A Comparison of Opportunistic and Deterministic Forwarding in Mobile Wireless Networks
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Transcript of A Comparison of Opportunistic and Deterministic Forwarding in Mobile Wireless Networks
A Comparison of Opportunistic and Deterministic Forwarding in Mobile
Wireless Networks
Jonghyun Kim
Stephan Bohacek
Electrical and Computer Engineering
University of Delaware
Overview and objectives
Opportunistic Forwarding
Deterministic Forwarding
Simulation Environment
Simulation Results
Conclusions
Future Work
Outline
Overview and objectives
Exploiting path diversity
Originator
Final destination
- Many different paths exist- Deterministic and opportunistic best path exist- Deterministic best path is found in advance and it is not changed until the next deterministic best path update- Opportunistic best path is found on-the-fly and it is changed if a chance is arised
Opportunistic versus deterministic
Overview and objectives
• In deterministic forwarding, the route can be continually monitored. If the route degrades, refinement is triggered.
– Overhead to find refine routes
• However, in opportunistic forwarding, it is difficult to determine the quality of the route, and hence difficult to trigger refinement
– There is no single route whose quality can be monitored– The goal of opportunistic forwarding is to use weak links. Thus the path that a particular packet uses is typically (hopefully) bad. (compare this to deterministic case)– Overhead to coordinate which node will forward the packet
Overview and objectives
Exploiting path diversity
2
1
5
6
7
93
4
10
118Originator
Final destination
When nodes are stationary, - Opportunistic best path : shorter hop, lower SNR, faster bit rate - Deterministic best path : longer hop, higher SNR, slower bit rate
When nodes are moving, what will happen to the performance in various metrics?
e.g ) : deterministic best path : opportunistic best path
Overview and objectives
Objectives
- Compare the performance between opportunistic and deterministic forwarding 1)when nodes are moving and 2)by considering various steepness of the relationship between SNR and packet error probability.- Observe how much opportunism is varying according to various steepness.
Overview and objectives
Opportunistic Forwarding
Deterministic Forwarding
Mixed Forwarding
Simulation Environment
Simulation Results
Conclusions
Future Work
Outline
Opportunistic Forwarding
Initial path
- A slightly modified AODV is used to find the initial path above.- Initially, originator’s priority node : node1 node1’s priority node : node5 node 5’s priority node : final destination
S
1
2
3
D4
OriginatorFinal destination
5RREP
6
Opportunistic Forwarding
First data transmission
- During first data transmission through the initial path, node 2, 3, and 4 can be aware of this communication by overhearing packets, so they will join J-Broadcast process, but node 6 will not join.- Thus, searching for path diversity is localized.
S
1
2
3
D4
5
Cooperative network range
6
DATA
1
2
3
4
5
Preferred node(s)
Target node
Backup node(s)
P5
P4
P3
- Pi is the probability that a transmission from node 2 will be correctly decoded by node i- Ptarget is transmission probability threshold
• Target node – The node such that Pi >= Ptarget and makes the most progress to the destination
• Preferred nodes– Nodes that make better progress to the destination– By definition, the probability of reaching a preferred node is less than Ptarget
• Back-up nodes– Nodes that make some progress to the destination, but not as much as the target node.– In many cases, the probability of reaching a back up node is greater than Ptarget
SD
1
2
3
4
5
Preferred node(s)
Target node
Backup node(s)
P5
P4
P3
SD
Node A makes better progress to the destination than node B if - node A has few hops to the destination and each hop has a probability of success > Ptarget
- node A and B have the same number of hops, but node A has a higher worst-SNR-to-go, where worst-SNR-to-go is the worst SNR to go to final destination along the path.
