Ultra-Wide Band, UWB, transmission technology is a relatively new development which may have the capability to provide for significant benefits for public safety, businesses and consumers. The available proposals and ideas (see UBW literature) are designed to ensure that existing and planned radio services, particularly safety services, are adequately protected. While comprehensive tests have not been completed, UWB devices appear to be able to operate on spectrum already occupied by existing radio services without causing interference, which would permit scarce spectrum resources to be used more efficiently. Intentional radiators, i.e., transmitters, are permitted to operate under a set of general emission limits or under provisions that allow higher emission levels in certain frequency bands. Intentional radiators generally are not permitted to operate in certain sensitive (such as allocated to radio astronomy) or safety-related frequency bands, designated as restricted bands, or in the frequency bands allocated for television ("TV") broadcasting.
UWB transmission is a signal whose fractional bandwidth, dbw, is larger than 0.25, where the fractional bandwidth is defined as
dbw = 2(fH - fL)/(fH + fL)
where fH is the upper frequency of the -20 dB emission point and fL is the lower frequency of the -20 dB emission point. This formula can also be written as (fH - fL)/fC where fC is the centre frequency. The centre frequency is calculated as (fH + fL)/2.
Specifically, it is proposed to define UWB devices as any device where the fractional bandwidth dbw is greater than 0.25 or occupies 1.5 GHz or more of spectrum.
It is also proposed to base the definition of an UWB device on the -10 dB bandwidth rather than the -20 dB bandwidth, because UWB devices will operate so close to the noise floor that in many cases it will not be possible to measure the -20 dB bandwidth. For the purpose of this definition, the centre frequency of the transmission is defined as the average of the upper and lower -10 dB points, i.e., (fH + fL)/2, as noted earlier. Finally, it is proposed that the bandwidth be determined using the antenna that is designed to be used with the UWB device.
UWB applications can be generally grouped into the following categories: Medical applications, Consumer communications applications, Automotive applications, Consumer and industrial construction applications, Ground penetrating radar (GPR) systems which are e.g. applied as a facility to trace land-mines, Industrial liquid level gauges, High performance data communications systems.
Addressing what frequency bands should be made available for UWB devices, the following is
considered:
a. critical safety systems operating in the restricted
frequency bands, including GPS operations, are protected against interference.
b. there is a broad variety of potential applications for UWB technology, each of which has
unique spectrum attributes and requirements.
c. it is noted that the various regions of the spectrum have different propagation
characteristics.
To this the following comments are added:
On Ground Penetrating Radar, GPR:
GPR is an UWB device that is designed to operate only when in contact with, or in close proximity (i.e., 1 meter) to, the ground for the purpose of detecting or obtaining the images of buried objects. GPRs should be designed to include a switch or other mechanism to ensure that operation occurs only when it is activated by an operator and the unit is aimed directly down at the ground.
GPRs must operate at frequencies in the region below 2 GHz in order to obtain the penetration depth and resolution necessary to detect and obtain the images of buried objects. GPRs can neither avoid nor notch out the restricted frequency bands. It is assumed that the risk of interference from GPRs is negligible because the overwhelming majority of their energy is directed into the ground where most of the energy is absorbed. Emissions in other directions can easily be shielded without affecting the operating characteristics of the GPR. In addition, GPRs are expected to have a low proliferation and usually operate at infrequent intervals. Thus, the interference potential of these devices should be low. It is proposed to allow GPRs to operate in any part of the spectrum, subject to the specified emissions limits to be defined.
Imaging objects inside or behind walls:
It is unclear whether the same arguments that apply to GPRs concerning penetration depth and resolution similarly apply to other imaging devices. In contrast to GPR's, through-wall imaging devices could aim their energy in any direction. The amount of attenuation can vary widely depending on the composition of the wall. Also, the frequency selection is not yet clear.
Other UWB applications:
Most other applications for UWB technology could operate in a variety of regions of the spectrum. It is believed that most UWB devices can generally operate in a variety of regions of the spectrum above approximately 2 GHz, without causing harmful interference to other radio services. The UWB signals will quickly fall off below the background noise because of the high propagation losses at 2 GHz and above. Further, most radio services operating above 2 GHz use directional antennas that generally discriminate against reception of undesired signals. It is, therefore, considered not to put any restrictions on UWB devices operating at frequencies above approximately 2 GHz.
The frequency range below ~2 GHz contains a variety of applications 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. There are a number of restricted frequency bands at or below 2 GHz, not counting the TV broadcast bands. Particularly, concerns are raised about the impact of any potential interference to the GPS band at 1559 - 1610 MHz and future Galileo bands 1164 - 1215 MHz and 1215 - 1300 MHz.
Alternative approaches to expressly prohibiting operations in the frequency bands below 2 GHz should be considered. For example, it is known that certain UWB applications may be feasible using extremely low signal levels.
GPRs typically have no more than 10 mW average power and 10 W peak power. Some GPRs use up to 200 mW average power and 1 kW peak power. Commercial UWB applications might be met with the same power levels given for spread spectrum and UNII devices of 1 W transmitter output power with a 6 dBi antenna. UWB technology may be developed for higher power applications such as wide-area mobile radio services. However, until now there is insufficient information on this issue.
On the presently available UWB information and proposals, CRAF has the following concerns:
[1] To base the definition of an UWB device on the -10 dB bandwidth
rather than the -20 dB bandwidth will probably give a dbw value which is not suited in
coordination with passive services, because of their different protection requirements. The
sensitivity requirements of a passive service might even require specification of the UWB
spectrum mask down to a value lower than -20 dB.
[2] Some passive applications are particularly susceptible to pulsed interference, such as pulsar
research.
[3] An Ultra-Wide Bandwidth device generates wanted emission over a range of frequencies with
radiocommunication services having each different requirements and protection criteria and
related regulations. Using such wide bandwidths, unavoidably intentional emission is generated
in frequency bands to which footnote 5.340 applies which states that in that frequency band
"all emissions are prohibited". This intentional emission is does not fall within the category
'unwanted', 'spurious', or 'out-of-band'. Therefore, the an UWB device must reduce its
emission in a band to which footnote 5.340 to below pdf level acceptable for the victim
service for all the time, i.e. effectively being switched off in that band.
[4] Considering the wide bandwidths involved, it is extremely difficult to find a frequency
interval suitable for UWB applications without a band to which footnote 5.340 applies. It is
not sure at this moment whether adequate UWB-filter technology exists to reduce the interfering
signal falling into a passive exclusive band to below the level of harmful interference
applicable to that band.
[5]The protection requirements are obviously different for different radiocommunication
services. The considerations and proposal presently available do not consider the specific
protection requirements for passive services. Also it must be taken into account that the
aggregate pfd level of the interfering signal must be below the level of harmful
interference for that service. It is far from certain that this can adequately be accomplished
by UWB systems.