Ultra Wideband 1 TABLE OF CONTENTS Ultra Wideband 2

U l t r a W i d e b a n d A Brief Description of the Wave of the Future
John Schell
University Of Maryland University College
March 15, 2002
TABLE OF CONTENTS
ABSTRACT (2)
INTRODUCTION (3)
DESCRIPTION (4)
Technology 5
Advantages 7
Applications 9
Challenges 10
THE FUTURE (11)
Technical 11
Military 11
Commercial 12
Summary 12 REFERENCES (13)
Abstract
Of all the competing wireless technologies currently available or under development, Ultra Wideband (UWB) shows the most promise. It provides the highest data rates with the lowest vulnerability to multipath interference. It uses a unique type of signal (RF doublet) in a unique way (low power pulses over a very large bandwidth). To date, there is little experience with the effects of multiple UWB transmitters in the real world. The technology must overcome concerns about interference with safety-of-life signals before achieving complete acceptance. Organizations including IEEE, DARPA, and
the FCC are examining UWB and its effects. Recent investigations, investments, and regulatory rulings point to a big future for Ultra Wideband applications.
Introduction
The wireless world is rapidly getting larger while the wireline one is growing at a much slower rate. The market for wireless devices is growing in many industries for a wide variety of applications. By 2008, wireless will surpass wire line as the dominant method of telecommunications worldwide, according to the consulting firm Ernst & Young (Zerega, 1999).
Though the most popular application of wireless technology has been the use of mobile phones for voice calls, recent technological advancements are changing that. Wireless Local Area Network (WLAN) segments are becoming more accepted with the development of 802.11 protocols. The term WPAN (Wireless Personal Area Network) is being used more often thanks to the growth of Bluetooth.
Of all the competing wireless technologies currently available or underdevelopment, Ultra Wideband (UWB) shows the most promise. It provides the highest bandwidths with the lowest vulnerability to multipath interference. Organizations no less influential than the IEEE (Institute of Electrical and Electronics Engineers), DARPA (Defense Advanced Research Projects Agency), and the FCC (Federal Communications Commission) have praised the potential of UWB and suggested a broad swath of applications for the fledgling system.
Sources from this paper are primarily drawn from two events. The FCC First Report and Order ruling came on Valentine’s Day, 2002, authorizing limited civilian use of UWB devices within certain frequencies and power levels. DARPA’s NETEX (Networking in Extreme Environments) Industry Day on September 10, 2001, invited several industry leaders to describe emerging technologies related to communications, security, and surveillance. Ironically, the terrifying events of the next day probably increased the relevance of such technologies more than anyone would have ever hoped.
Description
UWB applications are often classified as Short Range Wireless (SRW). This is a segment of the wireless market that is poised for massive growth in the near future. SRW technologies are primarily intended for indoor applications within 10 meters at bit rates up to hundreds of megabits per second.
A recent article in the IEEE’s Computer magazine (Leeper, 2001) suggested four potential reasons for SRW growth in the near future:
1.Increasing demand for low-cost portable devices providing high-bandwidth data
capability using less power than third-generation cellular phones.
ck of available frequencies and crowding in currently assigned unlicensed
frequencies.
3.Increasing availability of wired high-speed Internet access from homes,
businesses, and public places.
4.Decreasing costs and power requirements cost and power for signal processors
and semiconductors.
A UW
B system is defined as any radio system that has a bandwidth greater than 25 percent of its center frequency, or having a total bandwidth greater than 1.5 GHz. UWB devices often generate a bandwidth between 1.5 to 4 GHz wide. Some of the frequencies occupied by these bandwidths, often between 1 and 6 GHz, have already been assigned by the National Telecommunications and Information Administration (NTIA) and FC
C for other uses.
UWB gets away with transmitting on otherwise assigned frequencies by using very little power. Chapter 47, Part 15 of the US Code of Federal Regulations (47 CFR 15) sets the maximum power of radiation that electronic devices are allowed to emit without requiring a license. The intention of Part 15 is to limit the amount of a
device’s unintentional radiation that could interfere with neighboring devices. UWB emits less power than that specified in Part 15 (Leeper, 2001). However, because the radiation is intentional, the UWB device manufacturers have historically required a waiver to Part 15. As of early February, the FCC’s Office of Engineering and Technology had granted three waivers to Part 15, all to UWB developers: Time Domain Corporation, U.S. Radar Inc., and Zircon Corporation (Waivers, 2000).
Technology
Perhaps the most unique feature of UWB is its ability to operate without a carrier frequency. It relies entirely on individual pulses of RF energy. The pulses can be described as carrier-free baseband impulses. The low duty cycles result in low average energy densities (Fontana, 2001).
UWB devices transmit narrow individual pulses across a very broad spectrum. The diagram below (McCorkle, 2000) shows the range of frequencies used by UWB related to other wireless transmissions.
Theoretically, each pulse requires an amount of power too small to interfere with other transmissions at the same frequency. This theory cannot be proven until several UWB devices are deployed. However, UWB prevents the reverse from being true. That
is, other transmissions at UWB pulse frequencies cannot interfere with the UWB data. UWB spreads each data bit across multiple pulses transmitted at widely varying frequencies (Norwall, 2002).
