Transcript COGNITIVE RADIO TECHNICAL SEMINAR Presented by Sangeetha Nandan (1ay05cs057)

COGNITIVE RADIO
TECHNICAL SEMINAR
Presented by
Sangeetha Nandan (1ay05cs057)
INTRODUCTION

Cognitive radio is a paradigm for wireless
communication in which either a network or
a wireless node changes its transmission or
reception parameters to communicate
efficiently avoiding interference with licensed
or unlicensed users. This alteration of
parameters is based on the active monitoring
of several factors in the external and internal
radio environment, such as radio frequency
spectrum, user behavior and network state.
ARCHITECTURE OF CR
A. Physical Layer Functions

1) Spectrum Sensing: The main function of
the physical layer is to sense the spectrum
over all available degrees of freedom
(time, frequency and space) in order to
identify sub-channels currently available
for transmission.
2) Channel Estimation
 In
order to set up the link, channel
sounding is used to estimate the
quality of sub-channels between SUs
that want to communicate. The
transmission parameters (transmit
power, bit rate, coding, etc.) are
determined based on the channel
sounding results
3) Data Transmission

CR’s optimally uses the available spectrum as
determined by the spectrum sensing and
channel estimation functions. Therefore it
should have the ability to operate at variable
symbol rates, modulation formats (e.g. low
to high order QAM), different channel
coding schemes, power levels and be able to
use multiple antennas for interference
nulling, capacity increase (MIMO) or range
extension
B. Link Layer Functions
 Group

It is assumed that any secondary station will belong to a SU
Group. A newly arriving user can either join one of the existing
groups or create a new one through the Universal Control
Channel.
 Link

Management
Management
covers the setup of a link in order to enable the communication
between two SUs and afterwards the maintenance of this SU
Link for the duration of the communication.
 Medium Access

Control
As long as it can be assured that all Sub-Channels are used exclusively, i.e.
all Sub-Channels used by one SU Link cannot be used by any other SU
Link this problem comes down to a simple token-passing algorithm
ensuring that only one of the two communication peers is using the link
.
Types of Cognitive Radio
Depending on the set of parameters taken
into account in deciding on transmission and
reception changes, we can distinguish certain
types of cognitive radio.
The main two are:
 Full cognitive radio
 Spectrum sensing cognitive radio

(Contd.)
depending on the parts of the spectrum
available for cognitive radio, we can
distinguish:
 Licensed Band Cognitive Radio
(IEEE 802.22)
 Unlicensed Band Cognitive Radio
(IEEE 802.15)

FUNCTIONS OF CR
The main functions of Cognitive Radios
are:
 Spectrum Sensing :
detecting the unused spectrum and
sharing it without harmful interference
with other users.

(Contd.)

Spectrum sensing techniques can be
classified into three categories:
◦ Transmitter detection: cognitive radios must
have the capability to determine if a signal
from a primary transmitter is locally
present in a certain spectrum, there are
several approaches proposed:
 matched filter detection
 energy detection
 cyclostationary feature detection
Match filter detection

is obtained by correlating a known signal,
or template, with an unknown signal to
detect the presence of the template in
the unknown signal.
(Contd.)
◦ Cooperative detection: refers to spectrum
sensing methods where information
from multiple Cognitive radio users are
incorporated for primary user
detection.
(Contd.)
Spectrum Management: Capturing the
best available spectrum to meet user
communication requirements
 management functions can be classified as:
◦ spectrum analysis
◦ spectrum decision

(Contd.)

Spectrum Mobility: is defined as the
process when a cognitive radio user
exchanges its frequency of operation.
Cognitive radio networks target to use
the spectrum in a dynamic manner by
allowing the radio terminals to operate in
the best available frequency band,
maintaining seamless communication
requirements during the transition to
better spectrum .
(Contd.)

