Section 10.2. Applications
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10.2. ApplicationsBefore the FCC allocated spectrum for UWB devices in their First Report and Order on February 14, 2002, most UWB research was relegated to small, proprietary systems addressing military communications and radar. After the report and order, UWB has generated tremendous interest, and many new ideas for applications have come from both industry and academia. Table 10.1 presents example systems of some major UWB application spaces.
The following section reviews a wide range of applications that have been proposed for commercialization. 10.2.1. High Resolution Radar ApplicationsRadar is an important early application of UWB, and interested readers are referred to [1] for a more in-depth discussion of the subject. When radar systems use a UWB signal, the wide bandwidth and short pulse duration identify more target information, improve range accuracy, improve resilience to passive scatterers (clutter), mitigate destructive multipath effects from ground reflection, and enable a narrow antenna beam pattern [10]. The wideband pulses carry more information about the target, such as shape or material. Further, the pulse may have a low center frequency to penetrate solid structures. Finally, narrow pulses eliminate the ambiguity between polarity reversal and time delay found in a continuous wave narrowband signal, thus reducing clutter from magnetic reflectors. In traditional radar systems, resolution is proportional to wavelength. For impulse radar, the resolution of a target approximately depends on its bandwidth (or pulse width) as Equation 10.1 where DR is the target resolution (m), c is the speed of light (m/s), and t is the pulse width (sec). Thus, a Gaussian monocycle with a bandwidth of 7.5 GHz (~ 100 ps time duration) could achieve a resolution of DR = (3 x 108 m/s·100 x 10-12s)/2 = 0.015 m without extended signal processing. A single pulse is unlikely to both meet FCC regulations with regards to out-of-band emissions and have a 7.5 GHz bandwidth, so the actual resolution will be slightly larger. With added signal processing, the resolution can be improved close to the Cramer-Rao lower bound [4]. Because of its high resolution radar capability, UWB has been proposed for many novel radar applications, such as vehicular radar to enhance driver safety and comfort [11]. UWB radar can provide proximity sensing around the exterior of a car to detect any objects within range of the vehicle. Initially, applications will notify the driver of hazards. For example, a vehicular radar system would alert the driver through audio or visual output when it detects potential collisions at the side, front, or rear of the vehicle. Such a system may aid the driver by "seeing" blind spots while changing lanes, reversing, or parking. In later stages of development, multiple UWB sensors can be networked with other vehicular systems to provide autonomous control of tasks, such as parking, cruise control, transmission control, braking, airbags, safety belts, or suspension tuning. Because of its communication capability, UWB may even be applicable for complete control of autonomous vehicles on smart, networked roadways. UWB vehicular radar has been allocated spectrum from 22 GHz to 29 GHz with the stipulation that the center frequency and the highest radiation level must be above 24.075 GHz. A further restriction is placed on the direction of radiation, which must attenuate energy above 38 degrees to the horizontal plane by 25 dB with respect to Part 15 limits. This requirement is scheduled to grow stricter year-by-year as more vehicular radar devices are included as standard equipment on commercial vehicles. Another high resolution radar application is Ground Penetrating Radar (GPR), which detects objects buried underground [3]. The crowded infrastructure of cities places a crisscrossed web of water pipes, electrical lines, communications links, and other obstacles underground. Heavy construction equipment can damage these structures and even cause injury or loss of life. GPR provides precise location information for such obstacles, and it does not rely on records, which can be incomplete, inaccurate, inaccessible, or missing. Another valuable use of GPR is to detect abandoned land mines and unexploded ordinance [12]. GPR operates mostly in the low frequency band below 960 MHz because low frequencies penetrate substances such as soil and sand better than high frequencies. The operation of GPR is restricted to construction, law enforcement, fire and rescue, commercial mining, and scientific research. GPR is not seen as a severe source of interference to other devices because the device is positioned close to the ground and signal energy is directed into the ground. Through-walls imaging is based on the same principle as GPR; however, signal energy is now directed horizontally. Therefore, through-walls imaging has considerable potential to interfere with existing systems, and the FCC restricts it to the public safety sector for use by firefighters and law enforcement officials. Law enforcement is particularly interested in using through-walls imaging to look through the double hulls of boats for hidden compartments and concealed contraband. The military also has significant interest in through-walls imaging for urban warfare situations. UWB can provide resolution fine enough to identify the presence of humans through walls, and it can even detect the small, involuntary motions of respiration or heartbeats. Finally, UWB offers promise for medical imaging to enable health care professionals to look inside the body of a human or animal [13]. For example, UWB can detect movements of the heart, lungs, vocal cords, vessels, bowels, chest, bladder, or a fetus. Because UWB radar can resolve images with safe levels of radiation, it can be used even in sensitive patients, such as mothers in the final stages of pregnancy. UWB has a significant advantage over induced field devices, such as magnetic resonance imaging (MRI), which confines the patient to a small space. With the radiated field of UWB, the patient can be anywhere, and the imaging device moves while the patient remains in a comfortable position. Because UWB radar may function a few meters from the target, it can provide remote monitoring of patients through blankets and clothing. An initial medical application of UWB radar is early detection of breast cancer with space-time processing of UWB signals through an antenna array [14]. Figure 10.2 shows UWB detection of a 2 mm lesion 3.1 cm deep. Figure 10.2. UWB Detection of 2 mm Lesion (White Dot in Center). The Black Dots on the Outside Are Antennas in an Array.SOURCE: E. J. Bond, X. Li, S. C. Hagness, and B. D. Van Veen, "Microwave imaging via space-time beamforming for early detection of breast cancer," IEEE Transactions on Antennas and Propagation [14]. © IEEE, 2003. Used by permission.  