Transcript
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LTE: Schedulers
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LTE protocol architecture
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Packet scheduling model
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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
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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
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()+
(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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