In a world ravenous for radio frequencies, a tantalizing telecommunications technology promises to deliver revolutionary wireless applications without further congesting the spectrum. The wonder’s name is ultra-wideband (UWB). Its champions say it won’t add to spectrum congestion, because UWB uses the same spectrum as existing users, but without creating enough interference to disrupt their operations.
The key to this feat is UWB’s transmission technique. It emits an extremely low-power, picoseconds-fast, short-duration, pulsing signal, rather than a continuous wave. UWB’s signal also spreads across a multitude, perhaps thousands, of frequency bands. And UWB noise levels are said to be at the "snake’s belly" level on the noise floor.
Due to this stealthy approach, UWB emissions are claimed to zip through frequency bands unperceived by the applications licensed to use the bands. Like ethereal ghosts passing in the night.
With UWB, the spectrum could be used over and over, proponents say, by a number of applications simultaneously, rather than only by a single application allocated to a frequency. As to range, UWB is inherently short-range. As to uses, UWB is flexible, delivering:
-
High-speed, digital voice, data or video communications for secure and covert radios, home networking systems, portable phones, "last-mile" connections, and local area networks (LANs) for businesses, homes and schools;
-
High-resolution radar for see-through-walls devices, intruder-alert systems, collision-avoidance units, medical diagnostic imaging, and ground-penetrating radar; and
-
Precision positioning for tracking inventory in a warehouse, controlling assembly-line robots, or keeping tags on your child at an amusement park. UWB positioning devices offer centimeter-level accuracy and work anywhere–unaffected by multipath problems or non-line-of-sight locations.
Proponents also say UWB is a low-cost technology, using application-specific integrated circuits (ASICs). The newest chipsets from one UWB manufacturer, Time Domain Corp., uses IBM’s silicon-germanium technology. Called PulseON, it delivers UWB communication, radar and positioning features on a chip smaller than Lincoln’s head on a penny.
With such flexibility, UWB has the potential to become as ubiquitous as the transistor became during the 1960s. "This technology represents a paradigm shift," declares Ralph Petroff, president of Time Domain. "It is an enabling technology that will create entirely new products and new industries."
Now the Sticking Points
No doubt: UWB’s allure is enticing for the burgeoning wireless telecommunications industry. However, fundamental issues block UWB’s widespread debut. For one, it has no regulatory approval to operate in the radio spectrum. UWB is not precluded from the rules, per se; it just can’t meet current rule requirements. In the United States, the basic reasons are:
-
UWB’s inherent operation violates the regulatory prohibition against intentional emissions into the TV broadcast and restricted frequency bands, and
-
UWB’s peak emissions exceed the regulatory limit, based upon current emission-measurement procedures.
And despite the extraordinary claims that UWB will cause no harmful interference, a number of documented cases show it has indeed. A myriad of questions exist about how and why the interference occurs.
Could a single UWB device generate enough interference to disrupt transmissions of other frequency users? If UWB does proliferate, could its aggregate emissions wreak havoc across the spectrum?
Is UWB a "killer app," poised to break down unnecessary barriers constraining spectrum use? Or is UWB an "app killer," threatening to haphazardly cripple systems upon which the world relies?
The answers are essential for all current spectrum users, but perhaps no more so than for the Global Positioning System (GPS). Evolved beyond its military pedigree, GPS is today used by millions. Common applications range from geological surveying to guiding Girl Scouts hiking in a forest.
More seriously, GPS is critical to U.S. Department of Defense (DoD) operations and U.S. national security. And GPS is a cornerstone for commercial aviation. Furthermore, GPS and similar systems, like Russia’s Global Navigation Satellite System (GLONASS), are the enabling technologies upon which the international aviation community is building a safer and more efficient airspace management system. GPS is a safety-of-life application, not just for aviation, but for others; the newest example is GPS-based emergency 911 services being incorporated in U.S. cellular phones.
