short burst of upstream requests results in a downstream transmission of a large amount of data. Symmetric sessions such as Internet Protocol (IP) telephony over data networks are also becoming popular, providing an alternative to traditional telephony. The Internet access to home is a logical access that is physically implemented on other media such as cable TV wiring or telephone wiring. The distribution of the Internet in office areas is usually through local area networks (LANs). Wireless LANs (WLANs) in the offices are usually connected to the Internet through the LANs. These days all other private data networks, such as those used in the banks or airline reservation industries, are also connected to the Internet. As we saw in Example 2, the Internet is also the backbone for wireless data services.

1.1.3 Four Market Sectors for Wireless Applications

The market for wireless networks has evolved in four different segments that can be logically divided into two classes: voice-oriented market and data-oriented market. The voice-oriented market has evolved around wireless connections to the PSTN. These services further evolved into local and wide area markets. The local voice-oriented market is based on low-power, low-mobility devices with higher quality of voice, including cordless telephone, personal communication services (PCS), wireless PBX, and wireless telepoint. The wide area voice-oriented market evolved around cellular mobile telephone services that are using terminals with a higher power consumption, comprehensive coverage, and lower quality of voice. Figure 1.5(a) compares several features of these two sectors of the voice-oriented market. The wireless data-oriented market evolved around the Internet and computer communication network infrastructure. The data-oriented services are divided into broadband local and ad hoc and wide area mobile data markets. The wide area wireless data market provides for Internet access for mobile users. Local broadband and ad hoc networks include WLANs and wireless personal area networks (WPANs) which provide for high-speed Internet access, as well as evolving ad hoc wireless consumer products. Figure 1.5(b) illustrates several differences among the local- and wide-area wireless data networks.

Figure 1.5 Wireless market sectors: (a) voice-oriented networks and (b) data-oriented networks.

1.1.4 Evolution of Voice-Oriented Wireless Networks

Table 1.1 shows a brief chronology of the evolution of voice-oriented wireless networks. The technology for frequency division multiple access (FDMA) analog cellular systems was developed at AT&T Bell Laboratories in the early 1970s. However, the first deployment of these systems took place in the Nordic countries as the Nordic Mobile Telephony (NMT) about a year earlier than the deployment of the Advanced Mobile Phone System (AMPS) in the United States. Because the United States is a large country, the frequency administration process was slower and it took a longer time for the deployment. The digital cellular networks started in Nordic countries with the formation of the Groupe Special Mobile standardization group that became the Global System for Mobile Communications (GSM). The GSM standard group was originally formed to address the international roaming, a serious problem for cellular operation in the European Union (EU) countries. The standardization group shortly decided to go for a new digital time division multiple access (TDMA) technology because it could allow integration of other services to expand the horizon of wireless applications [HAU94]. In the United States, however, the reason for migration to digital cellular was that the capacity of the analog systems in major metropolitan areas such as New York City and Los Angeles had reached its peak value, and there was a need for increasing it in the existing allocated bands. Although Nordic countries, led by Finland, have always maintained the highest rate of cellular telephone penetration, in the early days of this industry the United States was by far the largest market. By 1994, there were 41 million subscribers worldwide, 25 million of them in the United States. The need for higher capacity motivated the study of code division multiple access (CDMA) that was originally perceived to provide capacity that was orders of magnitude higher than other alternatives, such as analog band splitting or digital TDMA.

Table 1.1 History of Voice-Oriented Wireless Networks

While the debate between TDMA and CDMA was in progress in the United States, deployment of GSM technology started in the EC in the early 1990s. At the same time, developing countries started their planning for cellular telephone networks, and most of them adopted the GSM digital cellular technology over the legacy analog cellular. Soon after, GSM had penetrated into more than 100 different countries. An interesting phenomenon in the evolution of the cellular telephone industry was the unexpected rapid expansion of this industry in developing countries. In these countries the growth of the infrastructure for wired POTS was slower than the growing demand for new subscriptions, and there was always a long waiting time to acquire a telephone line. As a result, in most of these countries telephone subscriptions were sold on the black market at a price several times the actual value. Penetration of cellular telephones in these countries was much easier because people were already prepared for a higher price for telephone subscriptions, and the expansion of cellular networks occurred much faster than POTS.

In the beginning of the race between TDMA and CDMA, CDMA technology was deployed in only a few countries. Besides, experimentation had shown that the capacity improvement factor of CDMA was smaller than expected. In the mid 1990s when the first deployment of CDMA technology started in the United States, most companies were subsidizing the cost to stay in race with TDMA and analog alternatives. However, from day one, the quality of voice using CDMA was superior to that of TDMA systems installed in the United States. As a result, CDMA service providers under banners like "you cannot believe your ears" started marketing this technology in the United States, which soon became very popular with the users. Meanwhile, with the huge success of digital cellular all manufacturers worldwide started working on the next generation IMT-2000 wireless networks. Most of these manufacturers adopted wideband CDMA (W-CDMA) as the technology of choice for the IMT-2000, assuming that W-CDMA eases integration of services, provides better quality of voice, and supports higher capacity.

The local voice-oriented wireless applications started with the introduction of the cordless telephone, which appeared in the market in the late 1970s. A cordless telephone provides a wireless connection to replace the wire between the handset and the telephone set. The technology for implementation of a cordless telephone is similar to the technology used in walkie-talkies which had existed since the Second World War. The important feature of the cordless telephone was that as soon as it was introduced to the market it became a major commercial success, selling tens of millions of units and generating an income exceeding several billion dollars. The success of the cordless telephone encouraged further developments in this field. The first digital cordless telephone was CT-2, a standard developed in the United Kingdom in the early 1980s. The next generation of cordless telephones was the wireless PBX using the digital European cordless telephone (DECT) standard. Both CT-2 and DECT had minimal network infrastructures to go beyond the simple cordless telephone and cover a larger area and multiple applications. However, in spite of the huge success of the cordless telephone, neither CT-2 nor DECT has yet been considered a very commercially successful system. These local systems soon evolved into PCS, which was a complete system with its own infrastructure, very similar to the cellular mobile telephone.

