scheduler

Report
LTE: Schedulers
Содержание
 Место планировщика в архитектуре
 Функции планировщика
 Виды планировщиков
2
LTE protocol architecture
3
Packet scheduling model

Channel-Quality Indicator

Inner Loop Link Adaptation
(fast)
• chooses MCS (СКК)

Outer Loop Link Adaptation
(slow)

Automatic Repeat-reQuest
4
Time-frequency scheduling

Physical Downlink Control Channel

Physical Resource Blocks

Discontinuous Reception (DRX)
5
Frame (bandwidth 1.4 MHz, 6 PRBs, 72 subcarriers)
― cell-specific Reference Signal
― Primary Synchronization Signal
― Secondary Synchronization Signal
― Physical Broadcast Channel
― Physical Hybrid ARQ Indicator
Channel
― Physical Control Format Indicator
Channel
― Physical Downlink Control Channel
― Unused by selected antenna port
6
Quality Metrics
 Throughput
 Fairness
 =


2
=1 

2
=1 
Xi - is the throughput for the i-th connection
 Packet Loss Rate, %
 Scheduling cost (memory, time, etc.)
7
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)
8
RR, PF, Maximum rate
 =  max 

 =  max



9
TTA
 Throughput To Average
,
 =  max

 ,
10
Simulation scenario
11
MT, PF, PF-PF, TTA - Throughput
12
MT, PF, PF-PF, TTA - Fairness
13
Scheduler with buffer estimation
 Следующие планировщики учитывают
задержку пакетов, переполнение буфера
14
MLWDF
 Modified Largest Weighted Delay First

 =  max ℎ, 
 
 = −
log 

Dhol is the head-of-line (HOL) delay of user i a time t
δ Acceptable packet loss rate for i-th user
τi threshold delay of the i-th user
MLDWF prioritizes the user with higher HOL packet delay and better channel
conditions relative to its average levels.
15
EXP-PF
 Exponential Proportional Fair

 ℎ, − 
 =  max exp
 
1+ 
 = −
1
X= 

log 


=1 ℎ, 
Ntr is the number of active real time flows
16
LOG-RULE
 Log Rule

 =  max  log  +  ℎ,
 
ai, bi, c are tunable parameters
17
EXP-RULE
 Exponential Rule

 =  max  
 
 ℎ,
+
1 
 ℎ,
18
FLS
 Frame Level Scheduler
 Выбираем простым алгоритмом
пользователей для 1 кадра (10мс).
• Используем PF
 Производим распределение по блокам уже
внутри кадра.
• Используем MT
19
PF, MLWDF, EXP-PF, EXP-LOG Rule Throughput
+ each user receives three downlink flows (one video, one VoIP, and data).
20
PF, MLWDF, EXP-PF, EXP-LOG Rule - PRL
Packet Loss Rate
21
Литература
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. 9–9, 2009.
22
QoS в LTE
23
Downlink Scheduling in LTE [8] . Part II
 New schedulers:
•
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]
24
GBR
QoS1class
QoS2class
Flows
Non-GBR
ℎ
=

priority
Multi-QoS aware Fair. TDPS [1]
 =   − 1 + (1 − )
 - Accumulated data rate
 - Instantaneous bearer data rate at n-th TTI
- Smoothing factor

ℎ − 3
25
Multi-QoS aware Fair. FDPS [1]
1) GBR QoS1class: Max SINR
Check: Ue buffer full or GBR achieved
yes
next Ue
2) Non-GBR metric: Max SINR
Each iteration everyone get one RB
26
Game Theory and Token Mechanism [2]
TD
FD
Sharply value – every flow get resources based on its contribution.
=

6
 ()
 
1+ 


  −  
 () 
-


 
 
 () =
(Proportional Fair)
 ()

Token queue length
Arrival rate of tokens (depends on flow)
27
Delay-Prioritized (DPS) [3]
For real time traffic
  =  −  ()
 = min  ()

Select max SINR for k-th Ue, update  ()
PRBs remain?
  -
Yes
Delay threshold
HOL delay
28
Best Effort and VoIP. TDPS [4]
 (, ) =  ,   (, )




,  =
ℎ (, )
 −   (, )
,  =  0,
 
  = 1
 (, )
(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)
29
Best Effort and VoIP. FDPS [4]


(, , )
,  =
ℎ (, )
Proportional fair scheduled (PFsch)
30
VoIP [5]
The limit of VoIP priority mode
is adaptively changed between
min and max according VoIP
packet drop ratio.
31
VoIP experiment [5]
32
Priority Set Scheduling. TDPS [6]
(BET)
Flows
Other
(, ) =
()
() =
()
−1
1
  − 1,  + ( − 1, )


(PF)
priority
Below-GBR
1
() =
()
Take N Ue
T- time window (99 lena)
(n) - Past average throughput of Ue n.
() - Instantaneous bearer data rate at n-th TTI
33
Priority Set Scheduling. FDPS [6]
ℎ
ℎ
(, )
,  =
ℎ ()
−1
1
  ℎ
ℎ  − 1,  + ℎ  − 1, 
=


   ℎ  
ℎ ( − 1, )
ℎ - Is an estimate of the user throughput if user was scheduled every sub frame
34
Scheduling input parameters
Name
Requested
bitrate
Average
datarate
1
X
X
2
X
Queue size
X
X
5
6
HOL
X
X
X
3
4
Max
delay
X
X
X
X
35
Scheduler in LENA
SCHEDULER
Data Control
Indication (DCI)
Allocation bitmap which identifies RBs
MAC Transport Block (TB) size
Modulation and Coding Scheme (MCS)
36
Transmit operations in downlink
37
Usage

If you want to use PSS scheduler in project:
•
•
•

Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
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 ());
38
Ns-3 experiment




1 eNB
50 Ues
Radius 5000 m
Pathloss Model –
FriisSpectrumPropagationLossModel
 Time 10 sec
 Traffic GBR_VOICE
 Bandwidth 25 PRB
System throughput Mbit/s
PF - 12
PSS 5 - 12.26
PSS 50 - 12.27
39
New Directions
 Carrier Aggregation
• A broader spectrum utilization
 Multi-User MIMO
• Same RB to different users
 Coordinated Multi-Point Transmission
• Coordinating and synchronization among different eNBs
 Scheduling in Heterogeneous Networks
• Inter-cell interference management by means of dynamic spectrum access
40
References

[1]

[2]

[3]

[4]

[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.”
Y. Zaki, T. Weerawardane, C. Gorg, and A. Timm-Giel, “Multi-QoS-Aware Fair
Proc. IEEE Veh. Tech. Conf., VTC-Spring, May 2011.
Scheduling for LTE”, in
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.
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.
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.
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