First, and Worst, Victim
Like UWB, GPS emits a very low-power, low-noise signal. If UWB causes harmful interference, GPS is likely to be UWB’s first victim.
In a comment to an FCC question about whether to prohibit operation of UWB within restricted bands and TV broadcast bands, one of the foremost UWB scientists and inventor of the UWB Micropulse Impulse Radar, Thomas McEwan, had an unequivocal response. "Yes. UWB emissions will negatively impact GPS and FAA radar, and possibly other vital services."
Providing supporting data, McEwan continued, "The following tests and calculations reveal the deleterious impact UWB will have on restricted band users…GPS operates at a very low margin above the thermal noise floor and is very susceptible to UWB impulses upsetting its moderate bandwidth raw data. That is a very serious problem. The proliferation of UWB systems will ensure the widespread, total failure of the Global Positioning System."
Other UWB proponents challenge McEwan’s assertions, but concerns about GPS’ susceptibility to interference are legitimate. One of the earliest instances was a mysterious outage during three days in October 1994, affecting a large region east of St. Louis, Mo. The culprit turned out to be electromagnetic interference from outdoor testing of aircraft antenna patterns by McDonnell Douglas.
While technology advancements continue to improve GPS receiver operation and to harden GPS against disruptive elements, the first priority is to keep its frequencies as clear of interference as possible. Failure to do so would put into question the reliability of GPS receivers and, therefore, preclude civil aviation authorities from approving GPS as a navigational aid.
The words of the U.S. federal spectrum watchdog, the National Telecommunications and Information Agency (NTIA), say it succinctly. In a 1999 filing on the need to protect GPS spectrum, the agency stated, "NTIA disagrees with the premise that interference suppression technology can serve as an appropriate substitute for GNSS [Global Navigation Satellite Systems] receiver protection limits."
Mixed Signals
Yet despite these considerations for GPS, UWB is being promoted as a spectrum panacea. A steamroller effort propelled by UWB manufacturers, lobbyists and congressmen is prodding the FCC to approve UWB–and quickly. With GPS at risk, its defenders have rallied to protect the system’s integrity. It’s a battle royal. If there’s a flashpoint, it occurred this past May, when two dichotomous events transpired.
The first event represented the greatest commercial endorsement for GPS. It emerged during the International Telecommunication Union’s (ITU’s) World Radiocommunication Conference (WRC) 2000. Revising the international treaty for Radio Regulations, WRC allocated more frequencies for and ensured international protection of frequencies used by GNSS, which include GPS, GLONASS and Europe’s new Galileo system. These actions carry authority, because ITU represents 130 countries as the organization sanctioned to coordinate global telecommunication networks and services. By creating hallowed spectrum for GNSS systems, WRC 2000 secured the foundation needed for the aviation industry to transition to Free Flight.
The second event could nullify this progress. It was the publication on May 10 of a notice of proposed rulemaking (NPRM) by the U.S. Federal Communications Commission (FCC) to allow unbridled operation of UWB on an unlicensed basis. The FCC press release announcing the NPRM heralded UWB as offering "enormous benefits for public safety, consumers and businesses. UWB devices appear to be able to operate on spectrum already occupied by existing radio services without causing interference."
FCC proposed to open the spectrum door to UWB by amending its Part 15 rules. These rules permit low-power, radio-frequency devices to be operated without an FCC license or the need for frequency coordination. Part 15 covers such products as garage door openers, cable-TV converter boxes, computer monitors and portable phones.
Incidentally, some Part 15 devices may be wideband emitters, but their bandwidth doesn’t come close to that used by UWB. Furthermore, UWB is a "time-domain" transmitter, which is quite different from the "frequency-domain" transmitters populating the spectrum universe.
Part 15 devices are either intentional radio-frequency radiators, as in portable phones, or unintentional radiators, as in computer monitors. In either case, the device must meet Part 15 emission standards that ensure a low probability of causing harmful interference to other spectrum users. If the device is an intentional radiator, as UWB would be, it cannot operate in certain sensitive or safety-related frequency bands, and its emissions cannot exceed certain limits.
