Data service is expected to rise sharply as a traffic stream on wireless networks. However, the allotted wireless spectrum and the compression techniques we have traditionally relied on will not allow us to make use of the existing wireless infrastructure as if it were a wireless Internet, let alone a platform for the delivery of multimedia content and TV programming. Visual traffic will play a very demanding role in the future of telecommunications networks, and the problems that traffic poses are magnified many times over with wireless media.
The future demands a new generation of infrastructure, and 3G is one step toward the broadband wireless realm. When you think about 3G, it is important to keep a number of things in mind. First, 3G is still under development. Although large-scale implementations were anticipated to occur beginning in 2001, 3G did not begin to flourish until several years after that. Aside from the fact that it requires licensing of new spectrum, as well as an entirely new infrastructure, 3G has been plagued by problems, including lack of 3G handsets, lack of interoperability between 2G and 3G networks, high costs for both operators and subscribers, and lower-than-promised performance. However, as of early 2006, there were around 245 million 3G subscribers worldwide, most of whom were serviced by CDMA2000 networks, with only a very small proportion subscribing to W-CDMA/UMTS.
Although we are not yet able to experience all the mobile broadband multimedia services and maximum data rates promised by 3G, we are seeing more deployments of 3G networks, and enhanced 3G service, referred to as 3.5G, is beginning to make an appearance. While we argue the lifetime of 3G, new generations, such as 4G and 5G, are already in development. At any point in time, new technologies are being developed and operating in labs that will emerge commercially within five to seven years. Between the time of the vision and the time of the implementation, enough changes will have occurred to render the solution somewhat outdated, yet the formalization of the new and improved version will still be too far off to be viable. (The visions of 4G and 5G are discussed later in this chapter.)
3G is designed for high-speed multimedia data and voice (see Figure 14.6). Its goals include high-quality audio and video and advanced global roaming, which means being able to go anywhere and automatically be handed off to any wireless system available. 3G is defined by the ITU under the International Mobile Telecommunications 2000 (IMT-2000) global framework. The main goals of IMT-2000 include achieving equivalency between wireline and wireless, support for messaging, Internet access, high-speed multimedia, improved throughput, QoS support, improved security, improved voice quality, and improved battery life. The IMT-2000 framework encompasses support for fixed applications and a broad range of mobility scenarios, from picocells serving in-building and local users to global coverage via satellites. It calls for global deployment with seamless roaming, support for position-location services (including emergencies, navigation, and location-specific services), and support for technological evolution.
Figure 14.6. 3G network coverage
IMT-2000 was formerly known as the Future Public Land Mobile Telecommunications System (FPLMTS). In 1992, the World Administrative Radio Conference (WARC) allocated 1,885MHz to 2,025MHz and 2,110MHz to 2,200MHz for IMT-2000, including 1,980MHz to 2,010MHz and 2,170MHz to 2,200MHz for satellite. In 2000, WARC allocated additional spectrum in three frequency bands: below 1GHz, at 1.7GHz (where many 2G systems currently operate), and in the 2.5GHz range. WARC is now referred to as World Radiocommunications Conference, and information on the next conference is available at www.itu.int.
Terrestrial IMT-2000 services operate in the FDD mode in the bands 1,920MHz to 1,980MHz and 2,110MHz to 2,170MHz, with mobile stations transmitting in the lower subband and base stations transmitting in the upper subband. The bands 1,885MHz to 1,920MHz and 2,010MHz to 2,025MHz are unpaired for TDD operation. The GSMA feels that several additional frequency bands should be nonexclusively designated for the use of IMT-2000 to provide for up to an additional 160MHz of spectrum. These bands include 698MHz to 806MHz, 2,500MHz to 2,690MHz, and 2,700MHz to 2,900MHz.
3G also includes a satellite component, known as Mobile Satellite Service (MSS), which is the only IMT-2000 system that can be used worldwide. Intended to take over when a user is out of range of terrestrial base stations, MSS requires the participation and cooperation of companies and governments worldwide. The target data rate for MSS is 100Kbps, compared to 2Mbps for terrestrial systems. MSS operators hope to offer services similar to those of terrestrial 2.5G and 3G networks, including data at ISDN speeds, toll-quality voice, video, and multimedia messaging.
3G applications include traditional voice services, involving high-quality voice transmission, global roaming, 144Kbps to 2Mbps for packet and circuit data, always-on data availability, high-speed mobile Internet access, and high-capacity e-mail. More importantly, 3G involves support for a wide variety of broadband applications, such as videoconferencing, navigation/mapping systems, streaming video and TV, common billing/user profiles, multimedia messaging, mobile voice and video over IP, calling line image, mobile entertainment, m-commerce payment solutions, and location-based services.
