COGNITIVE RADIO AND THE PRIMARY EXCLUSIVE REGION

JOBIN JOSEROLL NO:5

M.TECH S1 CE&SP

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

Cognitive Radio Introduction… spectrum utility

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

Cognitive radio and SDR

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..

Physical architecture

(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

CR network architecture

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

Spectrum sensing

Spectrum management

Spectrum mobility

Spectrum sharing

CR: Main functions

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

Primary exclusive region cont..

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

Interference

as R→

Lower bound is tight when is small, but becomes loose as

increases.

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 average total interference from the cognitive users in and

to Rxp is

Denote

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.

The interference is given by

As R→, the upper bound becomes

Comparisons of the bounds on E []:

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

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