1 multi-user diversity in single-radio ofdma ad hoc networks based on gibbs sampling marzieh veyseh...
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Multi-User Diversity in Single-Radio OFDMA Ad Hoc Networks Based on
Gibbs SamplingMarzieh Veyseh
J.J. Garcia-Luna-AcevesHamid R. Sadjadpour
MotivationConcurrency
• Frequency
• Code
• Space
2
fc1
Channel 1Channel 1
fc2 fc3 fc4 fc5
Channel 1Channel 1
Channel 3Channel 3
fcfc
Channel 1Channel 1 Code 1Code 1
Code 3Code 3Code 1Code 1Code 2Code 2
Code 3Code 3
fcfc
fcfc
fcfc
MotivationAdaptivity• Time
• Frequency, through different modulations…
Diversity
To use fading in our advantage and to improve rate…• MIMO• OFDAM-Multiuser diversity
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t1 t2 t3 t4 t5 t3
t1
• Proposed for infrastructure-based OFDMA networks• We think that utilizing OFDMA in ad hoc networks gives us the ability to achieve our goals:
1. Concurrency: multiple nodes use different portions of BW2. Diversity: multi-user diversity3. Adaptivity: subchannels can have different sizes
OFDMA
4
fcfc
Subchannel iSubchannel i
Subchannel 1Subchannel 1
Subchannel 2Subchannel 2
Subchannel 3Subchannel 3
Subchannel 4Subchannel 4
OFDMA Synchronization
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C-Tx
C-Tx
• In an ad hoc multi-transmitter scenario to avoid loss of orthogonality at a common neighbor to multiple transmitters, a quasi-synchronous network is required.
• Quasi-synchronous : transmitter start sending data at the same time• Multi-transmission synchronization achieved via control message
exchanges
Previous work
• Not much work on protocols for OFDMA for ad hoc networks
• CTRMA: In our previous work, we assigned non-overlapping channels unique within the two hop neighborhood based on some priority order. [OFDMA Based Multiparty Medium Access Control in Wireless Ad Hoc Networks, ICC, 09])
• CBD: We added diversity when distributing the assigned subchannels among neighbors[Cross-Layer Channel Allocation Protocol for OFDMA Ad Hoc Networks, Globecom 10]
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Gibbs SamplingGoal: • Maximize concurrency
– Design a MAC that assigns subchannels to each directional link on-demand and based on the present interference, and node’s needs
• Maximize diversity– Subchannel selection should be done based on minimizing fading– Gibbs sampling previously used to distribute channels among multiple 802.11 Aps : min direct interference
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GSA
C-Tx_1C-Tx_1
C-Tx_2C-Tx_2
C-RxC-Rx
C-RxC-Rx
aa
bb
Gibbs Sampling
f (X)e E(X )
e E(Y )
Y SV
8
Sy
yE
xE
v v
v
e
exf )(
)(
)(
• Graph , and state X…want to find),( EVG ))(min(: XEX
vVv xPxE
,
)()(
GSAGibbs Subchannel Assignment (GSA)
• We propose to use Gibbsian method by defining a new energy model and a MAC protocol that works to select subchannels (Schannel) for each communicating link.
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C-Tx (a)C-Tx (a)C-Tx (c)C-Tx (c)
C-RxC-Rx
bbvv
uu
)()(
1)( kPi
kCSIkE v
vv
Subchannel kSubchannel k
Kk
kE
kE
vv
v
e
ekf
'
' )(
)(
)(
))((arg kfMaxulinkchoose uUu
MDMA
Freq
Control
FreeTx Schannel_1
FreeTx Schannel_2
C-Tx
a
bd
RTM-TRTM-T
time
c
Freq
Control
FreeTx Schannel_1
FreeTx Schannel_2
C-Tx
a
bd
RTM-TRTM-T
Pilot
timePilot
cMDMAMDMA
Freq
Control
FreeTx Schannel_1
FreeTx Schannel_2
C-Tx
a
bd
RTM-TRTM-T
a b c d
CTR
Pilot
timePilot
c
vSINR(k)>Thr
e
MDMA
Freq
Control
FreeTx Schannel_1
FreeTx Schannel_2
C-Tx
a
bd
RTM-TRTM-T
a b c d
CTR
Data: C-Tx->aPilot
time
Broadcast
Broadcast Data: C-Tx->bPilot
cMDMA
C-Rx
a
b
c
dRTM-RRTM-R
Freq
time
Control
FreeRx Schannel_1
FreeRx Schannel_2
MDMA
C-Rx
a
b
c
dRTM-RRTM-R
Freq
time
a b c d
CTT
a b c d
CTT
Control
FreeRx Schannel_1
FreeRx Schannel_2
MDMA
C-Rx
a
b
c
dRTM-RRTM-R
Freq
time
STTSTT
a b c d
CTT
a b c d
CTT
Control
FreeRx Schannel_1
FreeRx Schannel_2
MDMA
C-Rx
a
b
c
dRTM-RRTM-R
Freq
time
STTSTT
a b c d
CTT Data: a->C-Rx
a b c d
CTT Data: b->C-Rx
Control
FreeRx Schannel_1
FreeRx Schannel_2
MDMA
Range =
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)0Pr()()1log(
)Pr()()1log(
kX
X
a
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PX
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Analysis
3
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)Pr(k
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)(4
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Average =4
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Analysis
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1.3
Analysis Result
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Analytically GSA is outperforming ideal scheduling
2.6 times
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Simulations
C-Tx
Assumptions
Subcarriers 2048
Subchannel 32 (wimax)
Randomly selected neighbors(K)
2 to 5
Channel, Rayleigh, Portable
20-taps, defined in
EN-300-744
SNR 10
SEEDS 10 random
b
a
c u
Matlab Simulations
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Simulations
C
Assumptions
Subcarriers 2048
Subchannel 32 (wimax)
Randomly selected neighbors(K)
2 to 5
Channel, Rayleigh, Portable
20-taps, defined in
EN-300-744
SNR 10
SEEDS 10 random
A
A
A B
B
B
Matlab Simulations
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MDMA
Comparison
McH Orthogonal channel assignment, adaptive rate selection, CH=3
CBD Orthogonal channel assignment, adaptive subchannel assignment,
GSA Adaptive subchannel assignment
GSA increases concurrency comparing to CBD
63%
2.3 times
Matlab Simulations
Model Developed in QUALNET
Number of nodes
50 stationary
SNR 10
Packet length
512 B
topology 10 random
Average number of
node’s neighbors
10
Bit rate 11Mbit/sec
Percentage of the
communicating neighbors 24
MDMA
NK
1.6 times
Qualnet Simulations
• Previous cross-layer MAC fail to effectively utilize OFDMA• We improved our previous works by
• Utilizing Gibbs method • Increasing two-hop neighbor concurrency • Attaining diversity
• Our analysis and simulations proved that MDMA’s performance with the same BW is • 1.6 times better than CBD• 2.2 times better than CTRMA• 2.4 times better than traditional multi-channel networks
• Future work– Mobility– 802.11n OFDMA
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ConclusionConclusion
Questions