Relay Selection and Power Allocation in Amplify-and-Forward Cognitive Radio Systems Based on Spectrum Sharing

Daqian Zhao, Zhizhong Zhang, Fang Cheng

School of Communication and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing, China.

DOI: 10.4236/cn.2013.53B2069                

Abstract

In this paper, we consider a spectrum sharing scheme that is a joint optimization of relay selection and power allocation at the secondary transmitter, which aims to achieve the maximum possible throughput for the secondary user. This paper considers the scenario where the primary user is incapable of supporting its target signal-to-noise ratio (SNR). More especially, the secondary transmitter tries to assist the primary user with achieving its target SNR by cooperative amplify-and-forward (AF) relaying with two-phase. By exhaustive search for all candidate secondary transmitters, an optimal secondary transmitter can be selected, which not only can satisfy the primary user’s target SNR, but also maximize the secondary user’s throughput. The optimal secondary transmitter acts as a relay for the primary user by allocating a part of its power to amplify-and-forward the primary signal over the primary user’s licensed spectrum bands. At the same time, as a reward, the optimal secondary transmitter uses the remaining power to transmit its own signal over the remaining licensed spectrum bands. Thus, the secondary user obtains the spectrum access opportunities. Besides, there is no interference between the primary user and the secondary user. We study the joint optimization of relay selection and power allocation such that the secondary user’s throughput is maximized on the condition that it satisfies the primary user’s target SNR. From the simulation, it is shown that the joint optimization of relay selection and power allocation provides a significant throughput gain compared with random relay selection with optimal power allocation (OPA) and random relay selection with water-filling power allocation (WPA). Moreover, the simulation results also shown that our spectrum sharing scheme obtains the win-win solution for the primary system and the secondary system.

Keywords

Spectrum Sharing; Cooperative Communication; Relay Selection; Power Allocation; Throughput; Maxi-mum Ratio Combining; Cognitive Radio Systems

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	P. Kolodzy and I. Avoidance, “Spectrum Policy Task force,” Federal Commun. Comm., Washington, DC, Rep. ET Docket, 2002 (02-135).
[2]	M. H. Islam, C. L. Koh, S. W. Oh, et al., Spectrum Survey in Singapore: Occupancy Measurements and Analyses[C]//Cognitive Radio Oriented Wireless Networks and Communications, 2008. Crown Com 2008. 3rd International Conference on. IEEE, 2008, pp. 1-7.
[3]	D. Datla, A. M. Wyglinski and G. J. Minden, “A Spectrum Surveying Framework for Dynamic Spectrum Access Networks,” Vehicular Technology, IEEE Transactions on, Vol. 58, No. 8, 2009, pp. 4158-4168. doi:10.1109/TVT.2009.2021601
[4]	III. J. Mitola and Jr. G. Q. Maguire, “Cognitive Radio: Making Software Radios More Personal,” Personal Communications, IEEE, 1999, Vol. 6, No. 4, pp. 13-18. doi:10.1109/98.788210
[5]	S. Haykin, “Cognitive Radio: Brain-empowered Wireless Communications,” Selected Areas in Communications, IEEE Journal on, Vol. 23, No. 2, 2005, pp. 201-220. doi:10.1109/JSAC.2004.839380
[6]	A. Jovicic and P. Viswanath, “Cognitive Radio: An Information-theoretic Perspective,” Information Theory, IEEE Transactions on, Vol. 55, No. 9, 2009, pp. 3945-3958. doi:10.1109/TIT.2009.2025539
[7]	C. H. Chen, C. L. Wang and C. T. Chen, “A Resource Allocation Scheme for Cooperative Multiuser OFDM-Based Cognitive Radio Systems,” Communications, IEEE Transactions on, Vol. 59, No. 11, 2011, pp. 3204-3215. doi:10.1109/TCOMM.2011.092011.100197
[8]	M. Shaat and F. Bader, “Asymptotically Optimal Resource Allocation in OFDM-based Cognitive Networks with Multiple Relays,” Wireless Communications, IEEE Transactions on, Vol. 11, No. 3, 2012, pp. 892-897. doi:10.1109/TWC.2012.011012.110880
[9]	L. Li, X. Zhou, H. Xu, et al., “Simplified Relay Selection and Power Allocation in Cooperative Cognitive Radio Systems,” Wireless Communications, IEEE Transactions on, Vol. 10, No. 1, 2011, pp. 33-36. doi:10.1109/TWC.2010.101810.100311
[10]	W. D. Lu, Y. Gong, S. H. Ting, et al., “Cooperative OFDM Relaying for Opportunistic Spectrum Sharing: Protocol Design and Resource Allocation,” Wireless Communications, IEEE Transactions on, 2012, Vol. 11, No. 6, pp. 2126-2135. doi:10.1109/TWC.2012.032812.110524
[11]	K. R. Budhathoki, M. Maleki and H. R. Bahrami, “Relay Selection and Power Allocation in Amplify-and-forward Cognitive Radio Systems[C]//Computing, Networking and Communications (ICNC), 2013 International Conference on. IEEE, 2013, pp. 686-690.
[12]	Y. C. Liang, K. C. Chen, G. Y. Li, et al., “Cognitive Radio Networking and Communications: An Overview,” Vehicular Technology, IEEE Transactions on, 2011, Vol. 60, No. 7, pp. 3386-3407. doi:10.1109/TVT.2011.2158673
[13]	K. J. R. Liu, “Cooperative Communications and Networking,” Cambridge University Press, 2009.