toward broadcast reliability in mobile ad hoc networks with double coverage
DESCRIPTION
Toward Broadcast Reliability in Mobile Ad Hoc Networks with Double Coverage. Presented by Fei Huang Virginia Tech April 4, 2007. Original Paper. - PowerPoint PPT PresentationTRANSCRIPT
Presented by Fei Huang
Virginia TechApril 4, 2007
Original PaperW. Lou and J. Wu, “Toward broadcast reliability in
mobile ad hoc networks with double coverage,” IEEE Transactions on Mobile Computing, Vol. 6, No. 2, Feb. 2007, pp. 148-163.
It makes use of broadcast redundancy to improve the delivery ratio in an environment with high transmission error rate.
OutlineBackgroundPreliminariesDouble-covered Broadcast AlgorithmProbability AnalysisPerformanceConclusions
BackgroundMobile ad hoc networks (MANETs) enable
wireless communications between participating mobile nodes without the assistance of any base station.
AB
Communications
A -> B
CD
E
F
G
H
BackgroundMobile ad hoc networks (MANETs) enable
wireless communications between participating mobile nodes without the assistance of any base station.
AB
Characteristics
ad hoc
CD
E
F
G
H
BackgroundMobile ad hoc networks (MANETs) enable
wireless communications between participating mobile nodes without the assistance of any base station.
AB
Characteristics
ad hoc
overhearing
CD
E
F
G
H
BackgroundExposed Terminal Problem: an outgoing transmission collides with an
incoming transmission
AB
Communications
A -> E & E -> F
CD
E
F
G
H
BackgroundHidden Terminal Problem: two incoming transmissions collide with
each other
AB
Communications
A -> D & F->D
CD
E
F
G
H
BackgroundBlind Flooding: every node forwards the packet once and
only once
AB
CD
E
F
G
H
BackgroundBlind Flooding: every node forwards the packet once and
only once
AB
Cons
broadcast storm problem
CD
E
F
G
H
BackgroundMANETs suffers from a high transmission
error rate because of the high transmission contention and congestion in broadcast
AB
CD
E
F
G
H
BackgroundSolution: select a subset of nodes to forward
the broadcast message without sacrificing the broadcast performance
How? This paper proposed a double-covered broadcast algorithm.
PreliminariesMANET can be described by graph G=(V,E)
V : nodes
AB
CD
E
F
G
PreliminariesMANET can be described by graph G=(V,E)
V : nodes, E: bidirectional links between nodes.
AB
CD
E
F
G
PreliminariesTwo nodes are neighbors only when their
distance is less than transmission range.
A
C
PreliminariesNk(v): the k-hop neighbor set of node v which
includes all nodes within k hops from v (and also includes v itself).
Hk(v): the k-hop node set of v which includes all nodes that are exactly k hops away from v.
Double-covered Broadcast (DCB) AlgorithmBasic Idea: When a sender broadcasts a
packet, it selects a subset of 1-hop neighbors as its forwarding nodes to forward the packet based on a greedy approach.
Such selected neighbors should satisfy two requirements:1) they cover all the sender’s 2-hop neighbors2) the sender’s 1-hop neighbors are either forwarding nodes or non-forwarding nodes covered by at least two forwarding nodes
Double-covered Broadcast (DCB) Algorithm
AB
CD
E
F
G
1 –hop neighbors
2 –hop neighbors
Forwarding nodes
C, D, E F, G C,E
H
Double-covered Broadcast (DCB) Algorithm
AB
CD
E
F
G
1 –hop neighbors
2 –hop neighbors
Forwarding nodes
C, D, E F, G C,E
H
1) C, E cover F,G
Double-covered Broadcast (DCB) Algorithm
AB
CD
E
F
G
1 –hop neighbors
2 –hop neighbors
Forwarding nodes
C, D, E F, G C,E
H
1) C, E covers F,G2) D is covered twice
by A and E.
Double-covered Broadcast (DCB) AlgorithmAfter receiving a new broadcast packet, each
forwarding node records the packet, computes its forwarding nodes, and rebroadcasts the packet as a new sender.
AB
CD
E
F
H
Double-covered Broadcast (DCB) AlgorithmThe retransmissions of the forwarding nodes are
overheard by the sender as the acknowledgement of the reception of the packet. The nonforwarding 1-hop neighbors of the sender do not acknowledge the receipt of the broadcast.
AB
CD
E
F
H
Double-covered Broadcast (DCB) Algorithm If the sender fails to detect all its forwarding nodes
retransmitting during a predetermined time, it assumes that a transmission failure has occurred for this broadcast. The sender then resends the packet until all the forwarding nodes’ retransmissions are detected or the maximum number of retries is reached. When the forwarding node receives a duplicated broadcast packet, it sends an ACK to acknowledge the sender.
AB
CD
E
F
H
A’s Timer
3
Double-covered Broadcast (DCB) Algorithm If the sender fails to detect all its forwarding nodes
retransmitting during a predetermined time, it assumes that a transmission failure has occurred for this broadcast. The sender then resends the packet until all the forwarding nodes’ retransmissions are detected or the maximum number of retries is reached. When the forwarding node receives a duplicated broadcast packet, it sends an ACK to acknowledge the sender.