As mentioned, UWB would trespass into restricted bands, and it can’t meet Part 15 emission standards. Yet, the FCC proposes to allow UWB to operate in restricted bands and to change its procedure for testing UWB emissions.
The NPRM states that Part 15’s current emission-measurement procedures "may be inappropriate for, and pose unnecessary restrictions to, UWB technology…." For example, Part 15 requires application of a "pulse desensitization factor" so a spectrum analyzer can measure an emission. Applying this factor to UWB is said to create a Catch-22 effect by making UWB’s peak signals exceed Part 15 emission limits. Many UWB experts say UWB signals should be measured by a different device, such as a sampling oscilloscope.
This is but one of many debates over how to accurately measure UWB emissions. Numerous variables exist because UWB emissions differ widely, depending on how UWB is used, such as for radar or for communication. The discord about something as important as UWB testing has heightened fears about FCC’s NPRM to allow wholesale, unlicensed operation of UWB.
Well aware of concerns about UWB interference, the FCC vowed to protect safety services "such as the Global Positioning System," against harmful interference. FCC stipulated that further UWB testing and analysis would be needed before granting UWB Part 15 status, particularly in the already saturated spectrum bands below 2 GHz.
Specifically, FCC promised it would "provide ample opportunity to complete these tests and ensure that the analysis of the test results are submitted in the record for public comment before adopting any final rules." Then FCC eradicated any mollifying effect of these assurances by requiring all test results by Oct. 30, 2000, a scant five months after the NPRM. The deadline set further shock waves through the GPS community, perhaps no where stronger than within commercial aviation, which has strong reasons to demand an interference-free GPS system (see the following story).
A pervasive criticism being hurled at the FCC is that it is rushing to judgement on UWB. The reasons why could reside within the FCC’s release announcing the NPRM: "It [UWB] could permit scarce spectrum resources to be used more efficiently, a core responsibility of the Commission in its role as the nation’s spectrum manager."
With the telecommunication industry baying at the FCC’s door like hungry wolves (and very deep-pocketed ones), the FCC is under the gun to update its spectrum management policies and bring new services to market. The United States already lags behind the industrial world in this regard.
Trouble is, much of the U.S. spectrum is already allocated, particularly the "sweet spot" under 2 GHz. A big occupant–some say much too big–is the U.S. government. Seeking a remedy in recent years, Congress mandated transfer of some government frequencies to the FCC, which is promptly auctioning them off.
One loser in this equation is aviation, which has experienced significant spectrum loss over the years. The trend is a sad incongruity, considering the continuing spikes in demand for aviation transportation and services. The epidemic of delays at U.S. airports this year is a clear symptom of aviation’s own "spectrum drought." Ironically, part of FAA’s solution to the problem is an air-traffic management/communications, navigation and surveillance (ATM/CNS) system based upon GPS–the very cornerstone that UWB interference may crush.
An FCC battle to recoup frequency has escalated to the Supreme Court. FCC wants to repossess 90 spectrum licenses granted to NextWave Telecom in 1996, because the company failed to make timely payments and then sought protection under bankruptcy laws. FCC wasn’t even waiting for the court decision and had scheduled to reauction NextWave’s spectrum in December.
In another congestion-relieving move, the FCC announced a new policy whereby spectrum licensees could "rent" out unused or underused frequencies. Hence, spectrum would become the world’s newest, hottest commodity. More pressure on the FCC arrived in mid-October 2000, when former-President Clinton ordered the FCC and the NTIA to designate spectrum for upcoming wireless services, known as 3G. The frequency bands targeted are 1710-1850 MHz (government-allocated and managed by NTIA) and 2500-2690 MHz (commercial-allocated and managed by FCC).
NTIA and FCC must determine how to share these frequencies between 3G services and existing users, or simply evict the existing users. Interim reports from NTIA and FCC indicate the process will not be pretty.
