Scheduling in LTE - Electrical and Computer Engineering

1 Scheduling in LTE. Gwanmo Ku Adaptive Signal Processing and Information Theory Research Group Apr. 27, 2012. Outline 2/22. LTE Overview Network & Signals Physical Resources in Time & Frequency Radio Protocol Architecture Control Information for Scheduling Operation Scheduling in LTE. Scheduling Operation CQI Reporting for Scheduling Schedulers in LTE. Summary & References 2/11. LTE Overview Network & Signals : E-UTRAN, OFDMA/SC-FDMA. Physical Resources : Physical Resources, Resource Unit, Scheduling Unit Radio Protocol Architecture : L1/L2/L3, Physical /Transport Channels Control Information for Scheduling Information Control & Data Regions Control Information for Scheduling LTE Network 4/22.

2 LTE Network (E-UTRAN). Internet * EPC : Evolved Packet Core * E-UTRAN : Evolved Universal Terrestrial Radio Access Network * UE : User Equipment * eNB : evolved Node B. LTE Signals 5/22. OFDMA & SC-FDMA(DFTS-OFDMA). Downlink Good Throughput Demands Techniques OFDMA. Multipath with CP High PAPR. Fading Higher Data Rate Broadband, Multi-carriers PAPR Issue Reliability CP. Low PAPR. SC-FDMA. With CP Fair Throughput Uplink +. *2048. Used Subcarriers 0. QPSK Subcarrier CP /. 16 QAM - DFT N-IFFT Quadrature Modulation Mapping P-S. 64 QAM. 0. * Except for MBMS (4096). Physical Resources 6/22. Time & Frequency Resources Frequency (# Sub-carriers).

3 N=2048*. Null Used Sub-carriers . Null Slot Time 1ms (Second). Sub-frame Frame 10ms Parameters (Except for MBMS : 4096 KHz, 2* ). System BW [MHz] 3 5 10 15 20. N / Freq. Spacing 2048 / 15 KHz # Used Subcarriers 72 180 300 600 900 1200. Resource Unit 7/22. Physical Resource Block (PRB). The Smallest User Assignment Resource Unit Frequency (#Subcarriers). 180 KHz PRB. (12 Sub-carriers). ms Time (6 or 7) (# Symbols). Parameters (Except for MBMS). CP Type # Symbols / Slot Normal CP 7. Extended CP 6. Scheduling Unit 8/22. Sub-frame (2 Slots). Smallest Scheduling Time Interval : TTI (1ms). Frequency (#PRBs). USER Assign PRB 1 PRB 1.

4 PRB1 PRB1. PRB0 PRB0. DL/UL Conf. 1 ms (Sub-frame : 2 Slots) Time Parameters (Except for MBMS). System BW [MHz] 3 5 10 15 20. # PRBs 6 15 25 50 75 100. (# Used Subcarriers ) (72) (180) (300) (600) (900) (1200). Radio Protocol Architecture 9/22. Protocol Architecture around PHY. Layer 3 Radio Resource Control (RRC). Logical Channels Control /. Layer 2 Medium Access Control (MAC) Measurements Transport Channels Layer 1 Physical Layer (PHY). Logical Channels : Type of information Transport Channels : How the information is transferred Physical/Transport Channels 10/22. Transport Channels Physical Channel Layer 2 Medium Access Control (MAC).

5 Broadcasting Paging Random Access Transport BCH MCH PCH DL-SCH UL-SCH RACH. Channels Multicasting Data Data Layer 1 Physical Layer (PHY). DCI. PBCH PMCH PDSCH PDCCH PUCCH PUSCH PRACH. Physical Channels DL Control UL Control PHICH PCFICH Scheduling Information Control Information for Scheduling 11/22. Scheduling Information : PDCCH. PRB . Slot 2i Slot 2i+1.. PCFICH PDCCH PDSCH. Information Sub-frame i of the length of Control Region . PRB 1. PRB 0. Symbol 0 Symbol 1 Symbol 2 1 Symbol 0 Symbol 1 Symbol 2 1. Control Region Data Region (Reference : p. 57 3 GPP TS (2009-12)). Scheduling Information : DCI in PDCCH. 12/22.

