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


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


• 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


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


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.




Mixed Forwarding


Simulation Results

Conclusions

Future Work

Outline


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


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.


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}


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


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)


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


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)


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).


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


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


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)


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



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)



-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





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)



-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




Second data transmission

S

1

2

3

D4

5DATA

Priority node list = {3,2,1}

- Node 1, 2 and 3 buffer the received data.



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



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.



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.



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



S

1

2

3

D4

5DATA


- 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?



S

1

2

3

D4

5

ACK

- Lowest priority node1 discards its buffered data.



S

1

2

3

D4

5ACKACK



S

1

2

3

D4

5DATA


- 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?





Simulation Results

Conclusions

Future Work

Outline


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,


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.



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



S

1

3

D4

5

2

: New deterministic best path





Simulation Results

Conclusions

Future Work

Outline


# 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


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


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


UDel Models – Channel models

Communication connectivity(11Mbps )

Variable nature of communication


http://udelmodels.eecis.udel.edu

UDel Models – Website





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


- 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


Bit

rat

e (M

bp

s)

1.5

2

2.5

3

3.5

1.5

2

2.5

3

3.5


64 128 256 512 1024 64 128 256 512 1024# of nodes

Simulation Results




Bit

rat

e (M

bp

s)

1.5

2

2.5

3

3.5

1.5

2

2.5

3

3.5


When node does not move

When node moves

64 128 256 512 1024 64 128 256 512 1024# of nodes

Simulation Results




Bit

rat

e (M

bp

s)

1.5

2

2.5

3

3.5

1.5

2

2.5

3

3.5


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


- 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


W1

W2

# of nodes64 128 256 512 1024 64 128 256 512 1024

Simulation Results


- 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.


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





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.





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

Thanks

Any questions, comments, suggestions ?

E-mail : [email protected] [email protected]

a comparison of opportunistic and deterministic forwarding in mobile wireless networks

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