Emerging Wireless Technologies Ultra Wideband Technology and Its

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					                                  Emerging Wireless Technologies
                       Ultra Wideband Technology and Its Effects on GPS
Foreword: The Public Safety Wireless Network                  in emergency response—any interference
(PSWN) Program is conducting an ongoing                       could be the difference between life and
assessment of advancements in the wireless
communications industry. The scope of this
                                                              death in such situations.
assessment is to identify emerging wireless services
and technologies for potential public safety use in the               The FCC recently adopted a First
near future and beyond. This article expands on a             Report and Order (ET Docket 98-153)
previous ultra wideband (UWB) article,                        permitting the marketing and operation of
concentrating on recent Federal Communication
Commission (FCC) rules regarding UWB technology
                                                              certain types of products that incorporate
and possible interference with the Global Positioning         UWB technology. On February 14, 2002,
System (GPS).                                                 the Order established different technical
                                                              standards and operating restrictions for three
                                                              types of UWB devices based on their
                                                              potential to cause interference. The Order
                                                              ensures that UWB will not interfere with
                                                              GPS. This article examines UWB and GPS
                                                              technologies, interference concerns between
                                                              the two technologies, FCC rulings, and the
                                                              impact on the public safety community.
                                                              What is UWB Technology?
Overview                                                              UWB is a new form of wireless
        Ultra wideband (UWB) technology                       technology based on the transmission of
can generally be defined as any wireless                      low-powered, coded impulses1 in a short-
transmission scheme occupying a bandwidth                     range environment. Pulsed transmission is
of more than 1.5 gigahertz (GHz). The                         an alternative to using conventional time-
Federal Communications Commission                             varying, sinusoidal waves traditionally used
(FCC) has proceeded cautiously with the                       in wireless communications.
UWB regulatory process because of the
uncertainty surrounding UWB interference                              This new technology supports direct
with other applications such as the Global                    transmission of digital information as a
Positioning System (GPS). Recent studies                      baseband signal rather than modulating the
have determined that first-generation UWB                     information within a sinusoidal carrier.
prototype transmitters can interfere with the                 Complementary Metal Oxide
GPS receiver equipment, a U.S.-built                          Semiconductor (CMOS) Integrated Circuit
network of navigation satellites that operate                 (IC) is used to control the transmission of
in the 1.2 and 1.5 GHz frequency bands.                       millions of low-powered, coded pulses at
        It is important to minimize, or
preferably eliminate, any interference the
UWB has with GPS because the public
safety community relies heavily on GPS
technology. Public safety agencies use GPS
                                                              1 UWB devices transmit impulses of power that last for
for command and control purposes, e.g.,
                                                                  short periods of time—on the order of picoseconds
determining the nearest location of field                         (1x10-12)for each transmission, similar to
personnel to an emergency. Timing is key                          electromagnetic pulses (EMP).

Emerging Wireless Services Assessment                     1                                                    May 2002
                                Application                                   Commercial Use   Government Use
Asset Tracking—locators/beacons to track mobile inventory and indoor
Emergency personnel position finding
Surveillance Radar—radar imaging precise enough to distinguish
specific features on aircraft/maritime craft, bringing real-time intelligence
to the battlefield
Ranging—commercial/industrial “ranging” applications to determine
precise distances between objects
Security Systems—imaging intrusion systems for alarming and tracking
of movement
Through-Wall and Underground Imaging and Radar—detection of
objects and conditions through structures
“Smart” Home—wireless links to cable, TV, Internet, computer, and
Wireless Local Area Networks (Wireless LANs)—indoor, short range,
high-bandwidth data and video communications where many channels
are needed simultaneously (i.e., rural last mile, home server, in-building
wireless LANs, and in-building communications)
Portable Wireless LANs—easily set-up wireless links for data and video
transmission to give greater mobility (Personal Area Networks [PAN])
Covert Communications—radios for squad-level operations that allow
anonymous communications without identification
                                            Table 1 – UWB Applications [2]

