Are you interested
in this topic. Then mail to us immediately to get the full report.
THE success of future wireless systems will depend on the concepts
and technology innovations in architecture and in efficient utilization
of spectral resources. There will be a substantial need for more
bandwidth as wireless applications become more and more sophisticated.
This need will not be satisfied by the existing frequency bands
being allocated for public mobile radio even with very evolved
and efficient transmission techniques. Also wide ranges of potential
spectral resources are used only very rarely. In the presented
approach that is called spectrum pooling, different spectrum owners
(e.g. military, trunked radio etc.) bring their frequency bands
into a common pool from which rental users may rent spectrum.
Spectrum pooling reflects the need for a completely new way of
radio resource management. Interesting aspects of the spectral
efficiency gain that is obtained with the deployment of spectrum
rental system needs to be highly flexible with respect to the
spectral shape of the transmitted signal. Spectral ranges that
are accessed by licensed users have to be spared from transmission
power. OFDM modulation is a candidate for such a system as it
is possible to leave a set of subcarriers unmodulated. Thus, providing
a flexible spectral shape that fills the spectral gaps without
interfering with the licensed users. A schematic example of this
method is given in Fig. 1. Furthermore, spectrum pooling systems
are not supposed to compete with existing and upcoming 2G and
3G standards. They are rather meant to be a complement in hot
spot areas with a high demand for bandwidth (e.g.airports, convention
centers etc.). Hence, it is straightforward to apply modified
versions of OFDM based wireless LAN standards like IEEE802.11a
many modifications to consider in order to make wireless LANs
capable of spectrum pooling. They range from front end via baseband
processing to higher layer issues. One important task when implementing
spectrum pooling is the periodic detection of idle subbands of
the licensed system delivering a binary allocation vector as shown
in Fig. 1. A detailed description of how to perform this in an
optimal fashion is given. We propose an approach where any associated
mobile terminal of the rental system conducts its own detection.
This detection is the first step in a whole protocol sequence
that is illustrated in Fig. 2. Having finished the detection cycle,
the results are then gathered at the access point as visualized
in Fig. 2b). The received information can be processed by the
access point which basically means that the individual binary
(allocated/deallocated) detection results are logically combined
by an OR operation.
a common pool allocation vector which is mandatory for every mobile
terminal is broadcast in a last phase as shown in Fig. (2c). It
is shown that this distributed technique is more reliable and
yields a higher system throughput than only having the access
point conduct a spectral detection. However, if the collection
of the detection results is realized by sending a MAC layer data
packet for each mobile terminal, the signaling overhead will be
very high as the number of mobile terminals can be as high as
250 in the considered wireless LAN systems.
Now, one could
reduce the number of detecting mobile terminals. Unfortunately,
this approach has several drawbacks.
The random choice of the
detecting rental users would not guarantee an optimal spatial
distribution of the detecting mobile terminals. The transmission
of these results would still take a lot of time and their correct
reception is disturbed by rental users that have accessed their
subbands since the last detection cycle. One further problem is
the redundancy in the measurement data. Several mobile terminals
can encounter the same constellation of licensed user accesses.
We investigated techniques like the adaptive tree walk protocol
to reduce the amount of measurement data packets but none of them
was satisfactory with respect to duration and robustness.
You may also like this : Electronics Meet Animal Brains, Satellite Radio, Search For Extraterrestrial Intelligence, Line-Reflect-Reflect Technique, Low Power UART Design for Serial Data Communication, Light emitting polymers, Cruise Control Devices, Boiler Instrumentation and Controls , SPECT, Sensors on 3D Digitization , Asynchronous Chips , Optical packet switch architectures , Digital Audio Broadcasting , Cellular Neural Network , FRAM , Wireless Fidelity , Synthetic Aperture Radar System, Touch Screens , Tempest and Echelon, VoCable , Data Compression Techniques , Fractal Image Compression, Computer Aided Process Planning , Space Shuttles and its Advancements , Space Robotics , Welding Robots , Sensotronic Brake Control , Mobile IP , Power System Contingencies , Lightning Protection Using LFAM , Wideband Sigma Delta PLL Modulator, Bioinformatics , Extreme Ultraviolet Lithography , Animatronics, Molecular Electronics , Cellonics Technology , Cellular Digital Packet Data, CT Scanning , Continuously variable transmission (CVT) , High-availability power systems Redundancy options , IGCT , Iris Scanning , ISO Loop magnetic couplers , LWIP , Image Authentication Techniques , Seasonal Influence on Safety of Substation Grounding , Wavelet transforms, Cyberterrorism , Ipv6 - The Next Generation Protocol , Driving Optical Network Evolution,Electronics Seminar Reports, PPT and PDF.