The ITU started the process of defining the standard for 3G systems with IMT-2000. The European Telecommunications Standards Institute (ETSI; www.etsi.org) was responsible for the UMTS standardization process in Europe. The 3G Partnership Project (3GPP; www.3GPP.org) was formed in 1998, under the ETSI, to make a globally applicable 3G mobile phone system specification within the scope of the ITU's IMT-2000 project. 3GPP organizational members include ARIB (Japan), ATIS (United States), CCSA (China), ETSI (Europe), TTA (Korea), and TTC (Japan). 3GPP specifications are based on evolved GSM specificationswhat is today commonly known as the UMTS system. 3GPP has five main UMTS standardization areas: radio access network, core network, terminals, services and system aspects, and GERAN. 3GPP standards are structured as releases, and discussions of 3GPP often refer to the functionality of the various releases. Current 3GPP releases include the following:
The 3G Partnership Project 2 (3GPP2; www.3GPP2.org) was formed when ETSI refused to expand the scope of 3GPP to address CDMA2000. The American National Standards Institute (ANSI; www.ansi.org) then formed 3GPP2 to coordinate CDMA2000 developments. The 3GPP2 organizational members include ARIB (Japan), CCSA (China), TIA (United States), TTA (Korea), and TTC (Japan). More than 80 individual member companies are participating in 3GPP2. The work of producing 3GPP2's specifications resides in the project's four technical specification groups (TSGs), comprising representatives from the project's individual member companies. The TSGs include TSG-A, which covers access network interfaces; TSG-C, which covers CDMA2000 standards; TSG-S, which covers services and systems aspects; and TSG-X, which deals with core networks.
Despite the global efforts to define one standard for 3G, there remain different approaches. The IMT-2000 standard evolved with five possible radio interfaces based on three different access technologies: FDMA, TDMA, and CDMA. However, the majority of deployed 3G systems consist of the two main technologies: W-CDMA (known as UMTS in Europe) and CDMA2000. There are other important 3G variants, including Time Division Synchronous Code Division Multiple Access (TD-SCDMA), which is used primarily in China, and NTT DoCoMo's Freedom of Mobile Multimedia Access (FOMA), which is used in Japan. FOMA is based on W-CDMA and is compliant with IMT-2000. As shown in Table 14.1 and discussed in the following sections, there is a single W-CDMA standard with three modes.
Interface ITU Designation
W-CDMA (UMTS, UTRA, FDD), IMT DS
Single 5MHz channel
CDMA2000 (1X and 3X RTT), IMT MC
TD-SCDMA and UMTS TDD, IMT TC
DSSS (UMTS TDD), time code, TDD
1.6MHz or 5MHz channels
Universal Mobile Telecommunications System (UMTS), the European implementation of the 3G wireless phone system, uses W-CDMA. Its development was driven by the need for a ubiquitous, very-high-speed, low-latency, packet-based platform to provide broadband and other packet services to users at home, at work, or on the road. UMTS defines both narrowband (2Mbps in the 2GHz band) and broadband (100Mbps and faster in the 60GHz band) services. Personal mobility is a major objective of UMTS. The UMTS Forum (www.umts-forum.org) estimates that over 60% of revenues from the UMTS networks will be derived from data communications in the long term. New approaches to content aggregation and delivery will be needed to drive the uptake of UMTS services, introducing new players, including content providers, ISPs, and virtual mobile network operators.
GSM-based operators in the United States and elsewhere favor a standard based on the UMTS Universal Terrestrial Radio Access (UTRA) standard, which is more typically referred to as W-CDMA. W-CDMA has two proposed implementations: UMTS, which is based on FDD, and UMTS TDD/TD-CDMA, which is based on TDD. UMTS/W-CDMA operates in the frequency bands 1,920MHz to 1,980MHz and 2,110MHz to 2,170MHz, using FDD transmission. The minimum frequency band required is two 5MHz channels. The frequency reuse is N = 1, which means that all the frequencies can be reused in each cell, including adjacent cells. UMTS/W-CDMA uses the modulation scheme QPSK and supports both circuit- and packet-based services. The maximum user data rate it supports is 1,920Kbps, but real-world experience at the moment is actually 384Kbps. The 3.5G enhancement known as HSDPA (discussed later in this chapter) will offer data speeds up to 10Mbps, and with the addition of MIMO systems, 20Mbps may be possible.