precise intervals every second across a large                   signal transmission over a non-reliable
portion of electromagnetic spectrum. Tens                       medium, such as the wireless channel
to thousands of these pulses are transmitted
at different frequencies for every bit of                               The public safety community can
information passed. Upon receipt of the                         potentially benefit from UWB applications.
pulses, a communicating receiver processes                      One such UWB application would allow
them using a bank of matched receivers to                       officials to “see through” concrete and other
recover the transmitted pulses. This process                    debris and would be extremely helpful in
ensures precision timing with few errors,                       search and rescue operations. Other UWB
which is critical to the device’s                               applications are listed in Table 1.
                                                                What About GPS?
        As stated, UWB sends tens to
thousands of pulses per bit (ppb) of                                    GPS is a satellite navigation system
information at differing frequencies within                     funded and controlled by the U.S.
the 3 GHz to 10 GHz range. As the ppb rate                      Department of Defense (DoD). It was
increases, the processing gain1 increases,                      designed and is widely used for military
and in turn, the bit error rate (BER)                           purposes; however, an increasing number of
decreases. This technique permits a very                        civilian users also use GPS for navigation,
low-powered signal, with large processing                       location tracking, and many outdoor
gains. This technique is used in spread                         recreational activities. GPS provides
spectrum technology to ensure reliable                          specially coded satellite signals that can be
                                                                processed in a GPS receiver, enabling the
                                                                receiver to compute position, velocity, and
1 Processing gain–UWB receivers can accept multiple
    pulses per bit; the pulses are averaged for each bit,
    and that averaging increases the likeliness that each
    bit will be accounted for—hence a gain.

Emerging Wireless Services Assessment                       2                                         May 2002
                                        Figure 1 - UWB Regulated by FCC and NTIA [2]

        GPS’s popularity has grown rapidly                       operation under Part 15 rules. Part 15 of the
since its inception, and the user community                      rules states that non-licensed operation of
wants to limit potential scenarios that might                    low-power transmitter devices is permitted
affect GPS performance. Many police, fire,                       if interference to a licensed radio system is
and emergency medical service agencies use                       mitigated. However, UWB operation occurs
GPS receivers for command and control                            over a wide bandwidth, which can result in
purposes to determine the nearest location of                    transmissions in restricted frequency bands.
field personnel to an emergency, enabling a                      This is prohibited under the existing Part 15
faster response time in life-or-death                            rules. In addition, the current emission
situations. GPS can also provide assistance                      measurement requirements detailed in Part
with search and rescue missions by                               15 were developed for narrowband systems,
providing real-time location information                         and are probably inappropriate for, and
while field personnel are searching for                          possibly pose unnecessary restrictions on,
victims or suspects. The GPS user                                UWB devices.
community raised the most concern about
UWB technology and the potential                                         On May 11, 2000, the FCC issued a
interference that it could cause to GPS                          Notice of Proposed Rulemaking (NPRM)
receivers. The potential for this interference                   that proposed that some UWB devices
has become a major roadblock to the FCC                          operate on an unlicensed basis under Part 15
approval of UWB technology.                                      Rules. The FCC specifically proposed that
                                                                 safety devices, such as GPS, be protected
FCC Ultra Wideband Rulemaking                                    from harmful interference. Further, this
                                                                 NPRM stated that UWB devices should be
        In September of 1998, the FCC                            exempt from licensing and frequency
issued a Notice of Inquiry (NOI) to                              coordination, allowing the technology to
investigate the authorization of UWB                             operate under a new UWB section of Part 15
transmission systems on an unlicensed basis                      of the FCC Rules. The FCC has proceeded
under Part 15 of FCC Rules. The responses                        cautiously due to the uncertainty
highlighted two main obstacles to UWB                            surrounding UWB and whether it will cause

