This document analyzes the performance of energy detection algorithms for spectrum sensing in cognitive radio systems. It discusses how energy detection works by formulating the spectrum sensing problem as a binary hypothesis test to determine if a primary user is present or absent. It finds that increasing the signal-to-noise ratio, sample size, or dynamic detection threshold can improve detection performance. However, it also notes that energy detection is very sensitive to noise uncertainty, which can seriously degrade performance, especially in low signal-to-noise environments. A dynamic thresholding approach is proposed to improve robustness to noise uncertainty.
Spectrum Sensing Detection with Sequential Forward Search in Comparison to Kn...IJMTST Journal
FCC is currently working on the concept of white space users “borrowing” spectrum from free license
holders temporarily to improve the spectrum utilization.
This project provides a relation between a Pf and the SNR value of any spectrum detector to have a
certain performance. Previous spectrum sensing detection techniques are only suitable for Low SNR and
are based on signal information values. But these methods are purely narrow band spectrum applications
In order to overcome the above said drawbacks we propose a novel method of spectrum sensing method
and is suitable for low and high SNR values, the sensed spectrum applicable for wide band applications.
Our proposed method does not require signal information at the receiver and channel information, because
this flexibility sensing rate is very high compared to previous techniques.
Spectrum Sensing Detection Techniques for Overlay UsersIJMTST Journal
Spectrum allocated Agency (FCC) is currently working on the concept of white space users “borrowing” spectrum from free license holders temporarily to improve the spectrum utilization, i.e known as dynamic spectrum access (DSA). CRN systems can utilize dispersed spectrum, and thus such approach is known as dispersed spectrum cognitive radio systems. This project provides a tradeoff between a false alarm probability (Pf) and the signal to noise ratio (SNR) value of any spectrum detector to have a certain performance. Moreover, the performance of the cyclostationary detector (CD) and the matched filter detector (MF) is better than the energy detector(ED) especially at low signal to noise ratio values. Unfortunately, the cyclostationary spectrum sensing method, performance is not satisfying when the wireless fading channels are employed. In this project we provide the best trade off for spectrum usage for over lay users.
On the Performance Analysis of Multi-antenna Relaying System over Rayleigh Fa...IDES Editor
In this work, the end-to-end performance of an
amplify-and-forward multi-antenna infrastructure-based relay
(fixed relay) system over flat Rayleigh fading channel is
investigated. New closed form expressions for the statistics of
the received signal-to-noise ratio (SNR) are presented and
applied for studying the outage probability and the average
bit error rate of the digital receivers. The results reveal that
the system performance improves significantly (roughly 3 dB)
for M=2 over that for M=1 in both low and high signal-tonoise
ratio. However, little additional performance
improvement can be achieved for M>2 relative to M=2 at high
SNR.
Performance Evaluation of Computationally Efficient Energy Detection Based Sp...IJRST Journal
The rapid growth of bandwidth demanding wireless technologies has led to the problem of spectrum scarcity. However, studies show that licensed spectrum is underutilized. Cognitive radio technology promises a solution to the problem by allowing unlicensed users, access to the licensed bands opportunistically. A prime component of the cognitive radio technology is spectrum sensing. Many spectrum sensing techniques have been developed to sense the presence or not of a licensed user. This paper evaluates the performance of the energy detection based spectrum sensing technique in noisy, fading, jamming, interference environments. Both single user detection and cooperative detection situations were investigated. Closed form solutions for the probabilities of detection and false alarm were derived. The analytical results were varied by numerical computations using Monte Carlo method with MATLAB. The performance of the computationally efficient energy detection (CE-ED) techniques were evaluated by use of Receiver Operating Characteristics (ROC) curves over additive white Gaussian noise (AWGN) and fading (Rayleigh & Nakagami-m) channels. Results show that for single user detection, the energy detection technique performs better in AWGN channel than in the fading channel models. The performance of cooperative detection is better than single user detection in fading environments.
