ULTRAWIDEBAND: an electronic free lunch? The FCC is on the brink of legalizing communication and radar. designfeature By Warren Webb, Technical Editor

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1 designfeature By Warren Webb, Technical Editor David Flaherty WE MAY SOON BE SHARING OUR CELL-PHONE, TELEVISION, SATELLITE, NETWORKING, AND EMERGENCY RADIO FREQUENCIES WITH A RADICALLY DIFFERENT WIRELESS TECHNOLOGY THAT SPREADS TINY PORTIONS OF ITS SIGNAL UNDER THE NOISE FLOOR OF EXISTING COMMUNICATIONS BANDS. ULTRAWIDEBAND: an electronic free lunch? At a glance...86 Ultra wars...86 For more information...88 The FCC is on the brink of legalizing communication and radar transmitters that spew emissions across our previously sacred radio-frequency spectrum. The transmitter technology, UWB (ultrawideband), is based on a series of narrow, precisely timed pulses that generate a spectral bandwidth sometimes exceeding 5 GHz while producing insignificant interference within any specific frequency band. You can use UWB in radarlike applications to see through walls or measure precise distances and for short-range, high-bandwidth, wireless communication. Designers and investors are waiting anxiously for this government decision that may have a huge impact on future wireless projects. UWB is a fundamentally different information-transmission technique from today s modulated from continuouswave RF-carrier signals; therefore, the technology offers some unique applications. The military has for years been in- December 21, 2 edn 85

2 AT A GLANCE UWB (ultrawideband) signals hide under the noise floor and offer the potential to reuse previously allocated RF spectrums. Before authorizing its use, government regulators are testing UWB emissions to protect existing communications bands. Time-domain analysis of UWB signals uncovers numerous surface-penetratingradar, distance-measurement, and motiondetection applications. UWB vendors have demonstrated wireless Bluetoothlike networks with even higher data rates. Military-product developers laud the security and interception resistance of short-range, UWB communications. UWB offers a mostly digital architecture to enable low-cost, single-chip-product electronics. terested in UWB systems. Classified projects have produced low-power UWB communications systems that are extremely difficult to detect and disrupt. Ground- penetrating radar systems based on UWB detect buried mines, including those with plastic cases. Radarlike applications include precise distance measurement, backup proximity sensors, stud finders, and medical imaging. Search-and-rescue personnel already have an FCC-approved UWB-radar device that detects breathing or other motion through walls or concrete rubble. System designers have proposed that UWB technology can capture Figure 1 motion data for electronic white boards. Information-device designers can also expect short-range, local networks similar to Bluetooth but with much higher data rates. UWB will most likely fail to replace cellular communication because UWB is effective only over relatively (a) short distances. With roots in the early 196s, UWB technology originated with studies on characterizing microwave networks by their impulse-transient response. Recognizing potential radar and communications applications, the government clas- POWER (db) sified most early UWB work. A variety of names, including baseband, impulse, short-pulse, and carrier-free, (b) identified the technology until the 199s when the Department of Defense began using the term ultrawideband. The US Patent Office issued a large number of UWB signal-processing and application patents, and several disputes over technology ownership have dampened design enthusiasm (see sidebar Ultra (c) wars ). OUTLAW SIGNALS With careful circuit and antenna design, you can build a UWB transmitter that emits no more RF energy than the spurious emissions allowed under Part 15 of the FCC regulations. Part 15 covers low-power, unlicensed transmitters, computers, electrical devices, and other products that might generate RF in the normal course of their operation. These regulations were put in place to ensure AMPLITUDE POWER (db) TIME (NSEC) FREQUENCY (GHz) FREQUENCY (GHz) A UWB pulse stream (a) creates spectral lines at multiples of the pulse rate (b). Randomizing the pulse delay simulates white noise (c) (courtesy Time Domain Corp). that your computer does not interfere with your neighbor s television reception. The Part 15 rules allow only spurious or unintentional emissions; therefore, UWB transmissions are currently illegal, no matter how small the signal. 5 ULTRA WARS The media has hyped UWB (ultrawideband) as one of the most important inventions of modern times; this hype includes comparisons to the telephone, semiconductor technology, and probably sliced bread. These claims are exaggerated, but publicity has piqued the interest of investors and designers. Germany s Siemens and Quest Communications are investing in UWB companies. Despite illegal UWB transmissions, designers have made a mad rush to the Patent Office to protect intellectual property. Disputes between Time Domain Corp and LLNL (Lawrence Livermore National Laboratory, Livermore, CA) over timing of early patents has led to confusion and probably slowed UWB-product development. The University of California under contract with the Department of Energy operates LLNL, a government-research-and-development laboratory. The dispute lasted several years, and, as a result, the US Patent Office re-examined the patents, although there was little change to any patent. The dispute also precipitated an investigation by a science committee of the US House of Representatives into government technology-transfer policies. Investigators heard accusations that the LLNL was stealing technology from private industry, hiding the fact that the FCC disallowed UWB transmissions, and collecting millions of dollars in licensing fees while providing little support. Although these disputes have made little change in the original patents, you may want to warn your legal department before laying claim to any UWB technology. 86 edn December 21, 2

