chorus: collision resolution for efficient wireless broadcast
DESCRIPTION
Chorus: Collision Resolution for Efficient Wireless Broadcast. Xinyu Zhang, Kang G. Shin. University of Michigan. PHY layer. MAC layer. Outline. Design. Analysis & evaluation. Introduction. Summary. Chorus (broadcast). simulation. PHY PER . principles. motivation. network. - PowerPoint PPT PresentationTRANSCRIPT
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Chorus: Collision Resolution for Efficient Wireless Broadcast
Xinyu Zhang, Kang G. Shin
University of Michigan
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Outline
Introduction Design Summary
Chorus(broadcast)
PHY layer
MAC layer
Analysis & evaluation
PHY PER
network
simulationmotivation principles
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Motivation: CSMA/CA limitation
Traditional CSMA/CA (Collision Avoidance):
Principle: listen before talking --- akin to human world
Collision: packets overlap at receiver
Limitation:
Listen without interpretationCollision avoidance in all cases --- too conservative
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Rationale(1/3): CSMA/CR principle
CSMA/CR (CSMA with collision resolution):
CSMA/CR Principle:Collision caused by packets carrying the same data can be resolved!
A new MAC/PHY paradigm
Overcome the limitation of CSMA/CA
A
B
D
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Rationale(2/3): CSMA/CR advantage
Improving broadcast efficiency
(b) Chorus, a CSMA/CR based broadcast protocol
Taking advantage of spatial reuse and transmit diversity
A
B
C
D
E
S
(a) Traditional CSMA/CA based broadcast
A
B
C
D
E
S
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Chorus: collision resolution based broadcast
PHY
MAC
Resolve collisions via signal processing
Encourage resolvable collisions via intelligent sensing and scheduling
CSMA/CR
BroadcastA broadcast protocol with asymptotic latency)(r
Chorus
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Chorus: 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 ZA
B
D
Decode two versions of the packet: from preamble and postamble, respectively
Multipacket collision resolution:
A
A'
B CHead packet P1
Tail packet P2
D E
A'' B'' C''
A''' B'''
packet P3
packet P4
D''
Head and tail packet: iterative collision resolution
Other packets: hard decoding
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CSMA/CR: MAC layer
Cognitive sensing and scheduling
Basic rules in SEND:If the channel is busy, and the packet in the air is exactly one of the packets in the transmit queue, then start transmitting the pending packet.Otherwise, degenerate to 802.11
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Chorus: CSMA/CR-based broadcast
S
Extension to 802.11 broadcast mode
Anonymous and decentralized
Performance analysis
Asymptotic broadcast delay (unit disk graph model):
DLr.
DhLr .Lowerbound: Upperbound:
header lengthpkt length
network radius data rate
)(r
Best known result for CSMA/CA broadcast: )log( nr
Asymptotic throughput:
3D
)(3 hLLD
Lowerbound: Upperbound:
11
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Achievable SNR:
Achievable PER:
PHY layer performance analysis
21 PERPERPER
Error propagation effect (based on a Markov chain model):
},{max 21 SNRSNRSNR
While resolving a given collision, the error propagation probability decays exponentially with the error length.
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Implement Chorus in ns-2
• Simulated application and MAC layers
• Analytical model for PHY-layer packet reception
Benchmark protocol: double coverage broadcast (DCB)
* W. Lou, J. Wu, “Toward Broadcast Reliability in Mobile Ad Hoc Networks with Double Coverage,” IEEE Trans. on Mobile Computing, vol. 6, no. 2, 2007
• Forwarding set selection: remove redundant transmissions
• Each node covered by two forwarders (retransmission improves reliability)
Chorus: Network-level simulation
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PDR and delay in lossy networks
: reception probability at transmission range
Chorus is more resilient to packet losses.
Scalability:
Chorus is less affected by network size.
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Achievable throughput:
Chorus can support much higher throughput.
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Multiple broadcast sessions:
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Conclusion
Chorus(broadcast)
PHY
MACCSMA/CR
transmit diversity
spatial reuse
Chorus: achieve optimal broadcast performance via a software radio based MAC/PHY.
Thank you!
Error propagation effect: a Markov chain model
Probability that error propagation stops, i.e., the next bit is correct even when the current bit is erroneous.
:bcP
:eP BER of clean symbols
15.0 bcPCan be bounded:
Max error length:G FLG
data lengthoffset between collided pkts
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Steady state error length distribution:
bc
Gbc
e PPP )1(11
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GiPP ibcei ,,2,1,)1( 1
0
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Impact of packet size:
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Related Work [1/2]
Broadcast for 802.11 based wireless ad hoc networks
Most focused on forwarding node selection to prevent broadcast storming
* W. Lou, J. Wu, “Toward Broadcast Reliability in Mobile Ad Hoc Networks with Double Coverage,” IEEE Trans. on Mobile Computing, vol. 6, no. 2, 2007
* R. Gandhi, S. Parthasarathy, A. Mishr, Minimizing Broadcast Latency and Redundancy in Ad Hoc Networks, ACM MobiHoc’03
* S.-H. Huang, P.-J. Wan, X. Jia, H. Du, W. Shang, Minimum-Latency Broadcast Scheduling in Wireless Ad Hoc Networks, IEEE INFOCOM’07
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Related Work [2/2]
ZigZag decoding
Interference cancellation
* S. Gollakotam, D. Katabi. ZigZag Decoding: Combating Hidden Terminals in Wireless Networks, in Proc. of ACM SIGCOMM, 2008.
* D. Halperin, et. al. Taking the Sting out of Carrier Sense: Interference Cancellation for Wireless LANs, in Proc. of ACM MobiCom, 2008
A MAC/PHY layer technique. Only works when one packet has much higher SNR than the other.
Similar decoding algorithm. Rely on MAC layer retransmission to obtain multiple collided version of the same packets
PHY/MAC layer technique to combat hidden terminals
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