Spectrum Sensing Detection with Sequential Forward Search in Comparison to Kn...IJMTST Journal
FCC is currently working on the concept of white space users “borrowing” spectrum from free license
holders temporarily to improve the spectrum utilization.
This project provides a relation between a Pf and the SNR value of any spectrum detector to have a
certain performance. Previous spectrum sensing detection techniques are only suitable for Low SNR and
are based on signal information values. But these methods are purely narrow band spectrum applications
In order to overcome the above said drawbacks we propose a novel method of spectrum sensing method
and is suitable for low and high SNR values, the sensed spectrum applicable for wide band applications.
Our proposed method does not require signal information at the receiver and channel information, because
this flexibility sensing rate is very high compared to previous techniques.
Spectrum Sensing Detection Techniques for Overlay UsersIJMTST Journal
Spectrum allocated Agency (FCC) is currently working on the concept of white space users “borrowing” spectrum from free license holders temporarily to improve the spectrum utilization, i.e known as dynamic spectrum access (DSA). CRN systems can utilize dispersed spectrum, and thus such approach is known as dispersed spectrum cognitive radio systems. This project provides a tradeoff between a false alarm probability (Pf) and the signal to noise ratio (SNR) value of any spectrum detector to have a certain performance. Moreover, the performance of the cyclostationary detector (CD) and the matched filter detector (MF) is better than the energy detector(ED) especially at low signal to noise ratio values. Unfortunately, the cyclostationary spectrum sensing method, performance is not satisfying when the wireless fading channels are employed. In this project we provide the best trade off for spectrum usage for over lay users.
On the Performance Analysis of Multi-antenna Relaying System over Rayleigh Fa...IDES Editor
In this work, the end-to-end performance of an
amplify-and-forward multi-antenna infrastructure-based relay
(fixed relay) system over flat Rayleigh fading channel is
investigated. New closed form expressions for the statistics of
the received signal-to-noise ratio (SNR) are presented and
applied for studying the outage probability and the average
bit error rate of the digital receivers. The results reveal that
the system performance improves significantly (roughly 3 dB)
for M=2 over that for M=1 in both low and high signal-tonoise
ratio. However, little additional performance
improvement can be achieved for M>2 relative to M=2 at high
SNR.
Performance Evaluation of Computationally Efficient Energy Detection Based Sp...IJRST Journal
The rapid growth of bandwidth demanding wireless technologies has led to the problem of spectrum scarcity. However, studies show that licensed spectrum is underutilized. Cognitive radio technology promises a solution to the problem by allowing unlicensed users, access to the licensed bands opportunistically. A prime component of the cognitive radio technology is spectrum sensing. Many spectrum sensing techniques have been developed to sense the presence or not of a licensed user. This paper evaluates the performance of the energy detection based spectrum sensing technique in noisy, fading, jamming, interference environments. Both single user detection and cooperative detection situations were investigated. Closed form solutions for the probabilities of detection and false alarm were derived. The analytical results were varied by numerical computations using Monte Carlo method with MATLAB. The performance of the computationally efficient energy detection (CE-ED) techniques were evaluated by use of Receiver Operating Characteristics (ROC) curves over additive white Gaussian noise (AWGN) and fading (Rayleigh & Nakagami-m) channels. Results show that for single user detection, the energy detection technique performs better in AWGN channel than in the fading channel models. The performance of cooperative detection is better than single user detection in fading environments.
