Power limited Cooperative Diversity in Rayleigh Fadin

g for Wireless Ad-hoc Networks

July 20, 2006

Nam-Soo Kim , Ye Hoon LeeCheongju Univ., Seoul National Univ. of Technology

Mobile radio communication lab.

■ 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

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I. Introduction

II. System model

Fig. 1 System model of considered cooperative diversity.

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S

R

D

■ Received signal at destination node - first time slot (1)

- second time slot

(2) where, Channel gain ; ,

Noise ; , N(0, No) Tx power ; ,

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II. System model (Cont.)

DSDsS nxhPy

DRDRR nuhPy

SDh SRh

sP RPDn

RSRs nxhP u

■ 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)

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III. Selection diversity combining

D

)/exp(1

)Pr( )(,

SD

DoutDP

,

1

( ) Pr( )

2 2 1 ( )

exp ( ) /

R out R

SR RD SR RD

SR RD SR RD

P

K

SD

■ Outage probability

- Selection combining (assume two independent path)

(7)

- MRC combining (assume high SNR [12,13] )

(8)

where, =

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outRoutDout PPP ,, )(

20222

SD

2

))(11

(2

)(SRDSR

out P

NP

SR PP /

III. Selection diversity combining (cont.)

IV. Effect of power limit ■ Power limit coefficient, define

(9) - Outage prob. of selection combining

(10)

- Outage prob. of MRC

(11)

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SR

RD

max,

)11

(2

)(SD

2

SRSRoutP

SRSRSR

outR

K

P

/)1(exp)2

(2

1

)(

1

,

  

 

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Fig. 2. Outage probability of cooperative diversity with selection combining.

V. Numerical results and discussions

0 5 10 15 20 25 30 35 40 45 5010

-4

10-3

10-2

10-1

100

Out

age

Pro

b.

RDSD 2.0

no div.

sc div.

(dB) / R

RDSD 5.0

RDSD 0.1

RDSD 2.0

RDSD 5.0

RDSD 0.1

Gain(dB) Avg. SNR

13.5

15

17

SD RD SR

0.5 0.5 SD RD SR

0.2 0.2 SD RD SR

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Fig. 3. Outage probability versus ( )

V. Numerical results and discussions (Cont.)

-30 -25 -20 -15 -10 -5 0 5 1010

-6

10-5

10-4

10-3

10-2

10-1

100

101

Out

age

Pro

b.

)( dB

dBSR 10/

dBSR 15/

dBSR 20/

SC

MRC

SRSD

• Power limited areas

– error floor

• Excess power areas

– insignificant improvement

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

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31 10outP SD SR RD

Performance gain is more significant as the received SNR from the direct path is reduced

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.

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[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.

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