At the end of 2005, 146 W-CDMA licenses had been awarded in 48 countries, and there were 100 commercial W-CDMA networks operating in 42 countries, plus 4 more W-CDMA operators in precommercial stages (see the Global Mobile Suppliers Association, at www.gsacom.com). Also at the end of 2005, the total number of W-CDMA subscribers was over 40 million, and some 2 million new subscribers were being added monthly. In addition, there were 272 W-CDMA device models available on the market from 37 device suppliers, with 14 models supporting HSDPA.
3.5G Standards: The 3G Evolution
The 3G evolution describes the seamless, compatible evolutionary path of enhancements to the existing GSM technology family. These enhancements will enable GSM operators to improve their ability to provide mobile broadband multimedia services by supporting higher data transfer speeds and greater system capacity. Because this is an evolutionary path, the generic benefits associated with the GSM family are maintained, including global roaming, seamless billing, network compatibility, and huge economies of scale.
The 3G evolutionary path consists of a series of well-defined technology enhancements, including High-Speed Downlink Packet Access (HSDPA), High-Speed Uplink Packet Access (HSUPA), and High-Speed OFDM Packet Access (HSOPA). The first of these to be realized, HSDPA, provides performance improvement in the downlink channel. The following sections describe each of these standards.
HSDPA is part of the 3GPP/UTRAN (UMTS Terrestrial Radio Access Network) FDD Release 5 W-CDMA specifications. In 3GPP standards, HSDPA evolved from and is backward compatible with Release 99 W-CDMA systems. Release 4 specifications provide efficient IP support, enabling provision of services through an all-IP core network. Release 5 specifications focus on HSDPA to provide data rates from 8Mbps to 14Mbps (and 20Mbps for MIMO systems) over a 5MHz bandwidth in W-CDMA downlink to support packet-based multimedia services. HSDPA makes use of QPSK for noisy channels and 16-QAM modulation for clearer channels. As discussed in Chapter 5, "Data Communications Basics," QPSK is more robust and can tolerate higher levels of interference than 16-QAM but has a lower transmission bit rate. 16-QAM, on the other hand, offers twice the bit rate but is more prone to errors than QPSK due to interference and noise, and hence it requires stronger forward error correction (FEC).
Similar to the way EDGE enhances GSM/GPRS, HSDPA enhances W-CDMA. HSDPA doubles the air interface capacity and delivers a four- or five-fold increase in downlink data speeds. It also shortens the round-trip time between network and terminals and reduces variance in downlink transmission delay. The combination of faster data rates and increased spectral efficiency should result in lower cost per data bit transmitted. The theoretical peak rate is 14.4Mbps, but the realistic end-user experience is initially likely to be 1.8Mbps or possibly up to 3.6Mbps. The high download speeds offered by HSDPA will greatly enhance a wide range of mobile services, from Web browsing to video downloads.
HSDPA is a packet-based data service in the W-CDMA downlink channel. It was designed from the beginning to support IP and packet-based multimedia services. HSDPA offers many service-enhancing features, including Adaptive Modulation and Coding (AMC), which is a modulation technique that can be determined dynamically, depending on the conditions of the wireless channel at the time. Another key feature of HSDPA is the use of MIMO, which results in great improvements in capacity. (MIMO is discussed in Chapter 13.) MIMO antenna systems are the work item in the 3GPP Release 6 specifications, which support even higher data transmission rates (up to 20Mbps).
Another important enhancement to HSDPA is that error control is greatly improved through the use of hybrid automatic repeat request (HARQ). HARQ is a variation of the ARQ error control method that gives better performance than ordinary ARQ, particularly over wireless channels, albeit at the cost of increased implementation complexity. ARQ is an error control method for data transmission in which the receiver detects transmission errors in a message and automatically requests a retransmission from the transmitter. Generally, when the transmitter receives the ARQ, the transmitter retransmits the message until either it is correctly received or the error persists beyond a predetermined number of retransmissions. The simplest version of HARQ combines FEC (which is discussed in Chapter 13) and ARQ by encoding the data block plus error detection information with an error correction code prior to transmission. When the coded data block is received, the receiver first decodes the error correction code. If the channel quality is good enough, all transmission errors should be correctable, and the receiver can obtain the correct data block. If the channel quality is bad and not all transmission errors can be corrected, the receiver will detect this situation, using the error correction code, and then the received coded data block is discarded and a retransmission is requested by the receiver. Other features of HARQ include fast cell search and advanced receiver design.
