Procedia Engineering 15 (2011) 2349 – 2353

1877-7058 © 2011 Published by Elsevier Ltd.doi:10.1016/j.proeng.2011.08.440

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ProcediaEngineering

Procedia Engineering 00 (2011) 000–000

www.elsevier.com/locate/procedia

Advanced in Control Engineering and Information Science

Cooperative Spectrum Sensing Algorithm Based on the Relay Juan Chen*, Xueqiang Zheng, Mengping Zhu

Institute of Communications Engineering, PLA University of Science and Technology, Nanjing 210007, China

Abstract

Cooperative spectrum sensing is investigated in cognitive radio (CR) networks over Rayleigh fading channels. By utilizing the relay to enhance the reliability of the sensing information reporting, cooperative spectrum sensing algorithm based on the relay is proposed. Physical network coding is used for the relay and the method for relay selection is discussed. The simulation results show that cooperative spectrum sensing algorithm based on the relay can achieve better performance.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [CEIS 2011]

Keywords: cognitive radio; cooperative spectrum sensing; relay; physical network coding

1. Introduction

In cognitive radio networks, cognitive radio (CR) needs to have cognitive radio capabilities, such as sensing the spectrum reliably to check whether it is being used by a primary user (PU). A number of different methods are proposed for identifying the presence of signal transmission, such as matched filter detection, energy detection, feature detection techniques and wavelet approach [1]. However, due to the fading and the shadowing effects, the sensing performance for one cognitive radio will be degraded. To enhance the sensing performance, cooperative spectrum sensing has been discussed.

In realistic environment where both the sensing channels and reporting channels are characterized by fading channels. The reporting channel is usually not ideal. Some previous works have been done considering the reporting error for cooperative spectrum sensing. In [2], the reporting channel experiences Rayleigh fading was considered and the bound of the false alarm probability was given. The effect of the amplify-and-forward cooperation protocol on the spectrum sensing capabilities of cognitive radio network was studied in [3][4], but the cognitive radios need to know much prior information. In [5], space-time (ST)

* Corresponding author. Tel.: +00-86-25-84615320 E-mail address: zxqq302@163.com.

2350 Juan Chen et al. / Procedia Engineering 15 (2011) 2349 – 23532 Juan Chen ，et al/ Procedia Engineering 00 (2011) 000–000

coding was used for cooperative spectrum sensing, but the performance was constrained because the information exchange between cognitive radios may not be correctly performed. In [6][7], cooperative relay and network coding (NC) were researched in cognitive radio networks for cognitive radio communications, but they were not applied to cooperative spectrum sensing. In this paper, we address some further work to against the reporting errors by utilizing the relay. Cooperative spectrum sensing algorithm based on the relay is proposed by considering the use of physical network coding (PNC). The method of relay selection is discussed.

The rest of this paper is organized as follows. In Section 2, the system model is briefly introduced. In Section 3, the cooperation spectrum sensing algorithm based on the relay is given. The simulation results are shown in Section 4. Finally, the conclusion is given in Section 5.

2. System model

In this paper, we consider the problem of cooperative spectrum sensing at a central mode as illustrated in Fig.1, which includes one primary user, one base station (BS), one relay (R). Cognitive radios are randomly distributed within the coverage radius of the base station.

In cognitive radio network, when cognitive radios are sensing the channel, the sampled received signal of the cognitive radios has two hypotheses. Hypothesis 1H denotes the primary user is active, and hypothesis denotes the primary user is inactive. 0H

1

0

: ( ) ( ) ( ) 1,2,...: ( ) ( ) 1,2,...

i i i

i i

H y k h s k n k i NH y k n k i N

= ∗ + == =

( )y k ( )

(1)

swhere is the signal received by cognitive radio, k N( )

is the transmitted signal of the primary user, is the number of the cognitive radios. The signal s k ih

( )in k 2nσ ( )

is distorted by the channel gain , which is assumed to be constant during the detection interval, and is further corrupted by the zero-mean additive white Gaussian noise with the variance . Without loss of generality, s k ( )in kand are assumed to be

independent of each other. 2 2/i i s iE σ=r h denotes the signal-to-noise ratio (SNR), where sE is the signal energy of the primary user.

Fig.1. Cooperative spectrum sensing system model

2351Juan Chen et al. / Procedia Engineering 15 (2011) 2349 – 2353Author name / Procedia Engineering 00 (2011) 000–000 3

Fig.2. Cooperative spectrum sensing algorithm based on the relay

3. Cooperative spectrum sensing algorithm based on the relay

In this section, we will employ the relay to improve the performance of cooperative spectrum sensing by applying physical network coding [8][9].

