Broadband is a word that once implied military radar systems operating from 2 to 18 GHz. The term has taken on different meaning in recent years, becoming almost synonymous with technologies that support commercial high-speed data communications. In fact, broadband technology is an umbrella term that now applies to a host of wired, wireless, and optical technologies for high-speed voice, data, and video communications.
What is driving an increased need for broadband communications? Factors include increased use of the Internet for sending large file attachments, the use of the Internet for multimedia content is growing, on-line gaming, growth of video conferencing or, in short, the growth of information in its various forms, including audio, voice, data, and video.
For example, the traditional model of video broadcasting has involved sending composite signals via RF channels to any number of customers in a reception area. With the inception of cable-television (CATV) services, the model included customers with access to a cable line. Newer models based on personalized broadcast services such as video on demand involve "broadcasting" programming to one customer at a time. The older models effectively used available bandwidth by allowing group access to common programming. With personalized broadcast services, the potential exists for any number of different program "packages," each with an allotment of bandwidth, whether access is wired, optical, or wireless.
It has become apparent that no single technology will serve the needs of global broadband access. In a white paper produced by Intel Corp., "Broadband Wireless: The New Era in Communications," Sean Maloney, executive vice president and general manager of Intel Communications Group notes that "it is not a case of one technology becoming universal, or one technology replacing another. The technologies will co-exist, creating more robust solutions that will enable a lot of new and exciting possibilities." The white paper, which is available for free download from the company's website (www.intel.com), includes third-generation (3G) cellular systems and wireless local-area networks (WLANs) at 2.4 and 5 GHz as part of the wireless portions of a global broadband network.
Software giant Microsoft (Redmond, WA, www.microsoft.com) has recognized the importance of broadband communications by forming the Windows Media Broadband Jumpstart initiative to work with partners and customers on jumpstarting broadband business models. Before the broadband industry can take off, Microsoft feels that guiding principles for broadband access to be widely accepted include the following: the cost of broadband access needs to drop dramatically to be within the reach of most consumers; the quality of streamed video, which is limited by the architecture of the Internet, must be improved; compelling content needs to be developed so that consumers have a reason to invest in a broadband connection; and improved business models must be created to increase revenues and lower overall costs for the broadband industry.
The 3G cellular networks have been promoted as broadband networks capable of providing high-speed voice and data services, although these networks are still largely based on providing high-quality mobile voice services. Although these mobile-communications networks offer the promise of high-speed data access of typically 2 Mb/s, these data rates pale in comparison to broadband fiber-optic networks or even high-capacity WLANs. WLANs operate at several frequencies and data rates, such as the earliest IEEE 802.11b standard at 2.4 GHz and 11 Mb/s and the later IEEE 802.11a at 5 GHz and 54 Mb/s in the US.
Perhaps the greatest remaining hurdle to universal broadband communications access is what many have referred to as "the last mile" in the communications link. This last mile in a cable-television (CATV) network, for example, is the cable itself, since it is typically terminated in an access box or set-top receiver that is then connected to a customer's devices, such as a television set. A CATV infrastructure offers about 750 MHz of bandwidth (one 8-MHz analog video channel supports about 50 Mb/s data through a cable modem), but a single cable through a branch can only support a limit number of users, since each must occupy a separate portion of bandwidth.
The CATV infrastructure is presently used to provide broadband communications by means of cable modems. Although originally constructed with copper coaxial cables, most modern CATV systems are combinations of copper and fiber-optic cables known as hybrid fiber coax (HFC) systems. Fiber is typically used for long signal runs, with optical signals converted to electrical signals and carried along copper coaxial cables to subscribers.
Signals in a broadband CATV network travel downstream (to the subscriber's cable modem) and upstream (from the subscriber's cable modem). Downstream signals in the US occupy 6-MHz channels (8 MHz in Europe) from 65 to 850 MHz while downstream signals are sent from 5 to 65 MHz in the US and 5 to 42 MHz in Europe, occupying typically 2-MHz-bandwidth channels. Downstream signals are modulated with 64-state or 256-state quadrature amplitude modulation (QAM) while upstream signals are modulated with 16QAM or quadrature-phase-shift-keying (QPSK) modulation.