So, it is no wonder that when UWB supporters came to FCC, singing of a way to deliver new services without further congesting the spectrum, the FCC was happy to listen. And quite possibly happy to expedite its rulemaking.
On the other hand, the FCC began eyeballing UWB approval three years ago. Momentum forward came on Jan. 29, 1998, when U.S. Radar petitioned for a waiver to Part 15, to allow it to operate a UWB ground-penetrating radar. A second petitioner popped up on Feb. 2, 1998, when Time Domain Corp. requested a waiver, to operate a UWB through-the-wall imaging radar. Then on April 14, 1998, Zircon Corp. strolled in, seeking a waiver for its UWB through-wall imaging radar.
FCC issued public notices of the petitions, sought comments, and called NTIA into the deliberation, because the devices would operate in restricted federal bands. The work between the two agencies eventually produced waiver approvals and ruffled feathers (see Waiver sidebar, page 25). But well before NTIA agreed to the waivers, FCC gave UWB a big boost, by issuing a Notice of Intent (NoI) to permit UWB radio operation on "an unlicensed basis under Part 15."
That notice, adopted Aug. 20, 1998, attracted 86 filings from 79 parties. Responses from UWB proponents far outweighed those from other spectrum users. The response from the aviation community was anemic, with a solitary comment from the FAA and a scant two comments from the U.S. GPS Industry Council, which represents GPS manufacturers and users.
The FAA acknowledged that UWB was a promising technology, but objected to FCC’s NoI, based upon questions about interference, particularly if UWB systems proliferate. FAA referred to documented cases of interference caused by such low-power devices as "TV antenna amplifiers, baby monitors, personal computers, and UWB operations. In each case, these instances caused disruption to air traffic flow." Another concern was how to track down UWB interference sources if they were not licensed.
In conclusion, FAA stated, "The policy of prohibiting non aviation use of radio spectrum used to support aeronautical safety services must be maintained. Revising the rules to allow UWB systems to operate in restricted bands will erode the protection of the bands used for aeronautical safety services and result in unnecessary degradation of the high levels of safety required by our air traffic control system."
Equally adamant that FCC not jeopardize GPS integrity, the U.S. GPS Industry Council suggested that UWB systems could use a filter or a "notch" to prevent their signals from entering the GPS band. But most UWB experts agree that notching would prove detrimental to UWB operation. As an alternative, some UWB sources suggest avoiding the GPS band by simply operating above 2 GHz or even higher.
The GPS Industry Council also reminded FCC that "the burden of proof here must be on the proponents of new services to show that they do not create harmful interference in the GPS bands, and no such showing has been forthcoming from UWB proponents." Many other GPS proponents agree that the UWB manufacturers have conveniently moved the shoe to the other foot by saying, "You need to tell us what level of interference GPS can handle."
The FCC digested the feedback from the NoI for 15 months, then published the NPRM in May 2000. Comments have gushed in like a spring flood. When the comment period ended on Oct. 27, the docket was overflowing with 438 comments from a range of interests (see Comments sidebar, page 24).
Nearly every commenter acknowledged that UWB offers intriguing potential. Filers also repeatedly cautioned the FCC to heed first the priority to protect safety-of-life frequencies. Other themes oft-repeated comments were:
-
UWB performance is very hard to measure. Even UWB experts were not consistent in suggestions on how to accurately measure UWB emissions.
-
Very little is known about the interactions between UWB and other transmitters, and far more testing is needed before the FCC will have enough valid data to decide whether to allow UWB operations.
-
The time the NPRM allowed for testing is far too short and the current testing is far too restricted.
-
The FCC should not grant UWB approval or only grant approval at the higher, less congested frequencies (definitely above 2 GHz) until more is known about UWB interaction with other transmitters.
-
The FCC should require licenses for UWB devices that operate across restricted bands, to enable authorities to track down any emitters of harmful interference.