10.2.2. Communications ApplicationsBecause of potential interference to and from narrowband devices, early UWB research was primarily for military communications applications. Most research was performed quietly before the FCC opened the spectrum for UWB in February 2002. Thus, many military systems developed prior to 2002 provided long-range communication capability with power levels that exceed current regulations [15, 16]. Examples include aircraft-to-aircraft communications, augmentation of graphic display plans (GDP) for instrument landing in inclement weather, communication and control for unmanned aerial vehicles, sensors for monitoring aerospace structures, and secure location and RF identification systems for soldiers in urban combat situations [15]. More recent applications focus on wireless personal area networks (WPANs), which connect a limited number of devices in a small coverage area (within 10 m). Current UWB radios for WPANs must meet the FCC power limits; hence, they radiate much less power than earlier systems. Taking full advantage of the high data rate of UWB, the IEEE 802.15.3a standard endeavors to define medium access and physical layers with the highest data rate possible for WPAN applications. UWB promises to deliver extremely high data rates (up to Gbps range) for multimedia applications and quick download times for large data files. To support these applications, the UWB physical layer for IEEE 802.15.3a offers data rates of 110 Mbps at 10 meters, 200 Mbps at 4 meters, and, optionally, 480 Mbps or higher at a shorter distance. Such data rates allow high-quality multimedia services and comfortable download times (seconds as opposed to minutes) for large media files [17]. Currently, the most common application for UWB WPAN communications is cable replacement for high-speed devices. Cabling is a bulky and aesthetically displeasing means of connecting devices, and it also tethers devices together to limit device mobility. XtremeSpectrum Inc.[1] proposed cable replacement for home networking [18], and Intel Corporation proposed cable replacement for office environments [19]. In fact, there are proposals for wireless Universal Serial Bus (USB) and wireless IEEE 1394 for consumer electronic (CE) devices [20]. These standards would connect peripherals, such as digital video players, projectors, MP3 players, portable disk drives, camcorders, high-resolution digital cameras, PDAs, printers, scanners, web cams, home theaters, CD players, keyboards, or mice [21]. UWB could even provide a standard interface for wireless docking of laptops [19] or wireless interchip connections.
Because cables are inconvenient in clothing, another cable replacement proposal enables wearable peripherals for health, entertainment, military, or medical purposes [22]. In Figure 10.3, UWB could clean up the awkward clutter of cables within a wearable computer system. Figure 10.3. Communications Applications of UWBSOURCE: (a). Richard DeVaul, images of MIThril 2000 System and prototype [86]. © MIT Media Lab, 2000. Used by permission. SOURCE: (b). R. Fisher, R. Kohno, H. Ogawa, H. Zhang, M. Mc Laughlin, and M. Welborn, "DS-UWB Physical Layer Submission to 802.15 Task group 3a," doc.: IEEE 802.15-04/137r0 [18]. © IEEE, 2004. Used by permission. SOURCE: (c). R. Kohno, H. Zhang, and H. Nagasaka, "Ultra Wideband impulse radio using free-verse pulse waveform shaping, Soft-Spectrum adaptation, and local sine template receiving," IEEE 802.15-03/097 [19]. © IEEE, 2003. Used by permission.  Time Domain Corporation has noted that environments for the proposed applications would likely be shared among multiple families or multiple businesses within a single building or confined space. Additionally, a large number of devices may be networked, so most of these applications require a standard that exploits the spatial reuse property of UWB. Operation of UWB communications in such an environment requires high aggregate data rate, low cost, low power, and small size; so performance can be measured as [18] Equation 10.2 where P is the performance metric, Spatial Capacity is in bits per second per square meter of coverage, Power is in Watts, Cost is the cost of the device, and Size is the amount of physical space the device occupies (in cubic meters). Figure 10.3 shows conceptual pictures of home, office, and wearable UWB scenarios. 10.2.3. Location Aware Communications ApplicationsUWB offers a unique blend of radar and communications applications known as Location Aware Communications. The upcoming IEEE 802.15.4a standard takes advantage of that combination in a UWB physical layer that emphasizes low data rate, low power, and location awareness instead of high throughput. The goal of the standard is to provide simple, pervasive, and seamless wireless connectivity among devices. Although this prospective standard is still in the initial stages of development, it has generated tremendous interest, with the promise to more fully exploit the unique low power and ranging characteristics of UWB. Suggested application spaces include home automation, industrial automation, and tracking of people, assets, or geographically localized phenomena. The following applications are based on the response to the IEEE 802.15.4a Call for Applications [23, 24]. Many parties desire to use UWB to provide communications devices that can locate people. Aether Wire & Location, Inc. and the city of Chicago propose a location aware communications device for