Cable modems on a CATV network compete with integrated services digital network (ISDN) or digital subscriber line (DSL) technologies on twisted-pair copper cables as part of a wired broadband access solution, with rates ranging from about 128 kb/s for ISDN to a maximum of 50 Mb/s for DSL.
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In 1998, the US Federal Communications Commission held the first of two auctions for 1.3-GHz of spectrum for local multipoint distribution service (LMDS) services from 28 to 31 GHz. The fixed broadband wireless service was expected to solve the "last-mile" access problem to homes and businesses. Ironically, the first FCC auction was not successful in selling the total of 986 licenses for 493 geographic basic trading areas (BTAs) in the US; a second auction was needed in 1999 to complete the sale of LMDS licenses.
Basically, an LMDS system consists of the network operations center (NOC), which houses the network management system, a fiber-based infrastructure to connect the separate NOCs, a base station which is usually mounted on a cellular communications tower (this is where the conversion from fiber to wireless takes place), and customer premises equipment (CPE) which is usually mounted on the outside of a customer's house and includes conversion and modulation/demodulation circuitry inside the house. The cellular-like LMDS technology relies on time-division-multiple-access (TDMA) and frequency-division-multiple-access (FDMA) technology to support multiple customers within a three-to-five-mile coverage radius with data rates from 64 kb/s to 155 Mb/s.
Unfortunately, because it operates at such high frequencies, LMDS has not enjoyed the rapid reductions in cost seen by chip sets and components at lower cellular frequencies. Since LMDS components approach millimeter-wave frequencies, they require much finer dimensions and manufacturing tolerances than their cellular/PCS counterparts, as well as more-expensive test equipment for testing. Although the LMDS infrastructure can be assembled with costs comparable to those of a cellular infrastructure, it is the high cost of the CPE gear that has proven to be a stumbling block for the widespread use of LMDS as a "last mile" solution.
Still, all the FCC licenses were sold, and a large number of telecommunications companies, including Cisco Systems, Motorola, and XO Communications, have invested in LMDS technology for their high-speed, high-bandwidth data links, with the hopes of ultimately expanding the infrastructure to the subscriber. Earlier this year, XO Communications announced successful trials of its LMDS-based broadband wireless access system in San Diego, CA and Irvine, CA. The company holds wireless licenses covering about 95 percent of the US population in the top 30 cities.
Amidst the long list of corporate LMDS license holders is Virginia Tech University (Blacksburg, VA, www.lmds.vt.edu/vtlmds.htm), the only university to hold LMDS licenses (four A-block LMDS licenses cover most of Southwest Virginia as well as parts of North Carolina and Tennessee). As part of the initial 1998 FCC auction, the Virginia Tech Foundation acquired these licenses via unopposed bidding. The licenses have a ten-year term with an opportunity for renewal provided that minimum infrastructure build-out requirements are met. (Each geographic area has two licenses, denoted A-block and B-block licenses, with some differences in spectrum.) The University's Center for Wireless Telecommunications (CWT), headed by Dr. Charles Bostian, has made use of the licenses to conduct research on the use of advanced wireless technology applied to rural mountainous areas. The licenses cover about 16,000 square miles and about 1.6 million homes. The university will act not as a service provider but as a catalyst in the application of technology, working with service providers and equipment manufacturers to bring broadband services to the rugged area.
