Chap 2. lte channel structure .eng
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This document provides an overview of the LTE physical channel structure and procedures between the eNB and UE. It describes the LTE architecture and introduces the main physical channels including downlink channels like PBCH, PDCCH, PDSCH and uplink channels like PUSCH, PUCCH, PRACH. It explains the channel mapping and provides examples of the initial access procedure and synchronization signal transmission. Key concepts covered are radio interface protocol stacks, channel coding, multiple access, and reference signals.
Chap 2. lte channel structure .eng
- 2. 2/62 Contents Chanel information Physical channel structure Basic procedure between eNB and UE
- 4. 4/62 LTE/SAE Architecture eNB MME / S-GW MME / S-GW eNB eNB S1 S1 S1 S1 X2 X2 X2 E-UTRAN SAE (System Architecture Evolution) SAE = LTE packet core Network (Evolved Packet Core : EPC) LTE = evolved UMTS Radio Access Network LTE (Long Term Evolution) Use flat architecture without specific radio network controller LTE Base station = eNB (eNB = „evolved‟ node B)
- 5. 5/62 PDCP/RLC/MAC sublayers terminated in eNB on the network side User Plane Protocol Stack eNB PHY UE PHY MAC RLC MAC PDCPPDCP RLC Header compression In-sequency delivery at handover Duplicate detection Ciphering for user/control plane Integrity protection for control plane AM/UM/TM ARQ (Re-)segmentation Concatenation In-sequence delivery Duplicate detection Logical - transport channel mapping Multiplexing/demultiplexing Traffic volume measurement HARQ Priority handling Transport format selection * PDCP : Packet Data Convergence Protocol RLC : Radio Link Control MAC : Medium Access Control (H)ARQ : (Hybrid) Automatic Repeat Request
- 6. 6/62 Control Plane Protocol Stack eNB PHY UE PHY MAC RLC MAC MME RLC NAS NAS RRC RRC PDCP PDCP Broadcast, Paging RRC connection setup Radio bearer control Mobility functions UE measurement control EPS bearer management Authentication ECM_IDLE mobility handling Paging originated in ECM_IDLE Security Control * RRC : Radio Resource Control NAS : Non Access Stratum EPS : Evolved Packet System ECM : EPS Connection Management
- 7. 7/62 Layer-2 Structure for Downlink Segm. ARQ etc Multiplexing UE1 Segm. ARQ etc ... HARQ Multiplexing UEn HARQ BCCH PCCH Scheduling / Priority Handling Logical Channels Transport Channels MAC RLC Segm. ARQ etc Segm. ARQ etc PDCP ROHC ROHC ROHC ROHC Radio Bearers Security Security Security Security ... CCCH
- 8. 8/62 Layer-2 Structure for Uplink Multiplexing ... HARQ Scheduling / Priority Handling Transport Channels MAC RLC PDCP Segm. ARQ etc Segm. ARQ etc Logical Channels ROHC ROHC Radio Bearers Security Security CCCH
- 9. 9/62 Logical Channel/Transport Channel/Physical Channel Logical channel Between RLC & MAC Established per radio bearer Defined by what kind of information is carried within Transport channel Between MAC&PHY Used to define how traffics are processed (MCS level, TB size, CRC size) Physical channel Physical layer for the real transmission 7 types channels
- 10. 10/62 Channel Mapping - Downlink BCH PCH DL-SCHMCH Downlink Physical channels Downlink Transport channels PBCH PDSCHPMCH PDCCH BCCH PCCH CCCH DCCH DTCH Downlink Logical Channels System Info. Paging Common Control Info at no RRC Connection Dedicated Control Dedicated Traffic
- 11. 11/62 Channel Mapping - Uplink Uplink Physical channels Uplink Transport channels UL-SCH PUSCH RACH PUCCHPRACH CCCH DCCH DTCH Uplink Logical Channels
- 12. 12/62 BCCH/BCH/P-BCH System information (MIB) No PDCP, RLC TM, transparent MAC BCCH/DL-SCH/PDSCH System information (SIBs) No PDCP, RLC TM, transparent MAC PCCH/PCH/PDSCH Paging message No PDCP, RLC TM, transparent MAC Logical Channel/Transport Channel/Physical Channel
- 13. 13/62 CCCH/UL(DL)-SCH/PUSCH(PDSCH) Initial RRC messages, fixed size in UL Transmitted during random access No PDCP, RLC TM, Transparent MAC DCCH/UL(DL)-SCH/PUSCH(PDSCH) RRC message (including NAS message coming from/going to MME) PDCP/RLC AM/non-transparent MAC DTCH/UL(DL)-SCH/PUSCH(PDSCH) Normal user traffic PDCP/RLC AM or UM/non-transparent MAC Logical Channel/Transport Channel/Physical Channel
- 14. 14/62 Example – Attach Procedure
- 15. 15/62 Physical Channels and Signals Physical Downlink Channel (eNB UE) PBCH (Physical broadcast channel) DL bandwidth, system frame number, PHICH configuration transmission PCFICH (Physical control format indicator channel) Transmit the number of OFDM symbols with PDCCH on downlink subframe to UE Transmit every subframe PDCCH (Physical downlink control channel) Transmit downlink resource allocation on downlink traffic and paging signal Transmit Uplink scheduling grant PDSCH (Physical downlink shared channel) Transmit downlink traffic and paging signal (eNB -> UE) PHICH (Physical hybrid ARQ indicator channel) Transmit ACK/NACK for Uplink data(PUSCH)
- 16. 16/62 Physical Channels and Signals Physical Uplink Channel (UE eNB) PUSCH (Physical uplink shared channel) Transmit uplink traffic PUCCH (Physical uplink control channel) Transmit ACK/NACK on Downlink data(PDSCH) Transmit Scheduling request, downlink channel info.(CQI) PRACH (Physical random access channel) Transmit random access preamble when It need Initial access, re-access, requesting UL resources Signal Synchronization signal (primary, secondary) Use it when UE get the synchronization with Base station DL/UL reference signal DL CQI measurement and DL / UL channel estimation UL SRS (Sounding reference signal) UE is periodically upload to eNB for checking the uplink channel status.
