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System Design for Cognitive Radio Communications. Mustafa Emin Şahin Hüseyin Arslan ELECTRICAL ENGINEERING DEPARTMENT UNIVERSITY OF SOUTH FLORIDA TAMPA, FL, USA. Outline. Cognitive Radio Concept Opportunistic Spectrum Usage Spectrum Sensing Cooperation of Transmitter and Receiver - PowerPoint PPT Presentation
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System Design for Cognitive Radio Communications
Mustafa Emin ŞahinHüseyin Arslan
ELECTRICAL ENGINEERING DEPARTMENTUNIVERSITY OF SOUTH FLORIDA
TAMPA, FL, USA
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Outline
Cognitive Radio Concept
Opportunistic Spectrum Usage Spectrum Sensing Cooperation of Transmitter and Receiver Spectrum Shaping by Adaptive Pulse Design
Range of Cognitive Communications
Numerical Results
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Current State of Wireless
Wireless communication systems are evolving substantially
New mobile radio systems aim at higher data rates and a wide variety of applications
Higher capacity and performance required through a more efficient use of limited resources
Two cutting edge solutions are UWB and cognitive radio
UWB is considered to supplement Cognitive Radio
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Cognitive Radio Traditional system design allocates fixed amounts of
resources to the user
Adaptive design identifies the requirements of the user, and then allocates just enough resources
Introducing advanced attributes to the adaptive design Multi-dimensional awareness Sensing Learning
Cognitive Radio
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Cognitive Radio Concept
Opportunistic Spectrum Usage Spectrum Sensing Cooperation of Transmitter and Receiver Spectrum Shaping by Adaptive Pulse Design
Range of Cognitive Communications
Numerical Results
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Opportunistic Spectrum Usage
Opportunistic Spectrum Usage: licensed bands can be utilized by secondary users when
they are not being used by their owners leads to the most efficient exploitation of the entire
spectrum
The operation of unlicensed systems should not affect the primary users
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Spectrum Sensing Cognitive radios periodically scan the spectrum and detect
the white bands The target spectrum to be sensed should be limited
The received signal can be sampled (after the down-conversion) at or above the Nyquist rate and can be processed digitally
The computational burden associated with spectrum sensing can be restricted to a reasonable level limited hardware complexity
The analog front-end required for a very wide spectrum scan (wideband antenna, wideband amplifiers and mixers), which have a rather high cost, can be avoided
It can be prevented that a single type of cognitive radio occupies the majority of the bands that are open to opportunistic usage
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Spectrum Sensing Spectrum allocation for different types of
cognitive radios can be done by regulatory agencies depending on the intended range and the throughput requirements
high data rate cognitive radios aiming at wide range applications (like TV broadcast systems)wider target spectra at lower frequency bands
relatively low rate, short range communication devices (like cordless phones) narrower bands at higher frequencies
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Cooperation of Transmitter and Receiver Both the transmitter and the receiver have transmission
and reception capabilities In order to match the results of the spectrum sensing, each
of them transmits the information regarding the white spaces they have detected
The transmission of spectrum sensing results is done via low power UWB signaling
Since UWB transmission will be underlay, it can be done simultaneously with the real data communication without affecting each other
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Cooperation of Transmitter and Receiver
A low-complexity and low cost solution is OOK based impulse radio UWB signaling using energy detector receivers
Once both parties receive the spectrum sensing information from the other party, they logically ’AND’ the white spaces
Depending on these common white spaces, each party designs a new pulse shape
what the receiving party uses as the template to match the received pulse will be (almost) the same as the transmitted pulse by the other party a successful matched filtering
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Spectrum Shaping Cognitive transceiver has to be able to
dynamically shape the spectrum of the transmitted pulse to fill the spectrum opportunities
possible options employing OFDM carriers as in the case of UWB-OFDM employing Prolate Spheroidal Wavelet Functions (PSWF)
leakage from the opportunity bands to the licensed systems in the adjacent bands should be kept at a negligible level
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Spectrum Shaping
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Spectrum Shaping An alternative method based on the usage of
raised cosine filters The center frequencies and bandwidths of each
opportunity are determined The most suitable raised cosine filters are
selected The selected filters are multiplied with digitally
generated cosine signals Sum of the separately generated signals is
transmitted
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Spectrum shaping via raised cosine filtering
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Cognitive Radio Concept
Opportunistic Spectrum Usage Spectrum Sensing Cooperation of Transmitter and Receiver Spectrum Shaping by Adaptive Pulse Design
Range of Cognitive Communications
Numerical Results
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Range of Cognitive Communications In order to exchange the sensing information,
there should not be a gap between the sensing ranges of both parties
the receiving sensitivity of both parties has an important role in determining the range of communication
We assume a rather high sensitivity around −120dBm to −130dBm and free space propagation according to the Friis equation the range of one-to-one cognitive communication is limited to 50m to 150m
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Range of Cognitive Communications
Network of Cognitive Transceivers
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Range of Cognitive Communications A network of collaborating cognitive nodes
may be an effective solution if the targeted range is wider than 50-150 m,
or if the cognitive devices are experiencing
shadowing (and are hardly able to detect the primary users)
Consider a cognitive network whose nodes communicate with each other using UWB to exchange spectrum information
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Range of Cognitive Communications Looking at the BER expression for OOK modulated
UWB signals
it is seen that increasing Ns results in lower BER, a very advantageous feature of UWB called processing gain
By applying enough processing gain, farthest nodes in a cognitive network can share the spectrum sensing information
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Range of Cognitive Communications processing gain lowered throughput; not a limiting factor
because a quite low data rate is enough to transmit the spectrum sensing information
By enabling all the nodes in a cognitive network talk to each other via UWB, there is no need to allocate a separate channel for sharing the sensing
information, or to employ a centralized controller
The sensing information received from all the other nodes in the network can be combined in each node, and pulse design can be done
This way, the range of cognitive communications can be extended to the coverage area of a medium-sized network
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Cognitive Radio Concept
Opportunistic Spectrum Usage Spectrum Sensing Cooperation of Transmitter and Receiver Spectrum Shaping by Adaptive Pulse Design
Range of Cognitive Communications
Numerical Results
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Numerical Results List of Simulation Parameters
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Numerical Results BER vs. the distance between the nodes for UWB signaling
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Numerical Results Repetition rate required for reliable UWB signaling vs.
distance (taking the BER at 40m as a reference)
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Numerical Results Probability of the licensed transmitter (transmitting at -60 dBm)
being detected by the cognitive network at different node sensitivity levels
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Thanks for attending !
ANY QUESTIONS?