Comparative Analysis of Distortive and Non-Distortive Techniques for PAPR Red...IDES Editor
OFDM is a popular and widely accepted modulation
and multiplexing technique in the area of wireless
communication. IEEE 802.15, a wireless specification defined
for WPAN is an emerging wireless technology for short range
multimedia applications. Two general categories of 802.15
are the low rate 802.15.4 (ZigBee) and high rate 802.15.3
(UWB). In their physical (PHY) layer design, OFDM is a
competing technique due to the various advantages it renders
in the practical wireless media. OFDM has been a popular
technique for many years and adopted as the core technique
in a number of wireless standards. It makes the system more
immune to interference like InterSymbol Interference (ISI)
and InterCarrier Interference (ICI) and dispersive effects of
the channel. It is also a spectrally efficient scheme since the
spectra of the signal are overlapping in nature. Despite these
advantages OFDM suffers from a serious problem of high
Peak to Average Power. This limits the system’s capabilities
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Performance optimization of hybrid fusion cluster based cooperative spectrum ...Ayman El-Saleh
This presentation shows performance Optimization of Hybrid Fusion Cluster-based Cooperative Spectrum Sensing in Cognitive Radio Networks. For more details, send an email to ayman.elsaleh@gmail.com
Exact secure outage probability performance of uplinkdownlink multiple access...journalBEEI
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IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Comparative Analysis of Distortive and Non-Distortive Techniques for PAPR Red...IDES Editor
OFDM is a popular and widely accepted modulation
and multiplexing technique in the area of wireless
communication. IEEE 802.15, a wireless specification defined
for WPAN is an emerging wireless technology for short range
multimedia applications. Two general categories of 802.15
are the low rate 802.15.4 (ZigBee) and high rate 802.15.3
(UWB). In their physical (PHY) layer design, OFDM is a
competing technique due to the various advantages it renders
in the practical wireless media. OFDM has been a popular
technique for many years and adopted as the core technique
in a number of wireless standards. It makes the system more
immune to interference like InterSymbol Interference (ISI)
and InterCarrier Interference (ICI) and dispersive effects of
the channel. It is also a spectrally efficient scheme since the
spectra of the signal are overlapping in nature. Despite these
advantages OFDM suffers from a serious problem of high
Peak to Average Power. This limits the system’s capabilities
and increases the complexity. This paper compares the signal
distortion technique of Amplitude Clipping and the
distortionless technique of SLM for Peak to Average Power
reduction
Mimo radar detection in compound gaussian clutter using orthogonal discrete f...ijma
This paper proposes orthogonal Discrete Frequency Coding Space Time Waveforms (DFCSTW) for
Multiple Input and Multiple Output (MIMO) radar detection in compound Gaussian clutter. The proposed
orthogonal waveforms are designed considering the position and angle of the transmitting antenna when
viewed from origin. These orthogonally optimized show good resolution in spikier clutter with Generalized
Likelihood Ratio Test (GLRT) detector. The simulation results show that this waveform provides better
detection performance in spikier Clutter.
Performance optimization of hybrid fusion cluster based cooperative spectrum ...Ayman El-Saleh
This presentation shows performance Optimization of Hybrid Fusion Cluster-based Cooperative Spectrum Sensing in Cognitive Radio Networks. For more details, send an email to ayman.elsaleh@gmail.com
Exact secure outage probability performance of uplinkdownlink multiple access...journalBEEI
In this paper, we study uplink-downlink non-orthogonal multiple access (NOMA) systems by considering the secure performance at the physical layer. In the considered system model, the base station acts a relay to allow two users at the left side communicate with two users at the right side. By considering imperfect channel state information (CSI), the secure performance need be studied since an eavesdropper wants to overhear signals processed at the downlink. To provide secure performance metric, we derive exact expressions of secrecy outage probability (SOP) and and evaluating the impacts of main parameters on SOP metric. The important finding is that we can achieve the higher secrecy performance at high signal to noise ratio (SNR). Moreover, the numerical results demonstrate that the SOP tends to a constant at high SNR. Finally, our results show that the power allocation factors, target rates are main factors affecting to the secrecy performance of considered uplink-downlink NOMA systems.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
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An Optimized Energy Detection Scheme For Spectrum Sensing In Cognitive RadioIJERD Editor
With rapid growth of wireless devices, the Scarcity of Spectrum resources arises ,due to the improper and inefficient usage of available spectrum band. This problem can be alleviated by Cognitive radio . The major function of the cognitive radio rely on efficient sensing of available spectrum and Spectrum sensing techniques have been used to enhance the detection performance. Among these techniques, Energy detection is considered to be the implemented in practice because of less complexity. In this paper we propose an Adaptive threshold scheme which improves the detection performance under low SNR region. In this paper, noise uncertainty factor is considered wherein the Probability of error is minimized in various SNR regions.
