eliminating channel feedback in next generation cellular...

EliminatingChannelFeedbackinNextGenerationCellularNetworks

DeepakVasishtSwarun Kumar,Hariharan Rahul,DinaKatabi

CellularTrafficisIncreasingGlobalmobiledatatrafficwillincrease8fold in2015-2020

CISCO

0

10

20

30

2015 2016 2017 2018 2019 2020

DataDem

and

(Exabytes/mon

th)

Spectrumcannotaccommodatethisincrease

LTEstandardbody,3GPP,isproposingmulti-antennasolutionsinnewreleases:• Beamforming• CoordinatedMulti-point• Full-DimensionalMIMO

Basestationneedstoknowchannels toclient

MoreAntennas

ChannelAcquisitionUsefeedbackfromtheclient

Feedbackoverheadisoverwhelming

…

FeedbackisOverwhelming• Largeincurrentnetworks,useslossy compression[3GPPTS36.2112010,Irmer etalIEEECommunications2011]

• Prohibitiveforfuturedeploymentswithupto32antennas

• AccordingtoLTEstandardbody,3GPP:“IdentifyingthepotentialissuesofCSIacquisitionand

developingthepropersolutionsareofgreatimportance”

R2F2• Usesuplinkchannelstoestimatedownlinkchannels• Removesfeedbackoverhead• Evaluatedindoorsandoutdoorsinwhitespaces

640 660 680 700 720 740Frequency(MHz)

R2F2testbed CommercialCarriers

Idea:UseReciprocityLikeinWiFiInWiFi,UplinkChannel=DownlinkChannel

Idea:UseReciprocityLikeinWiFi

Doesnotworkforcellularnetworks:Uplinkanddownlinkondifferentfrequencies

InWiFi,UplinkChannel=DownlinkChannel

ProblemStatement

Howdoweestimatechannelsononefrequencyfromchannelsonadifferentfrequency?

ProblemStatement

UplinkChannelsatFrequency1

DownlinkChannelsatFrequency2

Idea:SamePathsonUplink&Downlink

UplinkChannelsatFrequency1

DownlinkChannelsatFrequency2

Pathsalongwhichsignalisreceived

RF-basedLocalizationSystems

−1 −0.5 0 0.5 10

0.5

1

cos θ

Ampl

itude

600𝑀𝐻𝑧User

𝜃

BaseStation

RF-basedLocalizationSystems

−1 −0.5 0 0.5 10

0.5

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

0.5

1

cos θ

Ampl

itude

600𝑀𝐻𝑧 650𝑀𝐻𝑧User

𝜃

BaseStation

Localizationsystemsdon’tdirectlyapply

Idea:SamePathsonUplink&Downlink

UplinkChannelsatFrequency1

DownlinkChannelsatFrequency2

Pathsalongwhichsignalisreceived

PathstoChannels:IdealRepresentation

User

BaseStation

𝜃)

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

𝜙)

𝜙+

PathstoChannels:MeasuredRepresentation

User

BaseStation

𝜃)

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

Limitednumberofantennasleadstoconvolution

withsinc

𝜙)

𝜙+

𝑆-(𝑎), 𝜙), 𝜃))

𝑆-(𝑎+, 𝜙+, 𝜃+)

PathstoChannels:Superposition

User

BaseStation

𝜃)

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

𝑆- 𝑎), 𝜙), 𝜃) + 𝑆-(𝑎+, 𝜙+, 𝜃+)

PathstoChannels:FFT

User

BaseStation

𝜃)

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

ℎ)F

𝐹𝐹𝑇(𝑆- 𝑎), 𝜙), 𝜃) + 𝑆-(𝑎+, 𝜙+, 𝜃+))

−1 −0.5 0 0.5 10

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0.4

0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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0.6

0.8

1

cos θ

Ampl

itude

User

BaseStation

ℎ)

ℎ+

𝜃)

F

F

UplinktoDownlinkChannelsUplink(f)

Downlink(f’)

−1 −0.5 0 0.5 10

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0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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0.4

0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

User

BaseStation

F

F

UplinktoDownlinkChannelsUplink(f)

Downlink(f’)

ℎ)

ℎ+

??