3.1. Cooperative Spectrum Sensing Algorithm based on the Relay

We will describe the proposed cooperative spectrum sensing technique based on the use of a simple example of two CRs. Assume that the local spectrum sensing has been completed at cognitive radios, sensing information of cognitive radios are 1X and 2X , respectively.

Suppose time is partitioned into time frames with length . In any frame, there can be two types of transmissions going on in the network. One is the reporting transmission between the cognitive radios and the base station. The other one is the relaying transmission among them. The arrangement of the active transmissions into these two types is shown in Fig.2.

tΔ

1X andAs illustrated in Fig.2, CR1 and CR2 broadcast sensing information 2X to the relay and the BS simultaneously, then the relay encodes the received information to 3X and then sends the network code 3Xto BS.

X 3 1 2X X= ⊕ (2)

1The base station decodes the information received from the relay and cognitive radios, the decoded

sensing information is X ′and 2′

2 1 31 2 3

.X

X X XX X X

′ = ⊕⎧⎨ ′ = ⊕⎩

(3)

3.2. Selection of the Relay

Assume that the bit error rate between the relay and BS is RBPe , the bit error rates between the two reporting cognitive radios and the relay are R1Pe and 2RPe , the bit error rates between the two reporting cognitive radios and the relay are 1BPe and 2BPe

(1B RW= −

. Then the bit error rates of the reporting result through the network decoding are

'Pe1 2 )Be 2 )RWPe P Pe+ −(1B Pe (4)

2352 Juan Chen et al. / Procedia Engineering 15 (2011) 2349 – 23534 Juan Chen ，et al/ Procedia Engineering 00 (2011) 000–000

'1

'2 1 1(1 ) (1 )B RW B B RWPe Pe Pe Pe Pe= − + − (5)

where BPe '2and BPe are the bit error rates which BS decoded from the network codes, RW

( ) ( )2 1 2 1 1 2(1 )(1 ) 1

Pe is the bit error rate which BS received from the relay.

RW RB R R RB R R R RPe Pe Pe Pe Pe Pe Pe Pe Pe= − − + − + − (6)

The relay in the relay set must meet the following condition to enhance the performance of the reporting.

{ }' ' ' '1 2 1 1 2 2, &B B B B B BPe Pe Pe Pe Pe Pe< < (7)

{ }' '1 2x ,maThen the rule of best relay selection is to choose the least B BPe Pe

0 1 0.5P P= =

among the relay set.

4. Simulation results

In this section we present some simulation results to demonstrate the sensing performance of cooperative spectrum sensing algorithm based on the relay (CSS-PNC) and the cooperative spectrum sensing based on space-time code (CSS-ST) in [5], the direct reporting without any processing is also shown for comparisons of the receiver operating characteristics curves (ROC). There are one primary user, one base station, two cognitive radios for sensing and the sensing SNR of the received signal from the primary user are [1dB 4dB]. We assume that the probabilities of the existence or not for the primary user are .

In figure 3, the SNRs for direct reporting of the two sensing users are [7dB -10dB], the SNR between the two cognitive radios are -13dB, the SNRs between the two cognitive radios and the relay are [12dB 12dB], the SNR between the relay and base station is 7dB. In figure 4, only one reporting channel can be used, the SNR for direct reporting is 7dB, the SNR between the two cognitive radios are -3dB, the SNRs between the two cognitive radios and the relay are [12dB 12dB], the SNR between the relay and base station is 7dB.

From Fig.3, we can see that when there exist poor reporting and exchanging channels, the performance of cooperative spectrum sensing algorithm based on the relay is better than the algorithm based on space-time coding. From Fig.4, we can see that when there exists destroyed reporting channel, the performance of cooperative spectrum sensing algorithm based on space-time coding rapidly worsen.

10-3

10-2

10-1

100

0.5

0.6

0.7

0.8

0.9

1

Qf

Qd

CSS-PNCCSS-STdirect

10-3

10-2

10-1

100

0.5

0.6

0.7

0.8

0.9

1

Qf

Qd

CSS-PNCCSS-STdirect

Fig.3. ROC of the novel algorithm Fig.4. ROC of the novel algorithm

2353Juan Chen et al. / Procedia Engineering 15 (2011) 2349 – 2353Author name / Procedia Engineering 00 (2011) 000–000 5

5. Conclusion

Cooperative spectrum sensing taking into account the reporting error is studied. A novel cooperative spectrum sensing algorithm with the relay is proposed by applying physical network coding. The method of relay selection is given. The simulation results show that the performance of the novel algorithm can achieve better performance. The algorithm design for multi-reporting users is our future research.

Acknowledgements

This paper is supported by the National Basic Research Program of China(973 program) under Grant No 2009CB320400, State key Program of National Natural Science of China under Grant No 60932002.

References

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