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LTE: Schedulers

LTE: Schedulers. Содержание. Место планировщика в архитектуре Функции планировщика Виды планировщиков. LTE protocol architecture. Packet scheduling model. C hannel- Q uality I ndicator I nner L oop L ink A daptation (fast) c hooses MCS ( СКК )

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LTE: Schedulers

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  1. LTE: Schedulers

  2. Содержание • Место планировщика в архитектуре • Функции планировщика • Виды планировщиков

  3. LTE protocol architecture

  4. Packet scheduling model • Channel-Quality Indicator • Inner Loop Link Adaptation (fast) • chooses MCS (СКК) • Outer Loop Link Adaptation (slow) • Automatic Repeat-reQuest

  5. Time-frequency scheduling • Physical Downlink Control Channel • Physical Resource Blocks • Discontinuous Reception (DRX)

  6. Frame (bandwidth 1.4 MHz, 6 PRBs, 72 subcarriers) • cell-specific Reference Signal • Primary Synchronization Signal • Secondary Synchronization Signal • Physical Broadcast Channel • Physical Hybrid ARQIndicator Channel • Physical Control Format Indicator Channel • Physical Downlink Control Channel • Unused by selected antenna port

  7. Quality Metrics • Throughput • Fairness • Packet Loss Rate, % • Scheduling cost (memory, time, etc.) Xi- is the throughput for the i-thconnection

  8. 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)

  9. RR, PF, Maximum rate

  10. TTA • Throughput To Average

  11. Simulation scenario

  12. MT, PF, PF-PF, TTA - Throughput

  13. MT, PF, PF-PF, TTA - Fairness

  14. Scheduler with buffer estimation • Следующие планировщики учитывают задержку пакетов, переполнение буфера

  15. MLWDF • Modified Largest Weighted Delay First Dhol is the head-of-line (HOL) delay of user i a time t δAcceptable packet loss rate for i-th user τi threshold delayof the i-thuser MLDWF prioritizes the user with higher HOL packet delay and better channel conditions relative to its average levels.

  16. EXP-PF • Exponential Proportional Fair X Ntris the number of active real time flows

  17. LOG-RULE • Log Rule ai, bi, c are tunable parameters

  18. EXP-RULE • Exponential Rule

  19. FLS • Frame Level Scheduler • Выбираем простым алгоритмом пользователей для 1 кадра (10мс). • Используем PF • Производим распределение по блокам уже внутри кадра. • Используем MT

  20. PF, MLWDF, EXP-PF, EXP-LOG Rule - Throughput + each userreceives three downlink flows(one video, one VoIP, anddata).

  21. PF, MLWDF, EXP-PF, EXP-LOG Rule - PRL Packet Loss Rate

  22. 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 CellularNetworks: 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.

  23. QoS в LTE

  24. 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]

  25. Multi-QoS aware Fair. TDPS [1] QoS1class QoS2class GBR priority Flows Non-GBR • Accumulated data rate • Instantaneous bearer data rate at n-th TTI • Smoothing factor

  26. 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

  27. Game Theory and Token Mechanism [2] TD Sharply value – every flow get resources based on its contribution. FD (Proportional Fair) • Token queue length • Arrival rate of tokens (depends on flow)

  28. Delay-Prioritized (DPS) [3] For real time traffic Select max SINR for k-thUe, update PRBs remain? Yes • Delay threshold • HOL delay

  29. Best Effort and VoIP. TDPS [4] • 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)

  30. Best Effort and VoIP. FDPS [4] Proportional fair scheduled (PFsch)

  31. VoIP [5] The limit of VoIP priority mode is adaptively changed between min and max according VoIP packet drop ratio.

  32. VoIP experiment [5]

  33. Priority Set Scheduling. TDPS [6] Below-GBR (BET) priority Flows Take N Ue Other (PF) T- time window (99 lena) • Past average throughput of Ue n. • Instantaneous bearer data rate at n-th TTI

  34. Priority Set Scheduling. FDPS [6] • Is an estimate of the user throughput if user was scheduled every sub frame

  35. Scheduling input parameters

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

  37. Transmit operations in downlink

  38. 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 numof UE selected by TD scheduler • Guarantee Bit Rate (GBR) or Maximum Bit Rate (MBR) can be configured in epc bearer respectively • enumEpsBearer::Qci q = EpsBearer::yourvalue; // define Qcitype • GbrQosInformationqos; • 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 ());

  39. 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

  40. 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

  41. 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. MohdRamli, 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.”

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