Emerging Wireless Services Assessment                        3                                         May 2002
interference with other services, such as                   mining companies, and construction
cellular telephones and GPS. Figure 1                       companies.
depicts how the National
Telecommunication Industry Association                      Wall Imaging Systems—Also
(NTIA) and FCC are involved with UWB                        operate below 960 MHz or in the 3.1
regulatory process.                                         GHz to 10.6 GHz frequency band.
                                                            These systems are designed to detect
Recent Federal Communication                                the location of objects through a
Commission Ruling                                           “wall.” Operation is restricted to law
                                                            enforcement, fire and rescue
    The First Report and Order issued by                    organizations, scientific research
the FCC on February 14, 2002, arrived after                 institutions, commercial mining
a long and controversial decision process for               companies, and construction
the FCC. Because UWB technology                             companies.
employs a range of frequencies already used
by wireless telephone carriers and various                  Through-Wall Imaging Systems—
federal agencies, it took the NTIA 3.5 years                Operate below 960 MHz or in the 1.9
to negotiate a compromise that would ensure                 MHz to 10.6 GHz frequency band.
UWB transmission would not interfere with                   These systems are similar to wall
existing cellular telephone and security                    imaging systems; however, through-
systems, as well as GPS. The Order (ET                      wall imaging systems use different
Docket 98-153) permits the marketing and                    techniques to detect the movements
operation of certain types of products that                 of people or objects located behind
incorporate UWB technology. It also                         structures such as walls. Operation
establishes different technical standards and               is limited to law enforcement and
operating restrictions for three types of                   fire and rescue organizations.
UWB devices based on their potential to
cause interference: imaging systems                         Medical Systems—Operate in the
(including ground penetrating radars [GPR],                 3.1 GHz to 10.6 GHz frequency band
wall and through-wall imaging, medical                      and are used for a variety of health
imaging, and surveillance devices);                         applications at the direction of or
vehicular radar systems; and                                under the supervision of a licensed
communications and measurements systems.                    healthcare practitioner.

•    Imaging Systems—Permits operation of                   Surveillance Systems—Operate in
     GPRs and other imaging devices under                   the 1.9 GHz to 10.6 GHz frequency
     Part 15 Rules, subject to certain                      band. Operation is limited to law
     frequency and power limitations. At the                enforcement, fire and rescue
     request of the NTIA, the FCC will notify               organizations, public utilities, and
     or coordinate with NTIA prior to the                   industrial utilities.
     operation of all imaging systems
     including—                                      •   Vehicular Radar Systems—Operate in
                                                         the 24 GHz band using directional
          GPRs—Operate below 960 MHz or                  antennas on land transportation vehicles.
          in the 3.1 GHz to 10.6 GHz                     These devices are used to detect the
          frequency band. Operation is                   location and movement of objects near a
          restricted to law enforcement, fire            vehicle, enabling features such as near
          and rescue organizations, scientific           collision avoidance.
          research institutions, commercial

Emerging Wireless Services Assessment            4                                         May 2002
                                        Figure 2 - UWB and Regulatory Timeline [2]

•    Communication and Measurement                               University to research the compatibility of
     Systems—Operate in the 3.1 GHz to                           UWB and GPS and to conduct tests to
     10.6 GHz frequency band. These                              quantify interference problems. The
     systems (e.g., wireless LANs) are                           majority of tests measured UWB impact on
     designed to ensure that operation can                       the accuracy and performance of a high
     only occur indoors.                                         grade GPS aviation receiver. Other tests
                                                                 measured UWB impact on the loss-of-lock
Figure 2 portrays major milestones in the                        performance for two different receivers, the
development of UWB technology and the                            original aviation receiver and a low-cost
regulatory process.                                              original equipment manufacturer’s (OEM)
                                                                 receiver similar to devices that will be used
Can UWB Interfere with GPS?                                      in cellular telephones for Enhanced 9111
                                                                 location information. In the study released
        Independent research groups have                         by Stanford University in March 2001, all
recently performed studies on commercial                         tests showed the same sensitivity to UWB
GPS receivers operating in the same general                      signal type, and the worst interference cases
vicinity as first-generation UWB prototypes.                     for all three receivers occurred when a
The UWB devices inhibited all GPS                                discrete UWB device operated within the
functionality within a 20-foot radius of                         GPS band. Further, the Stanford study
operation. Results from such studies                             concluded, “The results strongly suggest that
support the FCC’s decision to limit full-                        UWB transmissions that overlap or come
scale production of UWB equipment until                          near to the GPS band must be carefully
further investigation of UWB interference
on other technologies can be performed.
                                                                 1 A detailed description of Enhanced 911 (E911) can be
      In 1999, the Department of
                                                                      found on a previous Emerging Technologies article
Transportation requested Stanford                                     titled, “Enhanced 911– Enhanced Wireless
                                                                      Emergency Communications.”