The composition of UWB transmission signals is complex. A 31.25 µs timeslot carries 1 full-duplex bit. However, the bit is transmitted multiple times within the timeslot. 1023 doublets spaced 10 ns apart compose one timeslot. Doublets are pairs of RF pulses sent at different frequencies. The first pulse of a doublet is an indicator of a data pulse to come. The second pulse is a binary 0 or 1, depending on its delay after the first pulse. 29 Timeslots form one 29-bit Epoch, lasting 1 ms. One packet contains
32 Epochs. 32 packets form an Era, which requires 1024 ms (Fleming, 2001).
A UW
B receiving device must know what to look for within the reception underneath the Part 15 power limit to differentiate signal from noise. The device compares the RF signal it receives with an expected waveform. The receiver multiplies the RF signal with the pseudorandom-noise signal and then averages the result over time. This averaging process subtracts the noise. Since UWB systems spread each bit of information over several pulses, the data rate is a submultiple of the pulse rate (Webb, 2000).
The best performance metrics for UWB have come from XtremeSpectrum, a manufacturer of embedded radio modem integrated circuits. Their analysis has shown UWB data rates of 50 Mbps having a BER of 10-5 using 20 µW transmit power. A transmitter using 2.67 µW achieved a 7 Mbps data rate with the same BER (McCorkle, 2000).
Advantages
Immunity to Multipath Propagation
Problems due to multipath propagation are suffered by other forms of wireless transmission in obstructed environments, but not by UWB. Within UWB receivers, a correlation receiver locks onto the first data pulse to arrive and gates out multipath pulses that may follow (Webb 2000). Sometimes an indirect signal resulting from multipath is the only one to reach the receiver. Signals using other transmission methods would suffer from attenuation in such circumstances. Due to its characteristics, however, the reflected UWB signal is simply experiencing spatial diversity and is still useful to the receiver (McCorkle, 2000).
Efficiency: Spatial, Cost, and Power
One method of portraying the benefits of UWB over competing technologies is by comparing their spatial efficiency. Leeper (2001) has put forward a comparison of the spatial efficiency of several SRW technologies. Though bits per second per cubic meter has often been used in the past as a standard metric for spatial efficiency, Leeper prefers to use square meters because “the relevant coverage area usually involves a two-dimensional rather than a three-dimensional space.” The basis for his comparison is below, followed by a chart putting the relative SRW methods side-by-side.
IEEE 802.11b: This technology has a range of 100 meters in free space. In a circle with a 100-meter radius, three IEEE 802.11b systems can operate
simultaneously, each offering a peak over-the-air speed of 11 Mbps. The total aggregate speed of 33 Mbps, divided by the area of the circle, yields a spatial capacity of approximately 1 Kbps per square meter.
(33 Mbps/ ð(100m)2 = 1.05 Kbps/m2)
Bluetooth: In its low-power mode, Bluetooth has a range of 10 meters in free space. In a circle with a 10-meter radius, 10 Bluetooth piconets can operate simultaneously, with 5 of those offering an aggregate over-the-air speed of 10 Mbps. Divided by the area of the circle, this yields a spatial capacity of approximately 30 Kbps per square meter.
(10 Mbps/ ð(10m)2 = 31.8 Kbps/m2)
IEEE 802.11a: This technology has a projected range of 50 meters in free space. In a circle with a 50-meter radius, twelve IEEE 802.11a systems can operate simultaneously, each offering a peak over-the-air speed of 54 Mbps. The total aggregate speed of 648 Mbps, divided by the area of the circle, yields a spatial capacity of approximately 83 Kbps per square meter.
(648 Mbps/ ð(50m)2 = 82.51 Kbps/m2)
UWB: This technology has a projected range of 10 meters in free space. In a circle with a 10-meter radius, six UWB systems can operate simultaneously, each offering a peak over-the-air speed of 50 Mbps. The total aggregate speed of 300 Mbps, divided by the area of the circle, yields a spatial capacity of approximately 1000 Kbps per square meter.
(300 Mbps/ ð(10m)2 = 955 Kbps/m2)
This metric can be extended to incorporate relative costs, and becomes bps/m2/dollar (spatial capacity per dollar). To include the final significant factor in wireless transmission, power requirement, the formula can be adapted to measure spatial capacity per dollar per watt, or bps/m2/dollar/watt. Whichever of these metrics is applied, UWB wins every time.
Networking Capabilities
SRW devices can connect to each other when they are within 10 meters of each other. These connections can be controlled or created automatically, depending on the users preferences. The connections are formed spontaneously and last for the duration of the devices’ proximity (Leeper, 2001). UWB devices extend that function by multiplying these connections into temporary networks. When several UWB nodes are close together, and all are available to be networked together, the nodes limit the network size by clustering into independent sub-networks (Fleming, 2001).
