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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.
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■ 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
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II. System model
Fig. 1 System model of considered cooperative diversity.
Mobile radio communication lab.
S
R
D
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■ 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
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■ 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
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■ Outage probability
- Selection combining (assume two independent path)
(7)
- MRC combining (assume high SNR [12,13] )
(8)
where, =
Mobile radio communication lab.
outRoutDout PPP ,, )(
20222
SD
2
))(11
(2
)(SRDSR
out P
NP
SR PP /
III. Selection diversity combining (cont.)
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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
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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
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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.
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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.
Mobile radio communication lab.