DAC: Distributed Asynchronous Cooperation for Wireless Relay Networks 1 Xinyu Zhang, Kang G. Shin...
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Transcript of DAC: Distributed Asynchronous Cooperation for Wireless Relay Networks 1 Xinyu Zhang, Kang G. Shin...
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DAC: Distributed Asynchronous Cooperation
for Wireless Relay Networks
Xinyu Zhang, Kang G. Shin
University of Michigan
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Outline
Introduction Design Conclusion
DAC(routing)
PHY layer
MAC layerCSMA/CR
Implementation & evaluation
GNURadio/USRP
analysis
simulation
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Motivation: sync problem in cooperative relaying
Non-orthogonal cooperative relaying
Multiple transmitters sending the same packet (V-MISO)
A
B
CS
Major obstacle towards practical use:
Sync among distributed relays
In theory, realized via STBC or beamforming
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DAC: asynchronous non-orthogonal relaying
(b) DAC, asynchronous non-orthogonal relaying
(a) Synchronous non-orthogonal relaying protocol
A
B
CS
A
B
CS
Preserve transmit diversity
Circumvent the sync problem
DAC:
Via a new MAC/PHY: CSMA/CR (CSMA with collision resolution)
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The DAC network stack
PHY
MAC
Resolve collisions via signal processing
Encourage resolvable collisions via intelligent sensing and scheduling
CSMA/CR
Cooperative relaying
Asynchronous, non-orthogonal relaying protocol
DAC
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CSMA/CR: PHY layer
Resolve the collided packet by iterative decoding
S --- the received symbol.
A’ --- estimated based on A
C = S – A’
P1
P1
A
A'
B
B'
C
C'
S=A' + C
D E
D' E' Y' Z'
Y Z
Key problem: how to reconstruct A’ based on A?
A
B
C
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Challenges and solutions:
Channel estimation (phase and amplitude): correlation
Frequency offset estimation: Costas loop
Symbol and sample level timing offset: MM circuit
Identify exact start time of packets: sample level correlation
Transmitter distortion: reverse engineering tx filter
A
A'
B
B'
C
C'
S=A' + C
D E
D' E' Y' Z'
Y Z
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Implementation on GNURadio and verification on an SDR network:
A
D
B
A, B transmit the same packets to D
PER performance of forward-direction collision resolution
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CSMA/CR: MAC layer
Key rule: If the channel is busy, and the packet on the air is the one to transmit, then start the transmission.
Sensing and scheduling:
--- encourage resolvable collision
Otherwise, degenerate to CSMA/CA
P1P1
P1
P1
A
B
C
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DAC: CSMA/CR-based cooperative relaying
Objective:
Improve throughput performance of cooperative relaying using collision resolution
Basic idea:
7
5
6
S
8
9
D
3
4
1
2
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DAC (Distributed Asynchronous Cooperation)
Add secondary relays to primary relays
11How to select relays?
Establish a primary path
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DAC: relay selection
Select secondary relays:
Optimal relay selection:
primary relay
'iR
1iR1iRiRS D
secondary relay
Select resulting in minimum delay from to 'iR 1iR 1iR
A model-driven approach, based on average link quality
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DAC: Diversity-multiplexing tradeoff
Q: Does DAC improve total network throughput?
1S
2S 2D
1D
Interference range
2R
1R
3RThroughput ++
Secondary relay provides diversity gain for the primary path, but may reduce the multiplexing opportunity of other flows.
Throughput −−
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Network model:
Homogeneous erasure network with reception probability
Grid network:
Arbitrary network topology:
p
86.0p
64.0p
Wireless LAN: 1p
:d throughput of DAC
:c throughput of the single-path routing protocol
Analytical results:
Sufficient conditions for :cd
A: DAC improves the throughput of lossy networks (e.g. Roofnet)
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Implement DAC in ns-2
Benchmark protocol: ETX routing
* D. Couto, D. Aguayo, J. Bicket and R. Morris, A High-throughput Path Metric for Multi-hop Wireless Routing, In Proc. of ACM MobiCom, 2003
DAC: Simulation experiments
• Routing metric: expected transmission count
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Single-unicast scenario:
DAC throughput gain ranges from 1.1 to 2.9, avg 1.7
Throughput gain is higher for low-throughput paths
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Multiple-unicast scenario:
DAC results in higher network throughput
DAC shows a higher level of fairness
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Multiple-unicast scenario, non-lossy networks:
DAC may have lower network throughput
DAC still maintains a higher level of fairness
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Related work:
Iterative cancellation:
* S. Gollakotam, D. Katabi. ZigZag Decoding: Combating Hidden Terminals in Wireless Networks, in Proc. of ACM SIGCOMM, 2008.
Cooperative relaying:
* R. Mudumbai, et al. On the Feasibility of Distributed Beamforming in Wireless Networks, in IEEE Trans. On Wireless Communications. Vol. 6, No. 5, May 2007.
* J. Zhang, J. Jia, Q. Zhang and E. M. K. Lo, Implementation and Evaluation of Cooperative Communication Schemes in Software-Defined Radio Testbed. In Proc. of IEEE INFOCOM, 2010
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Conclusion
Circumvent sync problem in cooperative relaying via PHY layer signal processing
DAC (Distributed Asynchronous Cooperation):
Diversity-multiplexing tradeoff
Collision tolerant scheduling & relay selection
DAC: asynchronous cooperative relaying, based on a SDR PHY
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Thank you!