Performance Evaluation of Energy Detector Based Spectrum Sensing for Cognitiv...IJECEIAES
This paper presents the performance evaluation of the Energy Detector technique, which is one of the most popular Spectrum Sensing (SS) technique for Cognitive Radio (CR). SS is the ability to detect the presence of a Primary User (PU) (i.e. licensed user) in order to allow a Secondary User (SU) (i.e unlicensed user) to access PU’s frequency band using CR, so that the available frequency bands can be used efficiently. We used for implementation an Universal Software Radio Peripheral (USRP), which is the most used Software Defined Radio (SDR) device for research in wireless communications. Experimental measurements show that the Energy Detector can obtain good performances in low Signal to Noise Ratio (SNR) values. Furthermore, computer simulations using MATLAB are closer to those of USRP measurements.
Performance analysis of cooperative spectrum sensing using double dynamic thr...IAESIJAI
Increased use of wireless technologies and in turn more utilization of available spectrum is subsequently leading to the increasing demand for wireless spectrum. This research work incorporates spectrum sensing detection consisting of a double dynamic threshold followed by cooperative type spectrum sensing. The performance has been analyzed using two modulation schemes, quadrature-amplitude-modulation (QAM) and binary-phase-shift-keying (BPSK). Improved probability of detection has been witnessed using the double dynamic threshold where a comparison of average values of local decision (LD) and the observed value of energy (EO) has been considered instead of using direct values of local decisions and
energy. Further, the probability-of-detection (𝑃𝑑) is found to be better with QAM as compared to the BPSK. From the results, it has been observed that the detection of primary users is also affected by the number of samples. The simulation environment considered for this work is MATLAB and the performance of cooperative spectrum sensing for 500 and 1000 samples with -9db and -12 SNR by considering different false alarm values i. e 0.1, 0.3 and 0.5 has been analyzed. The further scope shall be to enhance the primary user detection by considering different QAM schemes and different signal to noise ratio (SNRs).
Performance of cognitive radio networks with maximal ratio combining over cor...Polytechnique Montreal
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Security performance analysis for power domain NOMA employing in cognitive ra...journalBEEI
The power domain non-orthogonal multiple access (NOMA) technique introduces one of the fundamental characteristics and it exhibits the possibility of users to decode the messages of the other paired users on the same resources. In cognitive radio inspired NOMA (CR-NOMA), the base station (BS) has to serve untrusted users or users with different security clearance. This phenomenon raises a security threat particularly in such CR-NOMA. This paper develops a tractable analysis framework to evaluate the security performance of cooperative non-orthogonal multiple access (NOMA) in cognitive networks, where relay is able to serve two far NOMA users in the presence of external eavesdropper. In particular, we study the secrecy outage probability in a two-user NOMA system. This situation happens in practical the BS is pairing a legitimate user with another untrusted user. Main reason is that the non-uniform distribution in terms of trusted and untrusted users in the cell. By performing numerical results demonstrate the performance improvements of the proposed NOMA scheme in comparison to that of several situations in terms of different parameters. Furthermore, the security performance of NOMA is shown to verify the derived expressions.
