wireless communication

1. PRESENTATION ON
COOPERATIVE SENSING
IN COGNITIVE RADIOS
PRESENTED BY:-
SHEWANGI
M.E(IT)
16-812

2. INTRODUCTION
 The concept of cognitive radio was first proposed by Joseph
Mitola in 1998.
 CR is a system or model for wireless communication. It uses
methodology of sensing and learning from the environment.
 Cognitive radio works on SDR (software defined radio).
 The ever increasing demand for higher data rate in wireless
communication in the face of limited or underutilized spectral
resources has motivated the introduction of cognitive radio.

3. figure 1 : Elements of cognitive radio
Cognitive radio
Spectrum
Sensing
Spectrum
Decision
Spectrum SharingSpectrum Mobility

4.  Licensed Spectrum :- These are licensed bands,
means that individual companies pay a licensing fee
for the exclusive right to transmit on assigned
channels within that band in a given geographic area..
Applications: Mobile telephony, GPRS
 Unlicensed Spectrum:- Unlicensed wireless
technologies don't require any permission, so long as
products and users going with the rules associated
with that unlicensed band (for example, maximum
transmission power). Unlicensed wireless
technologies are, by nature, vulnerable to
interference. .
Applications: WLAN, Wi-Fi

5. SPECTRAL SENSING
 The Secondary User (SU) will continuously monitor the
Primary User (PU), if it is free and if it is engage after
sometime , SU will quit that particular PU and switch to
another frequency band to avoid intrusion. This
technique is known as spectrum sensing.
 In the new spectrum management, licensed users can
share their spectrum with unlicensed users (referred to
as secondary users), thereby increasing the efficiency
of spectrum utilization. This method of sharing is often
called Dynamic Spectrum Access (DSA).

6. FIGURE 2: SPECTRUM SENSING TECHNIQUES

7. TYPES OF SENSING
 Cooperative sensing :-Decision about presence or
absence of PU is made on the basis of sensing
information provided by other SU/CR users present in
same network, having stronger PU signal.
Techniques used in cooperative sensing
 Centralized sensing
 Distributed sensing
 Relay assisted sensing

8. CENTRALIZED SENSING
 In centralized sensing, a central unit collects
sensing information from cognitive devices,
identifies the available spectrum, and broadcasts
this information to other cognitive radios or directly
controls the cognitive radio traffic.
 The cognitive radio central node or can also
organise the various sensor nodes to undertake
different measurements at different times. In this
way it is possible to undertake a number of different
sense actions at the same time. For example, some
nodes may be instructed to detect on channel signal
levels, while others may be instructed to measure
levels on adjacent channels to determine suitable
alternatives in case a channel change is required.

9. Distributed sensing:- In this method cognitive radio
communicate with each other and takes mutual decision
on the basis of presence and absence of primary user. The
iteration is repeated until one decision is made. It has no
master node.
Distributed sensing is more advantageous than centralized
sensing in the sense that there is no need for a backbone
infrastructure and it has reduced cost.
Relay assisted sensing :- In this method ,each cognitive
radio senses the channel and if primary user is detected by
cognitive radio then that channel is vacated without giving
prior knowledge to other cognitive radio nodes. In this
method, sensing information is given in multiple hops and
these hops are called relays.

10. NON COOPERATIVE SENSING
Non-Cooperative sensing :- Cognitive Radio works
on its own, it does not have coordinate with the
others for sensing
Techniques used in non cooperative sensing
 Matched filter method
 Energy detection method
 cyclo stationary method

11. ENERGY DETECTOR METHOD
 If the secondary user cannot gather sufficient
information about the PU signal, the optimal
detector (due to fewer complexities) is an energy
detector, also called as a radiometer . It is common
method for detection of unknown signals.
 It requires less sensing time and has low power
consumption.
 Disadvantage of this technique that it is unable to
distinguish between PU from other signal source.
This technique has low accuracy as compared to
other techniques.

12. MATCHED FILTER DETECTION
 This filter is used only when the secondary user has
preliminary information about the primary user.
 The basic requirement for best possible performance
is that cognitive radio needs to have prior knowledge
of primary signal transmitted by primary user.
 It needs less detection time as compared to other
techniques. In CR, such knowledge is not readily
available to secondary user therefore; the complexity
of this method becomes high. So this method is not
used practically.

13. CYCLOSTATIONARY METHOD
 In this technique, a cyclostationary signal can vary
periodically with time and this periodicity is used to
detect presence or absence of PU. Due to presence
of this periodicity, these cyclostationary signal
exhibit spectral relationship which is absent in
stationary noise.
 This method is robust to noise uncertainties and
perform better than energy detection. This method
has another good advantage that it is able to
differentiate between CR transmission from various
types of PU signal. It improves the overall CR
throughput.

14. ISSUES IN COOPERATIVE SENSING
 Probability of detection: It is the probability that CR
user will declare the presence of PU truly when it is
present. A miss in detection of PU will lead to
interference with the PU.
 Probability of false alarm: is probability that CR user
will declare the presence of Primary user when it is
actually not present.
 Probability of accurate detection: It is sum of
probability of detection if PU is present and
probability of no detection as PU is absent.

15. FIGURE 3: ELEMENTS OF COOPERATIVE SENSING TECHNIQUE

16. COOPERATIVE ELEMENTS
 Cooperation models consider the modeling of how CR
users cooperate to perform sensing.
 Sensing techniques are used to sense the RF
environment, taking observation samples, and
employing signal processing techniques for detecting
the PU signal or the available spectrum
 Hypothesis testing is a statistical test to determine the
presence or absence of a PU. This test can be
performed individually by each cooperating user for
local decisions or performed by the fusion center for
cooperative decision

17.  Control channel and reporting concerns about how
the sensing results obtained by cooperating CR
users can be efficiently and reliably reported to the
fusion center or shared with other CR users.
 Data fusion is the process of combining the
reported or shared sensing results for making the
cooperative decision. Based on their data type, the
sensing results can be combined by signal
combining techniques or decision fusion rules.

18.  User selection plays important role in determining
the performance of cooperative sensing because it
is used for cooperative gain. It removes issues like
shadowing and fading and reduces the cooperation
overhead. There are various user selection
schemes like centralized and cluster based.
 Knowledge base is a database that stores all
information related to primary user. It serves two
roles in cooperative sensing. It improves detection
performance. Also, it reduces the burden of
cooperative sensing by extract the spectrum
information

19. COGNITIVE RADIO BENEFITS
 Spectrum Efficiency
 Higher bandwidth services
 Improved Quality of service
 Improved coverage
 Less expensive radio