Opportunistic Forwarding
J-Broadcast
- JBC packet contains worst-SNR-to-goD.- Node 3, 4, and 5 within D’s radio range receive JBC and compute worst-SNR-to-go.- Relay-set 1 = {3, 4, 5}
S
1
2
3
D4
5JBC
Communication range*Consider only node 5 worst-SNR-to-goD = inf SNRD = 20 JViaD = min (SNRD, worst-SNR-to-goD) = 20 worst-SNR-to-go5 = JViaD = 20 Target node = D Priority node list = {D}
Opportunistic Forwarding
J-Broadcast
- Relay-set 2 = {1, 2, S}- Priority node list ={preferred node(s), target node(s), backup node(s)}
S
1
2
3
D4
5
*Consider node 2 worst-SNR-to-go{3,4,5} = {15, 18, 20} SNR{3,4,5} = {23, 20, 17} JVia{3,4,5} = min (SNR{3,4,5}, worst-SNR-to-go{3,4,5}) = {15, 18, 17} worst-SNR-to-go2 = max(JVia{3,4,5}) = 18
*Consider node S worst-SNR-to-go3 = 15 SNR3 = 13 JVia3 = min (SNR3, worst-SNR-to-go3) = 13 worst-SNR-to-goS = 13 Target node = 3 Priority node list = {3}
JBC
Opportunistic Forwarding
J-Broadcast
- Relay-set 2 = {1, 2, S}- Priority node list ={preferred node(s), target node(s), backup node(s)}
S
1
2
3
D4
5
*Consider node 2 worst-SNR-to-go{3,4,5} = {15, 18, 20} SNR{3,4,5} = {23, 20, 17} JVia{3,4,5} = min (SNR{3,4,5}, worst-SNR-to-go{3,4,5}) = {15, 18, 17} worst-SNR-to-go2 = max(JVia{3,4,5}) = 18 Target node = 4 (maximum JVia index) Preferred node = 5 (larger worst-SNR-to-go5) Backup node = 3 (smaller worst-SNR-to-go3) Priority node list = {5, 4, 3}
*Consider node S worst-SNR-to-go3 = 15 SNR3 = 13 JVia3 = min (SNR3, worst-SNR-to-go3) = 13 worst-SNR-to-goS = 13 Target node = 3 Priority node list = {3}
Preferred node(s)
Target node
Backup node(s)
Opportunistic Forwarding
J-Broadcast
- Relay-set 3 = {S}- Node S has two relay-set
3
D4
5
*Consider node S - As a member of relay-set 3, worst-SNR-to-go{1,2} = {17, 18} SNR{1,2} = {21, 22} JVia{1,2} = min (SNR{1,2}, worst-SNR-to-go{1,2}) = {17, 18} worst-SNR-to-goS = max(JVia{1,2}) = 18 Target node = 2 Backup node = 1
- As a member of relay-set 2, worst-SNR-to-goS = 13 Target node = 3
Combined target node = 2 (maximum JVia index) Combined preferred node = 3 (shorter hop) Combined backup node = 1 (smaller worst-SNR-to-go1) Combined priority node list = {3,2,1}
S
1
2
JBC
Opportunistic Forwarding
J-Broadcast
- Relay-set 3 = {S}- Node S has two relay-set
S
1
2
3
D4
5
*Consider node S - As a member of relay-set 3, worst-SNR-to-go{1,2} = {17, 18} SNR{1,2} = {21, 22} JVia{1,2} = min (SNR{1,2}, worst-SNR-to-go{1,2}) = {17, 18} worst-SNR-to-goS = max(JVia{1,2}) = 18 Target node = 2 Backup node = 1
- As a member of relay-set 2, worst-SNR-to-goS = 13 Target node = 3
Combined target node = 2 (maximum JVia index) Combined preferred node = 3 (shorter hop) Combined backup node = 1 (smaller worst-SNR-to-go1) Combined priority node list = {3,2,1}
Backup node
Target node
Preferred node
Can only S join multiple relay-sets? YesWhat about other nodes? NoThey cannot because if a node receive a burst on JBCs, it joins a certain relay-set and it does not process JBC with the same sequence number any more.
Use hop count for each node to construct better priority nodes. Using hop count makes node receives more various JBCs (from different hops)
Opportunistic Forwarding
J-Broadcast
S
1
2
3
D4
5
RS0RS1RS2
RS3
- Now, each node in relay-set knows target node(s), preferred node(s), and backup node(s).
Opportunistic Forwarding
J-Broadcast
S
1
2
3
D4
5
: deterministic best path going though target nodes : opportunistic better paths over deterministic best path in terms of shorter hops or better progress to destination. : opportunistic worst path going through backup nodes.
Jonghyun Kim and Stephan Bohacek, Exploiting Multihop Diversity through Efficient Localized Searching with CDMA and Route Metric-based Power Control, MSWiM’06, Torremolinos, Malaga, Spain, October 2006
Opportunistic Forwarding
J-Broadcast
The constraint to broadcast JBC : Probability of successful transmission to downstream nodes (PST) must exceed target transmission probability (TTP).