-
The FCC should follow its traditional path of requiring new technologies to first prove they cause no interference before taking steps to allow their use.
Several commenters chided the FCC for stating in the NPRM that "UWB appears to cause no interference," citing that FCC had no scientific basis upon which to base that statement.
While the docket had enough comments to choke a horse, it didn’t have the test results upon which the GPS/UWB outcome hinges. Three parties are conducting tests: Stanford University, under a Department of Transportation (DoT) contract; the Applied Research Laboratories at the University of Texas (ARL:UT), under a Time Domain contract; and the NTIA, through its Institute for Telecommunication Sciences.
NTIA filed a letter saying its tests of several federal radios would not be done until mid-January and its GPS test data wouldn’t arrive until the end of February.
ARL:UT (which has a UWB research department and is a DoD-affiliated research unit with 30 years experience in GPS) delivered a large bulk of data to the FCC, but still had to conduct the aggregate-effect tests of numerous
UWB devices on GPS. No analysis accompanies ARL:UT’s data, nor will ARL:UT comment on results. The data is available on ARL:UT’s Website at http://sgl.arlut.utexas.edu/asd/Cure/testplan_form.html.
Interestingly, the data will be analyzed not by the FCC, but by Johns Hopkins University’s Applied Physics Lab–under a contract paid for by Time Domain. Also of interest, Johns Hopkins’ lab performed in 1999 a "GPS Risk Assessment Study" for the FAA, the Air Transport Association (ATA), and the Aircraft Owners and Pilots Association (AOPA).
The study sought to determine whether GPS could "satisfy performance requirements to be the only navigation system installed in an aircraft and the only service by FAA for operations in the National Airspace System." Of its three main conclusions, the study stated, "Risks to GPS signal reception can be managed, but steps must be taken to minimize the effects of intentional interference."
Also delivered to FCC by the Oct. 30 deadline were some results of the testing being done by Stanford University, under a DoT contract. The remaining test data was expected to arrive by January. These tests clearly support the argument that UWB can disrupt GPS operations.
According to the DoT, "The testing completed thus far is producing solid technical results that clearly show certain UWB parameters can affect accuracy and loss-of-lock in a GPS aviation receiver from single-emitter UWB testing.
"In sum," DoT concluded that "the ongoing debate about test data and its implications, the utter indispensability of the safety-of-life systems at risk, and preliminary information showing a real threat to those systems, all require that the Commission exercise caution…questions must be resolved in favor of obtaining more information prior to authorizing UWB operations generally."
Following its advice, DoT just contracted for another UWB/GPS study to add to the evidence. This one will be done by Rockwell Collins, testing yet another aviation receiver. The results are to be delivered to FCC during the first quarter of 2001.
Is UWB an app killer or a killer app? The jury’s still out and it is likely to be a long time before a verdict is delivered. In the meantime, aviation cannot afford to relax its GPS guard.
The Comments
The FCC asked for UWB comments and was deluged. Despite the Oct. 27, 2000, deadline, comments kept rolling in, rising to 475 as November ended. The FCC has more than 3,500 pages to digest, much of it replete with technical language and engineering graphs.
Studying the list of filers, it’s easy to draw conclusions about the composition of the community. For example, the aviation community is primarily represented by associations, with surprisingly few comments from individual companies making or using GPS. In contrast, the UWB pool is plentiful and rich with comments from individual UWB manufacturers, researchers and users. Time Domain ranks first overall in comments, having submitted a whopping 54 filings comprising 671 pages. But even without Time Domain’s voluminous presence, the percentage of UWB comments is dominant.
The UWB industry also has done one heck of a marketing job to the public. The crop of comments from potential UWB user is impressively supported by:
-
Medical institutions, which want to use UWB for medical monitoring, imaging and wireless LANs;
-
Municipalities, which want to use UWB radar and communication for police, fire and rescue purposes; and
-
Educational institutions, which see UWB as a way to economically network computers throughout schools.
