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Fully up-to-date coverage of the inner-workings of 3G
This revised and updated edition of 3G Wireless Networks covers the changes taking place within the arena of 3G—the wireless technology that enables voice, full-featured video, CD-quality sound, and Web browsing anywhere in the world. The book covers key standards and protocols and the critical issues of compatibility, internetworking, and voice/data convergence. You will learn how to successfully design and integrate WCDMA/UMTS, CDMA2000, and SCDMA into existing cellular/PCS networks.
The growth in the number of mobile subscribers is expected to continue for some years, with the number of mobile subscribers surpassing the number of fixed network subscribers at some point in the near future. Although it may appear that such predictions are optimistic, it is worth pointing out that in the past, most predictions for the penetration of mobile communications have been far lower than what actually occurred. In fact, in several countries, the number of mobile subscribers already exceeds the number of fixed subscribers, which suggests that predictions of strong growth are well founded. It is clear that the future is bright for mobile communications. For the next few years at least, that future means third-generation systems, the subject of this book.
Before delving into the details of third-generation systems, however, it is appropriate to review mobile communications in general, as well as first- and second-generation systems. Like most technologies, advances in wireless communications occur mainly through a process of steady evolution (although there is the occasional quantum-leap forward). Therefore, a good understanding of third-generation systems requires an understanding of what has come before. In order to place everything in the correct perspective, the following sections of this chapter provide a history and a brief overview of mobile communications in general. Chapter 2, "First Generation (1G)," and Chapter 3, "Second Generation (2G)," provide some technical detail on first- and second-generation systems, with the remaining chapters of the book dedicated to the technologies involved in third-generation systems.
Further progress was made in the 1930s with the development of frequency modulation (FM), which helped in battlefield communications during the Second World War. These developments were carried over to peacetime, and limited mobile telephony service became available in the 1940s in some large cities. Such systems were of limited capacity, however, and it took many years for mobile telephone to become a viable commercial product.
Meanwhile, however, other countries were making progress, and a commercial AMPS system was launched in Japan in 1979. The Europeans also were active in mobile communications technology, and the first European system was launched in 1981 in Sweden, Norway, Denmark, and Finland. The European system used a technology known as Nordic Mobile Telephony (NMT), operating in the 450-MHz band. Later, a version of NMT was developed to operate in the 900-MHz band and was known (not surprisingly) as NMT900. Not to be left out, the British introduced yet another technology in 1985. This technology is known as the Total Access Communications System (TACS) and operates in the 900-MHz band. TACS is basically a modi-fied version of AMPS.
Many other countries followed along, and soon mobile communications services spread across the globe. Although several other technologies were developed, particularly in Europe, AMPS, NMT (both variants), and TACS were certainly the most successful technologies. These are the main first-generation systems and they are still in service today.
First-generation systems experienced success far greater than anyone had expected. In fact, this success exposed one of the weaknesses in the technologies—limited capacity. Of course, the systems were able to handle large numbers of subscribers, but when the subscribers started to number in the millions, cracks started to appear, particularly since subscribers tend to be densely clustered in metropolitan areas. Limited capacity was not the only problem, however, and other problems such as fraud became a major concern. Consequently, significant effort was dedicated to the development of second-generation systems.
Like first-generation systems, various types of second-generation technology have been developed. The three most successful variants of second-generation technology are Interim Standard 136 (IS-136) TDMA, IS-95 CDMA, and the Global System for Mobile communications (GSM). Each of these came about in very different ways.
The first step in digitizing this system was the introduction of digital voice channels. This step involved the application of time division multiplexing (TDM) to the voice channels such that each voice channel was divided into time slots, enabling up to three simultaneous conversations on the same RF channel. This stage in the evolution was known as IS-54 B (also known as Digital AMPS or D-AMPS) and it obviously gives a significant capacity boost compared to analog AMPS. IS-54 B was introduced in 1990.
Note that IS-54 B involves digital voice channels only, and still uses analog control channels. Thus, although it may offer increased capacity and some other advantages, the fact that the control channel is analog does limit the number of services that can be offered. For that reason, among others, the next obvious step was to make the control channels also digital. That step took place in 1994 with the development of IS-136, a system that includes digital control channels and digital voice channels.
Today AMPS, IS-54B, and IS-136 are all in service. AMPS and IS-54 operate only in the 800-MHz band, whereas IS-136 can be found both in the 800-MHz band and in the 1900-MHz band, at least in North America. The 1900-MHz band in North America is allocated to Personal Communications Service (PCS), which can be described as a family of second-generation mobile communications services.
The first GSM network was launched in 1991, with several more launched in 1992. International roaming between the various networks quickly followed. GSM was hugely successful and soon, most countries in Europe had launched GSM service. Furthermore, GSM began to spread outside Europe to countries as far away as Australia. It was clear that GSM was going to be more than just a European system; it was going to be global. Consequently, the letters GSM have taken on a new meaning—Global System for Mobile communications.
Initially, GSM was specified to operate only in the 900-MHz band, and most of the GSM networks in service use this band. There are, however, other frequency bands used by GSM technology. The first implementation of GSM at a different frequency happened in the United Kingdom in 1993. That service was initially known as DCS1800 since it operates in the 1800- MHz band. These days, however, it is known as GSM1800. After all, it really is just GSM operating at 1800 MHz.
Subsequently, GSM was introduced to North America as one of the technologies to be used for PCS—that is, at 1900 MHz. In fact, the very first PCS network to be launched in North America used GSM technology.
CDMA is a technique whereby all users share the same frequency at the same time. Obviously, since all users share the same frequency simultaneously, they all interfere with each other. The challenge is to pick out the sig-nal of one user from all of the other signals on the same frequency. This can be done if the signal from each user is modulated with a unique code sequence, where the code bit rate is far higher than the bit rate of the information being sent. At the receiving end, knowledge of the code sequence being used for a given signal allows the signal to be extracted.
Although CDMA had been considered for commercial mobile communications services by several bodies, it was never considered a viable technology until 1989 when a CDMA system was demonstrated by Qualcomm in San Diego, California. At the time, great claims were made about the potential capacity improvement compared to AMPS, as well as the potential improved voice quality and simplified system planning. Many people were impressed with these claims and the Qualcomm CDMA system was standardized as IS-95 in 1993 by the U.S. Telecommunications Industry Association (TIA). Since then, many IS-95 CDMA systems have been deployed, particularly in North America and Korea. Although some of the initial claims regarding capacity improvements were perhaps a little overstated, IS-95 CDMA is certainly a significant improvement over AMPS and has had significant success. In North America, IS-95 CDMA has been deployed in the 800-MHz band and a variation known as J-STD-008 has been deployed in the 1900-MHz band....