09 LTE Scheduling

8/12/2019 09 LTE Scheduling

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LTE: Schedulers


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LTE protocol architecture

3


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Packet scheduling model

4

Channel-Quality Indicator

Inner Loop Link Adaptation

(fast)

chooses MCS ()

Outer Loop Link Adaptation

(slow)

Automatic Repeat-reQuest


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Time-frequency scheduling

5

Physical Downlink Control Channel

Physical Resource Blocks

Discontinuous Reception (DRX)


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Quality Metrics

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Throughput

Fairness

Packet Loss Rate, %

Scheduling cost (memory, time, etc.)

= 2 2=

Xi- is the throughput for the i-thconnection


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Schedulers

Proportional Fair (PF)

Maximum Rate (Maximum Throughput)

Round Robin (RR)

Joint Time and Frequency domain schedulers

Throughput to Average (TTA)

Buffer-aware schedulers

Modified Largest Weighted Delay First (MLWDF)

Exponential Proportional Fair (EXP-PF)

EXP-LOG Rule

Frame Level Scheduler (FLS)

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RR, PF, Maximum rate

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max max


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TTA

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Throughput To Average

max , ,


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Simulation scenario

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MT, PF, PF-PF, TTA - Throughput

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MT, PF, PF-PF, TTA - Fairness

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Scheduler with buffer estimation

,

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MLWDF

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Modified Largest Weighted Delay First

max

,

log

Dholis the head-of-line (HOL) delay of user i a time t

Acceptable packet loss rate for i-th user

ithreshold delay of the i-th user

MLDWF prioritizes the user with higher HOL packet delay and better channel

conditions relative to its average levels.


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EXP-PF

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Exponential Proportional Fair

max

exp,

1

log

Ntris the number of active real time flows

X ,=


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LOG-RULE

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Log Rule

max log ,

ai, bi, c are tunable parameters


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EXP-RULE

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Exponential Rule

max , 1 ,


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FLS

Frame Level Scheduler

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1 (10).

PF

.

MT


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PF, MLWDF, EXP-PF, EXP-LOG Rule -Throughput

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+ each user receives three downlink flows(one video, one VoIP, and data).


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PF, MLWDF, EXP-PF, EXP-LOG Rule - PRL

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Packet Loss Rate


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1. 4G LTE and LTE-Advanced for Mobile Broadband

2. LTE for UMTS - OFDMA and SC-FDMA Based Radio Access (2009)

3. Downlink Packet Scheduling in LTE Cellular Networks: Key Design Issues and a

Survey

4. 3GPP LTE Downlink Scheduling Strategies in Vehicle-to-Infrastructure

Communications for Traffic Safety Applications

5. Comparative Performance Study of LTE UplinkSchedulers

6. B. Sadiq, R. Madan, and A. Sampath, Downlink scheduling for multiclass traffic

in lte, EURASIP J. Wirel. Commun. Netw., vol. 2009, pp. 99, 2009.

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QoS LTE

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Downlink Scheduling in LTE [8] . Part II

New schedulers:

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Multi-QoS aware Fair [1]

Game Theory and Token Mechanism [2]

Delay-Prioritized (DPS) [3]

Best Effort and VoIP [4]

VoIP [5]

Priority Set Scheduling [6]


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Multi-QoS aware Fair. TDPS [1]

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Flows

GBR

Non-GBR

QoS1class

QoS2class

priority

1 (1 )- Accumulated data rate

- Instantaneous bearer data rate at n-th TTI

- Smoothing factor

3


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Multi-QoS aware Fair. FDPS [1]

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1) GBR QoS1class: Max SINR

Check: Ue buffer full or GBR achieved

2) Non-GBR metric: Max SINR

yesnext Ue

Each iteration everyone get one RB


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Game Theory and Token Mechanism [2]

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Sharply valueevery flow get resources based on its contribution.TD

6

()+

(Proportional Fair)

() () () - Token queue length- Arrival rate of tokens (depends on flow)

FD


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Delay-Prioritized (DPS) [3]

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For real time traffic

()

min ()Select max SINR for k-th Ue, update ()

PRBs remain? Yes

- Delay threshold

- HOL delay


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Best Effort and VoIP. TDPS [4]

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(, ) , (,)

(,)(n,t)(,)- Required activity (depending on the traffic)

- Incremented every TTI and reset to 0 every time, Ue n is scheduled

- Delay sensitivity, determines traffic priorities

- Number of Ue after TDPS (parameter)

, (,)

, 0, (,)

1


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Best Effort and VoIP. FDPS [4]

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, (,,)(,)Proportional fair scheduled (PFsch)


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VoIP [5]

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The limit of VoIP priority modeis adaptively changed between

min and max according VoIP

packet drop ratio.


