The rush to provide broadband communications to the masses has encouraged a variety of innovative technology solutions, although not all of them provide ideal performance.
Emerging technologies are not always enduring technologies. Consumers, for example, may one day fondly recall 5.25-in. floppy computer disks, Beta and VHS videotapes, minidisk recorders, analog televisions, and vacuum-tube radios as representative of technologies past. At microwave frequencies, the importance of vacuum tubes is quickly waning, while increased use of monolithic circuits is quickly eroding the role of discrete transistors, diodes, and hybrid circuits. Of course, with every fading technology, usually two or three new ones emerge to compete for the void.
Perhaps no phenomenon in modern civilization has spurred technology development more than the desire to "be connected." Where "cellular" was the communications buzzword of the 1990s, "broadband" has become the mantra of this decade's communications equipment developers. The majority of broadband technologies adhere to well-developed standards, including the IEEE's various wireless-local-area-network (WLAN) standards (such as 802.11a/b/g). But two of the technologies that hope to compete for at least part of the broadband communications market, in homes and small businesses, are still going through the "definition" process: ultrawideband (UWB) communications and broadband-over-power-line (BPL) communications.
The term UWB was actually coined by DARPA in the 1990s. The basic premise of UWB technology is the use of "carrierless" time-sequenced pulses to provide high data rates (more than 100 Mb/s) at short distances (about 10 m). In the frequency domain, the pulses occupy about 7 GHz of bandwidth from 3.1 to 10.6 GHz, but appear to other communications systems as white noise because of the low transmitted power. After several years of testing and evaluation by the US Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA), the FCC cleared the way in 2002 for commercial UWB development. UWB devices must comply with an FCC spectral mask (power levels of about –41 dBm/MHz) to ensure coexistence with other radio systems.
The low power spectral density of UWB technology should minimize its effects on existing communications systems. Unfortunately, as with the standards battles that delayed commercial growth of WLANs, UWB proponents now fall into several different camps, largely based on either the original direct-sequence (DS) architecture or on a newer multiband approach using orthogonal-frequency-division-multiplexing (OFDM) methods. Two industry groups support the separate approaches, the UWB Forum (www.uwbforum.org) for the original DS-UWB method (backed by Motorola and Freescale Semiconductor) and the Multiband OFDM Alliance (MBOA, www.multibandofdm.org), with Agere Systems and Intel. In addition, Pulse-LINK (Carlsbad, CA, www.pulselink.net) has developed a version of UWB technology that uses cable-television (CATV) lines to achieve rates as high as 1 Gb/s. The first consumer UWB products are not expected until 2006.
On the surface, BPL technology would appear almost ideal. Its infrastructure—power lines—is already in place, and the technology can make use of those power lines to provide voice and high-speed Internet access to anyone with electricity. Since AC is transmitted at 50 or 60 Hz, most of a power line's frequency range is available for broadband communications. Unfortunately, the frequencies at which power-line communications (PLC) systems operate, typically in the high-frequency (HF) through very-high-frequency (VHF) bands, are already occupied by amateur radios among other applications. Although the FCC amended its Part 15 regulations (Subpart G for Access BPL) concerning technical requirements, measurement techniques, and administrative requirements to clear the way for BPL, the NTIA is also concerned about BPL affecting more than 18,000 frequency channels used by National Weather Service, FBI, and other government agencies. One of the inherent problems with BPL technology is its use of unshielded power lines, which tend to serve as giant antennas radiating electromagnetic (EM) radiation when used as part of a BPL network. Partly for this reason, BPL technology has essentially been banned in Japan, although trials have been conducted with various degrees of success throughout Europe.
In the US, the amateur (ham) radio community has been quite vocal in their objections to currently implemented BPL technology (over 100 BPL trials are currently being run throughout the US). Unlike "lost-in-the-noise" UWB signals, power lines carrying BPL signals radiate noticeable levels of interference, enough to disrupt not only amateur-radio communications but potentially emergency civil and government radios as well.