Applications
“Economic forces and physical laws are driving the growth of a new wireless infrastructure that will become as ubiquitous as lighting and power infrastructures are today” (Leeper, 2000). If that is truly the case, UWB is poised to dominate such ubiquity. The US military has already found several applications for UWB in its short history. Classified military projects have produced low-power UWB communications systems that are extremely difficult to detect and disrupt (Webb, 2000).
According to the DARPA presentation, "NETEX: Networking in the Extreme", UWB is favored over other wireless technologies to work in dense urban terrain (Maeda, 2001). A defense contractor who is supplying the military with UWB equipment, Time Domain Inc., is one of the major patent holders for the technology. They have listed several projects which they believe they could quickly develop with existing
technology. These potential applications include imaging radar systems that can “see” through walls to locate survivors or hostages, secure tactical short-range radios for military and police in urban environments, a radar security fence, and multi-sensor robots for reconnaissance in high-risk zones (Scott, 2001).
In their recent ruling (New, 2002) allowing UWB for commercial uses, the FCC
outlined standards for three types of civilian UWB devices:
1) Imaging systems including Ground Penetrating Radars (GPRs), wall, through-
wall, medical imaging, and surveillance devices.
2) Vehicular radar systems.
3) Communications and measurement systems.
Challenges
UWB obtains its bandwidth by using spectrum that may be allocated to other purposes using more power. License holders and users of those other purposes are concerned that UWB’s low power signal may interfere with their devices. In particular, some users depend on clear reception of signals for safety. One fear is that unlicensed use of UWB devices could cause Global Positioning System (GPS) receivers to lose contact with GPS satellites. Though no conclusive evidence shows that UWB causes a problem for these signals, it has not been ruled out.
In initially allowing use of UWB systems, The FCC noted in its 2000 Notice of Inquiry that it is concerned about protecting other signals upon which safety depends: We have a number of concerns about generally permitting the
operation of UWB devices in the region of the spectrum below
approximately 2 GHz. This is perhaps the most heavily occupied
region of the spectrum and is used for public safety, aeronautical
and maritime navigation and communications, AM, FM and TV
broadcasting, private and commercial mobile communications,
medical telemetry, amateur communications, and GPS operations.
(Notice, 2000)
Regardless of its concern for public safety systems, the FCC nevertheless took no action to prevent UWB use above 3.1 GHz. Earlier tests found possible interference with surveillance and weather radars, microwave landing systems and radar altimeters (Norwall, 2002). Prior to the FCC ruling, concerns within the Pentagon nearly succeeded in destroying UWB’s chances of becoming commercially available (Scott, 2001). According to Michael Wascom, Vice President of the Air Transport Association, a January 2001 study conducted by the NTIA reported potential UWB interference with air traffic control radar systems (Operators, 2001). In fact, several U.S. federal agencies and universities have tested UWB devices to measure interaction with other signals. Though all of tests indicate UWB devices should have negligible effects, the GPS community and others are challenging those results (Laureate, 2001).
The Future
Technical
The IEEE Journal on Selected Areas in Communications has issued a current Call for Papers (CFP) to address developments in UWB technology and policy. Issues to discuss include the need, due to "such open network paradigm", to redefine protocol layers higher than the physical layer to take advantage of UWB's potential. The key is to increase user mobility in a scalable, distributed, IP-based network. Papers are due July, 1, 2002, for publication during the 4th Quarter 2002 (Melazzi, 2002).
Military
DARPA has budgeted funds to study UWB channel properties and effects on other spectrum users. It will research link margin improvements and reductions in the size and power consumption of UWB devices. Other research includes the modification of multiple access protocols to "utilize the unique capabilities of UWB systems". Fiscal Year 2002 funding for this research is included within $8 million for "Close-In Sensing". That funding is reduced to $3.5 million in 2003, but $6 million then is
available for "Networking Extreme Environments", which is exclusively UWB research (Fiscal, 2002).
Commercial
The FCC’s latest ruling on UWB was the first to allow UWB transmission without a waiver to Part 15. Understanding the concerns for protecting radio services that provide safety, the commission ruled to limit radiation power to a level lower than hoped for by potential manufacturers and customers. The FCC characterized the new standard as “a cautious first step” with UWB technology. Noting that interference issues are still unresolved, the Commission nevertheless wanted to allow some UWB development and sales, while simultaneously studying the “real-world” effects of the signal.
The commissioners were clearly eager to help the new UWB technology get to market, and apologized for what they termed "ultraconservative" restrictions. They also promised to actively respond to any reports of interference. The FCC intends to review the new standards within the next six to twelve months, in hopes of further relaxing the power limitations and allowing additional applications (New, 2002).
Summary
The recent spurt of investigations, investments, and regulatory rulings indicate an exploding interest in Ultra Wideband technology. Though most signs point to a promising future for UWB, there is little experience yet with the effects of multiple UWB transmitters in the real world. It uses a unique type of signal (the RF doublet) in a unique way (low power pulses over a very large bandwidth). The technology must overcome concerns about interference with safety-of-life signals before achieving complete acceptance. Successful operation without interference will certainly lead to numerous anticipated applications.
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