6 DCI Formats DCI Formats Purpose UL Scheduling 0 Scheduling + TPC for PUSCH. 1 Scheduling for PDSCH, TPC for PUCCH. 1A Compact Scheduling for PDSCH, TPC for PUCCH. 1B MIMO Compact Scheduling for PDSCH, TPC for PUCCH. DL Scheduling 1C Very Compact Scheduling for PDSCH. 1D Compact Scheduling for PDSCH with Power Offset, TPC for PUCCH. 2 Closed Loop MIMO Compact Scheduling for PDSCH, TPC for PUCCH. 2A Open Loop MIMO Compact Scheduling for PDSCH, TPC for PUCCH. 3 TPC for PUCCH, PUSCH 2bit Power Adjustment UL Power Control 3A TPC for PUCCH, PUSCH 1bit Power Adjustment User Identification C-RNTI. 13/22. User Identification With C-RNTI (Cell specific Radio Network Temporary Identifier).

7 DCI. CRC. Attachment DCI +. 16 bit CRC scrambled with RNTI. DCI (DCI + RNTI)mod2. (Reference : p. 56 3 GPP TS (2009-12)). 2/11. Scheduling in LTE. Basic Scheduling Operations Resource Assignment CQI Reporting for Schedulers Schedulers in LTE. Example : DL Scheduling Basic Scheduling Operation 15/22. Purpose Efficient SCH(Data) Resources Assignments Consideration Traffic Volume, QoS (Buffer Status, Priority ). Channel Condition Scheduling Interval Dynamic Scheduling by MAC : One TTI (1ms : One Sub-frame). Semi-Persistent for VoIP : Multiple TTIs by RRC. Resource Assignment : PRBs & Associated MCS. Resource Assignment 16/22.

8 Per UE # PRBs Assignment Channel Dependent Resource Allocation User Assignment based on Channel Quality CQI / MCS / TBS. eNB. 1. DL RS. 2. CQI Reporting MCS Spectral Efficiency UE PRBs 3. DL Transmission Transport Block Size CQI Reporting for Scheduling 17/22. Reporting modes Frequency Wideband Or Sub-band Time Periodic or Aperiodic In time : Periodic (PUCCH/PUSCH) & Aperiodic (PUSCH). In Frequency Wide-band CQI : 4 bit Differential Sub-band CQI : 2 bit (Sub-band CQI Wideband CQI). Differential Spatial CQI : 3bit for MIMO. Schedulers in LTE. 18/22. MAC Schedulers PDCP : Packet Data Convergence Protocol ROHC : Robust Header Compression ARQ : Automatic Repeat Request HARQ : Hybrid ARQ.

9 DL Scheduling 19/22. DL MAC Scheduler User N N Transport Blocks ACK/NACK User 1 (Dynamic Size for N Users). CQI. HARQ CRC Redundancy for Error Detection Redundancy for Data Detection MAC Scheduler Coding + RM. Retransmission Modulation Scheme QPSK, 16 QAM, 64 QAM. Data Modulation Resource Assignment Resource Mapping Power Assignment Antenna Mapping Multi-Antenna Antenna Mapping Processing 2/11. Conclusion & References Summary 21/22. LTE Overview LTE Network, Physical Resources Signaling Scheduling Information in PHY. Scheduling in LTE. PRB & MCS Assignment CQI Reporting Process for Schedulers MAC Schedulers in LTE. DL Scheduling Process References 22/22.

10 LTE Web LTE L1(PHY) Standards TS 36201 : LTE PHY Overview TS 36211 : LTE PHY Modulation TS 36212 : LTE Multiplexing and Channel Coding TS 36213 : LTE PHY related Procedures TS 36214 : LTE Measurements LTE L2/L3(MAC/RRC) Standards TS 36300 : LTE L2/L3 Overview TS 36321 : LTE MAC. TS 36331 : LTE RRC.