A novel scheme to improve the spectrum sensing performanceIJCNCJournal
Due to limited availability of spectrum for license
d users only, the need for secondary access by unli
censed
users is increasing. Cognitive radio turns out to b
e helping this situation because all that is needed
is a
technique that could efficiently detect the empty s
paces and provide them to the secondary devices wit
hout
causing any interference to the primary (licensed)
users. Spectrum sensing is the foremost function of
the
cognitive radio which senses the environment for wh
ite spaces. Energy detection is one of the various
spectrum sensing techniques that are under research
. Earlier it was shown that energy detection works
better under AWGN channel as compared to Rayleigh c
hannel, however the conventional spectrum sensing
techniques have a high probability of false alarm a
nd also show a better probability of detection for
higher
values of SNR. There is a need for a new technique
that shows a reduced probability of false alarm as
well
as an increase in the probability of detection for
lower values of SNR. In the present work the conven
tional
energy detection technique has been enhanced to get
better results.
Performance Comparison of Energy Detection Based Spectrum Sensing for Cogniti...irjes
With the rapid deployment of new wireless devices and applications, the last decade has witnessed a growing
demand for wireless radio spectrum. However, the policy of fixed spectrum assignment produces a bottleneck for more
efficient spectrum utilization, such that a great portion of the licensed spectrum is severely under-utilized. So the concept of
cognitive radio was introduced to address this issue.The inefficient usage of the limited spectrum necessitates the
development of dynamic spectrum access techniques, where users who have no spectrum licenses, also known as secondary
users, are allowed to use the temporarily unused licensed spectrum. For this purpose we have to know the presence or
absence of primary users for spectrum usage. So spectrums sensing is one of the major requirements of cognitive radio.Many
spectrum sensing techniques have been developed to sense the presence or absence of a licensed user. This paper evaluates
the performance of the energy detection based spectrum sensing technique in noisy and fading environments.The
performance of the energy detection technique will be evaluated by use of Receiver Operating Characteristics (ROC) curves
over additive white Gaussian noise (AWGN) and fading channels.
IRJET- Rapid Spectrum Sensing Algorithm in Cooperative Spectrum Sensing for a...
Fl2410041009
1. Chandrasekhar Korumilli, Chakrapani Gadde, I.Hemalatha / International Journal of
Engineering Research and Applications (IJERA) ISSN: 2248-9622
www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1004-1009
Performance Analysis of Energy Detection Algorithm in
Cognitive Radio
Chandrasekhar Korumilli1, Chakrapani Gadde2, I.Hemalatha3
1
( P.G.Student Department of Electronics and Communications, Sir CRR College of engineering, Eluru)
(2P.G.StudentDepartment of Electronics and Communications, Sir CRR College of engineering, Eluru)
3
( Associate prof Department of Electronics and Communications, Sir CRR College of engineering, Eluru)
ABSTRACT spectrum from primary licensed users or to share
In cognitive radio systems, secondary the spectrum with the primary users. A cognitive
users should determine correctly whether the
primary user is absent or not in a certain radio is able to able to fill in the spectrum holes and
spectrum within a short detection period. serve its users without causing harmful interference
Spectrum detection schemes based on fixed to the licensed user. To do so, the cognitive radio
threshold are sensitive to noise uncertainty; the must continuously sense the spectrum it is using in
energy detection based on dynamic threshold order to detect the re-appearance of the primary
can improve the antagonism of noise user [3]. Once the primary user is detected, the
uncertainty; get a good performance of cognitive radio should withdraw from the spectrum
detection while without increasing the computer instantly so as to minimize the interference. This is
complexity uncertainty and improves detection very difficult task as the various primary users will
performance for schemes are sensitive to noise be employing different modulation schemes, data
uncertainty in lower signal-to-noise and large rates and transmission powers in the presence of
noise uncertainty environments. In this paper variable propagation environments and interference
we analyze the performance of energy detector generated by other secondary users [1].
spectrum sensing algorithm in cognitive radio. The paper is organized as follows. Section 2
By increasing the some parameters, the discuss the spectrum sensing problem, overview of
performance can be improved as shown in the spectrum sensing methods and the performance of
simulation results. energy detector spectrum sensing algorithm in
Keywords - cognitive radio, detection threshold, cognitive radio. Section 3 discusses the
dynamic threshold detection, noise uncertainty performance of dynamic threshold based spectrum
detection in cognitive radio systems. Section 4
1. INTRODUCTION discusses the conclusion and future in this field of
With the development of a host of new study.
