| Ultra Wideband Technology Tutorial |
Ultra Wideband Technology Tutorial
- an overview or tutorial about UWB, Ultra Wideband technology
UWB, or Ultra-Wide Band technology offers many advantages,
especially in terms of very high data transmission rates which are well beyond
those possible with currently deployed technologies such as 802.11a, b, g, WiMax
and the like. As such UWB, ultra wideband technology is gaining considerable
acceptance and being proposed for use in a number of areas. Already Bluetooth,
Wireless USB and others are developing solutions, and in these areas alone its
use should be colossal.
Basic concepts
As the name implies UWB, ultra wide band technology, is a form of transmission
that occupies a very wide bandwidth. Typically this will be many Gigahertz, and
it is this aspect that enables it to carry data rates of Gigabits per second.
The fact that UWB transmissions have such a wide bandwidth
means that they will cross the boundaries of many of the currently licensed
carrier based transmissions. As such one of the fears is that UWB transmission
may cause interference. However the very high bandwidth used also allows the
power spectral density to be very low, and the power limits on UWB are being
strictly limited by the regulatory bodies. In many instances they are lower than
the spurious emissions from electronic apparatus that has been certified. In
view of this it is anticipated that they will cause no noticeable interference
to other carrier based licensed users. Nevertheless regulatory bodies are moving
forward cautiously so that users who already have spectrum allocations are not
affected.
Two UWB, ultra wideband technologies
Despite the single named used for the ultra wideband (UWB) transmissions, there
are two very different technologies being developed.
- Carrier free direct sequence ultra wideband technology:
This form of ultra-wideband technology transmits a series of impulses. In
view of the very short duration of the pulses, the spectrum of the signal
occupies a very wide bandwidth.
- MBOFDM, Multi-Band OFDM ultra wideband technology: This
form of ultra wideband technology uses a wide band or multiband orthogonal
frequency division multiplex (MBOFDM) signal that is effectively a 500 MHz
wide OFDM signal. This is 500 MHz signal is then hopped in frequency to
enable it to occupy a sufficiently high bandwidth.
Both these systems are described in greater detail in
articles within the Wireless Technologies section of the Radio-Electronics.Com
website.
Advantages and disadvantages
Both these systems have their advantages and disadvantages, each one having its
supporters and applications for which it is most suited. The impulse based
technology, also called direct sequence ultra wideband (DS-UWB) in view of some
of the techniques used is being used for a number of high data rate data
transmissions such as short range video transmissions. MBOFDM on the other hand
is being adopted for Wireless USB where it performs well.
FCC UWB definition
To date the FCC in the USA has approved UWB, ultra wideband technology for
indoor and short range outdoor communication, but with restrictions on the
frequencies over which the transmission can spread as well as the power limits.
This will enable the UWB ultra wideband transmissions to communicate
successfully, but without affecting existing 'narrowband' transmissions
To achieve these requirements the FCC has mandated that UWB,
ultra wideband transmissions can legally operate in the range 3.1 GHz up to 10.6
GHz, at a limited transmit power of -41dBm/MHz. Additionally the transmissions
must occupy a bandwidth of at least 500 MHz, as well as having a bandwidth of at
least 20% of the centre frequency. To achieve this last requirement, a
transmission with a centre frequency of 6 GHz, for example, must have a
bandwidth of at least 1.2 GHz. Consequently, UWB provides dramatic channel
capacity at short range that limits interference.
The fact that very low power density levels are transmitted
means that the interference to other services will be reduced to limits that are
not noticeable to traditional transmissions. Additionally the lowest frequencies
for UWB, ultra wideband have been set above 3 GHz to ensure they do not cut
across bands currently used for GPS, cellular and many other services.
Summary
UWB, ultra wideband technology is still in its infancy. Despite this it is being
recognised as a technology with a huge capability and as such it is being
adopted in many new areas. Many silicon manufacturers have already developed
solutions which are being demonstrated, and more are being developed.
Accordingly this new technology shows a significant degree of promise and should
be a major force in the wireless industry in years to come. Which flavour of
UWB, ultra wideband technology is the more widely used, and the areas in which
they are adopted remains to be seen.
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