Emerging Wireless Technology Features "X-Ray Vision"

The Federal Communications Commission (FCC) has recently approved ultrawideband (UWB), a technology with unique advantages (and disadvantages) compared to currently used wireless technologies, for public applications. Along with traditional wireless uses"connecting peripherals in LANs is one example"UWB can also detect images through solid objects, such as people on the opposite side of a wall. This has led to the technology having both strong proponents and opponents.

While UWB works at lower power levels, how it applies its power is different from traditional wireless transmitters. A UWB transmitter spreads a low-power signal over a wide portion of the RF spectrum, generally 1 GHz wide or more, above 3.1GHz. The FCC has chosen UWB frequencies to minimize interference to other commonly used equipment, such as televisions and radios. This frequency range also puts UWB equipment above the 2.4 GHz range of microwave ovens and modern cordless phones, but below 802.11a wireless Ethernet, which operates at 5 GHz. UWB equipment transmits very narrow RF pulses. The low power and short pulse period means the signal, although of wide bandwidth, falls below the threshold detection of most RF receivers. Traditional RF equipment uses an RF carrier to transmit a modulated signal in the frequency domain, moving the signal from a baseband to the carrier frequency used by the transmitter. UWB is "carrier-free", since the technology works by modulating a pulse, on the order of tens of microwatts, resulting in a waveform occupying a very wide frequency domain.

The wide bandwidth spread of UWB makes it relatively secure against interference and offers inherent privacy from eavesdropping, but also means that a UWB signal can, potentially, interfere with other signals. In addition, the low-power constraints placed on UWB by the FCC, due to its potential interference with other RF signals, significantly limits the range of UWB equipment.

Target consumer applications for UWB include such things as cable elimination between a PC and peripherals (an application shared by Bluetooth technology), movie transmission from a DVD or VHS player to a television, or wireless transmission of high-quality music throughout a house or office. Automotive manufacturers could use UWB technology for collision-avoidance systems, including something as mundane as preventing someone from driving into their garage wall.

Far more interesting, however, are UWB's "radar-like" imaging applications. These applications include finding people trapped in a burning house, locating hostages and hostage-takers behind walls, and finding objects, such as mines, buried in the ground. Heightened security at airports and other public buildings can use UWB technology to detect weapons on individuals and bombs in luggage and packages. However, low-power constraints currently place severe limits on the range of equipment used for these purposes. Another promising UWV use is medical imaging, either in place of or complementary to existing x-ray and ultrasound systems.

A few companies have already started developing UWB products, including XtremeSpectrum, Time Domain, and Aether Wire and Location. XtremeSpectrum is developing products to enable battery-powered and other consumer devices, including digital cameras, DVDs, DVRs, camcorders, MP3 players, and set-top boxes, to send and receive multiple streams of digital video and/or audio. Time Domain has developed a UWB chip set targeting three core technologies: wireless communications, precision location and tracking, and high-definition portable radar. Aether Wire is working on miniature, distributed-position location and low data-rate communication devices. The company has, as a goal, "the development of coin-sized devices that are capable of localization to centimeter accuracy over kilometer distances." You can visit www.aetherwire.com/CDROM/General/appl1.html for a summary of applications using Aether's technology.

Cost is one factor to consider when comparing UWB to other technologies for WLAN applications. At this time, the maturer Bluetooth, for example, is around 1/3 the price of UWB. However, as technology scales and UWB development increases, the cost differential between Bluetooth and UWB should decrease. Range is another limitation of current UWB, due to FCC restrictions, limiting its use for home networking or audio/video distribution to intra-room applications. Furthermore, for these applications, UWB is limited by walls to a much greater extent than are Bluetooth or 802.11 technologies.

In addition to the frequency spectrum and power limitations placed on UWB by the FCC is another concern"privacy violation. Any technology that can "see" through solid objects can be used for illegal purposes as well as for admirable ones. In theory, a UWB-enabled system could "look through" the walls of a house to locate valuable objects and to note when the occupants are not at home. However, this is a dilemma shared by many technologies we use to enhance public safety"increased security versus decreased personal freedom. Luggage and personal searches at airports via x-ray and metal detection are common examples of giving up privacy for better security"a price most of us willingly pay. Future UWB-fueled systems will just be another technology that will provide many benefits along with having the potential to contribute to illegal activities. Such is the world we now occupy.