and ever expanding wireless applications and
services, spectrum resources are facing huge 2. SPECTRUM SENSING PROBLEM
demands. Currently, spectrum allotment is done by
providing each new service with its own fixed 2.1 ENERGY DETECTION
frequency block. As more and more technologies Spectrum sensing is a key element in
are moving towards fully wireless, demand for cognitive radio communications as it must be
spectrum is enhancing. In particular, if we were to performed before allowing unlicensed users to
scan the radio spectrum, including the revenue-rich access a vacant licensed band. The essence of
urban areas, we find that some frequency bands in spectrum sensing is a binary hypothesis-testing
the spectrum are unoccupied for some of the time, problem
and many frequency bands are only partially
occupied, whereas the remaining frequency bands H0: X (N) =W (N)
are heavily used [1]. It indicates that the actual H1: X (N) =S (N) +W (N) (1)
licensed spectrum is largely under-utilized in vast
temporal and geographic dimensions [2].A remedy Where N is the number of samples,
to spectrum scarcity is to improve spectrum N=2TW, T is duration interval ,W is bandwidth, S
utilization by allowing secondary users to access (N) is the primary user’s signal, W (N) is the noise
under-utilized licensed bands dynamically and X (N) is the received signal. H0 and H1 denote
when/where licensed users are absent. that the licensed user is present or not, respectively.
Cognitive radio is a novel technology The noise is assumed to be additive white Gaussian
which improves the spectrum utilization by noise (AWGN) with zero mean and is a random
allowing secondary users to borrow unused radio process. The signal to noise ratio is defined as the
ratio of signal power to noise power
1004 | P a g e
2. Chandrasekhar Korumilli, Chakrapani Gadde, I.Hemalatha / International Journal of
Engineering Research and Applications (IJERA) ISSN: 2248-9622
www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1004-1009
Under the assumption of absolutely no
deterministic knowledge about the signal X (n),
i.e., we assume that we know only the average
power in the signal. In this case the optimal
detector is energy detector or radiometer can be
represented as [23]
N 1
DY Y n X n
1 H1
N n 0
H0 (2)
Where D(Y) is the decision variable and is
the decision threshold, N is the number of samples.
If the noise variance is completely known, then
from the central limit theorem the following
approximations can be made [24]
DY H 0 ~ N n ,2 n N
2 4
Figure 1 ROC curves of energy detection
DY H 1 ~ N
P n ,2( P n ) 2
2 2
N (3)
scheme with different SNR
Where P is the average signal power and 2
n is the
Figure 2 is the numerical results of (7) for
given PFA (0.0.9), SNR=-15dB. It shows that the
noise variance. Using these approximations performance is improved by increasing N, and
The probability expressions are probability of detection can be improved by
2 increasing N value even if the SNR is much lower,
n
PFA Pr D(Y ) H 0 Q as long as N is large enough without noise
2 4 N uncertainty.
n (4)
(P n )
2
PD Pr D(Y ) H 1 Q
2( P 2 ) 2 N
n (5)
(P n )
2
PMd 1 PD 1 Q
2( P 2 ) 2 N
n (6)
Where Q (·) is the standard Gaussian
complementary cumulative distribution function
(CDF). PD, PFA and PMd represent detection
probability, false alarm probability and missing
probability respectively.
From (4) and (5) eliminating threshold
N 2 Q 1 PFA Q 1 PD SNR
2 2
(7) Figure 2 ROC curves of energy detection
scheme with different N
P
Where SNR , n is the normalized noise
2
n
2
power.
