Cooperative Spectrum Sensing Technique Based on Blind Detection Method

International Journal of Advanced Engineering, Management and Science (IJAEMS) [Vol-2, Issue-10, Oct- 2016]
Infogain Publication (Infogainpublication.com) ISSN: 2454-1311
www.ijaems.com Page | 1772
Cooperative Spectrum Sensing Technique Based
on Blind Detection Method
B. Vijayalakshmi1
, P. Siddaiah2
1
GVP College of Engineering for Women, Visakhapatnam, India,
2
Acharya Nagarjuna University (ANU), Guntur, India
Abstract— Spectrum sensing is a key task for cognitive
radio. Our motivation is to increase the probability of
detection of spectrum sensing in cognitive radio. The
spectrum-sensing algorithms are proposed based on the
statistical methods like EVD,CVD of a covariance matrix.
In this Two test statistics are then extracted from the sample
covariance matrix. The decision on the signal presence is
made by comparing the two test statistics.The Detection
probability and the associated threshold are found based on
the statistical theory. In this paper, we study the
collaborative sensing as a means to improve the
performance of the proposed spectrum sensing technique
and show their effect on cooperative cognitive radio
network. Simulations results and performances evaluation
are done in Matlab and the results are tabulated.
Keywords— Cooperative Spectrum, Cognitive radio,
Spectrum Sensing, Eigenvalue-based Detection.
I. INTRODUCTION
The electromagnetic spectrum comprises of frequency
spectrum with varied bandwidths. The radio frequency
spectrum involves electromagnetic radiation with
frequencies between 300 Hz to 3000 GHz. The use of
electromagnetic spectrum is licensed by governments for
wireless and communication technologies. Spectrum
scarcity is the main problem as the demand for additional
bandwidth is going to increase. Measurement studies have
shown that the licensed spectrum is relatively unused across
many time and frequency slots. The Federal
Communications Commission (FCC) published a report
prepared by Spectrum Policy Task Force (SPTF) This
report indicates that most of the allotted channels are not in
use most of the time and some are partially occupied while
others are used most of the time. One of the most important
and recommended solution for the problem of spectrum
scarcity is cognitive radio (CR) as described by Joseph
Mitola in his doctoral dissertation Cognitive radio
technology is considered as the best solution because of its
ability to rapidly and autonomously adapt operating
parameters to changing requirements and conditions Main
functions of cognitive radio are spectrum sensing, spectrum
management, spectrum mobility and spectrum sharing.
Spectrum sensing detects the unused spectrum. There are
several spectrum sensing techniques that were proposed for
cognitive radio. These techniques are mainly categorized
into two:
1) Blind sensing techniques
2) Signal specific sensing techniques
While the blind sensing techniques don’t need any prior
knowledge about the transmitted signal, signal specific
sensing techniques need some information about the
features of the signal such as carrier frequency, symbol
period, modulation type, etc. This classification leads to
decide whether one of these choices best fit the CR.The
method does not need channel and signal information as
prior knowledge. has better performance compared with
eigenvalue without noise power. The proposed method has
a higher probability of detection at low SNR compared with
Maximum eigenvalue. In this paper a new scheme of the
algorithms are implemented using random matrix theories
(RMT) which produce accurate results. The sensing based
on the concept of sample covariance matrix and eigenvalues
is proposed. The ratios of distributions and probabilities of
detection (Pd) and the probabilities of false alarm (Pfa) are
calculated for the proposed algorithms. Thresholds values
for given Pfa are also established Also several simulations
are done based on the sample covariance matrix we extract
the test statistics and compare the results..
The rest of this paper is organized as follows: The detection
algorithms and in Section II and Section III gives the
performance analysis and finds thresholds for the
algorithms. Simulation results for various types of signals
are given in Section IV. Conclusions are drawn in Section
V.