JBCsofsendersi
iiO SNRBRFPST ),(11 0
0BR = lowest bit-rate
= probability of successful transmission to downstream node i
),( 0 ii SNRBRF
depends on the steepness of the relationship between SNR and packet error probability
),( 0 ii SNRBRF
Need to explain the equation using graphical view
Opportunistic Forwarding
J-Broadcast
The constraint to broadcast JBC : Probability of successful transmission to downstream nodes (PST) must exceed target transmission probability (TTP).
JBCsofsendersi
iiO SNRBRFPST ),(11 0
Downstream nodes (JBC senders)
Opportunistic Forwarding
PEP/SNR relationship
Pro
b. o
f p
ack
et e
rro
r
SNR (dB)
nominalsteepsteepest
shallowestshallowershallow
-5 0 5 10 15 20 2510
-4
10-3
10-2
10-1
100
2 Mbps
-5 0 5 10 15 20 2510-4
10-3
10-2
10-1
100
Black : shallowestBlue : nominalRed : steepest
Dotted : 1MbpsSolid : 2Mbps
Opportunistic Forwarding
PEP/SNR relationship
In case of steepest curve, when BR = 2Mbps, SNR >= 20.5 always F(BR, SNR) = 1 when BR = 2Mbps, SNR < 20.5 always F(BR, SNR) = 0 Thus, opportunism is disappeared because F(BR, SNR) is deterministic (i.e. there is no randomness of the probability of successful transmission)
Pro
b. o
f p
ack
et e
rro
r
SNR (dB)
nominalsteepsteepest
shallowestshallowershallow
-5 0 5 10 15 20 2510
-4
10-3
10-2
10-1
100
2 Mbps
-5 0 5 10 15 20 2510-4
10-3
10-2
10-1
100
Black : shallowestBlue : nominalRed : steepest
Dotted : 1MbpsSolid : 2Mbps
Opportunistic Forwarding
PEP/SNR relationship
In case of shallowest curve, maximum opportunism occurs because randomness of the probability of successful transmission becomes high.
Pro
b. o
f p
ack
et e
rro
r
SNR (dB)
nominalsteepsteepest
shallowestshallowershallow
-5 0 5 10 15 20 2510
-4
10-3
10-2
10-1
100
2 Mbps
-5 0 5 10 15 20 2510-4
10-3
10-2
10-1
100
Black : shallowestBlue : nominalRed : steepest
Dotted : 1MbpsSolid : 2Mbps
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5DATA
Priority node list = {3,2,1}
- Node 1, 2 and 3 buffer the received data.
Opportunistic Forwarding
Second data transmission
Backup nodes are not included into the bit rate calculation because the maximum bit rate would be set to reach these backup nodes and hence the preferred nodes would have little chance to receive the data packet.
Bit rate constraint to transmit data :
nodeornodespreferredj
jij
ii
O
TTPSNRBRFthatsuch
BRratebit
)),(1(1:
max
target
}12,10,8,6,4,2,1{}7,6,5,4,3,2,1,0{ BR
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5ACK
- Assume that highest priority node 3 successfully decoded the data.- Lower priority node 1 and 2 overhear ACK, so they discard the buffered data because they know that node 3 will transmit the data.
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5ACKACK
Why is ACKACK needed? To avoid collisions that happen when the communication range of either ACK sender (node 3) or ACKACK sender (node S) can cover a lower priority node (node 1 or 2) only in one direction. Thus, bi-directional ACK and ACKACK collision avoidance is needed.
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5ACK
- Node 2 cannot receive ACK due to an obstacle.- Without ACKACK, node 2 will send its buffered data which causes collision with node 3’s data
Obstacle
*Example of the communication range covered only in one direction
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5DATA
Priority node list = {3,2,1}
- If the first priority node 3 could not decode the data, the second priority node 2 waits for a predefined time. During that time, if node 2 does not overhear ACK or ACKACK, node 2 transmits ACK.
*What if the first priority node cannot decode the data?
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5
ACK
- Lowest priority node1 discards its buffered data.
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5ACKACK
Opportunistic Forwarding
Second data transmission
S
1
2
3
D4
5DATA
Priority node list = {5,4,3}
- Repeat this until a route failure occurs.- After route failure, repeat this procedure performed so far.
*What if the first priority node cannot decode the data?
Overview and objectives
Opportunistic Forwarding
Deterministic Forwarding
Simulation Environment
Simulation Results
Conclusions
Future Work
Outline
Deterministic Forwarding
Most of the protocols for opportunistic forwarding are still usedhere, but the main differences are as follows
- Packets go through only target nodes
-
-
- Dose not use ACK, and ACKACK packets
- Path quality monitoring is performed
),(max 0 iiJBCsofsendersi
D SNRBRFPST
TTPBRFthatsuch
BRratebit
inode
ii
D
)(:
max
target
Usually, In case of steepest curve, equality occurs.
