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
𝐽𝑥𝑖 =
𝑛
𝑛
2
𝑖=1 𝑥𝑖
𝑛
2
𝑖=1 𝑥𝑖
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
𝑘 = 𝑎𝑟𝑔 max 𝑅𝑖
𝑖
𝑘 = 𝑎𝑟𝑔 max
𝑖
𝑅𝑖
𝑅𝑖
9
TTA
 Throughput To Average
𝑅𝑖,𝑓
𝑘 = 𝑎𝑟𝑔 max
𝑖
𝑓 𝑅𝑖,𝑓
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
𝑅𝑖
𝑘 = 𝑎𝑟𝑔 max 𝐷ℎ𝑜𝑙,𝑖 𝛼𝑖
𝑖 𝑅𝑖
𝛼𝑖 = −
log 𝛿𝑖
𝜏𝑖
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
𝑅𝑖
𝛼𝑖 𝐷ℎ𝑜𝑙,𝑖 − 𝑋
𝑘 = 𝑎𝑟𝑔 max exp
𝑖 𝑅𝑖
1+ 𝑋
𝛼𝑖 = −
1
X= 𝑁
𝑟𝑡
log 𝛿𝑖
𝜏𝑖
𝑁𝑟𝑡
𝑖=1 𝐷ℎ𝑜𝑙,𝑖 𝛼𝑖
Ntr is the number of active real time flows
16
LOG-RULE
 Log Rule
𝑅𝑖
𝑘 = 𝑎𝑟𝑔 max 𝑏𝑖 log 𝑐 + 𝑎𝑖 𝐷ℎ𝑜𝑙,𝑖
𝑖 𝑅𝑖
ai, bi, c are tunable parameters
17
EXP-RULE
 Exponential Rule
𝑅𝑖
𝑘 = 𝑎𝑟𝑔 max 𝑏𝑖 𝑒𝑥𝑝
𝑖 𝑅𝑖
𝑎𝑖 𝐷ℎ𝑜𝑙,𝑖
𝑐+
1 𝑁𝑡𝑟
𝑗 𝐷ℎ𝑜𝑙,𝑗
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
𝑀𝑄𝑜𝑆𝑤𝑒𝑖𝑔ℎ𝑡
𝜇=
𝑅𝑎𝑐𝑐𝑢𝑚
priority
Multi-QoS aware Fair. TDPS [1]
𝑅𝑎𝑐𝑐𝑢𝑚 = 𝛼𝑅𝑎𝑐𝑐𝑢𝑚 𝑛 − 1 + (1 − 𝛼)𝑅𝑖𝑛𝑠𝑡
𝑅𝑎𝑐𝑐𝑢𝑚 - Accumulated data rate
𝑅𝑖𝑛𝑠𝑡 - Instantaneous bearer data rate at n-th TTI
- Smoothing factor
𝛼
𝑀𝑄𝑜𝑆𝑤𝑒𝑖𝑔ℎ𝑡 − 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.
𝜇=
𝑒𝑥𝑝
6
𝑊 (𝑡)
𝑑𝑖 𝑖
1+ 𝑊
𝑑𝑖𝑘
𝑑𝑖
𝑊𝑖 𝑡 − 𝐻𝑂𝐿 𝑑𝑒𝑙𝑎𝑦
𝑄𝑖 (𝑡) 𝑟𝑖
-
𝑑𝑖𝑘
𝑑𝑖
𝑅𝑒𝑎𝑙 𝑡𝑖𝑚𝑒
𝑁𝑅𝑒𝑎𝑙 𝑡𝑖𝑚𝑒
𝑉𝑖 (𝑡) =
(Proportional Fair)
𝑄𝑖 (𝑡)
𝑟𝑖
Token queue length
Arrival rate of tokens (depends on flow)
27
Delay-Prioritized (DPS) [3]
For real time traffic
𝑑𝑖 𝑡 = 𝑇𝑖 − 𝐷𝑖 (𝑡)
𝑘 = 𝑎𝑟𝑔min 𝑑𝑖 (𝑡)
𝑖
Select max SINR for k-th Ue, update 𝑑𝑘 (𝑡)
PRBs remain?
𝑇𝑖 𝐷𝑖 -
Yes
Delay threshold
HOL delay
28
Best Effort and VoIP. TDPS [4]
𝜇𝑇𝐷 (𝑛, 𝑡) = 𝜏 𝑛, 𝑡 𝑅𝐴𝑡𝑟𝑎𝑓 (𝑛, 𝑡)𝐷𝑆𝑡𝑟𝑎𝑓
𝑉𝑜𝐼𝑃
𝑅𝐴
𝑅𝐴𝐵𝐸
𝐺𝐵𝑅
𝑛, 𝑡 =
𝑅𝑠𝑐ℎ (𝑛, 𝑡)
𝑁𝑚𝑢𝑥 − 𝑉𝑜𝐼𝑃 𝑅𝐴𝑉𝑜𝐼𝑃 (𝑛, 𝑡)
𝑛, 𝑡 = 𝑚𝑎𝑥 0,
𝑁𝑏𝑒𝑠𝑡 𝑒𝑓𝑓𝑜𝑟𝑡
𝐷𝑆 𝐵𝐸 = 1
𝑅𝐴𝑡𝑟𝑎𝑓 (𝑛, 𝑡)
𝜏(n, t)
𝐷𝑆 𝑡𝑟𝑎𝑓 (𝑛, 𝑡)
𝑁𝑚𝑢𝑥
-
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]
𝜇
𝐹𝐷
𝑑(𝑛, 𝑘, 𝑡)
𝑛, 𝑡 =
𝑅𝑠𝑐ℎ (𝑛, 𝑡)
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
𝑅(𝑛, 𝑡) =
𝐷(𝑛)
𝜇(𝑛) =
𝑅(𝑛)
𝑇−1
1
𝑅 𝑡 − 1, 𝑛 + 𝑅(𝑡 − 1, 𝑛)
𝑇
𝑇
(PF)
priority
Below-GBR
1
𝜇(𝑛) =
𝑅(𝑛)
Take N Ue
T- time window (99 lena)
𝑅(n) - Past average throughput of Ue n.
𝐷(𝑛) - Instantaneous bearer data rate at n-th TTI
33
Priority Set Scheduling. FDPS [6]
𝜇𝑃𝐹𝑠𝑐ℎ
𝑅𝑠𝑐ℎ
𝑑(𝑘, 𝑛)
𝑘, 𝑛 =
𝑅𝑠𝑐ℎ (𝑛)
𝑇−1
1
𝑈𝑒 𝑖𝑠 𝑠𝑐ℎ𝑒𝑑𝑢𝑙𝑒𝑑
𝑅𝑠𝑐ℎ 𝑡 − 1, 𝑛 + 𝑅𝑠𝑐ℎ 𝑡 − 1, 𝑛
=
𝑇
𝑇
𝑈𝑒 𝑖𝑠 𝑛𝑜𝑡 𝑠𝑐ℎ𝑒𝑑𝑢𝑙𝑒𝑑 𝑏𝑦 𝑇𝐷
𝑅𝑠𝑐ℎ (𝑡 − 1, 𝑛)
𝑅𝑠𝑐ℎ - 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.
41