Some technologists are not daunted by the historically expensive costs of higher-frequency electronics as a solution for broadband communications. Doug Lockie, former Executive Vice-President of Endwave Corp. (Sunnyvale, CA) and author or co-author of nine patents in microwave and millimeter-wave components and subsystems, recently founded GigaBeam Corp. (Chantilly, VA) with Lou Slaughter, former CEO of Loea Communications Corp. Lockie serves as Chief Technology Officer (CTO) and Slaughter as Chief Executive Officer (CEO) for the new company. Motivated by the FCC's October 2003 ruling to authorize commercial licensing rules for millimeter-wave bands of 71 to 76 GHz, 81 to 86 GHz, and 92 to 95 GHz, Lockie, Slaughter, and company have developed point-to-point wireless systems based on millimeter-wave bands at 71 to 76 GHz and 81 to 86 GHz to transmit data at multigigabit-per-second rates. Although the high frequencies have traditionally represented high costs, the company points out the tremendous capacity represented by the spectrum, with 1 Gb/s being the equivalent of 1000 DSL lines or about 647 T1 lines.
Lockie's former company, Endwave Corp., features component- and system-level solutions at microwave and millimeter-wave frequencies, including transceivers from 11 to 95 GHz for data rates from 1.5 to 622 Mb/s. The firm's AllegrA lines of transceivers for PDH radios includes standard products at 18 through 38 GHz. Terabeam Corp. (www.terabeam.com) also offers point-to-point broadband systems such as its Gigalink product line at millimeter-wave frequencies, including a license-free 60-GHz system. Terabeam recently merged with YDI Wireless (Falls Church, VA, www.ydi.com) to become a wholly owned subsidiary of YDI.
The large potential market for last-mile broadband access has even spurred the development of some truly innovative ways to apply traditional technologies, such as free-space optics (FSO) in which line-of-sight lasers or light-emitting diodes (LEDs) are used to transmit voice, data, and video at bandwidths to 2.5 Gb/s over distances as great as 4 km. Developed over 30 years ago by the US military and NASA, the unlicensed broadband technology can support any communication protocol. Each FSO system consists of an optical transceiver with a laser transmitter and a receiver for full-duplex communications. Proponents of FSO technology such as LightPointe (San Diego, CA, www.lightpointe.com) hope to increase bandwidth to 10 Gb/s in the near future through the use of wavelength-division-multiplexing (WDM) techniques. The company's FlightLite system, which is targeted at enterprise LANs, provides data rates to 1.25 Gb/s with a system package of less than 9 lbs.
Traditional fiber-optic systems should be part of the "mix" of technologies solving the "last mile" broadband access problem, with service providers such as Verizon Communications (www.verizon.com) recently revealing their intention to install optical last-mile connections to subscribers where feasible. Verizon announced last month that it would deploy the LambdaXtreme Transport system from Lucent Technologies (www.lucent.com) for its next-generation optical long-distance network. The DWDM-based system supports long-haul optical communications at 10 and 40 Gb/s, and carries as much as 2.56 Tb/s (64 channels at 40-Gb/s) channels for distances to 1000 km. Earlier in the year, Verizon completed deployment of a national broadband network of 9.7 million miles of fiber-optic cable as part of its Enterprise Advance growth initiative in support of broadband services.
Newer optical equipment providers such as Terrawave Communications (Hayward, CA, www.terawave.com) have built upon traditional fiber-optic technology through the use of a passive-optical-network (PON) approach. The company's technology exceeds the usual 20 km range of optical links though the use of low-loss optical splitters which allow branching the network into a large treelike configuration covering an approximate 484 square-mile service area.
Additional "delivery" technologies for broadband services include satellite communications systems, such as the geostationary satellite networks managed by Intelsat providing broadcast, telephone, and Internet services, and the low-earth-orbit-satellite (LEOS) systems managed by Globalstar LLC (Milpitas, CA), as well as high-speed data access over power lines for data rates to 1 Gb/s.
All of these broadband system solutions pose challenges for component and device suppliers. For example, Dave Robertson, product line director, High-Speed Converters, at Analog Devices (Wilmington, MA) feels that broadband communications represents a "big crowd of opportunities with technologies at different levels of maturity." Given his company's wide array of device-oriented product lines, from data converters and logarithmic amplifiers to complete wireless chip sets, the firm would appear to be well poised to serve broadband communications no matter which system or systems ultimately handle the load.