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Introductioncognitive radio conceptcognitive radio requirementsCR architectureCR functionsPrimary exclusive regionProblem formulationNetwork modelChannel and signal modePrimary outage constraintWorst case interference to primary receiverUpper and lower bound calculationComparison of boundsConclusion
contents
Cognition(noun):Cognition is the mental process involved in knowing
learning and understanding things.
Cognitive Radio: Cognitive radio is an intelligent wireless communication
system that is aware of its surrounding environment and uses the
methodology of understand-by-building to learn from the environment and
adapt its internal states to statistical variations in the incoming RF stimuli by
making corresponding changes in its operating parameters.
Cognitive radio concept…
• Proposed by Joseph Mitola III and Gerald in 1998.
• Avoids interference with licensed and unlicensed users.
• Monitors factors in radio environment such as radio
frequency spectrum, user behavior, network state.
• Monitors spectrum and chooses frequencies that minimize
interference to existing communication activity.
• Occupies unused frequency slots and communicates.
Cognitive radio concept contd…
Device
Send information about vacant band to the receiver
Send data to receiver
Search for devices to be communicated
NO
yes
Search for vacant RF band
If present
Negligible interference to licensed users.
Capability to adapt itself with link qualities.
Ability to sense and measure parameters about environment,
channel etc.
Ability to exploit spectrum opportunities.
Adjustable data rate, transmit power, information security and
limited cost.
Flexible pulse shape and bandwidth.
Provide access to multiple users simultaneously.
Cognitive radio requirements
SDR is a general-purpose device in which the same radio tuner and
processors are used to implement many waveforms at many
frequencies.
Provide a very flexible radio functionality by avoiding the use of
application specific fixed analog circuits and components.
Properties of carrier frequency, signal bandwidth, modulation, and
network access are defined by software.
Combination of cognitive engine, SDR, and the other supporting
functionalities (e.g. sensing) results in cognitive radio.
Cognitive radio and SDR cont..
(a) Cognitive radio transceiver and (b)wideband RF/analog
front-end architecture.
In the RF front-end, the received signal is amplified, mixed
and A/D converted.
In the baseband processing unit, the signal is modulated or
demodulated and encoded/decoded.
Physical architecture cont..
Cognitive radio and cognitive networks have same definition
except cognitive networks have more broader perspective that
also include all the network elements.
Applications in dynamic spectrum access, and co-existence and
interoperability of different wireless networks.
Features includes advanced interference management strategies,
efficient use of wireless resources, safe and secure wireless
access methodologies, and excellent Quality of Service (QoS).
Cognitive radio networks
Components of the CR network architecture can be classified as the primary network and the
cognitive network.
Basic elements of the primary and unlicensed networks are:
Primary user
Primary Base-Station
Cognitive Radio User
Cognitive Radio Base-Station
Different access types includes:
Cognitive Radio Network Access
Cognitive Radio Ad Hoc Access
Primary Network Access
CR network architecture cont..
The first phone call over a cognitive radio network was made on Monday 11 January 2010 in Centre for Wireless Communications at University of Oulu using CWC's cognitive radio network cramnet , that has been developed solely by CWC researchers
Depending on the set of parameters divided as
Full Cognitive Radio
Spectrum Sensing Cognitive Radio
Depending on the parts of the spectrum available for cognitive
radio divided as
Licensed Band Cognitive Radio
Unlicensed Band Cognitive Radio
Cognitive radio types
Detecting the unused spectrum and sharing it without harmful
interference with other users.
Primary user detection the most efficient way.
Spectrum sensing techniques are divided into 3 categories
Transmitter detection
Cooperative detection
Interference based detection
Spectrum sensing
Capturing the best available spectrum to meet user
communication requirements.
Cognitive radios should decide on the best spectrum band to
meet the Quality of service requirements over all available
spectrum bands.
Management functions are classified as
Spectrum analysis
Spectrum detection
Spectrum management
Process where a cognitive radio user exchanges its frequency
of operation.
Target to use the spectrum in a dynamic manner by allowing
the radio terminals to operate in the best available frequency
band.