3 UWB proponents have petitioned the FCC to change the regulations, arguing that the emissions would have Figure 2 the same effect on other systems whether they were intentional or unintentional. In May 2, the FCC issued a Notice of Inquiry to investigate the use of UWB radio systems without a license. The FCC initiated a testing plan and asked industry and other government agencies to comment. To date, the aviation community has voiced the biggest objections. It contends that a large number of UWB transmitters operating in a local area could raise the noise floor enough that the noise would interfere with or prevent reception of low-level navigation signals, such as GPS (Global Positioning System). The FCC and the National Telecommunications and Information Administration s Office of Spectrum Management plan to complete detailed interference testing by March 21. Technically, many experts define UWB as an emission in which the 3-dB bandwidth is at least 25% of its center-frequency. Emissions consist of a narrow burst of energy in the form of one pulse or a few cycles of a center-frequency carrier. Pulse widths typically range from 1 psec to 1.5 nsec. A low average power, measured in milliwatts, characterizes these pulses. You can use a UWB waveform to carry information by modulating the recurring position of the transmitted signal. For example, a pulse can FOR MORE INFORMATION... represent a digital one if it arrives earlier than expected or a digital zero if it arrives later than expected. Figure 1 shows time- and frequencydomain representations of a typical UWB pulse train. The pulse width is approximately 5 psec, which yields a center frequency of 2 GHz. Figure 1b shows the spectral distribution for an unmodulated stream of pulses with spectral lines appearing at multiples of the pulse-repetition frequency. This figure also shows a half-power bandwidth slightly faster than 2 GHz. With simple pulse-position modulation, the frequency distribution looks similar to that in Figure 1b. Mixing the modulated data stream with a pseudorandom-noise delay removes the strong spectral lines (Figure 1c). The pseudorandom-noise also divides the signal into channels, allowing multiple UWB transmitters to operate in the same local region without interference. To extract a UWB transmission from beneath the noise floor, the receiver must correlate the RF signal with an expected waveform. The receiver multiplies the received signal with the pseudorandomnoise signal and then averages the result over time. Because the received signal is integrated over time, the continuous averaging process eliminates the noise. UWB systems typically spread 1 bit of information over several pulses to give the receiver enough information to extract the averaged signal from the noise; therefore, the data rate is a submultiple of the pulse rate. MANY PATHS HOME UWB receivers are also effective in removing delayed reflections or multipath For more information on products such as those discussed in this article, go to our information-request page at When you contact any of the following organizations directly, please let them know you read about them in EDN. Aether Wire & Location Inc Enter No. 31 Lawrence Livermore National Laboratory MIR Program Office Enter No. 32 RANGE ADJUST NOISE VARIABLE DELAY DISPLAY McEwan Technologies LLC Enter No. 33 MultiSpectral Solutions Inc Enter No. 34 PULSE- REPETITION INTERVAL GATE IMAGE PROCESSING PULSE UWB RECEIVER INTEGRATOR Time Domain Corp Enter No. 35 Ultra Wideband Working Group Enter No. 36 TRANSMIT RECEIVE WALL RADAR- RANGE LIMITS UWB radar systems see through walls by gating echoes only from the range of interest. SUPER INFO NUMBER For more information on the products available from all of the vendors listed in this box, enter No. 37 at ims.ca/ednmag/. TARGET 88 edn December 21, 2