In the technical communities of the early 1990s, PCS systems were differentiated from the cellular systems as presented in Figure 1.5(b). A PCS service was considered the next generation cordless telephone designed for residential areas, providing a variety of services beyond the cordless telephone. The first real deployment of PCS systems was the personal handy phone (PHP), later renamed as personal handy system (PHS), introduced in Japan in 1993. At that time, the technical differences between PCS services and cellular systems were perceived to be smaller cell size, better quality of speech, lower tariff, lesser power consumption, and lower mobility. However, from the user's point of view the terminals and services for PCS and cellular looked very similar; the only significant differences were marketing strategy and the way that they were introduced to the market. For instance, around the same time in the United Kingdom DCS-1800 services were introduced as PCS services. The DCS-1800 was using GSM technology at a higher frequency of 1,800 MHz, but it employed a different marketing strategy. The last PCS standard was the personal access communications system (PACS) in the United States, finalized in 1995. All together, none of the PCS standards became a major commercial success or a competitor with cellular services.

In 1995, the Federal Communications Commission (FCC) in the United States auctioned the frequency bands around 2 GHz as the PCS bands, but PCS-specific standards were not adopted for these frequencies. Eventually the name PCS started to appear only as a marketing pitch by some service providers for digital cellular services, in some cases not even operating at PCS bands. Although the more advanced and complex PCS services evolving from simple cordless telephone application did not succeed and were merged into the cellular telephone industry, the simple cordless telephone industry itself still remains active. In more recent years, the frequency of operation of cordless telephone products has shifted into unlicensed industrial, scientific, and medical (ISM) bands rather than the licensed PCS bands. Cordless telephones in the ISM bands can provide a more reliable link using spread spectrum technology.

1.1.5 Evolution of Data-Oriented Wireless Networks

Table 1.2 provides the chronology of data-oriented wireless networks. As shown in Figure 1.5(b), data-oriented wireless networks are divided into the wide area wireless data and local broadband and ad hoc networks. Wireless local networks support higher data rates and ad hoc operation for a lower number of users. The broadband wireless local networks are usually referred to as WLANs and the ad hoc local networks as WPANs. The concept of WLANs was first introduced around 1980. However, the first WLAN products were completed about 10 years later. Today a key feature of the local broadband and ad hoc networks is operation in the unlicensed bands. The first unlicensed bands were the ISM bands released in the United States in 1985. Later in 1994 and then in 1997, unlicensed PCS and U-NII (Unlicensed National Information Infrastructure) bands were also released in the United States. The major WLAN standard is the IEEE 802.11 started in the late 1980s and completed in 1997. The IEEE 802.11 and 802.11b operate in the ISM bands and the IEEE 802.11a in the U-NII bands. The competing European standard for WLANs is the HIgh PErformance Radio LAN (HIPERLAN). The HIPERLAN-1 was completed in 1997, and the HIPERLAN-2 is currently under development. In 1996, the wireless ATM working group of the ATM (Asynchronous Transfer Mode) Forum was formed to merge ATM technology with wideband local access. More recently, after the announcement of Bluetooth technology in 1998, WPANs have attracted tremendous attention. The coverage of WPANs is smaller than traditional WLANs, and they are intended for ad hoc environments to interconnect such personal equipment as the laptop, cell phone, and headset together. At the time of this writing, the IEEE 802.11 products generated around half a billion dollars per year. In the past couple of years, huge investments have been poured into WLAN and WPAN chip set developments all over the world. These investments expect sizable incomes from the possible incorporation of WLANs into the prosperous cellular industry and a large WPAN market for consumer products and home networking. A more complete history of WLANs and WPANs is provided in Chapter 10.

Table 1.2 History of Data-Oriented Wireless Networks

Mobile data services were first introduced with the ARDIS (now called DATATAC) project between Motorola and IBM in 1983. The purpose of this network was to allow IBM field crew to operate their portable computers wherever they want to deliver their services. In 1986, Ericsson introduced Mobitex technology, which was an open architecture implementation of the ARDIS. In 1993, IBM and nine operating companies in the United States started the CDPD (cellular digital packet data) project, expecting a huge market by the year 2000. In the late 1990s the GPRS (general packet radio service) data services that are integrated in the successful GSM systems and can support an order of magnitude higher data rates than previous technologies attracted considerable attention. These higher data rates are perceived to be essential for wireless Internet access, the most popular wireless data application. The third generation (3G) cellular systems are planning to provide up to 2 Mbps mobile data service that is substantially higher than the GPRS data rates. These data rates, however, would not have the comprehensive coverage of GPRS. The early mobile data networks, ARDIS and Mobitex, were independent networks owning their infrastructure. As time passed, CDPD overlaid its infrastructure over the AMPS systems, and GPRS was actually integrated within the GSM infrastructure. This gradual assimilation of the mobile data industry into the cellular telephone industry will be completed in the next-generation cellular systems.

With the integration of PCS and mobile data industries in the next-generation cellular systems we see the emergence of two industries: the next-generation traditional cellular systems operating in licensed bands and the local broadband and ad hoc networks operating in unlicensed bands.