on the advantage of multi-hop extensions to ieee 802.11 infrastructure mode
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NYMAN 2004 1
On the advantage of multi-hop extensions to IEEE 802.11
infrastructure modeSathya Narayanan
PanasonicPei Liu
Shivendra PanwarPolytechnic University
NYMAN 2004 2
Overview We study the effect of using multi-hopping
Instead of reducing the transmission rate of nodes use multi-hop (two-hop) transmissions at highest rate (11 Mbps).
The SIR (Signal-To-Interference Ratio) experienced by nodes when the transmission power is reduced at edge nodes to reach an intermediate node, rather than the access point directly. This improves the throughput of nodes at the edge of the network.
Important note: Advantages discussed from both forwarding nodes and source nodes perspective.
NYMAN 2004 3
IEEE 802.11 MAC Infrastructure mode and ad hoc
mode DCF Operation Multiple rates
11 Mbps, 5.5. Mbps, 2 Mbps, 1 Mbps Single hop MAC
NYMAN 2004 4
Advantages of multi-hop extension Studying the effect of multi-hop
extensions w.r.t The network throughput in a multi-
rate network The SIR experienced by edge nodes
Initial study demonstrates possible improvements in both area Result in next few slides …
NYMAN 2004 5
Simulation 24 nodes – AP in the middle Manual rate selection High speed nodes at 11 Mbps Low speed nodes at 1 Mbps
Increase the number of slow nodes to study impact on throughput
NYMAN 2004 6
Avg. throughput per node (Total 24 nodes)
0.0020000.0040000.0060000.0080000.00
100000.00120000.00140000.00160000.00
1 2 3 4 5 6 7 8 9 10 11
Number of nodes at 1 Mbps
Bits
per
sec
ond
Analytical
Simulation
Average Throughput per node drops for all nodes when slower nodes are introduced in the network
NYMAN 2004 7
Total useful throughput of the network
0.00
500000.001000000.00
1500000.002000000.00
2500000.003000000.00
3500000.00
1 3 5 7 9
11Number of nodes at 1 Mbps
Bits
per
sec
ond
Total througput of thenetwork with slownodes
Total througput of thenetwork usingforwarding with allnodes @ 11 Mbps
Total useful throughput of the network increases when multi-hop (two) is used maintaining higher data rate at all nodes
NYMAN 2004 8
Forwarding node Increase in total throughput is not an
incentive for the forwarding node to participate in multi-hop scheme.
What is the effect on the throughput experienced by forwarding node?
Assumption: Each forwarding node only has to support one slow node
NYMAN 2004 9
Avg. traffic per forwarding node - Total 24 nodes
0
50000
100000
150000
200000
1 2 3 4 5 6 7 8 9 10 11
Number of nodes at 1 Mbps
Bits
per
sec
ond
Average data trafficper node with slownodes
Average traffic forforwarding nodes (and slow nodes) -current MAC
Average traffic forforwarding nodes (and slow nodes) -new opportunisticMAC
Current MAC: The available throughput at the forwarding node is equally shared with the slow node.
Opportunistic MAC: The total available throughput of the network is equally shared among all nodes
NYMAN 2004 10
Bandwidth improvement for the forwarding node
-60000
-40000
-20000
0
20000
40000
60000
1 2 3 4 5 6 7 8 9 10 11
Number of nodes at 1 Mbps
Bits
per
sec
ond
Bandwidthimprovement -currentMAC
Bandwidthimprovement - newOpportunistic MAC
NYMAN 2004 11
Percentage improvement
-60-40-20
020406080
100120
1 2 3 4 5 6 7 8 9 10 11
Number of nodes at 1 Mbps
Perc
enta
ge in
crea
se
Percentageimprovement - currentMAC
Percentageimprovement-newopportunistic MAC
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A
B
A
C
A
C
B
C
A
B
B
C
B
A
d
ii
i
Rayleigh fading model
NYMAN 2004 13
Simulation C Program Calculate interference at each point
in the cell from proximal cells at the same channel Each point represented by polar co-
ordinates R = 1:100:1 Theta = 1:360:1
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b
NYMAN 2004 15
Downstream Coverage
NYMAN 2004 16
Downstream coverage with reduced transmission power at edge node
NYMAN 2004 17
Upstream coverage
NYMAN 2004 18
Upstream coverage using multi-hop and reduced transmission power
NYMAN 2004 19
Review comments Simple answer to most of the
comments: Work in progress ;)
NYMAN 2004 20
Reviewer 1: Not clear on: 1. how the network topology would impact the
results and in general the effects of multi-hop extensions.
2. What is the performance v.s. cost tradeoffs of the proposed solution.
3. how would things change if each forwarding node can be responsible for more than one slower node. Would there still be enough benefits for the forwarding nodes?
4. Results are based on analysis/simulation. Any verification using experiment done or planned in the future? How would that be done?
NYMAN 2004 21
Reviewer 1: Some response
Not clear on: 1. how the network topology would impact the results and in general the effects of multi-hop extensions. 2. What is the performance v.s. cost tradeoffs of the proposed solution.
3. how would things change if each forwarding node can be responsible for more than one slower node. Would there still be enough benefits for the forwarding nodes?Response: That was a simplifying assumption. As long
as the forwarding node shares only a part of its available bandwidth it will have the benefits. If more than one slow node use the same forwarding node, the slow nodes could probably loose their benefit.
4. Results are based on analysis/simulation. Any verification using experiment done or planned in the future? How would that be done?
NYMAN 2004 22
Reviewer 1: Some response
Not clear on: 1. how the network topology would impact the results and in general the effects of multi-hop extensions. 2. What is the performance v.s. cost tradeoffs of the proposed solution.3. how would things change if each forwarding node can be responsible for more than one slower node. Would there still be enough benefits for the
forwarding nodes?
4. Results are based on analysis/simulation. Any verification using experiment done or planned in the future? How would that be done?Answer: More open questions left in the
simulation/analysis area (some raised here). Plan is to address those questions first. No plan for experimental study right now.
NYMAN 2004 23
Reviewer 2: The capacity and coverage improvement of
multi-hop networks has been well documented. The paper presents a opnet simulation of 802.11 systems
in a multi-hop system. 1. The problem with multi-hop systems however are
additional delays and additional collisions.2. Instead of restricting themselves to just throughput
and coverage benefit analysis, the authors should also discuss the added multi-hop delays and scalability issues to make their message more powerful.
NYMAN 2004 24
Reviewer 2: Some response
The capacity and coverage improvement of multi-hop networks has been well documented. The paper presents a OPNET simulation of 802.11 systems in a multi-hop system. Answer: We don’t know of any coverage improvement
work in a cellular, 3 frequency band environment.Our contribution is in demonstrating incentive for
forwarding nodes participation.1. The problem with multi-hop systems however are
additional delays and additional collisions.2. Instead of restricting themselves to just throughput and coverage benefit analysis, the authors should also discuss the added
multi-hop delays and scalability issues to make their message more powerful.
NYMAN 2004 25
Reviewer 2: Some response
The capacity and coverage improvement of multi-hop networks has been well documented. The paper presents a opnet simulation of 802.11 systems in a multi-hop system.
1. The problem with multi-hop systems however are additional delays and additional collisions.Answer: Actually the delay should go down because of
the higher transmission rates maintained in a two hop situation. Additional collisions is possible only when transmission power reduction is used – we need study the effect of proposed reduction factors on the carrier-sense threshold.
2. Instead of restricting themselves to just throughput and coverage benefit analysis, the authors should also discuss the added multi-hop delays and scalability issues to make their message more powerful.
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