experimental investigation of coexistence interference on multi-radio 802.11 networks.pdf

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

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)

1 Arsham Farshad, Mahesh Marina, Francisco Garcia Experimental Investigation of Coexistence Interference on Multi-Radio 802.11 Networks

Introduction

Coexistence InterferenceReceiver Blocking

Receiver Blocking

Receiver blocking is a result of limited dynamic range of poweramplifier and A/D converter.


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.


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!


Introduction

Our Goals

Goals:Ease antenna and channel separation constraints.

Reduce multi-radio platform dimensions and deployment costs.Increase spectrum usage efficiency.


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.


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


Multi-Radio Coexistence Interference: Multiband Case

Minimum Antenna Separation for Interfaces inDifferent Bands I

2

4

6

8

10

12

14

16

18

20

5 10 14 17 20 23

Min

imum

Ant

enna

Sep

arat

ion(c

m)

Transmit Power (dBm) for the Transmission Interface

6Mbps, Same Polarization54Mbps, Same Polarization

Minimum antenna separation at different bit-rates and interferer transmit power levels.



Minimum Antenna Separation for Interfaces inDifferent Bands II

2

4

6

8

10

12

14

16

18

20

5 10 14 17 20 23

Min

imum

Ant

enna

Sep

arat

ion(c

m)

Transmit Power (dBm) for the Transmission Interface

6Mbps, Same Polarization6Mbps, Diff. Polarization

54Mbps, Same Polarization54Mbps, Diff. Polarization

Minimum antenna separation at different bit-rates, polarizations and interferer transmit powerlevels.



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.



Throughput Performance with Closely SpacedAntennas

0

5

10

15

20

25

30

35

6 9 12 18 24 36 48 54 0

0.25

0.5

0.75

1

UDP

Thro

ughp

ut(M

bps)

Nor

mal

ized

UDP

Thr

ough

put

Rates(Mbps)

Throughput-Same PolarizationNormalized Throughput-Same Polarization

Throughput-Diff. PolarizationNormalized Throughput-Diff. Polarization

Received UDP throughput for different bit-rates, 6cm antenna separation and 17dBm txpower.


Multi-Radio Coexistence Interference: Single-Band Case

Maximum Achievable Bit-Rates When Using WidelySeparated Channels within a Band (5GHz)

69

12

18

24

36

48

54

5dBm 10dBm 14dBm 17dBm 20dBm 23dBm

Max

imum

Ach

eiva

ble

Rate

s(Mbp

s)

Transmit Power for the Transmission Interface

Same Polarization Diff. Polarization

Maximum achievable bit-rates for interfaces configured with widely separated channels within the5GHz and 40cm antenna separation.



Microscopic View of MAC Behaviour in Presence ofACI I

0

20

40

60

80

100

10 20 30 40 50 60 70 80

MAC

Bus

y Ti

me

(%)

Time(s)

channel 36 channel 40 channel 44 channel 48

BusyTime-Same Polarization

Percentage of time MAC is sensed Busy due to transmission on the adjacent channel.



Microscopic View of MAC Behaviour in Presence ofACI II

0

20

40

60

80

100

10 20 30 40 50 60 70 80

MAC

Bus

y Ti

me

(%)

Time(s)


BusyTime-Same PolarizationBusyTime-Diff. Polarization




Microscopic View of MAC Behaviour in Presence ofACI III

0

20

40

60

80

100

10 20 30 40 50 60 70 80 0

1

2

3

4

5

6M

AC B

usy

Tim

e (%

)

RX

UDP

Thro

ughp

ut(M

bps)

Time(s)


BusyTime-Same PolarizationBusyTime-Diff. Polarization

Throughput-Same PolarizationThroughput-Diff. Polarization


Using differently polarizedantennas reduces the required channel separation down to 2channels.


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.


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.


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.


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?).


Conclusions

Questions?

IntroductionExperiment SetupMulti-Radio Coexistence Interference: Multiband CaseMulti-Radio Coexistence Interference: Single-Band CaseDifferent Antenna Polarizations, Network Performance Study

experimental investigation of coexistence interference on multi-radio 802.11 networks.pdf

Documents