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ResourceAllocationforLTEMulticast(eMBMS):GroupPartitioningandDynamics
JiasiChen*,Mung Chiang*,JeffreyErman+,Guangzhi Li+,K.K.Ramakrishnan1,Rakesh KSinha+
*PrincetonUniversity,+AT&TLabs– Research,1UniversityofCalifornia,Riverside
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MobileCore
Internet
ContentServersBasestationsDevices
MobileTrafficontheRise
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ContentEvolution:• Streamingmedia,socialnetworking,videoconferencing•Mobile datagrew69%in2014[CiscoVNI]
NetworkEvolution:•MajorLTErollouts(T-Mobile,Sprint),and3Grollouts(India)•Mobile networkonlyviableInternetoption inmanyplaces
DeviceEvolution:• Smartphone sales+20%in3Q2014• Highresolutiondevices
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MulticastusingeMBMS
• LTEEvolvedMultimediaBroadcastMulticastService(eMBMS)forefficientbroadcastdelivery
• Targetedserviceareaswithcommonuserinterests– Sportsstadium– Macy’sThanksgivingParade
• Recentlydemoedat2014and2015footballSuperbowl
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SystemArchitecture
• DeploymentonstandardeMBMSarchitecture– MCEdecidesonmulticastresource allocationacrossmultipleeNBs
• Resourcesareflexiblysplitbetweenmulticastandunicast
Internet
MulticastCoordination
Entity
Videostreamingserver
eNBClients
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Time10,20,40,80,160,or320ms
Frequency50subchannelsfor20MHzcarrier Unicastresourceblock
Multicast resourceblock
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ConflictbetweenMulticast+Cellular
• Multicast:samecontent,samerateforallusers
• Cellular:differentrateforeachuserdependingonchannelconditions– Proportional fairschedulers
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5 bits perwirelessresourceblock
3bits perwirelessresourceblock
2bits perwirelessresourceblock
Ourproposal:groupusersbasedonsimilarityofchannelconditions
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ToyExample:AllUnicast
Totalrate=3+9+12+6=30Totalutility=log(3)+log(9)+log(12)+log(6)=7.57
A
B
D
C
4 bits/RB
2bits/RB
1 bit/RB
3bits/RB
Scheduler
UserA UserB UserC UserD
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ToyExample:AllMulticast
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Totalrate=9+9+9+6=33Totalutility=log(9)+log(9)+log(9)+log(6)=8.38
A
B
D
C
4 bits/RB
2bits/RB
1 bit/RB
3bits/RB
Scheduler
UserA,B,C UserD
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ToyExample:GroupMulticastUsers
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Totalbits=4+12+12+8=36Totalutility=log(4)+log(12)+log(12)+log(8)=8.43
A
B
D
C
4 bits/RB
2bits/RB
1 bit/RB
3bits/RB
Scheduler
UserA UserB,C UserD
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ResourceAllocationProblem
• Splitusersinterestedinmulticastcontentintogroups• AssignafractionofRBstoeachmulticastgroup
• Controlknobs– Whichmulticastuser inwhichgroup?– Howmanygroups?– Whatcodingrateforeachgroup?– Howmanymulticastresources foreachgroup?– Howmanyunicastresources foreachuser?
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OptimizationProblem
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eachmulticastuserbelongstoamulticastgroup
totalresources available
codingschemeofmulticastgroup
fractionofmulticastresources allowedbyeMBMS
maximize
subject to
unicastutility+multicastutility
variables
howmanymulticastgroupsunicastresourcesmulticastresources
membersofeachmulticastgroup
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howmanymulticastgroupsunicastresources
OptimizationProblem
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eachmulticastuserbelongstoamulticastgroup
B:numberofbasestationsT:numberofRBsUb:setofunicastusersatbasestationbdi:bits/RBofunicastuserici:bits/RBofmulticastuseriĉk:bits/RBofmulticastgroupkα:fractionofresourcesallowedformulticast(0.6)
totalresources available
codingschemeofmulticastgroup
fractionofmulticastresources allowedbyeMBMS
maximize
subject to
variables
unicastutility+multicastutility
multicastresources
membersofeachmulticastgroup
à Hardtosolvemixedintegernonlinearproblem!
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OverallProblem
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utility
(K,{Gk},{xk},{yi})
(K,{Gk}). .Problem1:Forfixedusergrouping,
optimally allocateresources
Problem2:findoptimalusergrouping
Resourceallocator
(K,{Gk})
(K,{Gk},{xk},{yi})
UU
bruteforcesolution inexponential time!
convexoptimizationusingKKTconditions
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Keyidea:sorttheusers
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Lemma: Ifthesolution containsanunorderedgrouping,thenthesolution isnotoptimal.