firefighters [24]. In a burning building, heavy smoke and darkness impair both audio and visual communications. With a UWB communications system, firefighters may monitor environmental conditions, communicate with each other, and locate injured personnel. Aether Wire proposes a similar application for soldiers to positively and quickly identify friendly soldiers to reduce accidental deaths and injuries [24]. Harris Corporation stipulates that military communications should adopt a modulation scheme with low probability of detection and intercept for stealth communications [25]. Samsung and Staccato Communications have proposed smart home applications that manage almost all aspects of the home, including doors, keys, TV, radio, and computers [24]. The system keeps track of individual users and their preferences. As individuals move throughout the smart home, a tracking system could automatically adjust room temperatures and activate entertainment devices to a particular television channel or website. General Atomics offers proximity sensors that provide security for cars, computers, or homes, which automatically lock and unlock as the owner travels in and out of range [24]. LB & J consulting suggests that UWB could be used to track students and personnel in school buildings [24]. In schools, the tracking system could control access to school buildings, conduct instant roll call, produce reports to analyze incident patterns, monitor school bus transportation, and engage parents in student supervision. Ubisense Ltd. proposes to increase productivity in office environments by locating key personnel [24]. Privacy and security concerns, however, would have to be addressed before such systems could be implemented. Location-aware communications capability can also be used to manage assets. UWB expedites the inventory control process because the network can automatically scan individual containers and report status information without physical examination of the container's contents. Further, UWB performs well in a densely packed environment, such as stacked pallets in trucks or stacked containers in ships. Aether Wire has suggested precision asset location and autonomous manifesting applications for the Department of Defense, which is the largest United States transporter of goods [24]. Inforange offers a similar suggested application for tracking packages during shipment to reduce the amount of lost and misrouted packages [24]. They propose a transmit-only device to save power in the tags. General Atomics extends this idea to tracking for inventory control in warehouses and retail shops [24]. A similar technology could be used as small, discrete security tags for high-valued items, such as leather jackets in retail stores [24]. Both Ubisense and MSSI have suggested tracking life-saving equipment in hospitals, as it is not always possible to locate equipment quickly in an emergency [2, 26]. Tracking mobile objects is another application that uses UWB's radar capability. One idea is a UWB network that provides a protective security "bubble" around a geographic area. The radar capability of UWB would detect intruders and track their motion. In a networked environment, this could provide accurate tracking over a large geographic area. In outer space, UWB could automatically track an astronaut outside of a spacecraft or track the position of two spacecraft that are docking. Time Derivative and Q-Track suggest unique applications for professional sports to track balls, athletes, or racecars [24]. On farms and in wildlife sanctuaries, a tracking system could automatically track the movement of cattle or wildlife. In the proposed applications for IEEE 802.15.4a, several companies mention sensor networks, which stand to derive huge benefits from the low power and location aware properties of UWB [26, 28]. Position location capability aids in network configuration and provides a service for the networking and application layers. Aether Wire notes the demand for sensor networks to monitor industrial automation and control [24]. They cite the high cost ($10 to $25 per foot) of wiring for pipe sensors, which typically exceeds the cost of the sensors. Mobile nodes may take advantage of UWB's location capability to organize and perform tactical maneuvers [29]. Staccato and Aether Wire suggest UWB for heating, ventilation, and air conditioning (HVAC) control for home and office environments [24]. Extending this idea, Echelon Corporation proposes to add UWB radios to water and gas meters to report readings directly to the consumer and also to the utility company through power lines [30]. Another possibility is monitoring a human for early warning of seizures or heart beat monitoring [31]. ST Microelectronics notes that the location aware capability allows such networks to configure themselves (so that they become ad hoc networks), circumventing installation by a technician [24]. Samsung and CUNY want to augment the Global Positioning System (GPS) that is not usually receivable indoors, to enable location-assisted routing of network data. UWB is an excellent low-power physical layer for sensor networks [24]. The extremely low duty cycle of UWB allows sensors to conserve energy and operate for many years without maintenance [2]. Because of its robust operation in harsh multipath environments and penetration capability, UWB also supports sensor networks in warehouse and cargo hull environments, and can even be embedded in solid structures to provide a real-time non-invasive report on structural integrity. 10.2.4. Channel Sounding ApplicationsAnother potential application of UWB technology is channel sounding or measuring the impulse response of a wireless channel [3234]. I-UWB, with its extremely short duration pulses, provides subfoot resolution of multipath signals in a wireless channel. Such high resolution is not only useful for investigating UWB propagation mechanisms; it also provides useful information about the number, power, and relative delay of multipath signals for narrowband channels as well. More detailed information on the Channel Sounding applications of UWB technology is found in Chapter 2. |
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