Emerging Wireless Services Assessment                       5                                                    May 2002
regulated to ensure that there is no adverse       concerned about potential interference from
impact to GPS.”                                    UWB transmissions with radio systems used
                                                   by police, firefighters, and emergency
        As a result of the NPRM issued by          medical workers, and to GPS-based
the FCC on May 11, 2000, the NTIA                  technologies used to locate emergency
conducted two studies to determine whether         callers. The Commission is actively
UWB interferes with GPS. In March 2001,            listening to concerns voiced by the NTIA,
the NTIA issued a report concluding that           the Federal Law Enforcement Users Group
some UWB signals examined during testing           (FLEWUG), and the public safety
“exceeded measured GPS performance                 community in general. The First Report and
levels” at output levels “well below” other        Order ensures protection from interference
unlicensed devices, such as cordless               while allowing use of new mission-critical
telephones. The report also cautioned that         equipment for urban search and rescue and
UWB devices need to operate at very low            other related functions.
emission levels to avoid interference with
GPS signals.                                       Conclusion and Future Challenges

        Johns Hopkins University issued a                  In this article, the following topics
study that concluded UWB could operate in          were discussed: UWB and GPS
ways that make its transmissions appear            technologies, interference between the two
similar to the regular background noise of         technologies, and recent FCC rulings. UWB
miscellaneous radio transmissions. Johns           applications may greatly benefit the public
Hopkins researchers concluded that varying         safety community; however, challenges still
the timing of the UWB pulses, via a process        exist in ensuring the technology benefits its
called “dithering,” could make the signal          users and does not adversely affect other
more “noise-like.” However, the study              important technologies, such as GPS. The
cautioned that some pulse frequencies could        regulatory process is still progressing, but it
interfere with GPS receivers.                      is anticipated that standardization efforts
                                                   that mitigate effects of UWB transmission
         As the studies mentioned above            on other technologies will be required before
conclude, UWB transmissions can interfere          UWB becomes widely available to the
with GPS technology. With this knowledge,          consumer market.
it is clear why the FCC has decided to
proceed with caution regarding proposing                   This article also identified the
new rules relating to the proliferation of         importance of GPS to public safety
UWB technology. Because several future             organizations and other areas such as the
products may lend themselves to better             aviation industry. In summary, UWB does
mitigating interference-related problems           interfere with GPS in certain situations.
with the GPS system, the FCC will                  Although one main beneficiary of the
reevaluate its decision in the First Report        applications available through UWB
and Order in 6 to 12 months.                       technology will be the public safety
                                                   community; the technology will not be
Impacts on the Public Safety Community             useful if it interferes with other critical
                                                   technologies, such as GPS-based
        During the rule making process for         applications. The FCC is taking the
UWB, the Association of Public Safety              necessary steps to ensure this does not
Communications Officials (APCO)                    occur.
International requested that the FCC
“proceed with great caution.” APCO is

Emerging Wireless Services Assessment          6                                          May 2002
[1] http://www.uk.research.att.com/location/uwb.html
[2] http://www.ncs.gov/TelecomNews/01-1/TN2001-1.pdf

Emerging Wireless Services Assessment                              7   May 2002