eliminating channel feedback in next generation cellular … · 2016. 8. 26. · related work...
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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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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
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0.6
0.8
1
cos θ
Ampl
itude
−1 −0.5 0 0.5 10
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0.8
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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0.4
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
−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
0.2
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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
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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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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
0.2
0.4
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
0.4
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