Wireless "standards keepers" have kept a strong collective eye on the emerging technology known as ultrawideband (UWB) communications, perhaps as much for fear that it could interfere with existing wireless formats as much as for fear that it could become a viable, high-data-rate wireless option. Almost a year and a half after the US Federal Communications Commission (FCC) gave a green light for the use of about 7 GHz of bandwidth for low-power UWB transmitters and receivers, a number of significant players, including Intel, Motorola, and Taiyo Yuden, have announced their intentions to compete in the UWB playground. The future of the technology may depend on how well it can coexist with more established wireless formats, or possibly how quickly it can replace them.
By adopting a First Report and Order last February, the FCC permitted the marketing and operating of certain types of UWB devices, in about 7 GHz of spectrum from 3.1 to 10.6 GHz. That First Report and Order includes standards to protect the operation of existing and proposed radio services from interference caused by UWB devices. In contrast to a conventional communications system in which transmitted energy is focused within a relatively narrow band or channel, an UWB system spreads its transmissions over a fairly wide bandwidth but with a lower effective power level than in a conventional radio channel.
The technology is yet another development of military laboratories to find its way to commercial manufacturers, much like Global Positioning System (GPS) receivers and code-division-multiple-access (CDMA) technology for cellular telephones. The promise of sending high rates of data over low-cost, low-power UWB links has attracted numerous small and large companies and investors, and almost as many proposed "standards." To help sort through the different slants on UWB technology, the Institute of Electrical and Electronics Engineers (IEEE) 802.15.3 Task Group (www.ieee.org/groups/802/15/) is chartered to draft a new standard for wireless personal-area networks (WPANs). The proposed IEEE 802.15.3a specification (expected to be final in late 2004) will include a standard physical-layer definition for short-range, low-power, high-data-rate (100 Mb/s and more) WPANs.
A total of 23 proposals for the new UWB standard were submitted during a March IEEE meeting (from 31 original presentations), representing a variety of different modulation formats. In essence, the proposals fall into two camps on the use of the FCC's allotted bandwidth. One seeks to achieve high data rates at low power levels, without necessarily limiting the amount of FCC-allotted bandwidth that is occupied. The other favors a more "narrowband" use of spectrum, at first concentrating on the spectrum from 3.1 to 4.8 GHz, and then moving upward in frequency when the technology becomes more cost-effective at those higher frequencies.
With last month's meeting of the IEEE 802.15.3a Task Group, one of the proposals stood out as the leading candidate for the final IEEE 802.15.3a standard. The proposal is based on orthogonal frequency-division multiplexing (OFDM) and backed by the Multiband OFDM Alliance (MBOA). The alliance was formed just this June, and includes one of the UWB pioneers, Time Domain Corp. (www.timedomain.com), as well as some leading electronics suppliers, such as Focus Enhancements, Intel, Mitsubishi, Panasonic, Philips, Samsung, and Texas Instruments. Although the proposal garnered only 60 percent of the required 75 percent of the group's vote for confirmation of a standard, the MBOA plans to address task-group members' reservations (including compliance with FCC regulations) in time for the next meeting/vote in September.
Time Domain's PulsON 200 UWB evaluation kit is one of the first commercial UWB products to be marketed by any alliance member. It includes two of the company's UWB radios, a dedicated microprocessor for embedded applications development, a power supply, biphase pulse modulator, antenna, and several software tools. The kit operates over a 3.2-GHz bandwidth centered at 4.7 GHz with −11.5-dBm effective isotropic radiated power (EIRP) and pulse-repetition frequency of 9.6 MHz. It can achieve data rates ranging from 75 kb/s to 9.6 Mb/s.
Of course, one of the other UWB pioneers, XtremeSpectrum (www.xtremespectrum.com), remains outside of the MBOA, and with a rival proposal based on a different modulation and access scheme, direct-sequence CDMA (DS-CDMA). The company's Trinity chip set remains the only UWB chip set on the market, consisting of an RF front-end integrated circuit (IC), RF transceiver, MAC IC, and digital baseband IC. Constructed with silicon CMOS and silicon-germanium (SiGe) semiconductor process technologies, the chip set operates within the FCC's Class B limits for transmissions at less than 1 mW from 3.1 to 10.6 GHz. Although not an MBOA member, the company does have a formidable backer in Motorola (www.motorola.com). Also in support of the XtremeSpectrum chip set, several months ago Taiyo Yuden (www.t-yuden.com) announced that it had developed a ceramic chip antenna capable of transferring streaming video in UWB systems operating from 3.1 to 10.6 GHz.
The MBOA proposal is firmly rooted in UWB studies performed by Texas Instruments and Intel. Intel's interest in UWB technology, for example, is very much as a "next-generation Bluetooth" option capable of higher data rates than Bluetooth. The company is currently exploring the possibility of installing UWB technology on every microprocessor, and using UWB as the wireless connectivity approach between devices—rather than as a wireless networking tool, such as the IEEE 802.11 a/b/g WLAN standards. The company's website offers "Ultra-Wideband Technology for Short- or Medium-Range Wireless Communications" by Jeff Foerster and associates from the Intel Architecture Labs with an excellent analysis of data throughput for various UWB approaches.
At the May IEEE 802.15.3a Task Group meeting, TI's physical layer presentation on "Time-Frequency Interleaved Orthogonal Frequency Division Multiplexing (TFI-OFDM)" proposed the use of three bands centered at 3432, 3960, and 4488 MHz. Each band features 528-MHz bandwidth, with each OFDM symbol occupying more than 500 MHz at all times (as required by the FCC), and using average transmit power of −10.3 dBm per band. The approach is capable of data rates from 55 to 480 Mb/s.
TI's proposed system can actually support as many as 14 UWB bands of 528 MHz, although signal losses increase at higher frequencies, and thus the interest in the lower frequencies. The TFI-OFDM system avoids all transmission in the 5-GHz UNII band (currently occupied by IEEE 802.11a WLANs), and offers simple implementation in standard digital complementary metal-oxide semiconductor (CMOS) and simpler antennas than the broadband designs required for more broadband UWB systems.
Come September, the IEEE 802.15.3a Task Group may help to establish a WPAN standard. It should be noted that such as standard does not by any means represent the only use of UWB technology. In its First Report and Order (February 14, 2002), the FCC (www.fcc.gov) detailed a wide range of applications for UWB technology, including medical-imaging systems, ground-penetrating-radar (GPR) systems (which must be operated below 960 MHz or from 3.1 to 10.6 GHz), wall imaging systems (with similar frequency restrictions as GPRs), through-wall imaging systems (which must be operated below 960 MHz or from 1.99 to 10.6 GHz), medical systems, and surveillance systems (which must operate from 1.99 to 10.6 GHz). Additional applications include vehicular radar systems in the 24-GHz band, and communications and measurement systems from 3.1 to 10.6 GHz.