II. SPECTRUM SENSING BASED ON
STATISTICAL MODEL
The system comprises of a receiver/detector with an
antenna which is connected to signal processing unit to
process the signal. The received signal is sent to the
processing unit by an antenna. For detecting the signal, we
have used hypothesis testing. There are two hypothesis
namely H0 or null hypothesis and H1 or alternate
hypothesis. H0 is the representation for signal which is not
present or the signal which only has noise. H1 is the
representation where both signal and noise are present at
same time. The probability of detection and the probability
of false alarm are important for channel sensing. Probability
of false alarm(Pfa) describes the presence of the primary
user at the hypothesis H0 where as probability detection(Pd)
describes the presence of the primary user signal at the
hypothesis H1.Blind Signal Processing is one of the
spectrum sensing approaches which do not depend on the
information of the primary signal or noise and hence they
are called as blind detection schemes. Two of the most
popular blind detection schemes are the following :
• Covariance based spectrum sensing
• Eigen value based spectrum sensing
III. COVARIANCE BASED SPECTRUM
SENSING
Let xc(t) = sc(t) + ηc(t) be the continuous-time received
signal, where sc(t) is the possible primary user’s signal and
ηc(t) is the noise. ηc(t) is assumed to be a stationary process
satisfying
E(ηc(t)) = 0, E(η2c (t)) = σ2η, and
E(ηc(t)ηc(t +τ )) = 0 for any τ _= 0.
We are interested in the frequency band with central
frequency fc and bandwidth W. We sample the received
signal at a sampling rate fs, where fs ≥ W. Let Ts = 1/fs be
the sampling period. For notation simplicity, we define x(n)
Δ= xc(nTs), s(n) Δ= sc(nTs), and η(n) Δ= ηc(nTs).
There are two hypotheses:
1) H0, i.e., the signal does not exist, and
2) H1, i.e., the signal exists.
The received signal samples under the two hypotheses are
given by
H0 : x(n) =η(n) (1)
H1 : x(n) =s(n) + η(n) (2)
respectively, where s(n) is the transmitted signal samples
that passed through a wireless channel consisting of path
loss, multi path fading, and time dispersion effects; and η(n)
is the white noise, which is having mean zero and variance
σ2η. s(n) can be the superposition of the received signals
from multiple primary users. No synchronization is needed
here. diagonal elements of Rx should be nonzeros.
3.1 Covariance Based Spectrum Sensing Algorithm
outline
Step 1 : The received signal is sampled, as described above.
Step 2 : Choose a smoothing factor L and a threshold γ1,
where γ1 should be chosen to meet the requirement for the
probability of false alarm.
Step 3: Compute the autocorrelations of the received signal
λ(l), l = 0, 1, L − 1, and form the sample covariance matrix.
Step 4; Compute rnn(Ns)) where rnm(Ns) are the elements
of the sample covariance matrix ˆrx(Ns). Step 5: Determine
the presence of the signal based on T1(Ns), T2(Ns), and
threshold γ1. That is, if T1(Ns)/T2(Ns) > γ1, the signal
exists; otherwise, the signal does not exist.
3.2 Eigen value based detection Eigen values are scalar
values called lambda (λ) of a square matrix A, if there is a
nontrivial solution of a vector x called eigen vector such
that: (A -λI) x=0 Or (A- λI) =0. The idea of Eigen values is
used in signal. Detection is to find the noise in signal
samples by finding the correlation between samples. Ideally
noise samples are uncorrelated with each other. When there
is no signal, the received signal covariance matrix become
identity matrix multiply by noise power (2I) which results
all Eigen values of the matrix become same as noise
power.The main advantage of Eigen value based technique
is that it does not require any prior information of the PU’s
signal and it outperforms Energy detection techniques,
especially in the presence of noise covariance uncertainty.
3.3 Eigen value Detection Algorithms:
3.3.1 Maximum-Minimum Eigen value (MME)
Detection:
The algorithm steps for this detection method is as follow:
Step 1: Covariance Matrix of the received signal is
calculated
Step 2: Maximum and Minimum Eigen values of the Matrix
(λmax, λmin) are computed
Step 3: Decision: If λmax/λmin >γ1 “Signal exists”else
“Signal doesn’t exit”whereγ1 Threshold value for MME
Threshold value (γ) is set using Tracy-widom distribution
which is adaptive technique to set the threshold and it is
given by
3.3.2 Energy with Minimum Eigen value (EME)
detection:

