KTH MSc Thesis Final Presentation

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KTH MSc ThesisFinal Presentation

• Opportunistic Relay Protocol for IEEE 802.11
• Bilge Cetin

Opportunistic Relay Protocol for IEEE 802.11
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Outline

• Introduction
• The idea of relaying
• Problem statement
• Motivation
• Thesis goals
• Protocol design
• Analyzing ORP
• Simulation study
• Enhanced ORP
• Conclusion

Opportunistic Relay Protocol for IEEE 802.11
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Introduction

• Kickoff 4th October 2005
• At Computer and Network Architectures laboratory,
  SICS.
• Supervisors
• Laura Marie Feeney _at_ Sics
• Johan Montelius _at_ KTH
• Webpage http//www.sics.se/bilge/
• Previous research Analysis and protocol design
  for rate adaptation for simple relay networks.
• Credits Laura Marie Feeney, Daniel Hollos,
  Holger Karl, Martin Kubisch, and Seble Mengesha.

Opportunistic Relay Protocol for IEEE 802.11
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Idea of relaying
- A single 2 Mbps transmission path is replaced
with two 11 Mbps transmission paths.
Opportunistic Relay Protocol for IEEE 802.11
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Problem statement

• 802.11 MAC
• Gives equal chance to access the medium to each
  station
• Every station is supposed to have the same
  throughput
• A slow host transmitting at 2 Mbps captures the
  channel 5.5 times longer than hosts transmitting
  at 11 Mbps

Opportunistic Relay Protocol for IEEE 802.11
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Problem statement
- All stations are producing equal amount of
traffic destined to the AP
Opportunistic Relay Protocol for IEEE 802.11
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Motivation
- The underlying motivation is not just to
enhance the bit rate of one or more nodes but the
overall performance of the cell.
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Thesis goals

• Relay protocol deisgn for IEEE 802.11
• Theoretical analyze of the protocol
• Simulation study of the protocol

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Outline

• Introduction ?
• Protocol design
• Opportunistic relay protocol (ORP)
• Implicit relay indication
• Relay backoff
• ORP parameters
• Pitfall
• Analyzing ORP
• Simulation study
• Enhanced ORP
• Conclusion

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Opportunistic relay protocol (ORP)

• Initiator does not know if there is any relayer
  around
• Sends its data with relay indication to the
  channel
• Relayer overhears Initiators data and relays to
  the AP

Opportunistic Relay Protocol for IEEE 802.11
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Implicit relay indication

• Duration field of the MAC data frame indicates
  how long the channel is reserved after the data
  frame transmission.
• Initiator fills the duration field with
  relay backoff time PktSize/bitratefast ACK
  time
• Relayer makes a simple calculation to see if the
  overheard frame needs to be relayed
• Attempt to relay if duration field gtframe
  size/data rate ack time
• No need to relay if duration field ltframe
  size/data rate ack time.

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Implicit relay indication
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Opportunism

• Initiator doest need to make previous SNR
  calculations to search relayers
• Initiator doesnt need previous negotiation with
  the relayer
• If it cant find a relayer, reserved time will be
  wasted.

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Relay backoff

• Relay backoff mechanism is to avoid collisions
  among potential relayers
• The station which picks the smallest relay
  backoff time relays the data
• If two or more relayers picks the same smallest
  relay backoff time, collision happens.

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ORP parameters

• relay retry number
• Indicates how many times a station tries relaying
  cosequently
• relay retry time
• A station transmitting with slow bitrate,
  initiates relaying relay retry time later after
  the previous unsuccessful try

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Backward compatibility

• no modification is in frame format
• CSMA/CA and virtual carrier sense mechanisms are
  kept intact.
• Only need is to insert the relay intelligence to
  the IEEE 802.11 stations.
• When a node without the relay intelligence
  overhears a packet from the relay initiator, it
  updates its NAV and waits for the end of the
  reservation time
• Therefore it is possible normal IEEE802.11
  stations and new IEEE802.11 stations with ORP
  function in the same cell together.
• AP has to be ORP-aware

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Advantages

• Clever
• Opportunistic
• Less complexity
• Less overhead
• Backward compatible

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Outline

• Introduction ?
• Protocol design ?
• Analyzing ORP
• Relay protocol in practice
• Probability of finding a relayer
• Probability of relay collusion
• ORP Overhead
• Link throughput enhancement
• Simulation study
• Enhanced ORP
• Conclusion

Design and Simulation of relay protocol
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Relay protocol in practice