As Figure 14.7 illustrates, because HSDPA is built on a distributed architecture and implements key processing at the base station, closer to the air interface, HSDPA achieves low delay link adaptation. By taking advantage of techniques including a fast Layer 1 retransmission scheme (HARQ) and link adaptation, HSDPA delivers significantly improved packet data throughput performance.
Figure 14.7. HSDPA
All operators are expected to evolve to HSDPA as the new baseline for mobile wireless broadband. HSDPA is widely embraced by the vendor community, and the majority of existing W-CDMA operators are expected to upgrade their 3GSM networks to support HSDPA technology. Many operators have confirmed interest in and are considering, planning, deploying, or trialing HSDPA.
HSDPA is expected to provide a user applications experience between 3 and 10 times faster than with traditional UMTS. HSDPA is often compared to WiMax (which is discussed in Chapter 15). Early HSDPA will focus on data, voice, and mobility from the handset perspective. WiMax will focus on broadband data, initially to underserved areas because of its distance capability. An advantage of HSDPA is that, unlike WiMax, it requires no new infrastructure, just the downloading of new software to the handset, using the existing cellular infrastructure.
HSUPA is the sibling of HSDPA but has taken longer to reach consensus. Enhancements to the uplink data speed are being standardized in the 3GPP Release 6 specification. HSUPA is expected to use an uplink Enhanced Dedicated Channel (E-DCH) on which it will employ link adaptation methods similar to those employed by HSDPA: shorter transmission time interval (TTI), enabling faster link adaptation, and HARQ with incremental redundancy, making retransmission more effective. TTI is a parameter in many digital telecom networks related to encapsulation of data from higher layers into frames for transmission on the radio link layer. Link adaptation, a term used in wireless communications, describes the adaptation of various parameters, such as modulation, coding, signal, and protocol, to radio link conditions. The key is that the link adaptation process is dynamic and the parameters change as the radio link conditions change. In HSDPA, for example, this can take place every 2 milliseconds.
The HSUPA standard enables users to transmit data upstream at a speed of 5.8Mbps. As this standard appears commercially, mobile users will be able to exchange and access data and multimedia much more efficiently and enjoyably. HSUPA technology is expected to be introduced in 2007. Some consider HSUPA to be a 3.75G technology.
Jointly, downlink and uplink enhancements are referred to as High-Speed Packet Access (HSPA) services. Increased downlink and uplink speeds will further enhance user experiences and increase the use of applications and activities, especially where data is shared between users (e.g., with interactive multiplayer games).
HSDPA is just beginning to be deployed, and HSUPA isn't here yet, but vendors are already contemplating the next step beyond those technologies, HSOPA. Because it incorporates OFDM and MIMO, HSOPA promises to offer a 40Mbps download speed. Besides faster speeds, HSOPA is expected to dramatically reduce costs because OFDM allows more capacity with a given amount of spectrum. If HSOPA moves forward in the standards procedure, it is expected to make its commercial debut in late 2007 or early 2008.
TDD is specifically intended for high-data-rate services. Unlike W-CDMA, which uses FDD, UMTS TDD uses TDD and is designed to work in a single, unpaired frequency band. TDD uses a combined TDD and CDMA scheme. It was first defined by 3GPP in Release 99, and it has continued to evolve in the later releases.
UMTS TDD operates in the unpaired frequency bands 1,900MHz to 1,920MHz and 2,010MHz to 2,025MHz, using TDD transmission. To provide flexibility to service providers, UMTS TDD has also been rebanded to allow operation in other licensed spectrum bands, even up to 3.6GHz. UMTS TDD makes use of Direct Sequence Spread Spectrum (DSSS) and the QPSK modulation technique. It operates on a single 5MHz or 10MHz channel, and 20MHz channels are planned as well. The frequency reuse is N = 1, meaning the frequencies can be reused in all the cells. Peak download speeds of up to 12Mbps are promised.
One of the largest benefits of using TDD is that it supports variable asymmetry. This means than an operator can decide how much capacity is allocated to the downlink versus the uplink. Because data traffic patterns generally favor the downlink, the result is much better use of spectrum and higher efficiency. Another feature promoted by UMTS TDD proponents is mobility support, with claims that UMTS TDD allows subscribers to stay connected while traveling in excess of 75 mph (120 kph), as long as they remain within the network footprint. It also supports tower-to-tower handoff and network-to-network roaming. Finally, TD-CDMA devices consume significantly less power than other devices, resulting in improved talk times and standby times.