International Journal of Advanced Engineering, Management and Science (IJAEMS) [Vol
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Step 1: Covariance Matrix of the received signal is
calculated
Step 2: Average power Pavgof received matrix is calculated
Step 3: Minimum Eigen values of the Matrix (
computed
Step 4: Decision: If Pavg/λmin >γ2 “Signal exists”
else “Signal doesn’t exit” whereγ2 Threshold value
EME
Threshold value (γ2) is set using yamma distribution which
is adaptive technique to set the threshold and it is given by
3.5Cooperative Spectrum Sensing
In data combination method, each SU make local decision
based on its observed values compared with the chosen
threshold, and then forward the local decision, denoted
Di∈{0,1},to the FC to identify the PU is present or not.
There are usually three combination method based on the
decisions come from different cooperative users, such as
OR rule, AND rule and K-out-of-N rule.For OR rule, if
there just one SU to identify that the PU is active, the FC
will declare the PU active. Thus the cooperative probability
of detection Qd and probability of false alarm
where Pd,iPf,i are the SU local probability of detection and
probability of false alarm, N is the number of cooperative
users.
Assume each SU achieves identical Pd and P
spectrum sensing (i.e., Pd=Pd,i ,Pf=Pf,i
cooperative probability of detection and probab
alarm are
The cooperative missing probability is
Where Pm is the missing probability of local sensing user.
3.5.1 AND Rule:
AND rule is just opposite to OR rule, in which the FC will
declare the PU active only when all cooperative users
International Journal of Advanced Engineering, Management and Science (IJAEMS) [Vol
Infogainpublication.com)
received signal is
of received matrix is calculated
Step 3: Minimum Eigen values of the Matrix (λmin) is
2 “Signal exists”
2 Threshold value for
2) is set using yamma distribution which
is adaptive technique to set the threshold and it is given by:
In data combination method, each SU make local decision
d with the chosen
threshold, and then forward the local decision, denoted
{0,1},to the FC to identify the PU is present or not.
There are usually three combination method based on the
decisions come from different cooperative users, such as
N rule.For OR rule, if
there just one SU to identify that the PU is active, the FC
will declare the PU active. Thus the cooperative probability
of detection Qd and probability of false alarm Qfare
probability of detection and
probability of false alarm, N is the number of cooperative
and Pf in the local
i=1,2,…N). The
and probability of false
is the missing probability of local sensing user.
AND rule is just opposite to OR rule, in which the FC will
declare the PU active only when all cooperative users
identify that the PU is present. Qd and Qf under AND rule
are written as follows.
3.5.2 K-out-of-N rule :
K-out-of-N rule is a trade
rule. In this rule, when more than K users show that the PU
is active, the final decision of cooperative sensing is that the
channel is occupied. So under K
Qf are
Where Pm is the missing probability of local sensing user
IV. SIMULATION RESULTS
Covariance based detection
Table for covariance based detection
No of
samples
Matrix
size
T1
32 8x8 2.7297
64 2x2 2.6000
64 8x8 2.8028
512 8x8 2.8101
1024 4x4 2.7391
1024 8x8 2.8511
) ISSN: 2454-1311
Page | 1774
identify that the PU is present. Qd and Qf under AND rule
N rule is a trade-off between OR rule and AND
rule. In this rule, when more than K users show that the PU
is active, the final decision of cooperative sensing is that the
channel is occupied. So under K-out-of-N rule, the Qd and
is the missing probability of local sensing user
SIMULATION RESULTS
ovariance based detection
Table for covariance based detection
1/T2 Threshold Signal
status
2.7297 9.5008 Signal
not
present
2.6000 2.1455 Signal
present
2.8028 4.6613 Signal
not
present
2.8101 1.6718 Signal
present
2.7391 1.3028 Signal
present
2.8511 1.4446 Signal
present

EME:
Table for maximum minimum eigen value method
No of
samples
SNR
(dB )
λmax/λ
min
Thresho
ld(γ1)
Signal status
32 35 -
1.7862e
+018
1.7025 Signal not
present
1024 35 5.7361e
+015
0.2684 Signal
present
1024 200 -
2.2698e
+016
0.1157 Signal not
present
MME:
Table for energy with minimum eigen value method
Fig 7.5 MME: PD V/S PF for different SNR value
Fig 7.6: COOPERATIVE: PM V/S PF for single SNR value
Fig. 7.7: COOPERATIVE: PM V/S PF for different SNR
value
Fig.7.8: COOPERATIVE: PD V/S PF (AND, OR FUSION
TECHNIQUE
V. CONCLUSIONS
In this paper, several blind spectrum sensing methods based
on dimension analysis is explained in detail. Specifically,
collaborative sensing is considered as a solution to
problems in the presented sensing method.The sensing
detector of spectrum space create new opportunities and
challenges for this type of cooperative spectrum sensing
while it solves some of the traditional problems .We also
propose a new eigenvalue spectrum sensing algorithm based
on covariance matrix. The ratio of the minimum eigenvalue
No of
sampl
es
SNR(d
B )
λmax/λmi
n
Threshold(
γ1)
Signal status
32 35 -
1.7862e+0
18
1.7025 Signal not
present
1024 35 5.7361e+0
15
0.2684 Signal
present
1024 200 -
2.2698e+0
16
0.1157 Signal not
present
512 25 1.0317e+0
16
0.3633 Signal
present

to noise power is used as test statistic the method need only
noise power. The proposed method is better than maximum
eigenvalue detection and the energy detection for correlated
signals. By use of several parameters we have performed
simulations investigated the detection time of the analysis.
REFERENCES
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based Spectrum Sensing Algorithms for Cognitive
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[3] “Discrete Wavelet Packet Transform based Energy
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[4] Mr. Pradeep Kumar Verma, Mr. Sachin Taluja,Prof.
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[7] YongHong Zeng and Ying-Chang Laing, “Maximum-
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[8] B. Rawat, B. B. Bista, S. Shetty, and G. Yan. Waiting
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[9] Harry Urkowitz, (1967) Energy Detection of unknown
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