ResourceAllocationforLTEMulticast(eMBMS):GroupPartitioningandDynamics

JiasiChen*,Mung Chiang*,JeffreyErman+,Guangzhi Li+,K.K.Ramakrishnan1,Rakesh KSinha+

*PrincetonUniversity,+AT&TLabs– Research,1UniversityofCalifornia,Riverside

MobileCore

Internet

ContentServersBasestationsDevices

MobileTrafficontheRise

2

ContentEvolution:• Streamingmedia,socialnetworking,videoconferencing•Mobile datagrew69%in2014[CiscoVNI]

NetworkEvolution:•MajorLTErollouts(T-Mobile,Sprint),and3Grollouts(India)•Mobile networkonlyviableInternetoption inmanyplaces

DeviceEvolution:• Smartphone sales+20%in3Q2014• Highresolutiondevices

MulticastusingeMBMS

• LTEEvolvedMultimediaBroadcastMulticastService(eMBMS)forefficientbroadcastdelivery

• Targetedserviceareaswithcommonuserinterests– Sportsstadium– Macy’sThanksgivingParade

• Recentlydemoedat2014and2015footballSuperbowl

3

SystemArchitecture

• DeploymentonstandardeMBMSarchitecture– MCEdecidesonmulticastresource allocationacrossmultipleeNBs

• Resourcesareflexiblysplitbetweenmulticastandunicast

Internet

MulticastCoordination

Entity

Videostreamingserver

eNBClients

4

Time10,20,40,80,160,or320ms

Frequency50subchannelsfor20MHzcarrier Unicastresourceblock

Multicast resourceblock

ConflictbetweenMulticast+Cellular

• Multicast:samecontent,samerateforallusers

• Cellular:differentrateforeachuserdependingonchannelconditions– Proportional fairschedulers

5

5 bits perwirelessresourceblock

3bits perwirelessresourceblock

2bits perwirelessresourceblock

Ourproposal:groupusersbasedonsimilarityofchannelconditions

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

ToyExample:AllMulticast

7

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

ToyExample:GroupMulticastUsers

8

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

ResourceAllocationProblem

• Splitusersinterestedinmulticastcontentintogroups• AssignafractionofRBstoeachmulticastgroup

• Controlknobs– Whichmulticastuser inwhichgroup?– Howmanygroups?– Whatcodingrateforeachgroup?– Howmanymulticastresources foreachgroup?– Howmanyunicastresources foreachuser?

OptimizationProblem

10

eachmulticastuserbelongstoamulticastgroup

totalresources available

codingschemeofmulticastgroup

fractionofmulticastresources allowedbyeMBMS

maximize

subject to

unicastutility+multicastutility

variables

howmanymulticastgroupsunicastresourcesmulticastresources

membersofeachmulticastgroup

howmanymulticastgroupsunicastresources

OptimizationProblem

11

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!

OverallProblem

12

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

Keyidea:sorttheusers

13

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

OverallProblem

14

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.

Hangon…whataboutclient-drivencontrol?

Globallyoptimalsolutionmaynotbebestfortheindividualuser!

15

Multicastà UnicastSwitch

16

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:

17

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.

Dynamics

• Intheory:Globaloptimizationassumesthatnetworkoperatorcancontrolwhethertheuserisonmulticastorunicast

• Inpractice:Usersmaychoosehowtoaccessthecontentthroughmulticastorunicast

WhileonmulticastIfunicastrate>multicast rate

SwitchtounicastWhileonunicast

Ifmulticast rate>unicastrateSwitchtounicast

Useralgorithm

SummaryofAnalyticResults

19

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

SimulationSetup

• 74totalusers- 50unicastusers- 24multicastusers

• Coding ratestakenfromLTEspecification- 20- 733bits/resource block

• Fourcomparisonalgorithms- No-multicast- Naïve:1multicastgroup- Heuristic:4multicastgroups- Ourscheme:Variablenumberofmulticastgroups

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

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

KeyTake-Aways

23

Mismatchbetweenmulticast(samerates)andcellular(differentrates)

Partitionusersbasedonsimilarityofuserchannelconditions

Globallyoptimalsolutionnaturallydiscouragesuserswitching