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VoIP experiment [5]

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Priority Set Scheduling. TDPS [6]

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Flows

Below-GBR

Other () ()() priority

(, ) 1 1, 1 ( 1, )

- Past average throughput of Ue n.

- Instantaneous bearer data rate at n-th TTI

(n)()

() 1() (BET)(PF)

T- time window (99 lena)

Take N Ue


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Priority Set Scheduling. FDPS [6]

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, (,)()

1 1, 1 1, ( 1, )

- Is an estimate of the user throughput if user was scheduled every sub frame


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Scheduling input parameters

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Name Requested

bitrate

Average

datarate

Queue size Max

delay

HOL

1 X X2 X X

3 X X

4 X X X

5 X

6 X X


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Scheduler in LENA

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Allocation bitmap which identifies RBs

SCHEDULER

Data Control

Indication (DCI)

Modulation and Coding Scheme (MCS)

MAC Transport Block (TB) size


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Transmit operations in downlink

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Usage

If you want to use PSS scheduler in project: Ptr lteHelper = CreateObject ();

lteHelper->SetSchedulerType ("ns3::PssFfMacScheduler");

lteHelper->SetSchedulerAttribute("nMux", UIntegerValue(yourvalue)); the max num of UE selected by TD scheduler

Guarantee Bit Rate (GBR) or Maximum Bit Rate (MBR) can be configured in epc

bearer respectively

enum EpsBearer::Qci q = EpsBearer::yourvalue; // define Qci type

GbrQosInformation qos;

qos.gbrDl = yourvalue; // Downlink GBR

qos.gbrUl = yourvalue; // Uplink GBR

qos.mbrDl = yourvalue; // Downlink MBR

qos.mbrUl = yourvalue; // Uplink MBR

EpsBearer bearer (q, qos);

lteHelper->ActivateEpsBearer (ueDevs, bearer, EpcTft::Default ());

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Ns-3 experiment

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1 eNB

50 Ues

Radius 5000 m

Pathloss Model

FriisSpectrumPropagationLossModel

Time 10 sec

Traffic GBR_VOICE

Bandwidth 25 PRB

System throughput Mbit/sPF - 12

PSS 5 - 12.26

PSS 50 - 12.27


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References

[1] Y. Zaki, T. Weerawardane, C. Gorg, and A. Timm-Giel, Multi-QoS-Aware Fair Scheduling for LTE, in Proc. IEEE Veh. Tech. Conf., VTC-Spring, May 2011.

[2] M. Iturralde, A. Wei, and A.Beylot, Resource Allocation for Real Time Services Using Cooperative

Game Theory and a Virtual TokenMechanism in LTE Networks, in Proc. IEEE Personal Indoor Mobile

Radio Commun., PIMRC, Sydney, Australia, Jan. 2012.

[3] K. Sandrasegaran, H. A. Mohd Ramli, and R. Basukala, Delay-Prioritized Scheduling (DPS) for Real

Time Traffic in 3GPP LTE System, in Proc. IEEE Wireless Commun. And Net. Conf., WCNC, Apr. 2010.

[4] G. Monghal, D. Laselva, P. Michaelsen, and J. Wigard, Dynamic Packet Scheduling for Traffic Mixes

of Best Effort and VoIP Users in E-UTRAN Downlink, in Proc. IEEE Veh. Tech. Conf., VTC-Spring, Marina

Bay, Singapore, May 2010.

[5] S. Choi, K. Jun, Y. Shin, S. Kang, and V. Lau, MAC Scheduling Scheme for VoIP Traffic Service in 3G

LTE, in Proc. IEEE Veh. Tech. Conf., VTC-Fall, Baltimore, MD, USA, Oct. 2007

[6] G.Mongha, K.I. Pedersen, I.Z. Kovacs, P.E. Mogensen, " QoS Oriented Time and Frequency Domain

Packet Schedulers for The UTRAN Long Term Evolution", In Proc. IEEE VTC, 2008

[7] http://lena.cttc.es/manual/index.html

[8] F. Capozzi, G. Piro, L.A. Grieco, G. Boggia, P. Camarda, Downlink Packet Scheduling in LTE Cellular

Networks: Key Design Issues and Survey.
http://lena.cttc.es/manual/index.htmlhttp://lena.cttc.es/manual/index.html

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09 LTE Scheduling