Exhaustive partitionplacement: O(2M)
utilityofgroupk:
totalutility=utility(A,B,C)+utility(D,E)=3log(1*3)+2log(9*2)=3.94
totalutility=utility(A,B,E)+utility(C,D)=3log(1*3)+2log(5*2)=3.43
1 2 9 5 10bits/RB:A B CD E
unordered
1 2 5 9 10bits/RB:A B EC D
sorted
resourcesforgroupkcodingrateofgroupk
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OverallProblem
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utility
(K,{Gk},{xk},{yi})
(K,{Gk}). .Problem1:Forfixedusergrouping,
optimally allocateresources
Problem2:findoptimalusergrouping
Resourceallocator
(K,{Gk})
(K,{Gk},{xk},{yi})
UU
bruteforcesolution inexponential time!
convexoptimizationusingKKTconditions
Theorem:Problem1+2jointlysolveglobaloptimizationproblem.
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Hangon…whataboutclient-drivencontrol?
Globallyoptimalsolutionmaynotbebestfortheindividualuser!
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Multicastà UnicastSwitch
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à UserCprefers theno-multicast solution!…Attheexpense ofglobalutility.
Totalrate=3+9+12 +6=30
Totalutility=log(3)+log(9)+log(12)+log(6)=7.57
A
B
D
C
4 bits/RB
2bits/RB
1 bit/RB
3bits/RB
Totalrate=9+9+9 +6=33
Totalutility=log(9)+log(9)+log(9)+log(6)=8.38
A
B
D
C
4 bits/RB
2bits/RB
1 bit/RB
3bits/RB
Allunicast: Allmulticast:
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Unicastà MulticastSwitch
Totalrate=1 +20+20 +1000=1041
Totalutility=12.9
A
B
DC
11bits/RB
1000bits/RB
1 bit/RB
10bits/RB
Totalrate=3 +3+3 +1000=1009
Totalutility=10.2
A
B
DC
11bits/RB
1000bits/RB
1 bit/RB
10bits/RB
à UserAwantstojointhemulticastgroup!…Attheexpense ofglobalutility.
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Dynamics
• Intheory:Globaloptimizationassumesthatnetworkoperatorcancontrolwhethertheuserisonmulticastorunicast
• Inpractice:Usersmaychoosehowtoaccessthecontentthroughmulticastorunicast
WhileonmulticastIfunicastrate>multicast rate
SwitchtounicastWhileonunicast
Ifmulticast rate>unicastrateSwitchtounicast
Useralgorithm
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SummaryofAnalyticResults
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Scenario Switch Codingscheme
Analysis
A Uniàmulti Betteronunicast
Userneverwantstoswitchfromtheoperator’ssolution
B Uniàmulti Betteronmulticast
Useralwayswantstoswitch,butoperatorprevents
C Multià uni Betteronunicast
Numberofswitchingusersisupperbounded
D Multià uni Betteronmulticast
Userneverwantstoswitchfromtheoperator’ssolution
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SimulationSetup
• 74totalusers- 50unicastusers- 24multicastusers
• Coding ratestakenfromLTEspecification- 20- 733bits/resource block
• Fourcomparisonalgorithms- No-multicast- Naïve:1multicastgroup- Heuristic:4multicastgroups- Ourscheme:Variablenumberofmulticastgroups
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Whatdoestheusergroupinglooklike?
0 200 400 600 80002468
Coding Scheme (Bits/RB)
Num
ber o
f Use
rs
Group 1
0 200 400 600 80002468
Coding Scheme (Bits/RB)
Num
ber o
f Use
rs
Group 1Group 2Group 3Group 4
0 200 400 600 80002468
Coding Scheme (Bits/RB)
Num
ber o
f Use
rs
Group 1Group 2
Heuristic:4multicastgroups
Ourscheme:Variablegroups
Naïve:1multicastgroup
à Ourschemeadaptstotheuserdistributionofchannelconditions,andchoosesthemostintuitiveuserpartition
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0 5 10 15 20 250
2
4
6
8
10
User
Ave
rage
Rat
e (M
bps)
Group 1
0 5 10 15 20 250
2
4
6
8
10
User
Ave
rage
Rat
e (M
bps)
Group 1Group 2Group 3Group 4
Whatratedotheusersget?
à “Variablegroups”givesusersratecommensuratetotheirchannelconditions
0 5 10 15 20 250
2
4
6
8
10
User
Ave
rage
Rat
e (M
bps)
Group 1Group 2
betterchannelconditions betterchannelconditions betterchannelconditions
Heuristic:4multicastgroups
Ourscheme:Variablegroups
Naïve:1multicastgroup
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KeyTake-Aways
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Mismatchbetweenmulticast(samerates)andcellular(differentrates)
Partitionusersbasedonsimilarityofuserchannelconditions
Globallyoptimalsolutionnaturallydiscouragesuserswitching