• Stations inside the 2 Mbps transmission region
  makes hops of 11-11 Mbps
• Stations inside the 1 Mbps transmission region
  makes hops of 5.5-5.5 Mbps
• ORP will not work for downlink traffic

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Probability of finding a relayer

• Probabilty of finding a relayer is a function of
• transmission ranges
• number of nodes in the cell

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Probability of relay collusion

• Each relayer picks a random integer between 0 to
  relay contention window size
• Probability of relay collusion is a function of
• relay contention window
• Number of potential relayers

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ORP Overhead

• ORP inserts one PLCP (192 µsec), one SIFS (10
  µsec) and relay backoff time (300 µsec) to the
  system as overhead

a) IEEE 802.11 data transmission
b) Data transmission with ORP
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Link throughput enhancement
- The time, Initiator spends to transmit a data
without ORP
- Throughput of the slow direct link
- The time, Initiator spends to transmit a data
with ORP
- Throughput of the two hops link with ORP
- Link throughput enhancement with ORP
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Link throughput enhancement
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Outline

• Introduction ?
• Protocol design ?
• Analyzing ORP ?
• Simulation study
• Simulation setup
• Simulation results
• Enhanced ORP
• Conclusion

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Simulation setup

• Some simulation parameters
• transmitterPower100 mW
• Sensitivity_11_Mbps -89bBm
• Sensitivity_5.5_Mbps-91dBm
• Sensitivity_2_Mbps -93bBm
• Sensitivity_1_Mbps-94dBm
• thermalNoise-95 dB
• pathLossAlpha3
• carrierFrequency2.412E9 Hz
• relayRetryLimit3
• relayRetryTime10 sec
• relayContensionWindow15

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Simulation setup
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Simulation setup

• The packet size is set to 12000 bits (1500 bytes)
• Stations are randomly distributed through
  OMNETs random location assignment
• Stations are set to be stationary
• Number of nodes in the cell changes from 5 to 50
• All stations produce infinite traffic to the AP
• AP produces infinite traffic to the stations in
  the BSS
• All topologies are simulated with ORP and without
  ORP to compare
• 100 different seeds were used
• 1600 simulation runs were performed

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Simulation results Overall throughputs with and
without ORP
- Overall throughput, with ORP, increases as the
number of nodes increases in the cell until 25
nodes. Then it slowly decrease due to relay
collusions
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Simulation results Overall throughput
enhancement with ORP
- Overall throughput improves more than 25 with
ORP
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Simulation results Avarage number of relayers
per initiators

• The probability of finding a relayer increases as
  the cell gets more crowded.
• The number of relayers per initiator increases as
  well
• This leads to more relay collusions

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Summary

• ORP offers up to 25 overall throughput
  improvement
• Relaying is possible just for uplink
• ORP introduces overhead due to relay backoff time
  
• For small packet sizes, ORPs performance
  decreases
• Due to relay collusions ORPs performance
  decreases for crowded cells (more than 30
  stations)

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Outline

• Introduction ?
• Protocol design ?
• Analyzing ORP ?
• Simulation study ?
• Enhanced ORP
• Protocol design
• Simulation results
• Conclusion

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Enhanced ORP (eORP)

• Relayer adds its MAC address to the IEEE 802.11
  MAC data frame before relaying
• AP and initiator learn the relayer and keeps it
  in the memory
• Next relayed transmission is performed over this
  relayer

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eORP
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eORP

• No relay backoff time (except the first
  discovery)
• No relay collusion
• Uplink and downlink relaying are possible

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Simulation results Overall throughputs with and
without ORP
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Simulation results Overall throughput
enhancement with ORP
- Overall throughput improves more than 50 with
eORP
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Outline

• Introduction ?
• Protocol design ?
• Analyzing ORP ?
• Simulation study ?
• Enhanced ORP ?
• Conclusion
• Future work
• Contribution

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Future work

• A simulation study with mobile stations is
  beneficial to show that there is a slight
  degradation due to mobility.
• Due to security issues (WEP) of IEEE 802.11, AP
  needs further implementation for ORP and WEP
  implementations to cooperate.
• Adapting the ORP to the power save mode of IEEE
  802.11

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Contribution

• A backward compatible relay protocol for IEEE
  802.11
• was proposed and designed
• was analyzed through a theoretical study
• was implemented within a simulation program
• Bugs corrected and reported in 802.11 module of
  OMNET Mobility Framework
• ORP implementation shows a guideline to the
  students and scientists who want to study on
  IEEE802.11 in OMNET (MFw)

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• Questions???

Opportunistic Relay Protocol for IEEE 802.11