Spectrum Pooling :is a resource sharing
strategy that organizes the available
spectrum into a spectrum pool which is
then optimized for a given application .
Once a primary user appears, secondary
users need to cease transmission if they
will cause interference.
Cognitive radio network
The cognitive radio network is an intelligent
multi user wireless communication system
that embodies the following list of primary
tasks:
 •to perceive the radio environment (i.e.,
outside world) by empowering each user’s
receiver to sense the environment on a
continuous-time basis
 •to learn from the environment and adapt
the performance of each transceiver

(Contd.)
•to facilitate communication between
multiple users through cooperation in a
self-organized manner
 •to control the communication processes
among competing users through the
proper allocation of available resources

Software defined radio

Software-Defined Radio (SDR) system is
a radio communication system where
components that have typically been
implemented in hardware (e.g. mixers,
filters, amplifiers,
modulators/demodulators, detectors. etc.)
are instead implemented using software
on a personal computer or other
embedded computing devices.
(Contd.)

A basic SDR may consist of a computer (PC)
equipped with a sound card, or other analogto-digital converter, preceded by some form of
RF front end. Significant amounts of signal
processing are handed over to the general
purpose processor, rather than done using
special-purpose hardware. Such a design
produces a radio that can receive and transmit
a different form of radio protocol (sometimes
referred to as a waveform) just by running
different software. It is the enabler of Cognitive
radio.
Functions provided by SDRs
1. The radio hardware. The radio hardware
includes radio frequency circuitry and
signal processing devices.
 2. Software modules. Software modules
represent code that has been loaded into
field programmable gate arrays (FPGAs),
digital signal processors (DSPs), or
embedded general purpose processors.

(Contd.)

3. Middleware. The middleware layer
attempts to reduce the details of specific
devices and software modules to
common abstractions.

4. Device Manager: The device manager
loads radio configurations into the
hardware components and sets-up the
logical radios.
(Contd.)
5. Logical Radio Layer: Depending on the
radio configuration, the hardware and
software can be programmed to act like
multiple radio links .
6. Module Libraries: The module libraries are
collections of radio functions.
(Contd.)

7. Rules Engine and Policies: Policies are
used to limit the operation of the radio
due to regulatory, geographical, or
physical constraints.

8. Smart Controller: A “smart controller”
manages all of the radio resources
outlined above.
ISSUES IN CR
 Spectrum
management
 Spectrum utilization: presence
of white spaces
 Spectral co-existence
 Spectrum sharing
Spectrum management

spectrum management involves assigning
particular frequencies to specified users.
This can be done through administrative
methods or by means of a market
process, such as an auction. Additionally,
some spectrum may be reserved for
unlicensed use (this is sometimes referred
to as the spectrum commons). All users
satisfying certain restrictions, for example
on power levels, might have access to
unlicensed bands.
Spectral utilization
white spaces refer to frequencies
allocated to a broadcasting service but
not used locally
 unlicensed devices that can guarantee that
they will not interfere with assigned
broadcasts can use the empty white
spaces in spectrum

Spectral coexistence
Two approaches have been given:
 Collaborative approach: radio of different
technologies exchange information
regarding the frequency usage of the
spectrum.
 Non collaborative: radio devices sense the
frequency spectrum occupancy and
determine by itself the channel definition
without communicating with other users.

Spectral sharing


Stringent spectrum sensing requirements
◦ Various types of primary users
◦ Low SNR environment
◦ Fast wideband sensing
◦ Robust sensing (to noise uncertainty,
interference …)
Can the acquired on/off status be used to
protect primary users?
◦ Channel asymmetry
◦ Shadowing, hidden terminal issue
◦ Transmission power asymmetry
CONCLUSION
There are opportunities to explore
“spectrum white spaces”
 To promote white space reuse
◦ technically, though challenging, effective
solutions are needed to protect the
primary users
◦ economically, good business models are
needed to make both primary users and
secondary users happy!

(Contd.)

Cognitive radio -> cognitive radio networks
◦ How to acquire cognition
 PHY sensing
 Network layer traffic sensing
◦ Cognitive MAC: Control information sharing,
cooperation, …
◦ Distributed processing
◦ Other issues (security, trust, …)

Let us work together to make cognitive radio
(networks) from imagination to reality!
(Contd.)
Cognitive radio can be used in the
following fields:
 Signal processing
 Communication theory
 Radar systems
 Control theory

bibliography
Wikipedia.org
 IEEE xplore
 www.technologyreview.com
 www.cognitiveradio.wireless.vt.edu
 IEEE papers

THANK YOU