System Design for Cognitive Radio Communications

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System Design for Cognitive Radio Communications

Mustafa Emin ŞahinHüseyin Arslan

ELECTRICAL ENGINEERING DEPARTMENTUNIVERSITY OF SOUTH FLORIDA

TAMPA, FL, USA

CrownCom 2006Mykonos Island, Greece

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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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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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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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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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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 !

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System Design for Cognitive Radio Communications

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