AB
CD
E
F
H
A’s Timer
2
Double-covered Broadcast (DCB) Algorithm If the sender fails to detect all its forwarding nodes
retransmitting during a predetermined time, it assumes that a transmission failure has occurred for this broadcast. The sender then resends the packet until all the forwarding nodes’ retransmissions are detected or the maximum number of retries is reached. When the forwarding node receives a duplicated broadcast packet, it sends an ACK to acknowledge the sender.
AB
CD
E
F
H
A’s Timer
1
Double-covered Broadcast (DCB) Algorithm If the sender fails to detect all its forwarding nodes
retransmitting during a predetermined time, it assumes that a transmission failure has occurred for this broadcast. The sender then resends the packet until all the forwarding nodes’ retransmissions are detected or the maximum number of retries is reached. When the forwarding node receives a duplicated broadcast packet, it sends an ACK to acknowledge the sender.
AB
CD
E
F
H
A’s Timer
0
Double-covered Broadcast (DCB) Algorithm If the sender fails to detect all its forwarding nodes
retransmitting during a predetermined time, it assumes that a transmission failure has occurred for this broadcast. The sender then resends the packet until all the forwarding nodes’ retransmissions are detected or the maximum number of retries is reached. When the forwarding node receives a duplicated broadcast packet, it sends an ACK to acknowledge the sender.
AB
CD
E
F
H
A’s Timer
0
ACK
Double-covered Broadcast (DCB) Algorithm If the sender fails to detect all its forwarding nodes
retransmitting during a predetermined time, it assumes that a transmission failure has occurred for this broadcast. The sender then resends the packet until all the forwarding nodes’ retransmissions are detected or the maximum number of retries is reached. When the forwarding node receives a duplicated broadcast packet, it sends an ACK to acknowledge the sender.
AB
CD
E
F
H
A’s Timer
0
New forwarding
nodes
C, D
Double-covered Broadcast (DCB) AlgorithmPros:1)The scheme avoids the broadcast storm
problem2)The scheme avoids the ACK implosion
problem
Basic AlgorithmForwarding Node Set Selection Process
(FNSSP)
where X is all the candidate neighbors, U represents the uncovered 2-hop neighbors, and F is the set of forwarding nodes.
DCB Forwarding Node SelectionForwarding Node Set Selection Process – Double Coverage (FNSSP-DC):1. Each node v computes X=H(v) and
U=N2(v)-{v}.2. Node v uses the FNSSP to find F(v) in X to
cover U.
DCB Forwarding Node SelectionForwarding Node Set Selection Process – Enhanced Double Coverage (FNSSP-EDC):1. Each node v computes X=H(v)-N(u) and
U=N2(v)-N(u)-N(F(u)-{v}).2. Node v uses the FNSSP to find F(v) in X to
cover U.
DCBBoth FNSSP-DC and FNSSP-EDC algorithms provide a
set of forwarding nodes that cover all the nodes within a 2-hop neighbor set and doubly cover the nonforwarding nodes within a 1-hop neighbor set.
FNSSP-EDCN(2)={1,2,3,5,6} and N2(2)={1,2,3,4,5,6,7}(a)node 2 selects forwarding nodes {1,3,5}(b)node 5 selects forwarding nodes {2,4,6}. So node 2’s uncovered 2-hop
neighbor set is N2(2)-N(5)-N({4,6})={3}. Node 2 then selects {3}.
DCBReliability Issues1)Nonforwarding nodes: two chances to hear
the message2)Forwarding nodes: transmission error may
propagate
Two Reasons for Packet Loss1)High transmission error2)Out-of-range movement
DCBNetwork with Asymmetric Linksv will send ACK to u via w.
C
D
A
Probability AnalysisThe probability Pf(R) of a successful reception
for a 1-hop forwarding node f can be carried out by
where Q is the probability of a failed transmission, R is the number of retransmission attempts. fu
Probability AnalysisThe probability Pv(R=1)of a successful
reception for 1-hop nonforwarding node with a set of forwarding nodes {f1,f2,..fK-1} can be carried out by
where P=1-Q is the probability of a successful transmission, K is the number of forwarding nodes.
vuf1
f2
fK-1:
Probability AnalysisGenerally, the probability Pv(R)of a successful
reception for 1-hop nonforwarding node with a set of forwarding nodes {f1,f2,..fK-1} can be carried out by
where X represents the number of retransmissions for u to successfully deliver a packet and Y=1 when v receives the packet; otherwise Y=0.
vuf1
f2
fK-1:
Probability Analysis
vuf1
f2
fK-1:
Probability Analysis
vuf1
f2
fK-1:
From the above, we can derive that
Probability Analysis
vuf1
f2
fK-1:
Also, we can have
Probability Analysis
vuf1
f2
fK-1:
Combing the above, we have
Performance AnalysisPerformance is simulated in ns-2.Metrics:1) Broadcast delivery ratio. 2)Broadcast forwarding ratio. 3)Broadcast overhead. 4)Broadcast end-to-end delay.
Broadcast delivery ratio
Broadcast forwarding ratio
Broadcast overhead
Broadcast end-to-end delay
ConclusionsThis is a simple broadcast algorithm with satisfactory
result.It is reported that the DCB is sensitive to node’s
mobility.The performances is good and have a high delivery ratio.KEY: (1)Only a subset of nodes are selected as forwarding
nodes.(2) Double coverage of forwarding selection process
increases the reliability.DCB mainly increases the reliability of forwarding nodes
but not for nonforwarding nodes.