1. Power limited Cooperative Diversity in Rayleigh Fading for Wireless Ad-hoc Networks July 20, 2006 Nam-Soo Kim, Ye Hoon Lee Cheongju Univ., Seoul National Univ. of Technology Mobile radio communication lab.

2. ■ Background - Ad-hoc, sensor network Power limited system - Cooperative diversity Mitigate shadow fading Reduce power consumption of wireless ad-hoc networks Performance improvements using direct and relay nodes - MRC receiver Best performance in fading channel CSI required, sensitive to CSI error ■ Objective - Selection combining in AF - Effect of the Power-limited relay node Mobile radio communication lab. I. Introduction

3. II. System model Fig. 1 System model of considered cooperative diversity. Mobile radio communication lab.

4. ■ Received signal at destination node - first time slot (1) - second time slot (2) where, Channel gain ;, Noise ;, N(0, No) Tx power ;, Mobile radio communication lab. II. System model (Cont.)

5. ■ Outage probability - S-D nodes (direct path) (5) where, ; Instantaneous SNR of destination node ; Threshold SNR, ; Avg. SNR of S-D node - S-R-D nodes (indirect path) (6) Mobile radio communication lab. III. Selection diversity combining

6. ■ Outage probability - Selection combining (assume two independent path) (7) - MRC combining (assume high SNR [12,13] ) (8) where, = Mobile radio communication lab. III. Selection diversity combining (cont.)

7. IV. Effect of power limit ■ Power limit coefficient, define (9) - Outage prob. of selection combining (10) - Outage prob. of MRC (11) Mobile radio communication lab.

8. Fig. 2. Outage probability of cooperative diversity with selection combining. V. Numerical results and discussions Gain(dB) Avg. SNR 13.5 15 17

9. Mobile radio communication lab. Fig. 3. Outage probability versus ( ) V. Numerical results and discussions (Cont.) Power limited areas – error floor Excess power areas – insignificant improvement

10. VI. Conclusions ■ Performance of a selection combining cooperative diversity in Rayleigh fading channels - 13.5 dB gain (@, ) - ■ Effect of the power limited node - Selection combining is more sensitive than MRC. - power limited relay node – error floor ■ Insufficient power node is not recommended as a relay node in cooperative diversity systems Mobile radio communication lab. Performance gain is more significant as the received SNR from the direct path is reduced

11. References [1] M. Hasna and M.–S. Alouini, “Performance of two-hop relayed transmissions over Rayleigh fading channels,” Proceedings of IEEE VTC 2002, vol. 4, pp. 1992-1996, Sept. 2002. [2] J. N. Lanememan and G. W. Wornell, “Energy efficient antenna sharing and relaying for wireless networks,” Proceedings of IEEE WCNC 2000, vol. 1, pp.7-12, Sept. 2000. [3] V. Emamian, P. Anghel, and M. Mostafa Kaveh, “Multi-user spatial diversity in a shadow-fading environment,” Proceedings of VTC 2002-Fall, pp. 573-576, 2002. [4] P. A. Anghel and M. Kaveh, “Exat symbol error probability of a cooperative network in Rayleigh- fading environment,” IEEE Trans. on wireless commun., vol. 1, no. 5, pp. 1416-1421, Sept. 2004. [5] G. L. Stuber, Principles of Mobile Communication, Kluwer Academic Publishers, 2001. [6] A. Goldsmith, Wireless Communications, Cambridge University Press, 2005. [7] Nam-Soo Kim, Beongku An, and Do-Hyun Kim, “An architecture model for supporting power saving services for mobile wireless Ad-Hoc networks,” LNCS3560, pp. 415-416, Springer-Verlag, 2005. [8] M. O. Hasna and M.-S. Alouini, “Performance analysis of two-hop relayed transmissions over Rayleigh fading channels,” Proceedings of VTC 2002-Fall, vol. 4, pp. 1992-1996, Sept. 2002. Mobile radio communication lab.

12. [9] M. Yacuob, Foundation of Mobile Radio Engineering, CRC Press 1993. [10] M. K. Simon and M.-S. Alouini, Digital Communication over FadingCchannels, John Wiley & Sons, Inc., 2005. [11] N. Ahmed, M. A. Khojastepour, and B. Aazhang, “Outage minimization and optimal power control for the fading relay channel,” Proceedings of Information Theory Workshop, pp.458-462, Oct. 2004. [12] Xinmin Deng and A. M. Haimovich, “Power allocation for cooperative relaying in wireless networks,” IEEE commun. Letters, vol. 9, no. 11, pp. 994-996, Nov. 2005. [13] J. N. Laneman, D. N. C. Tse, and G. W. Wornell, “Cooperative diversity in wireless networks: efficient protocols and outage behavior,” IEEE Trans. Inform. Theory, vol. 50, no. 12, pp. 3062-3080, Dec. 2004. Mobile radio communication lab.