Maintains seamless communication requirements during the
transition to better spectrum.
Spectrum mobility
Cognitive network consisting of a single primary transmitter
and multiple secondary, or cognitive users.
Primary transmitter, located at the center of the network.
The PT communicates with primary receivers within a disc
called the primary exclusive region (PER).
Inside the PER, no cognitive users may transmit.
Outside the PER cognitive users may transmit, provided they
are at a certain protected radius from a primary receiver.
Primary exclusive region
radius of primary exclusive region.
ε: protected radius or protected band.
λ:cognitive band density.
Aggregated interference from the cognitive transmitters to
primary receiver within the PER is analyzed.
Bounds on the radius of the PER, showing its interdependence
on the receiver protected distance and other system
parameters.
Primary exclusive region cont..
A network in which the cognitive users are mobile, or are static
but joining and leaving the network at random is considered.
In the presence of the random interference from the cognitive
users, the primary user must be guaranteed an outage capacity.
Must hold in the worst case scenario, which has the primary
receiver at the edge of the PER.
Expected amount of interference from the cognitive users on
the primary user is calculated.
Problem formulation
Upper and lower bounds on this interference is found.
The average interference remains bounded irrespective of the
number of cognitive users.
A network model is assumed and lower and upper bounds for
the expected interference seen at the primary receiver is
formulated.
It has two type of users : primary and cognitive
Analyze on the distance from the primary users at which the
cognitive users can operate in order to ensure an outage
probability for the primary users.
Three models are considered :
Network model
Channel and signal models
The primary outage constraint
In signal mode there is no multiuser detection.
Also signals are statistically independent.
The outage constraint must hold for all primary users.
Pr [≤] ≤ β
Primary receiver at the edge of the PER.
Interference power experienced by the primary receiver is
found.
Worst interference to the primary receiver
The distance d between the interfering transmitter and primary
receiver is
d(r,θ) =
The expected interference power experienced by the primary
receiver from all users
where
λ-band density, P-transmitting power of user.
Two lower bounds and an upper bound on the interference
power.
A first lower bound on E[]:
re-center the network at the primary receiver Rxp.
new exclusive region has radius 2.
outer radius of R−
set of cognitive users included in the new ring will be a
subset of the original.
Upper and lower bounds on the average interference
A second lower bound on E[]:
Approximates the interference region by two half-planes.
Cognitive users in the two half-planes and which
touch the circle of radius + ε is considered.
The distance d from any point on this line to Rxp satisfies
d .
Ф is uniform in [-2, /2].
The second lower bound on the average interference is
As R→
The interfering transmitters close to the primary receiver for a
small ε or large this lower bound is tighter than the previous
one.
An upper bound on E []:
Re-center the network at the primary receiver.
Reduce the exclusive region radius, centered at Rxp to ε.
Extend the outer network radius, also centered at Rxp to
+ R.
Set of cognitive transmitters contained within these
two new circles is a superset of the original, creating
an
upper bound on the interference.
comparing upper bounds and lower bounds for various values
of fixing α=4, λ=1, P=1, ε=2.
Assume an infinite network with R→
The first lower bound is tight for small values of
The second lower bound is asymptotically tight as →
The upper bound is quite loose.
This bounds provide a good indication for the range of
interference power.
Crucial importance in the design of network parameters.
Guarantees primary users a certain level of performance.
Analyzes the average aggregated interference power.
Obtained bounds relating the design parameters , ε, P.
Bounds help in the design of cognitive networks with PER.
Conclusion
[1]M. Vu, N. Devroye, and V. Tarokh, “The primary exclusive region in cognitive networks," IEEE Consumer Commun. Networking Conf. (CCNC), Jan. 2008.[2]N. Hoven and A. Sahai, “Power scaling for cognitive radio," in Proc. International Conf. Wireless Networks, Commun. Mobile Computing, June 2005.[3] white paper, spectrum sensing[4] William H. Tranter, K. Sam Shanmugan, Principles of Communication Systems Simulation with Wireless Applications[5]http://www.wikipedia.org.
References