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LTE: Schedulers

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**Содержание Место планировщика в архитектуре Функции планировщика**

Виды планировщиков

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**LTE protocol architecture**

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**Packet scheduling model**

Channel-Quality Indicator Inner Loop Link Adaptation (fast) chooses MCS (СКК) Outer Loop Link Adaptation (slow) Automatic Repeat-reQuest

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**Time-frequency scheduling**

Physical Downlink Control Channel Physical Resource Blocks Discontinuous Reception (DRX)

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**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

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**Quality Metrics Throughput Fairness Packet Loss Rate, %**

Scheduling cost (memory, time, etc.) 𝐽 𝑥 𝑖 = 𝑖=1 𝑛 𝑥 𝑖 𝑛 𝑖=1 𝑛 𝑥 𝑖 2 Xi - is the throughput for the i-th connection

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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 𝑘=𝑎𝑟𝑔 max 𝑖 𝑅 𝑖 𝑅 𝑖 𝑘=𝑎𝑟𝑔 max 𝑖 𝑅 𝑖

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TTA Throughput To Average 𝑘=𝑎𝑟𝑔 max 𝑖 𝑅 𝑖,𝑓 𝑓 𝑅 𝑖,𝑓

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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**

Следующие планировщики учитывают задержку пакетов, переполнение буфера

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**MLWDF Modified Largest Weighted Delay First**

𝑘=𝑎𝑟𝑔 max 𝑖 𝑅 𝑖 𝑅 𝑖 𝐷 ℎ𝑜𝑙,𝑖 𝛼 𝑖 𝛼 𝑖 =− log 𝛿 𝑖 𝜏 𝑖 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.

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**EXP-PF Exponential Proportional Fair**

𝑘=𝑎𝑟𝑔 max 𝑖 𝑅 𝑖 𝑅 𝑖 exp 𝛼 𝑖 𝐷 ℎ𝑜𝑙,𝑖 −𝑋 1+ 𝑋 𝛼 𝑖 =− log 𝛿 𝑖 𝜏 𝑖 X= 1 𝑁 𝑟𝑡 𝑖=1 𝑁 𝑟𝑡 𝐷 ℎ𝑜𝑙,𝑖 𝛼 𝑖 Ntr is the number of active real time flows

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**LOG-RULE Log Rule 𝑘=𝑎𝑟𝑔 max 𝑖 𝑅 𝑖 𝑅 𝑖 𝑏 𝑖 log 𝑐+ 𝑎 𝑖 𝐷 ℎ𝑜𝑙,𝑖**

ai, bi, c are tunable parameters

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**EXP-RULE Exponential Rule**

𝑘=𝑎𝑟𝑔 max 𝑖 𝑅 𝑖 𝑅 𝑖 𝑏 𝑖 𝑒𝑥𝑝 𝑎 𝑖 𝐷 ℎ𝑜𝑙,𝑖 𝑐 𝑁 𝑡𝑟 𝑗 𝐷 ℎ𝑜𝑙,𝑗

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**FLS Frame Level Scheduler**

Выбираем простым алгоритмом пользователей для 1 кадра (10мс). Используем PF Производим распределение по блокам уже внутри кадра. Используем MT

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

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

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

Packet Loss Rate

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**Литература 4G LTE and LTE-Advanced for Mobile Broadband**

LTE for UMTS - OFDMA and SC-FDMA Based Radio Access (2009) Downlink Packet Scheduling in LTE Cellular Networks: Key Design Issues and a Survey 3GPP LTE Downlink Scheduling Strategies in Vehicle-to-Infrastructure Communications for Traffic Safety Applications Comparative Performance Study of LTE UplinkSchedulers 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.

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QoS в LTE

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**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]

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**Multi-QoS aware Fair. TDPS [1]**

QoS1class QoS2class GBR priority Flows 𝜇= 𝑀𝑄𝑜𝑆 𝑤𝑒𝑖𝑔ℎ𝑡 𝑅 𝑎𝑐𝑐𝑢𝑚 Non-GBR 𝑅 𝑎𝑐𝑐𝑢𝑚 = 𝛼 𝑅 𝑎𝑐𝑐𝑢𝑚 𝑛−1 +(1−𝛼) 𝑅 𝑖𝑛𝑠𝑡 𝑅 𝑎𝑐𝑐𝑢𝑚 Accumulated data rate Instantaneous bearer data rate at n-th TTI Smoothing factor 𝑅 𝑖𝑛𝑠𝑡 𝑀𝑄𝑜𝑆 𝑤𝑒𝑖𝑔ℎ𝑡 −3 𝛼

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**Multi-QoS aware Fair. FDPS [1]**

GBR QoS1class: Max SINR Check: Ue buffer full or GBR achieved Non-GBR metric: Max SINR yes next Ue Each iteration everyone get one RB

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**Game Theory and Token Mechanism [2]**

