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.