Adaptive Multiple Relay Selection Scheme for Cooperative Wireless Networks

1. Adaptive Multiple Relay Selection Scheme forCooperative Wireless Networks Gayan Amarasuriya, Masoud Ardakani and Chintha Tellambura {amarasur, ardakani, chintha}@ece.ualberta.ca WCNC 2010 University of Alberta, Canada

2. Outline: • introduction • single relay selection, multiple relay selection • motivation • proposed scheme • analysis • numerical results • conclusion

3. All participate relaying (APR): • all L relays cooperate • simple and efficient • optimal in the sense of diversity and coding gains • needs L+1 orthogonal time-slots •  low spectral-efficiency • low spectral efficiency can be overcome by •  selection a subset of available relays APR [Laneman, 2003]

4. Single relay selection (SRS): • only one relay cooperates  spectral-efficiency increases • SRS schemes • best SRS [Zhao, 2007]  • best–worst SRS [Bletsas, 2006]  • best–harmonic mean SRS [Bletsas, 2006]  • partial SRS [Sadek, 2006]  SRS

5. Multiple relay selection (MRS): • more than one relay cooperates  better trade-off between spectral-efficiency and available degree of freedom of the wireless channel • MRS schemes • Optimal MRS for orthogonal channels - • [Michalopoulos, 2006] • Optimal/suboptimal MRS for shared channels - • [Jing, 2009] • GSC-based MRS - [Ikki, 2009] MRS

6. Motivation: • best SRS  does not use available degree of freedom  SNR outage and BER are lower • optimal MRS  high search complexity  complexity increases exponential with number of relays • GSC-based MRS  may select more relays unnecessary  end-to-end SNR may far exceed the system requirements • above schemes require CSI of all relayed paths • We would like a MRS scheme which offers better trade-offs between the error/outage performance and spectral-efficiency!

7. Proposed MRS scheme: • Key idea Adaptive threshold checking at D [Chen, 2004], [Yang, 2005] • proposed scheme selects the first relays such that the combined SNR of the first relayed paths and the direct path exceeds a preset threshold .

8. Analysis: • The end-to-end SNR can be written as • The CDF of is given by • to make the analysis tractable, we use the well-known upper bound:  • the CDF, PDF and the MFG of are derived in closed-forms. • lower bounds are derived for (i) outage probability, (ii) average SER, and (iii) the average number of selected relays. • upper bounds are derived for (i) average SNR and (ii) ergodic capacity.

9. Analysis (ctd): • the CDF of can be derived as where and • The PDF of is given by

10. Analysis (ctd): • the average SER is derived as • the average number of selected relays is given by

11. Numerical results: • Average BER of BPSK

12. Numerical results (ctd): • Average number of selected relays

13. Numerical results (ctd): • Outage probability comparison

14. Numerical results (ctd): • Average BER of BPSK comparison

15. Conclusion: • Our MRS scheme • outperforms optimal SRS, GSC-based MRS and fixed Lc out of L relays in low-to-moderate SNRs. • utilizes the wireless resources adaptively in fading environments. • Future directions • performance in high SNRs can be improved by • first ordering the relays • then applying the proposed algorithm

16. References: • [Laneman, 2003] J. N. Laneman and G. W. Wornell, “Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks,” IEEE Trans. Inf. Theory, vol. 49, no. 10, pp. 2415–2425, Oct. 2003. • [Bletsas, 2006] A. Bletsas, A. Khisti, D. P. Reed, and A. Lippman, “A simple cooperative diversity method based on network path selection,” IEEE J. Sel. Areas Commun., vol. 24, no. 3, pp. 659–672, Mar. 2006. • [Zhao, 2007] Y. Zhao, R. Adve, and T. J. Lim, “Improving amplify-and-forward relay networks: optimal power allocation versus selection,” IEEE Trans. Wireless Commun., vol. 6, no. 8, pp. 3114–3123, Aug. 2007. • [Sadek, 2006] A. K. Sadek, Z. Han, and K. J. R. Liu, “A distributed relay-assignment algorithm for cooperative communications in wireless networks,” in IEEE International Conf. on Commun. ICC., vol. 4, Jun. 2006, pp. 1592–1597. • [Michalopoulos, 2006] D. S. Michalopoulos, G. K. Karagiannidis, T. A. Tsiftsis, and R. K. Mallild, “An optimized user selection method for cooperative diversity systems,” in IEEE Global Telecommun. Conf., Nov./Dec. 2006. • [Jing, 2009] Y. Jing and H. Jafarkhani, “Single and multiple relay selection schemes and their achievable diversity orders,” IEEE Trans. Wireless Commun., vol. 8, no. 3, pp. 1414–1423, Mar. 2009. • [Ikki, 2009] S. S. Ikki and M. H. Ahmed, “Performance analysis of generalized selection combining for amplify-and-forward cooperative-diversity networks,” in IEEE International Conf. on Commun., ICC., Dresden, Germany, Jun. 2009. • [Chen, 2004] Y. Chen and C. Tellambura, “An adaptive maximal ratio combining scheme and its performance analysis,” in 16-th international conf. on wireless commun., Wireless 2004, Calgary, Alberta, Canada, vol. 2, Jul. 2004, pp. 325–337. • [Yang, 2005] H.-C. Yang and M. S. Alouini, “MRC and GSC diversity combining with an output threshold,” IEEE Trans. Veh. Technol., vol. 54, no. 3, pp. 1081–1090, May 2005.

17. Thank You!