DODO ratebitratebitPSTPST so,
Deterministic Forwarding
Path quality monitoring
S
1
2
3
D4
5
: Deterministic best path
- S maintains the last worst-SNR-to-go obtained from the J-Broadcast process- Whenever S receives implicit ACK, it updates worst-SNR-to-go.
Deterministic Forwarding
Path quality monitoring
S
1
2
3
D4
5
- S will detect that the path quality goes bad, so it invokes the J-Broadcast process to find a new deterministic best path.
2
moved here
Deterministic Forwarding
Path quality monitoring
S
1
3
D4
5
2
: New deterministic best path
Overview and objectives
Opportunistic Forwarding
Deterministic Forwarding
Simulation Environment
Simulation Results
Conclusions
Future Work
Outline
Simulation Environment
# of scenarios : 5# of nodes : 64, 128, 256, 512, 1024# of steepness : 6# of trials : 60City map : Chicago downtownCBR traffic : 512 byte per 50 msSimulation time : 5 minutesMobility : UDel mobility simulatorChannel gain : UDel channel simulatorPacket simulator: Qualnet
Simulation Environment
real city map: GIS shapefiles or image
mobility trace
map data
processed map data channel gain matrix
channel gain trace
e.g., Qualnet, ns, Opnet
Base station editor
performed once per city
UDel Models – Simulation methodology
Map builder
Process map data
Mobility simulator Channel simulator2
Channel simulator1
Packet simulator
Statistics
Simulation Environment
UDel Models – Map models
Downtown Chicago
Simulation EnvironmentUDel Models – Mobility models
Pedestrian flow from a subway
Pedestrian crosswalk at a traffic light
Office workers inside a building
General view
Simulation Environment
UDel Models – Channel models
Communication connectivity(11Mbps )
Variable nature of communication
Simulation Environment
http://udelmodels.eecis.udel.edu
UDel Models – Website
Overview and objectives
Opportunistic Forwarding
Deterministic Forwarding
Simulation Environment
Simulation Results
Conclusions
Future Work
Outline
Simulation Results
# of nodes
Deterministic forwarding Opportunistic forwarding
Bit
rat
e (M
bp
s)
64 128 256 512 10241.5
2
2.5
3
3.5
4
1.5
2
2.5
3
3.5
4
nominalsteepsteepestshallowestshallowershallow
Second data (before nodes move)
- The smoother curve in PEP/SNR relationship and the higher node density, the more opportunism utilized.- The performance is same in steepest case as expected.
64 128 256 512 1024
Simulation Results
nominalsteepsteepestshallowestshallowershallow
- The smoother curve, the lower received power.- Lower averaged power, but still achieve good bit rate.
Re
cei
ved
po
we
r (d
Bm
)
-80
-79
-78
-77
-76
-80
-79
-78
-77
-76Deterministic forwarding Opportunistic forwarding
Second data (before nodes move)
# of nodes
64 128 256 512 1024 64 128 256 512 1024
Simulation Results
- The higher node density, the smaller number of hops.- Each point represents for both approaches and all different steepness.
Second data (before nodes move)#
of
ho
ps
2.3
2.35
2.4
2.45
2.5
2.55
2.6
2.65
2.7Deterministic and opportunistic forwarding
64 128 256 512 1024# of nodes
Simulation Results
- Deterministic forwarding (DF) is between 5% and 10% better.- When nodes move, channel information begins to be not correct. DF will trigger J-broadcast process if path quality is degraded, so it will obtain new channel information. But opportunistic forwarding (OF) will not.
Performance before the first route failure
Deterministic forwarding Opportunistic forwarding
Bit
rat
e (M
bp
s)
1.5
2
2.5
3
3.5
1.5
2
2.5
3
3.5
nominalsteepsteepestshallowestshallowershallow
64 128 256 512 1024 64 128 256 512 1024# of nodes
Simulation Results
- Deterministic forwarding (DF) is between 5% and 10% better.- When nodes move, channel information begins to be not correct. DF will trigger J-broadcast process if path quality is degraded, so it will obtain new channel information. But opportunistic forwarding (OF) will not.