TD Sharply value – every flow get resources based on its contribution. 𝜇= 𝑒𝑥𝑝 6 𝑑 𝑖 𝑊 𝑖 (𝑡) 1+ 𝑊 𝑑 𝑖𝑘 𝑑 𝑖 𝑅𝑒𝑎𝑙 𝑡𝑖𝑚𝑒 𝑑 𝑖𝑘 𝑑 𝑖 𝑁𝑅𝑒𝑎𝑙 𝑡𝑖𝑚𝑒 FD (Proportional Fair) 𝑉 𝑖 (𝑡)= 𝑄 𝑖 (𝑡) 𝑟 𝑖 𝑊 𝑖 𝑡 −𝐻𝑂𝐿 𝑑𝑒𝑙𝑎𝑦 𝑄 𝑖 (𝑡) Token queue length Arrival rate of tokens (depends on flow) 𝑟 𝑖

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**Delay-Prioritized (DPS) [3]**

For real time traffic 𝑑 𝑖 𝑡 = 𝑇 𝑖 − 𝐷 𝑖 (𝑡) 𝑘= 𝑎𝑟𝑔 min 𝑖 𝑑 𝑖 (𝑡) Select max SINR for k-th Ue, update 𝑑 𝑘 (𝑡) PRBs remain? Yes 𝑇 𝑖 Delay threshold HOL delay 𝐷 𝑖

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**Best Effort and VoIP. TDPS [4]**

𝜇 𝑇𝐷 (𝑛,𝑡)=𝜏 𝑛,𝑡 𝑅𝐴 𝑡𝑟𝑎𝑓 (𝑛,𝑡) 𝐷𝑆 𝑡𝑟𝑎𝑓 𝑅𝐴 𝑉𝑜𝐼𝑃 𝑛,𝑡 = 𝐺𝐵𝑅 𝑅 𝑠𝑐ℎ (𝑛,𝑡) 𝑅𝐴 𝐵𝐸 𝑛,𝑡 =𝑚𝑎𝑥 0, 𝑁 𝑚𝑢𝑥 − 𝑉𝑜𝐼𝑃 𝑅𝐴 𝑉𝑜𝐼𝑃 (𝑛,𝑡) 𝑁 𝑏𝑒𝑠𝑡 𝑒𝑓𝑓𝑜𝑟𝑡 𝐷𝑆 𝐵𝐸 =1 𝑅𝐴 𝑡𝑟𝑎𝑓 (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) 𝜏(n,t) 𝐷𝑆 𝑡𝑟𝑎𝑓 (𝑛,𝑡) 𝑁 𝑚𝑢𝑥

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**Best Effort and VoIP. FDPS [4]**

𝜇 𝐹𝐷 𝑛,𝑡 = 𝑑(𝑛,𝑘,𝑡) 𝑅 𝑠𝑐ℎ (𝑛,𝑡) Proportional fair scheduled (PFsch)

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VoIP [5] The limit of VoIP priority mode is 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]**

𝜇(𝑛)= 1 𝑅(𝑛) Below-GBR (BET) priority Flows Take N Ue 𝜇(𝑛)= 𝐷(𝑛) 𝑅(𝑛) Other (PF) 𝑅(𝑛,𝑡)= 𝑇−1 𝑇 𝑅 𝑡−1,𝑛 + 1 𝑇 𝑅(𝑡−1,𝑛) T- time window (99 lena) 𝑅(n) Past average throughput of Ue n. Instantaneous bearer data rate at n-th TTI 𝐷(𝑛)

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**Priority Set Scheduling. FDPS [6]**

𝜇 𝑃𝐹𝑠𝑐ℎ 𝑘,𝑛 = 𝑑(𝑘,𝑛) 𝑅 𝑠𝑐ℎ (𝑛) 𝑅 𝑠𝑐ℎ = 𝑇−1 𝑇 𝑅 𝑠𝑐ℎ 𝑡−1,𝑛 + 1 𝑇 𝑅 𝑠𝑐ℎ 𝑡−1,𝑛 𝑅 𝑠𝑐ℎ (𝑡−1,𝑛) 𝑈𝑒 𝑖𝑠 𝑠𝑐ℎ𝑒𝑑𝑢𝑙𝑒𝑑 𝑈𝑒 𝑖𝑠 𝑛𝑜𝑡 𝑠𝑐ℎ𝑒𝑑𝑢𝑙𝑒𝑑 𝑏𝑦 𝑇𝐷 𝑅 𝑠𝑐ℎ Is an estimate of the user throughput if user was scheduled every sub frame

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**Scheduling input parameters**

Name Requested bitrate Average datarate Queue size Max delay HOL 1 X 2 3 4 5 6

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**Data Control Indication (DCI)**

Scheduler in LENA SCHEDULER Data Control Indication (DCI) Allocation bitmap which identifies RBs MAC Transport Block (TB) size Modulation and Coding Scheme (MCS)

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**Transmit operations in downlink**

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**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 ());

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**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 PSS

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**New Directions Carrier Aggregation Multi-User MIMO**

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

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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 [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 [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] [8] F. Capozzi, G. Piro, L.A. Grieco, G. Boggia, P. Camarda, “Downlink Packet Scheduling in LTE Cellular Networks: Key Design Issues and Survey.”

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