For more information, see the UMTS TDD Alliance Web site (www.umtstdd.org).
TD-SCDMA was proposed by the China Communications Standards Association (CCSA; www.cwts.org/english/index.php) and approved by the ITU in 1999. The TD-SCDMA Forum (www.tdscdma-forum.org) includes eight member companies: China Mobile, China Telecom, China Unicom, Datang, Huawei, Motorola, Nortel, and Siemens. TD-SCDMA is primarily aimed at the mainland Chinese market, in support of voice services.
TD-SCDMA uses TDD, which significantly improves network performance by processing traffic in both the uplink and downlink directions. It transmits uplink traffic and downlink traffic in the same frame in different time slots. Uplink and downlink resources are assigned according to individual user needs. The S (for Synchronous) in its name signifies that TD-SCDMA can master both synchronous circuit-switched services (such as speech or video services) and asynchronous packet-switched services (such as Internet access). Data rates can range from 1.2Kbps to 2Mbps. In addition, TD-SCDMA improves performance by using the CDMA encoding transmission mode, supporting improved and highly efficient capacity and spectrum usage.
TD-SCDMA covers all application scenarios, being designed to address all cell sizes: metropolitan city centers, indoor and campus environments, hotspots, and rural areas. Because TD-SCDMA is based on TDD and uses unpaired frequency bands, it offers optimum efficiency for both symmetric and asymmetric data services. Due to its small bandwidth of 1.6MHz, this technology allows flexible spectrum allocation, depending on the type of information being transmitted. When asymmetrical data such as e-mail and Internet information are transmitted from the base station, more time slots are used for the downlink than for the uplink. A symmetrical split in the uplink and downlink takes place with symmetrical services such as telephony. Finally, seamless handoff between TD-SCDMA and GSM guarantees that no call is lost while the user is moving.
The main characteristics of TD-SCDMA are that it operates in the frequency band 2,010MHz to 2,025MHz in China (with wireless local loop applications in the 1,900MHz to 1,920MHz band) using the TDD mode. TD-SCDMA can operate in a minimum frequency band of 1.6MHz at 2Mbps or a 5MHz band at 6Mbps. The frequency reuse is N = 1 or N = 3, and TD-SCDMA supports the modulation schemes QPSK and 8-PSK.
Many believe that the TD-SCDMA air interface will be used by some of the operators Beijing is expected to license, though the time frame for awarding licenses has been delayed several times.
With existing networks nearing saturation and demand for wireless services continuing to grow, operators have been looking at technologies that will deliver increased capacity at the lowest possible cost. In fact, one of the biggest drivers behind 3G is capacity improvement, and network capacity is one of the key criteria for 3G technology selection. In 2000, CDMA2000 was the first 3G technology to be commercially deployed as part of the ITU's IMT-2000 framework. CDMA2000, the common name for IMT-2000 CDMA Multi-Carrier (CDMA-MC), increases data transmission rates for existing CDMA (cdmaOne) network operators. Figure 14.8 shows the infrastructure of a CDMA2000 wireless network.
Figure 14.8. A CDMA2000 network
Key features of CDMA2000 devices include color displays, GPS, digital and video cameras, push-to-talk, support for streaming-type real-time video-on-demand (VOD)/audio-on-demand services, and voice recognition functions.
cdmaOne and CDMA2000 are the most spectrally efficient technologies and support at least twice the maximum number of voice calls as current non-CDMA 2G technologies. The CDMA industry is also deploying new solutions that will further enhance the capacity of existing networks. CDMA's capacity advantages are real, with operators experiencing these benefits today. cdmaOne delivers the most capacity in the 2G world, even considering the latest frequency-hopping techniques and adaptive multirate voice codecs in GSM networks. CDMA2000, which is now being deployed worldwide, doubles the capacity of cdmaOne networks.
IS-95 HDR is being used as the underlying technology for CDMA2000. IS-95 HDR is optimized for IP packets and Internet access, and it can be used to enhance data capabilities in existing cdmaOne networks or in standalone data networks. With existing CDMA networks, a number of channels are changed from voice to data. Using a combination of TDM and CDMA, IS-95 HDR shares each channel among several users, but on an as-needed basis rather than as fixed time slots, as in TDMA. CDMA2000 promises a 2.4Mbps peak data rate in a standard 1.25MHz CDMA voice channel. The IS-95 HDR data rate varies, depending on the distance between the mobile phone and the base station.