Performance before the first route failure
Deterministic forwarding Opportunistic forwarding
Bit
rat
e (M
bp
s)
1.5
2
2.5
3
3.5
1.5
2
2.5
3
3.5
nominalsteepsteepestshallowestshallowershallow
When node does not move
When node moves
64 128 256 512 1024 64 128 256 512 1024# of nodes
Simulation Results
- Deterministic forwarding (DF) is between 5% and 10% better.- When nodes move, channel information begins to be not correct. DF will trigger J-broadcast process if path quality is degraded, so it will obtain new channel information. But opportunistic forwarding (OF) will not.
Performance before the first route failure
Deterministic forwarding Opportunistic forwarding
Bit
rat
e (M
bp
s)
1.5
2
2.5
3
3.5
1.5
2
2.5
3
3.5
nominalsteepsteepestshallowestshallowershallow
When node does not move
When node moves
64 128 256 512 102464 128 256 512 1024
# of nodes
Simulation Results
Performance before the first route failurenominalsteepsteepestshallowestshallowershallow
# o
f h
op
s
1.5
2
2.5
1.5
2
2.5Deterministic forwarding Opportunistic forwarding
- DF is 0.5% shorter on average. The result is quite close.
# of nodes
64 128 256 512 1024 64 128 256 512 1024
Simulation Results
Performance during the connection lifetimenominalsteepsteepestshallowestshallowershallow
- Path monitoring and route updates are more critical to maintain a path than allowing opportunistic forwarding.- The smoother curve in PEP/SNR relationship, the better performance.
Deterministic forwarding
Pac
ket
del
iver
y ra
tio
Opportunistic forwarding
0.986
0.988
0.99
0.992
0.994
0.996
0.998
1
0.986
0.988
0.99
0.992
0.994
0.996
0.998
1
# of nodes
64 128 256 512 1024 64 128 256 512 1024
Simulation Results
Performance during the connection lifetimenominalsteepsteepestshallowestshallowershallow
- Again, path monitoring and route updates are crucial to reduce route failure rate.- Degree of the PEP/SNR relationship curve impacts more on performance of OF than DF because W2 is wider than W1.
1/R
ou
te d
ura
tio
n
0.05
0.1
0.15
0.2
0.25
0.3
0.05
0.1
0.15
0.2
0.25
0.3
Deterministic forwarding Opportunistic forwarding
W1
W2
# of nodes64 128 256 512 1024 64 128 256 512 1024
Simulation Results
Performance during the connection lifetimenominalsteepsteepestshallowestshallowershallow
- Efficiency = duration for data pkts / duration for any packet including overhead.- Overhead for DF = JBC frames used in highly efficient J-Broadcast process, less AODV pkts- Overhead for OF = ACK, ACKACK frames per every data transmission, more AODV pkts.
Deterministic forwarding Opportunistic forwarding
Eff
icie
ncy
0.88
0.9
0.92
0.94
0.96
0.98
1
0.88
0.9
0.92
0.94
0.96
0.98
1
# of nodes
64 128 256 512 1024 64 128 256 512 1024
Overview and objectives
Opportunistic Forwarding
Deterministic Forwarding
Simulation Environment
Simulation Results
Conclusions
Future Work
Outline
Conclusions
Deterministic Opportunistic
Bit rate Slower Faster
Rx power Larger Smaller
# of hops Longer Shorter
When nodes are stationary
Opportunistic forwarding is preferred
Conclusions
Deterministic Opportunistic
Bit rate Faster Slower
Rx power Larger Smaller
# of hops Shorter Longer
PDR Higher Lower
Route failure rate Lower Higher
Efficiency Higher lower
When nodes move
Deterministic forwarding is preferred
Conclusions
- Opportunistic forwarding has good opportunism when nodes do not move, but when nodes move, opportunism begins to be disappeared due to losing channel information within cooperative network range.- Deterministic forwarding has no opportunism when nodes do not move, but when nodes move, the performance in various metrics is better than opportunistic forwarding due to regaining channel information.- When nodes are stationary, opportunistic forwarding is preferred.- When nodes are not stationary, deterministic forwarding is preferred.- The smoother curve in PEP/SNR relationship, the more opportunism.- Degree of the PEP/SNR relationship curve impacts more on performance of opportunistic forwarding than deterministic forwarding.
Overview and objectives
Opportunistic Forwarding
Deterministic Forwarding
Simulation Environment
Simulation Results
Conclusions
Future Work
Outline
Future Work
- Impacts of signal interferences on the performance- Explore the broader range of local cooperative network- Explore any opportunism in deterministic forwarding e.g. opportunism during repairing link failure by using nodes within the same relay-set and the next relay-set