Figure 1 shows the numerical results of
(7) for given PFA (0.0.9), sample number N=500,
with different SNR values with that the
performance is improved by increasing SNR value
1005 | P a g e
3. Chandrasekhar Korumilli, Chakrapani Gadde, I.Hemalatha / International Journal of
Engineering Research and Applications (IJERA) ISSN: 2248-9622
www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1004-1009
2.2 NOISE UNCERTAINTY environments. This indicates that the choice of a
fixed threshold is no longer valid under noise
Now, considering the case with uncertainty in the uncertainty and threshold should be chosen flexible
noise model [20], the distributional uncertainty of based on the necessities.
noise can be represented as
2 [ n / , n ]
2 2
is the noise uncertainty coefficient and >1
Now
n 2
PFA Q (8)
2 2 / N
n
(P n / N )
2
PD Q
(P 2 / ) 2 / N
n (9)
eliminating threshold and equating both
equations we have
N 2 Q1 PFA (1/ SNR)Q1PD SNR ( 1/ )2
2
(10) Figure 3 ROC curves of energy detection
scheme with different
Comparing (10) with (7), there is almost
no contribution to the whole expression results if 3. DYNAMIC THRESHOLD
there is a tiny change of ρ; however, SNR−2 and Performance of cognitive radio declined
(SNR − (ρ − 1/ρ)) −2 should be mainly discussed sharply due to noise uncertainty and cognitive
and compared. When ρ ≈ 1, then SNR−2 ≈ (SNR − users’ accessing will be serious interference to
(ρ − 1/ρ)) −2, the numerical value of (10) and (7) are licensed users. This should be avoided in dynamic
almost the same; When ρ is larger and suppose ρ = spectrum access technology. For this reason, a new
1.05, then (ρ − 1/ρ) = 0.0976 ≈ 0.1, if SNR = 0.1, algorithm combating the noise uncertainty is
well then (SNR − (ρ − 1/ρ)) −2 ≈ 0, substituting into presented [21][20].
equation (10) to be N →∞. In other words, only Assume that the dynamic threshold factor 𝜌
infinite detection duration can complete detection,
and 𝜌′ > 1 the distributional of dynamic threshold
which is impracticable. A tiny fluctuation of
in the interval ' [ ' / , ' ]
average noise power causes performance drop
seriously, especially with a lower SNR. Then the probability relationships are represented
Figure 3 shows the numerical result of as
(10) probability of false alarm on X-axis and
probability of detection on Y-axis for an SNR=- ' n
2
15dB, PFA = (0, 0.9), N=500 and varying the noise PFA
2 2 / N
uncertainty value. n (11)
From the Figure it is seen that the
performance gradually drops as the noise factor
increasing. This indicates that Energy detector is
P n
PD
2
very sensitive to noise uncertainty. It means that
cognitive users predict the spectrum to be idle no
P n 2
2
N
matter whether there are primary users present or (12)
absent. Consequently, cognitive users are harmful
to licensed users when primary users are present. After simplifying (11) and (12) we get the
This situation often occurs in cognitive radio relationship for SNR, N, PFA , PD and '
systems, particularly in lower signal-to-noise ratio
environments. In order to guarantee a good
N 2 Q 1PFA '2 1 SNRQ 1PD
2
performance, choosing a suitable threshold is very
important. Traditional energy detection algorithms
are based on fixed threshold and we have verified
'2 SNR '2 1
2 (13)
that performance decreased under noise uncertainty
1006 | P a g e
4. Chandrasekhar Korumilli, Chakrapani Gadde, I.Hemalatha / International Journal of
Engineering Research and Applications (IJERA) ISSN: 2248-9622
www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1004-1009
Figure 4 shows the performance of energy Eliminating threshold
detection scheme, probability of false alarm on X- we get the inter relationship for SNR, N, PFA , PD
axis and probability of detection on Y-axis.