More than 50 amateur-radio operators responded to a recent short editorial on BPL pollution in the Microwaves & RF UPDATE e-mail newsletter, expressing their discontent with BPL. For example, Bob Duggan (N4IA) noted "the BPL concept has already demonstrated substantial pollution across a wide spectrum in HF and VHF. Not only international broadcasting and hams are affected by BPL, but also various military, fire, police, and homeland security communications are degraded. We definitely do NOT need BPL!" Leonard Reynolds, a past contributor to this magazine from RF Micro Devices (Greensboro, NC), adds, "Hams are not the only people who would be injured by BPL being implemented. The FCC should be looking out for all of us, not just for certain industries who stand to profit while others of us are injured by having large sections of valuable RF spectrum degraded or made completely useless." Also, Roy Gilbert (K6RYM) of Logitech (Vancouver, WA) points out that "it seems outrageous that the FCC would allow even trial systems to be installed with all the data available that says it's going to be a problem."
To learn first hand about BPL interference, Microwaves & RF recently accepted the generous offer of the American Radio Relay League (ARRL, Newington, CT, www.arrl.org) to perform "drive-by" testing on a trial BPL system. Accompanied by Allen Pitts (W1AGP), ARRL's Media and PR Manager, Ed Hare, ARRL's Laboratory Manager, and ARRL technical advisor, Bruce Marcus of Marcus Electronics, studied the trial system that is currently being evaluated by power utility United Illuminating (New Haven, CT, www.uinet.com) in Shelton, CT. The BPL equipment, supplied by Amperion, Inc. (Lowell, MA), employs direct-sequence (DS) communications along a several-block section of the town's main street (Fig. 1).
Testing involved tuning a high-performance mobile radio receiver and antenna rig within the amateur radio band at various frequencies between 10 and 40 MHz and measuring interference levels as well as monitoring radio communications affected by the interference. The United Illuminating system (Fig. 2) consists of numerous utility-pole-mounted repeaters transmitting high-speed signals along the medium-power utility lines.
The worst levels of interference, as expected, were found in the closest proximity to the power lines, at levels that rendered major portions of the HF band unusable for radio operators. Of some surprise, however, was the extent of the interference even at a considerable distance from the BPL system. By driving the radio-equipped vehicle, which included a precision receiver from Rohde & Schwarz (Munich, Germany) and resonant-tuned antennas, along the main street, high levels of interference were monitored as far as one-half mile from the downtown area. The measured levels were high enough to render HF communications within the town, at best, difficult and, at worst, often impossible.
The results of these informal tests on this trial BPL system in Shelton, CT (Fig. 3) revealed some of the shortcomings in these early configurations of BPL technology. In this DS implementation, the system's unintentional radiation exists at levels that dramatically hinder the operation of the entrenched applications (amateur radios) in the HF and low-VHF bands. It is important to note that this is a single BPL system with a limited number of repeaters, and that multiple or more-sophisticated BPL systems would generate even higher levels of interference.
Before dismissing BPL as a viable technology for broadband services, however, it should be noted that not all BPL approaches wreak havoc on the amateur radio bands. Recently, Corridor Systems (Santa Rosa, CA, www.corridor.biz) proposed a BPL system based on the use of microwave frequencies (2 to 20 GHz), which would avoid the HF interference problem. The firm's equipment has been demonstrated in trials over PG&G's power grid in California and has achieved data rates exceeding 200 Mb/s.
Motorola, a company long-associated with two-way radio technology, recently announced its entry into the BPL market with a system that operates over a power-grid's low-voltage (LV) lines. The firm's Powerline LV system (www.motorola.com/canopy) was introduced this May at the United Telecom Council's "Telecom 2005" Expo (Long Beach. CA). The system combines the company's Canopy Broadband Internet Platform with enhanced HomePlug technology over LV lines to minimize interference.
BPL equipment suppliers are represented by several industry consortiums, including the HomePlug Powerline Alliance (www.homeplug.org), the Powerline Communications Association (www.plca.net), the French PLC Forum (www.plcforum.com), and the United Power Line Council (www.uplc.utc.org). To be fair, the ARRL site presents a fair amount of information on BPL technology, including lists of equipment suppliers and industry organizations.
The BPL interference issue is an important one, but the potential rewards for BPL and PLC technologies should provide adequate motivation for a practical solution. With the high cost of xDSL, cable, and wireless/satellite solutions, the power line may represent the most cost-effective alternative for broadband services in many geographic regions.
