Ultra broadband

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Ultra-broadband technology ( UWB ; English : Ultra-wideband ) describes an approach to short-range radio communication for the commercial mass market. The most important feature is the use of extremely large frequency ranges with a bandwidth of at least 500 MHz or at least 20% of the arithmetic mean of the lower and upper limit frequency of the frequency band used.

Basics

Spectrum of a short sine wave with a center frequency of 5 GHz. The width of the spectrum does not depend on the phase position.

The spectrum of a sine wave is a single spectral line. A spectrum that describes a sine of a limited duration, on the other hand, is a broader spectral line, the half- width of which increases as the number of sine oscillations of the signal decreases. With UWB, impulses of the shortest possible duration are generated. These no longer contain a complete sine wave. The spectrum that is emitted or received through the antenna, therefore, must in accordance with the laws of the Fourier transform of the more wider be, the shorter the pulse duration.

The time course and the spectrum of a pulse are linked: The product of time and spectral width ( and ) fulfills the inequality

The constant depends on the pulse shape . For a Gaussian pulse z. B.

In high-frequency technology, half-widths below about 50 ps are achieved, which results in a bandwidth of over 8.8 GHz. Only a small part of this is emitted via the antenna, the dimensions of which determine the center frequency and actual bandwidth of the signal. As can be seen in the adjacent picture, the Gaussian pulse is deformed by the natural resonance of the radiator with the center frequency 5 GHz and a group of a few short oscillations with a total duration of 0.9 ns is created. This corresponds to a broad spectrum with FWHM  ≈ 2 GHz. If it is possible to reduce the number of oscillations, the half width increases.

An essential characteristic of UWB is that the entire transmission power of a few milliwatts is distributed over such a large frequency range that no interference is to be expected for the radio operation of narrowband transmission methods. In the best case it is difficult or impossible to see that a transmission with UWB is taking place at all.

In contrast to "normal" radio technology, there is no carrier frequency that is modulated. Since individual pulses are generated, pulse phase modulation (also pulse position modulation ; English pulse-position modulation , PPM) is recommended . The polarity and the amplitude of the pulses can also be changed. If the times of the individual pulses differ sufficiently, several UWBs can be operated in the same spatial area without mutual interference.

Applications

Possible applications for UWB include:

  • very high-speed services over short distances (for example the exchange of video data between monitors, DVD players, televisions and other digital devices), including IEEE 802.15.3a
  • extremely inexpensive and energy-efficient devices with the possibility of position determination and moderate data rates, for example sensor networks (motion detectors through walls), including 802.15.4a
  • Ground radar
  • medical applications (monitoring of cardiac and respiratory functions, tumor diagnostics, support system for medical imaging systems)
  • communication that can hardly be located

There is also the option of digital radio transmission at high data rates for short distances. Impulse Radio represents one possibility of technical implementation . The information is not modulated onto a specific sinusoidal carrier frequency, but rather transmitted by a defined sequence of short pulses . This makes the carrier signal very broadband and the transmission power is distributed over a large spectral range.

After the regulatory process is expected to be completed at the end of 2006, UWB systems can be operated license-free in Europe, parts of Asia and other parts of the world in addition to the USA (since 2002). The license-free use of UWB as an overlay system is made possible by the extreme broadband capability of up to 7.5 GHz and the associated low spectral power density of a maximum of −41.3 dBm / MHz. For a narrowband receiver, a UWB signal appears like noise , which means that UWB can be used in the same frequency range as conventional transmission methods.

Regulatory Aspects

From a regulatory point of view, UWB communication is breaking new ground. The main problem from the perspective of the regulatory authorities is that UWB systems do not actively prevent interference with existing systems, but rather accept minor interference inherently. However, this interference is extremely small in relevant scenarios. However, since interference cannot theoretically be completely ruled out, there are reservations on the part of the regulatory authorities and providers of services with reserved frequency bands with regard to UWB. In particular, it is argued that UWB as an overlay system does not create new capacities, but rather, as an additional source of noise, reduces the safety reserves of the existing systems. However, these reserves would be required for the operation of a reliable service with low failure probabilities. Proponents of UWB, on the other hand, point out that, on the one hand, UWB emits very little power and thus has only a locally limited influence, and, on the other hand, a large part of the frequencies in one place at a time are not used anyway, and UWB thus makes unused resources usable.