𝜃)

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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0.8

1

cos θ

Ampl

itude

User

BaseStation

F

ChannelstoPathsUplink(f)

ℎ)

Goal:Tofindasetofpaths,thatcanproducechannelsℎ)

Recall:Eachpathisrepresentedby(𝑎, 𝜙, 𝜃)

𝜃)

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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1

cos θ

Ampl

itude

User

BaseStation

F

ChannelstoPathsUplink(f)

ℎ)

Goal:Tofind{𝑎7, 𝜙7, 𝜃7}79): ,thatcanproducechannelsℎ)𝜃)

Recall:Eachpathisrepresentedby(𝑎, 𝜙, 𝜃)

ChannelstoPathsGoal:Tofind{𝑎7, 𝜙7, 𝜃7}79): ,thatcanproducechannelsℎ)

ℎ;<= = 𝐹𝐹𝑇 ?𝑆- 𝑎7, 𝜙7, 𝜃7

:

79)

{𝑎7, 𝜙7, 𝜃7}79): = 𝑎𝑟𝑔𝑚𝑖𝑛{EF,GF,HF} ℎ) − ℎ;<=+

GettingPathsfromWirelessChannels

• Optimizationisnon-linearandconstrained

• Solvedusingstandardinteriorpointmethod

• ApproximateinitializationusingRF-localizationmethods

−1 −0.5 0 0.5 10

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0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

0.2

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0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

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0.6

0.8

1

cos θ

Ampl

itude

−1 −0.5 0 0.5 10

0.2

0.4

0.6

0.8

1

cos θ

Ampl

itude

User

BaseStation

F

F

UplinktoDownlinkChannelsUplink(f)

Downlink(f’)

ℎ)

ℎ+

𝜃)

Evaluation

Goal:TomeasuretheaccuracyofR2F2channelestimates

ExperimentalSetup

• UsedUSRPN210softwareradiosasclientsandbasestations

• Implementeda5antennaLTEbasestation

• Locatedbasestationclosetoacommercialbasestation

FrequencySeparation

• Usedfrequenciesfrom640to690MHzintheWhiteSpaces• Evaluationat30MHzUplink-Downlinkseparation• SameasmajorAT&TandVerizondeployments

640 660 680 700 720 740Frequency(MHz)

R2F2testbed CommercialCarriers

100m50m

IndoorTestbedBaseStationClient

80m60m

OutdoorTestbed

BaseStationClient

Beamforming

Beamforming

BeamformingComparison

0

0.2

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0.6

0.8

1

-5 5 15 25

CDF

SNR(dB)

NoBeamGroundTruth(ExplicitFeedback)R2F2

R2F2delivers90%oftheMIMOSNRgains,withzerofeedback

BeamformingComparison:DataRate

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50 60

CDF

Datarate (Mbps)

NoBeam

GroundTruth

R2F2

R2F2’sachieves1.7xdatarateimprovement

ComparisonwithRF-localization

0

0.2

0.4

0.6

0.8

1

-5 5 15 25

CDF

SNR(dB)

NoBeamGroundTruthR2F2RF-Loc

Deliversonly40%ofMIMOSNRgains

EffectofFrequencySeparation

012345678

0 10 20 30 40 50

SNRGa

in(d

B)

FrequencySeparation(MHz)

Application:EdgeClientNulling

Application:EdgeClientNulling

BS1BS2

Client2

Client1

EdgeNulling

0

0.2

0.4

0.6

0.8

1

-5 0 5 10 15

CDF

INR(dB)

Original

AfterNulling

5.3dB

RelatedWork

• CellularNetworks:Channelfeedbackcompression[ShuangetalVTC11,Raoetal14,XuetalAccessIEEE14],Statisticalchannelpredictionacrossfrequencybands[HanetalCHINACOM10,Hugl etalCOST02…]• BeyondCellularNetworks:Channelqualityprediction[SenetalMobicom 13,ShietalNSDI14,Radunovic etalCONEXT11…],Temporalchannelpredictions[CaoetalPMRC04,WongetalGLOBECOM’05,Dongetal GLOBECOM’01]

Conclusion

• R2F2estimateschannelsononefrequencyfromchannelsonadifferentfrequency

• R2F2accuratelyestimatesdownlinkLTEchannelsfromuplinkLTEchannels

• R2F2enablesMIMOtechniquesforFDDsystemswithzerochannelfeedback