Some 94% of current 3G deployments use CDMA2000, but this represents only a fraction of all operators. As more GSM operators convert to 3G W-CDMA technology and implement HSDPA, HSDPA could dwarf CDMA2000.
At the beginning of 2006, there were more than 300 million subscribers to CDMA networks, with an average growth rate of around 5 million subscribers per month, and CDMA2000 had surpassed 225 million subscribers as of March 2006 (see the CDMA Development Group Web site, at www.cdg.org).
CDMA2000 represents an entire family of technologies, including the following:
The next phase of CDMA2000, CDMA2000 3X, uses three 1.25MHz CDMA channels. It is part of the CDMA2000 specification for countries that require 5MHz of spectrum for 3G use. CDMA2000 3X is also known as 3X RTT, MC-3X, and IMT-CDMA Multi-Carrier 3X. CDMA2000 3X uses a pair of 3.75MHz channels (i.e., 3 x 1.25MHz) to reach higher data rates, with the promise to support integrated voice and data up to 3.09Mbps. CDMA2000 3X has not yet been deployed.
CDMA450 is a TIA/EIA-IS-CDMA2000 (CDMA-MC) system deployed at 450MHz. It includes the same family of technologies as CDMA2000. Currently, CDMA2000 1X and CDMA2000 1xEV-DO are commercially available for the 450MHz band, and CDMA2000 1xEV-DV is being developed.
The advantages of CDMA450 derive from the spectral efficiency and high-speed data capabilities of CDMA2000 and the expanded coverage afforded by a lower frequency band. CDMA450 provides a larger cell size compared to other bands, which translates to fewer cell sites and significantly lower capital and operating expenditures to service vast coverage areas. CDMA450 offers IMT-2000 services, such as high-quality voice and high-speed data access, and it represents an evolution path to advanced 3G services, allowing for a phased evolution. CDMA450 requires only a small amount of spectrum (1.25MHz), which is a significant consideration for NMT operators who have 4MHz to 5MHz allocated to them.
CDMA450 offers a solution for multiple markets. A number of operators in eastern and central European countries, Russia, and southeast Asia are using the 450MHz band to provide wireless services with first-generation analog equipment, based on the NMT standard. CDMA450 is the only technology commercially available to those operators that allows direct transition from a first-generation system to next-generation services. CDMA450 is also one of the few technologies that fits into 4MHz to 5MHz of spectrum (it requires 2 x 1.25MHz for a single channel and can fit three or four CDMA450 carriers, depending on the size of guard bands).
Providing access to communication services (voice and Internet access) is a key priority for governments and regulators around the world, especially in developing countries. Using lower-frequency bands offers a cost-effective solution for meeting these goals. Due to the favorable propagation characteristics of lower frequencies and their associated coverage benefits, there may be significant cost advantages associated with deploying a wireless system in the 450MHz band.
The 450MHz band can be used to provide broadband access for mobile or fixed data users. Many countries have indicated a need to provide their public safety communication markets with group communication, high-speed data access, push-to-talk, video streaming, and dispatch services. Some countries are also investigating the use of a high-speed data network to provide broadband access to schools, hospitals, and businesses. These networks could be seen as complementary to other cellular-based networks and could be employed in either a fixed, portable, or fully mobile setting, depending on the application.
3G Deployment Issues
A main barrier to 3G is that there is a lot of competition in this arena, with many different standards being advocated. Also, there is already an installed base of 2G and 2.5G networks, and companies want to protect their investment there. A number of important issues, including the following, have yet to be fully resolved:
Other barriers are differences in frequency allocations, proper assessment of the demand in terms of voice versus data versus video, and the cost and coverage associated with 3G versus what already exists and seems to be adequately accommodating medium-speed data. One of the biggest problems for 3G is a lack of significant consumer demand (which, in some cases, is a result of the reluctance of carriers, especially those in the United States, to envision services that people will pay for). In addition, Wi-Fi wireless LANs and WiMax wireless MANs, given what they can do for data, create some competition for 3G; Chapter 15 discusses these types of networks in detail.
Part I: Communications Fundamentals
Telecommunications Technology Fundamentals
Traditional Transmission Media
Establishing Communications Channels
Part II: Data Networking and the Internet
Data Communications Basics
Local Area Networking
Wide Area Networking
The Internet and IP Infrastructures
Part III: The New Generation of Networks
Broadband Access Alternatives
Part IV: Wireless Communications
Wireless Communications Basics
WMANs, WLANs, and WPANs
Emerging Wireless Applications