Ultrawideband and NTIA
By Joseph P. Camacho

The NTIA has been directly involved since 1997 in the issues associated with introducing ultrawideband (UWB) technology on an unlicensed basis into the marketplace. Companies working on UWB want the FCC to allow mass-market sales of their products without requiring individual licenses for each device.

After receiving requests from UWB developers, the FCC issued a notice of inquiry to gather information and investigate the possibility of permitting the operation of UWB radio systems on an unlicensed basis under Part 15 of its rules. The FCC issued a NPRM on a revision of Part 15 rules regarding UWB transmission systems. The key issue for NTIA is the interference potential of unfettered UWB use to critical federal radio systems (air traffic control radionavigation aids, global positioning system (GPS), weather radars, etc.). These systems operate in designated restricted bands previously unavailable for use by unlicensed devices.

What is Ultrawideband?

UWB is an emerging technology using the transmission of very short impulses of radio frequency (RF) energy whose characteristic spectrum signature extends across a very wide range of radio frequencies. One definition is that systems employing these UWB signals often have instantaneous bandwidths of at least 25 percent or more of the center frequency of the device and thereby do not conform to the U.S. frequency allocation table and the associated federal regulations. For example, an UWB system centered on 2 GHz may have an emission bandwidth of 1 GHz, but the energy density is very low. These UWB systems have shown promise in performing a number of useful telecommunications functions, making them very appealing for both commercial and government applications.

UWB technology has been used for ground-penetrating radar for subsurface investigations, detection of buried objects, and for geotechnical studies of underground structures. UWB techniques also are used to determine the level of liquids in large storage tanks. Through-wall UWB imaging systems are another application that would enable police, fire, and rescue personnel to locate persons. Low-cost tools are being developed for home workshops. In the area of communications, UWB technology can be used for short-range broadband wireless networks.

How does Ultrawideband Work?

In the area of emerging technologies, the term "ultrawideband" or UWB signal has come to signify a number of synonymous terms such as impulse, carrier-free, baseband, time domain, nonsinusoidal, and large relative bandwidth radio/radar signals. While traditional wireless devices transmit a continuous wave, an UWB device sends extremely short pulses of data in a binary format. The pulses are sent over a much wider occupied portion of the RF spectrum and are not "locked" on a single discrete frequency.

NTIA's Role

The NTIA is responsible for managing the federal government's use of the RF spectrum. The FCC is responsible for managing the RF spectrum used by the private sector, and state and local governments. In carrying out its responsibilities, the NTIA has undertaken numerous spectrum-related studies to assess spectrum use; studied the feasibility of reallocating spectrum used by the government or relocating government systems; identified existing or potential compatibility problems between systems; provided recommendations for resolving any compatibility conflicts; developed methods to promote the efficient and effective use of the radio spectrum; and improved spectrum management procedures.

Recent NTIA spectrum management efforts include extensive measurements and analyses to assess the interference potential of UWB transmitters to existing and planned federal government systems. Primary attention has been given to safety-of-life and aeronautical radionavigation services, with particular emphasis placed on GPS.

Before the NTIA can accept the operation of UWB devices in restricted bands used by critical federal radio systems, NTIA must assess the potential impact of UWB devices on these systems, as well as develop solutions to any problems identified. Likewise, the FCC must assess the potential impact of UWB devices to non-federal users and their systems that operate in restricted bands. NTIA will coordinate with the FCC on rules for accommodating UWB.

Part 15 Emissions

Part 15 of the FCC rules sets out regulations under which an intentional, unintentional, or incidental radiator may be operated without an individual license. However, the developer must certify that all equipment conforms to the rules. In the RF spectrum, certain frequency bands are designated as "restricted" because of the critical nature of the operations employing RF systems. Between 335.4-7250 MHz, these federal operations employ aeronautical radionavigation aids, GPS, air traffic control radars, satellite downlinks, aeronautical flight test telemetry, global maritime distress and safety system, etc. The restricted bands in this range are shown below:
Restricted Bands Between 335.4-7250 MHz
399.9-410 2310-2390
608-614 2483.5-2500
960-1240 2655-2900
1300-1427 3260-3267
1435-1626.5 3332-3339
1645.5-1646.5 3345.8-3358
1660-1710 3600-4400
1718.8-1722.2 4500-5150
2200-2300 5350-5460

In restricted frequency bands, only spurious or unintentional emissions at or below a specified field strength are permitted. Below 960 MHz, the unintentional radiation permitted in restricted bands is limited to a field strength of 200 v/m in a 100 kHz reference bandwidth. UWB transmitters are clearly intentional radiators, and the rule provisions applying to unintentional radiators do not apply to UWB devices. Due to their large bandwidth, UWB devices cannot operate without overlapping many of these restricted bands.

Scope of NTIA Measurements

The NTIA undertook a comprehensive program consisting of measurements, analysis, and simulations to characterize the potential for compatibility between UWB transmissions and selected federal radio systems operating in the restricted frequency bands between 335.4-7250 MHz.

These assessments were performed in two studies:
(1) UWB compatibility with GPS receivers; and
(2) UWB compatibility with selected federal radio systems.

The study for UWB compatibility with GPS receivers used a two-part approach consisting of measurement and analysis components. The measurement plan was published in the Federal Register for public comment. Two technical reports were published and are available at the NTIA web site (www.ntia.doc.gov). Two additional reports are near completion.

The study for UWB compatibility with other federal radio systems adopted a plan consisting of three components: measurements, analysis, and simulations to characterize UWB transmission and their potential to interact with federal radio systems. As with the previous study, the measurement plan was also published in the Federal Register for public comment. These two technical reports also are available at the NTIA web site. The selected federal radio systems in this assessment study were:

Based on the results of all the measurements, analyses, and comments in the NPRM, NTIA will coordinate with the FCC on the accommodation of UWB devices.

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