Also having healthy representation is the telecommunications industry, which is emerging as a good ally for GPS vis-a-vis concerns about UWB interference. One group is the broadcast community; another is cellular manufacturers and network providers. The latter fear UWB interference to cellular networks and to GPS-based emergency-911 positioning features the FCC is mandating them to install.
Top Frequent Filers
-
Time Domain Corp
-
Interval Research Corp.
-
U.S. Department of Transportation
-
U.S. GPS Industry Council
-
Multispectral Solutions Inc.
-
American Radio Relay League Inc.
-
Fantasma Networks
-
Sprint Corp.
-
National Telecommunications and Information Administration
-
Sirius Satellite Radio Inc.
-
Motorola Inc.
-
Aeronautical Radio Inc. and Air Transport Association of America Inc.
-
Xtreme Spectrum Inc.
-
WINForum
-
Ultra-Wideband Working Group
-
UCI
-
Zircon Corp.
-
Aether Wire & Location Inc.
-
Delphi Automotive Systems Corp.
-
XM Radio Inc.
Individual filings can be downloaded through FCC’s Website: www.fcc.gov.
The Waiver War
The first foray in UWB’s campaign to gain regulatory approval began in early 1998, when U.S. Radar, Time Domain and Zircon petitioned for FCC waivers to operate UWB devices under Part 15. Victory came two and a half years later, delayed largely by a turf spat between the nation’s two spectrum managers, FCC and NTIA. Because the waivers sought operation in federal restricted bands, NTIA’s approval was needed. Wary about allowing UWB to romp through its frequencies, NTIA meticulously studied the situation. When approvals came, they came with strict conditions:
-
Cease manufacturing and marketing if devices cause harmful interference or FCC adopts rules to prohibit their operation;
-
Obtain certification from the FCC showing equipment complies with NTIA conditions, Part 15 emission limits, and certain test standards;
-
Apply for new certification if the equipment or spectrum-related characteristics are modified;
-
Maintain records of all users, equipment nomenclature, FCC certification, user contact, and intended operation area;
-
Equipment users must coordinate detailed day-to-day operational areas through the FCC when working near federal radio stations, to avoid interference;
-
Users must notify FCC of any changes in equipment ownership or location;
-
Petitioners must label products stating they are operated under a waiver; operation must cease if harmful interference is caused to authorized radio stations and the user must inform FCC of the situation; and
-
All equipment marketed under the waiver must contain a switch (deadman, push-to-talk, etc.) to guarantee positive control of the operation.
NTIA granted four-year approvals to the three petitioners, with additional conditions specific to each approved product. While NTIA’s approval drew fire from aviation interests, the more worrying flameup occurred between NTIA and FCC. It began when FCC incorporated NTIA’s comments in its final ruling, passed it to NTIA, which wanted some changes. FCC incorporated the changes and adopted the item in February 2000. NTIA saw the document before its publication and again sought changes. Bottom line: the document was revised and adopted twice more and was still not done by July 2000. FCC cried, "Enough!" and published it–in the original form as adopted in February.
Perhaps riled by the episode, FCC promptly squashed a petition to reconsider the waivers, filed in July by the U.S. GPS Council, American Airlines and United Airlines. FCC then snarled at the NTIA through statements by FCC Chairman Kennard, Commissioner Susan Ness and Commissioner Harold Furchtgott-Roth.
The words of Furchtgott-Roth were most biting. Referring to "NTIA’s intrusive role in this proceeding," he stated, "Repeated NTIA editing of orders after adoption undermines our independence and the integrity of our processes…I believe it is important that the FCC consult with NTIA [but] once the staff has a complete record and develops its final recommendation for the Commission, NTIA should not be provided with additional drafts or have ‘sign off’ authority on revisions."
This incensed NTIA, because NTIA’s role is not as a "consultant" when it comes to regulating government bands. NTIA’s role is manager and final arbitrator.