and '
2
1
N 2 ' Q 1 PFA ' SNR Q 1 PD
(16)
2
'
' SNR
'
In (16), when ' ≈ ρ and ' ρ ≈ ρ/ ' ≈ 1,
' SNR ' ' ≈ 2
(SNR) and −2
' (1/ρ+SNR) ≈ (1+SNR). We substitute (16) with
the above approximate unequal expressions, and
we can get that the numerical value of (16) is
almost the same to (7). Therefore, dynamic
threshold detection algorithm can overcome the
noise uncertainty as long as a suitable dynamic
threshold factor is chosen. Comparing (16) with
(13), supposing SNR = 0.1 and ' and ρ both
closer to 1, it is clear that
Figure 4 ROC curves of energy detection
scheme with no noise uncertainty, with noise ' SNR ' '2 SNR 1 2 .
uncertainty, and with dynamic threshold Consequently, detection duration N has been
shortened largely to N= 500 with the same
Here we have taken a SNR=-15dB, PFA 0,0.09 , probability parameters PD and PFA as shown in
Figure 5 It can be concluded that as long as the
N=1500, noise uncertainty1.02 and dynamic
dynamic threshold factor is suitable, even if there is
threshold1.001.It is observed that the performance
noise uncertainty, we can get a better spectrum
is improved by using a dynamic threshold
performance. To attaining the same performance,
the detection time of dynamic threshold energy
3.1 NOISE UNCERTAINTY AND DYNAMIC
detection Algorithm is less than the traditional
THRESHOLD
version.
Figure 5 is the numerical results of (7),
We have discussed two cases that existing
(13) and (16). With the same parameters as before.
noise uncertainty and dynamic threshold
respectively, this section will give the expressions
that considering noise uncertainty and dynamic
threshold together, we got expressions of false
alarm probability and detection probability
The noise variance in the interval
2 2
, n
n
Now the probability relations are represented as
' n
2
PFA Q (14)
n 2
2
N
2
P n
'
PD Q (15)
2
2
P n
N Figure 5 ROC curves of energy detection
scheme with N=500, different ρ and '
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5. Chandrasekhar Korumilli, Chakrapani Gadde, I.Hemalatha / International Journal of
Engineering Research and Applications (IJERA) ISSN: 2248-9622
www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1004-1009
Dissertation, Virginia Polytechnic Institute
Where ρ = 1.00 denotes that the average and State University, September 2006.
noise power keeps constant (without noise [9] FCC, “Spectrum policy task force,”
uncertainty); ' = 1.00 denotes that the algorithm Technology Advisory Council
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4. CONCLUSION
IEEE Vehicular Technology Magazine, vol.
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3, no. 1, pp. 28–35, 2008.
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[14] H. P. Zhi Quan, Shuguang Cui and A.
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Sayed, “Collaborative wideband sensing for
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cognitive radios,” IEEE Signal Processing
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Authors
1
Chandrasekhar Korumilli
received his B.Tech from
Pragati Engineering College
in 2008. Currently he is
pursuing his M.Tech from SIR C.R.Reddy
College of engineering college, Eluru west
Godavari district, Adhrapradesh. His areas of
interest are wireless communications, computer
networking and Cognitive Radio. He has published
a paper in international journals relating to
“Throughput Improvement in Wireless Mesh
Networks by Integrating with Optical Network”
and presented papers in many international
conferences.
2
Chakrapani Gadde
received his B.Tech from
Lakireddy Balireddy College
of engineering in 2008.
Currently he is pursuing his
M.Tech from SIR C R
Reddy College of
engineering college, Eluru west Godavaridistrict,
Andhrapradesh. His areas of interest are wireless
communications and computer networking. He has
published papers in international journals relating
to “Mitigation of near far effect in GPS receivers”.
3
I.Hemalatha received B.Tech from Sir CRR
College of Engineering, M.Tech from JNTU
Kakinada. Currently she is working as an Associate
Prof at Sir C R Reddy College of Engineering,
Eluru west Godavari district, Andhrapradesh. She
is having Twelve years of teaching experience and
guided many students during this period. Her areas
of interest are Speech Processing and wireless
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