The first regulatory authority in the world to approve the regular operation of UWB devices for communication under certain boundary conditions was the US FCC in February 2002. In some other states, UWB communication is approved for experiments and demonstrations, in some cases only in certain test zones called UWB Friendly Zones (Singapore Feb. 2003, Hong Kong May 2005, Australia Dec. 2004).

The core of the FCC regulations is a frequency mask that defines the maximum power spectral density for each frequency. A distinction is made between indoor and hand-held UWB systems. Indoor systems must, as can be seen from the conceptual structure, only be suitable for use in buildings and must not deliberately radiate outside, for example from windows. The FCC cites AC power supply as an example of such evidence. Hand-held systems, on the other hand, may be operated inside and outside of buildings, but their structure and size must be recognizable as portable devices, i.e. they may not have fixed antennas on buildings, for example. Due to the stricter conditions for the operation of indoor devices, which suggest a lower level of interference, they are allowed to transmit with higher power in certain frequency ranges.

China approved the specification of the 24 GHz UWB Automotive Short Range Radar on November 19, 2012 .

UWB in conflict with passive radio applications

Passive radio applications, which include remote sensing and radio astronomy , are critically affected by the use of UWB. Radio astronomers in particular fear severe impairments. In contrast to narrowband radio services, which generate characteristic interference signals that can be recognized, filtered out or masked, the signals from UWB cannot be distinguished from noise from the outset and therefore cannot simply be removed from a received signal. The result is that interference signals caused by UWB simply worsen the signal-to-noise ratio and thus the measurement times are extended. Observations of weak and, above all, incoherent signal sources could thus be made impossible.

First estimates show that UWB devices at distances from urban settlements, as is typically possible in Europe, can certainly interfere with radio astronomical facilities.

The observation of extraterrestrial objects in frequency bands that were previously occupied by narrow-band transmitters and that could still be detected through masking and filtering is, however, even more impaired by UWB.

Radio astronomers therefore see UWB services as one of the greatest dangers for the future practice of this science.

Technical specifications

Frequency range 3.1-10.6 GHz
Transmission power 0.5 mW / −41.3 dBm / MHz
Range 10 - 50 m (depending on the application)
Data rate 480 - 1320 Mbit / s

Germany

On January 16, 2008, the Federal Network Agency released several frequency ranges between 30 MHz and 10.6 GHz for UWB. By far the highest transmission powers are allowed between 6 and 8.5 GHz.

The rigid lower and upper band limits of 30 MHz and 10.6 GHz were chosen in favor of the frequency specifications "<1.6 GHz" and "> 10.6 GHz" with an average spectral power density of −90 dBm / MHz and −85 dBm, respectively / MHz (eirp) abandoned.

This information complies with the requirements of the decision of the Electronic Communications Committee ECC / DEC / (06) 04 and the decision of the Commission (2007/131 / EC).

literature

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  1. ↑ Physikalisch-Technische Bundesanstalt (PTB): MRT radar combination: UWB radar as a medical sensor system
  2. ↑ Michael Eisenacher: Optimization of Ultra-Wideband Signals (UWB) , research reports from the Institute for Telecommunications at the University of Karlsruhe (TH), Volume 16, August 2006, ISSN  1433-3821
  3. ↑ Federal Communications Commission: Technical Requirements for Indoor UWB Systems , Code of Federal Regulations, Number 47 Paragraph 15.517, National Archives and Records Administration, October 2002
  4. ^ Salim Hanna: Ultra-Wideband Developments within ITU-R Task Group 1/8 , International Workshop on UWB Technologies, December 2005, pp. 3–7
  5. ↑ Liu Bin: SRD and its Challenge - SRD Management in China (p. 18), presentation of the "Ministry of Industry and Information Technology" (China) at the "ITU workshop on short range devices and ultra wide band" in Geneva from 3 June 2014
  6. ↑ Sharing Between UWB and Radio Astronomy Service , study by Ofcom
  7. ↑ https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Allgemeines/Presse/Pressemitteilungen/2008/PM20080116UltraWidebandTechnologieId12430pdf.pdf
  8. ↑ http://www.bundesnetzagentur.de/cae/servlet/contentblob/32374/publicationFile/2528/AllgemeinzutteilungId12424pdf.pdf

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