4 errors. A pulse may reach the receiver by multiple paths, such as the direct line of sight path or as a reflection from an intermediate object or building. Because the paths are unequal, the receiver sees two pulses. A correlation receiver locks onto the first pulse to arrive and gates out the second pulse, thus eliminating the multipath fading problem. Motion sensing, range finding, and radar applications of UWB signals use the same basic transmitter and receiver circuits as communications applications. Most of these applications use a time-gated receiver to select return pulses from a narrow range. For example, range gating can eliminate the initial reflections from a wall so that a radar system looks only at objects behind the wall (Figure 2). Similarly, a motion detector can be gated multiple times to respond selectively to motion within areas of interest. Pulse-emission and detection times for radar type applications are also randomized to eliminate beat-frequency false alarms from clockwise signals, such as radio and TV stations, to allow multiple motion detectors to be colocated without interference and to more evenly spread the spectrum so that it represents random noise. Prototype and demonstration designs are available, because most vendors are anticipating a favorable FCC decision. Communications, surface-penetrating radar, networking, and integrated chip sets are in the research or preproduction ARRAY Figure 4 64 CHANNELS RADAR MODULES Figure 3 The pager-sized UWB Localizer from Aether Wire and Location measures the real-time distance to every other Localizer in a communications network. ARRAY CONTROLLERS AC1 AC8 INTERFACE ELECTRONICS MASTER CONTROLLER SURVEY WHEEL LLNL developed the HERMES, which creates a 3-D image of the internal structure of a bridge. VEHICLE/ PACKAGE COMPUTER CONTROL SOFTWARE DATA MANAGEMENT IMAGING DISPLAY ANALYSIS stage. Several UWB-patent holders are also offering to license their technologies and assist manufacturers with designs. With support from DARPA (Defense Advanced Research Projects Agency) and private financing, Aether Wire and Location Inc have developed a UWB positionlocation and communication system (Figure 3). Each pager-sized transceiver, called a Localizer, measures the real-time distance to every other Localizer in the network. Aether engineers predict at least 1-cm resolution from 3 to 6m for the company s current fourth-generation design. Aether suggests a range of military and commercial applications including surveying, construction, inventory location, motion tracking, and keyless lock, for the Localizer system. Multispectral Solutions Inc has developed a series of communication- and radar-based products since its first UWB efforts in For example, its concept VETAS (Vehicular Electronic Tagging and Alert System), developed for the US Department of Transportation, provides a means of keeping problem drivers off the road. Instead of impounding a vehicle or jailing the driver, the VETAS tag transmits a picture of the convicted driver and vehicle information to receivers in nearby police vehicles. The UWB tag electronics operate from two AAA batteries and periodically transmits 4- kbps burst-rate data with a range of 8 to 2 ft. BRIDGE CAT SCANS The Federal Highway Administration sponsored a UWB project to diagnose problems in the nation s bridge decks. Corrosion of internal steel reinforcement is extremely difficult to detect, yet it can lead to sudden catastrophic bridge failures. The LLNL (Lawrence Livermore National Laboratory) developed the HERMES (High Performance Electromagnetic Roadway Mapping and Evaluation System) to inspect concrete and internal reinforcement (Figure 4). You can mount HERMES on a trailer and pull the system at traffic speeds while an array of 64 radar modules collect enough data to construct 3-D images of the internal structure of the bridge deck. Economic projections for HERMES show inspection savings of millions of dollars annually. HERMES is just one application of the LLNL s MIR (Micropower Impulse Radar) that has been licensed PRINTER ARCHIVE NETWORK to more than 25 manufacturers. MIR applications include liquid-level sensing, internalorgan-motion detection for medical monitoring, timeof-flight ranging, and through-the-wall imaging. The QDS electronic dipstick from McEwan Technologies ( nologies.com) is a refinement of MIR architecture, providing fluid-level sensing using time-domain reflec- 9 edn December 21, 2 VIDEO

5 tometry. The system, based on low-cost SMT (surface-mount-technology) components, measures the round-trip time for a UWB pulse to travel from the top of a tank to the fluid surface, where it reflects back to the top. A precision quartzcrystal timing circuit in the QDS makes measurements with a scale-factor stability of.3% over common outdoor temperatures. Time Domain Corp, another basic UWB patent holder, demonstrated an Ethernet LAN operating at T1 data rates (1.54 Mbps) and You can reach Technical Editor Warren Webb at , fax , wwwebb@ cts.com. greater during this summer s joint military-air and missiledefense exercise. The system used Time Domain s proprietary PulsON UWB chips a timer that can handle the 1-psec timing and a correlator containing THE EASE OF GENERATING UWB SIGNALS MAY ALSO CAUSE ONE OF UWB S BIGGEST PROBLEMS. a variable-gain amplifier and three independent correlating circuits. A third chip, a digital-baseband-signal processor and controller, is currently in design. Time Domain has selected IBM (www. ibm.com) to fabricate the SiGe (silicongermanium) ASIC chip set, which should be available in early 21. The ease of generating UWB signals may also cause one of UWB s biggest problems. You can transmit UWB signals by directly connecting an antenna to a pulse generator. The antenna partly determines the pulse width, power, and effective center frequency of the UWB emission. MultiSpectral Solutions contends that users may inadvertently change the center frequency, bandwidth, and radiated power with a bent antenna or by bringing a metal object near the antenna. These types of problems may force the FCC to impose a filtering requirement on all UWB systems to protect sensitive spectrums. Most experts agree that the technical problems can be worked out and that interest in UWB is growing. In fact, your competitors may already be investigating UWB. Take a look at the growing list of members in the UWB Working Group. You can join the working group or subscribe to a UWB discussion group through links on the site. However, it is decision time for the future of UWB technology as the government s interference testing program nears completion. You can expect the FCC to issue a ruling in early 21 that could unleash a brandnew technology for your product-design arsenal. Looking for a few good Design Ideas Have you recently solved a tricky design problem or devised an innovative solution to a difficult task? Let your colleagues in on the secret by publishing a Design Idea. EDN s Design Ideas are short, compact articles covering virtually any technology area: analog or digital circuits, programmable logic, hardware-design languages, systems, programming tips, useful utilities, test techniques, etc. And they re pretty easy to write: You don't have to submit a design for your complete system, just the idea that s the heart of your system. Send your idea for review. We pay $1 per published Design Idea; each one also appears on-line at your idea to Bill Travis at b.travis@cahners.com. 92 edn December 21, 2