Experimental Investigation of Coexistence Interference on Multi-Radio 802.11 Networks.pdf
Transcript of Experimental Investigation of Coexistence Interference on Multi-Radio 802.11 Networks.pdf
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Experimental Investigation of CoexistenceInterference on Multi-Radio 802.11 Networks
Arsham Farshad, Mahesh Marina, Francisco Garcia
School of Informatics,The University of EdinburghAgilent Technologies, Scotland
WiNMee 2012- Paderborn
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Introduction
Multi-radio Platforms: Advantages and Challenges
A multi-radio platform
Expected advantages:Reduce co-channel interferenceAchieve higher performanceAchieve more efficient spectrumusage
Challenges: Coexistenceinterference
Receiver blockingAdjacent channel interference (ACI)
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Introduction
Multi-radio Platforms: Advantages and Challenges
A multi-radio platform
Expected advantages:Reduce co-channel interferenceAchieve higher performanceAchieve more efficient spectrumusage
Challenges: Coexistenceinterference
Receiver blockingAdjacent channel interference (ACI)
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Introduction
Multi-radio Platforms: Advantages and Challenges
A multi-radio platform
Expected advantages:Reduce co-channel interferenceAchieve higher performanceAchieve more efficient spectrumusage
Challenges: Coexistenceinterference
Receiver blockingAdjacent channel interference (ACI)
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Introduction
Coexistence InterferenceReceiver Blocking
Receiver Blocking
Receiver blocking is a result of limited dynamic range of poweramplifier and A/D converter.
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Introduction
Coexistence Interference IAdjacent Channel Interference
Adjacent Channel Interference(ACI) is due to:Imperfect bandpass filter in the radio hardware.Use of partially overlapped channels.
ACI is caused by extraneous power from transmissions in adjacent channels.
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Introduction
Coexistence Interference IIAdjacent Channel Interference
Solutions:Channel & Antenna separation
Use channels from different bands (e.g., Dhananjay et. al.SIGCOMM09).
Chereddi2007, Nachtigall2008:For 40cm antenna separation, channel separation should be 4.Only 3 channels can be used in the first sub-band of 5GHz band.With two channel separation, 320cm separation betweenantennas is required!
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Introduction
Our Goals
Goals:Ease antenna and channel separation constraints.
Reduce multi-radio platform dimensions and deployment costs.Increase spectrum usage efficiency.
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Experiment Setup
Experiment Setup
3.5m 3.5mRX TX
Experiment setupRouter Platforms Gateworks Avila and Cambria, Ubiq-
uiti RouterStationPlatformOS/Firmware
Openwrt attitude r27891
Radio Interfaces Compex WLMAG54-23dBm and Mi-croTik R52Hn mini PCI cards
Device Drivers ath5k / ath9k r2011-06-22Antennas Cisco dualband dipole omni
([email protected], 5dBi@5GHz)Laird dualband omni ([email protected],5dBi@5GHz)
Gateworks Avila platformequipped with two Compex cards.
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Experiment Setup
Variable Parameters and Measurement Metrics
Measurement metrics:UDP ThroughputMinimum Antenna Separation: smallest antenna separation thatyields closest to maximum throughput.
Variable parameters:Antenna separationTransmission rate ( 6Mbps and 54Mbps)Transmission power for the Tx interfaceAntenna polarization
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Multi-Radio Coexistence Interference: Multiband Case
Minimum Antenna Separation for Interfaces inDifferent Bands I
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Transmit Power (dBm) for the Transmission Interface
6Mbps, Same Polarization54Mbps, Same Polarization
Minimum antenna separation at different bit-rates and interferer transmit power levels.
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Multi-Radio Coexistence Interference: Multiband Case
Minimum Antenna Separation for Interfaces inDifferent Bands II
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6Mbps, Same Polarization6Mbps, Diff. Polarization
54Mbps, Same Polarization54Mbps, Diff. Polarization
Minimum antenna separation at different bit-rates, polarizations and interferer transmit powerlevels.
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Multi-Radio Coexistence Interference: Multiband Case
Antenna Polarization
DefinitionThe direction of electric field of a radio wave relative to the ground.
Cross polarized antennas
Polarization state of a signal will be almost independent of thetransmitted polarization after sufficient reflection and bouncing ofsignal.
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Multi-Radio Coexistence Interference: Multiband Case
Throughput Performance with Closely SpacedAntennas
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Received UDP throughput for different bit-rates, 6cm antenna separation and 17dBm txpower.
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Multi-Radio Coexistence Interference: Single-Band Case
Maximum Achievable Bit-Rates When Using WidelySeparated Channels within a Band (5GHz)
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Maximum achievable bit-rates for interfaces configured with widely separated channels within the5GHz and 40cm antenna separation.
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Multi-Radio Coexistence Interference: Single-Band Case
Microscopic View of MAC Behaviour in Presence ofACI I
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Percentage of time MAC is sensed Busy due to transmission on the adjacent channel.
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Multi-Radio Coexistence Interference: Single-Band Case
Microscopic View of MAC Behaviour in Presence ofACI II
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channel 36 channel 40 channel 44 channel 48
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Percentage of time MAC is sensed Busy due to transmission on the adjacent channel.
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Multi-Radio Coexistence Interference: Single-Band Case
Microscopic View of MAC Behaviour in Presence ofACI III
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Percentage of time MAC is sensed Busy due to transmission on the adjacent channel.
Using differently polarizedantennas reduces the required channel separation down to 2channels.
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Different Antenna Polarizations, Network Performance Study
Network Topology Study for Differently PolarizedNodesExperiments Setup
Changing polarization changes theradiation pattern of the antenna.It could potentially have a negativeimpact on mesh network topology andlink qualities.
Experiment Setup:Using IFMesh multi-interface testbed inInformatics Forum at the University ofEdinburgh.Calculate ETX metric and measure UDPthroughput.
IFMesh multi-interface meshtestbed.
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Different Antenna Polarizations, Network Performance Study
Network Topology Study for Differently PolarizedNodes
Vertically Polarized Horizontally Polarized
Mean ETX increases from 1.2 to 1.5.UDP throughput degrades 17% in average.
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Conclusions
Our Achievements
Demonstrated the benefit of using antenna polarization to alleviatemulti-radio coexistence interference.
Reduce required antenna separation to as small as 3cm.Achieve up to four times higher bit-rates for widely separatedchannels in a single band case.Reduce channel separation to two channels in single-band setup.Using differently polarized antennas has a marginal effect on themesh network topology in indoor environments.
Characterized adjacent channel interference using directobservation of MAC behavior.
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Conclusions
Future Work
Exploiting polarization diversity on multi-interface nodes with morethan two interfaces.Investigate the coexistence interference in multi-interface 802.11nplatforms (cross-polarized configuration useful?).
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Conclusions
Questions?
IntroductionExperiment SetupMulti-Radio Coexistence Interference: Multiband CaseMulti-Radio Coexistence Interference: Single-Band CaseDifferent Antenna Polarizations, Network Performance Study