- 20. 20/62 DL Physical Channels & Signals Physical channels A set of Resource Elements carrying information originating from higher layers Physical Downlink Shared Channel, PDSCH Physical Broadcast Channel, PBCH Physical Multicast Channel, PMCH Physical Control Format Indicator Channel, PCFICH Physical Downlink Control Channel, PDCCH Physical Hybrid ARQ Indicator Channel, PHICH Physical Signals A set of Resource Elements NOT carrying information originating from higher layers Reference signal Synchronization signal
- 22. 22/62 Downlink Resource Grid Physical resource block parameters Number of symbols per slot Number of RBs
- 23. 23/62 RS Pattern and Control Channel Region
- 24. 24/62 Initial Access LTE Initial access procedure Cell search Receive System information Attach Power ON Cell Search and Selection Receive System Information Attach User data Tx/Rx Initial Access procedure
- 25. 25/62 Cell Search Cell search Find a cell to connect and estimate frame timing Provide the primary and secondary synchronization signals on the downlink to assist Cell-specific sequences are inserted in synchronization signals Support 504 unique physical-layer identities; NID cell (168 unique physical- layer cell-identity groups; NID (1), each group containing three unique identities; NID (2)) Physical-layer identity
- 26. 26/62 Synchronization Signals (FDD) PSS (primary synchronization signal) Estimate 5 msec timing and physical-layer identity Channel estimation information for SSS SSS (secondary synchronization signal) Physical-layer identity (Cell ID) is obtained Mapped to one of 168 cell ID groups (168 ID groups for 504 Cell IDs) Radio-frame timing (10msec) identification Max # of hypotheses;336 hypotheses (2 for half frame x 168 for ID groups)
- 27. 27/62 Downlink Reference Signal (RS) Three types of downlink reference signal Cell-specific reference signals, associated with non-MBSFN transmission (unicast RS) MBSFN reference signals, associated with MBSFN transmission UE-specific reference signals (Dedicated RS)
- 29. 29/62 Dedicated RS Three types of downlink reference signal UE-specific reference signals are supported for single-antenna-port transmission of PDSCH (transmitted on antenna port 5)
- 30. 30/62 PBCH PBCH Master information block of system information Use QPSK modulation System information (14 bits) is included DL system bandwidth (3 bits) System frame number (SFN: MSB 8 bits explicit, LSB 2 bits implicit) PHICH duration (1 bit) PHICH resource (2 bits) No explicit bits in PBCH to signal the number of TX antennas at the eNB (1, 2, or 4) Transmit 4 subframes with interval time(40 ms) Transmit every Subframe #0 40 ms timing is blind detection on UE
- 31. 31/62 PCFICH Use CFI (control format indicator) Transmission Information about the number of OFDM symbols used for transmission of PDCCH in a subframe is included Transmit first OFDM symbol The number of OFDM symbols using PDCCH NRB DL > 10 : 1, 2, 3 NRB DL <= 10 : 2, 3, 4
- 32. 32/62 PDCCH Transmit Scheduling assignment(physical downlink control channel) Transmit the aggregation of one or several control channel element (CCE) 1 CCE = 9 REGs = 36 REs 1 PDCCH = 1, 2, 4, 8 CCEs Possible to send several PDCCH in a subframe
- 33. 33/62 PDCCH Resource Element Group (REG) Basic RE mapping unit for downlink control information
- 34. 34/62 PDCCH
- 35. 35/62 PDCCH DCI formats DCI format 0 : UL-SCH assignments DCI format 1 : DL-SCH assignments for SIMO operation DCI format 1A : compact scheduling of one PDSCH codeword and for downlink transmission of paging, RACH response and dynamic BCCH scheduling DCI format 1B :used to support closed-loop single-rank transmission with possibly contiguous resource allocation DCI format 1C : downlink transmission of paging, RACH response and dynamic BCCH scheduling DCI format 1D : compact scheduling of one PDSCH codeword with precoding and power offset information DCI format 2 : scheduling PDSCH to UEs configured in closed-loop spatial multiplexing mode DCI format 2A : scheduling PDSCH to UEs configured in open loop spatial multiplexing mode DCI format 3 : transmission of TPC commands for PUCCH and PUSCH with 2- bit power adjustments DCI format 3A : transmission of TPC commands for PUCCH and PUSCH with single bit power adjustments
- 36. 36/62 PHICH Transmit hybrid-ARQ ACK/NACK for PUSCH transmission PHICH group 1 PHICH group = 8 PHICHs (normal CP) 1 PHICH group = 4 PHICHs (extended CP) The amount of PHICH resource is transmitted with 2 bits of PBCH Nh = 1/6, 1/2, 1, 2 The number of PHICH group N PHICH mapping
- 37. 37/62 PHICH
- 38. 38/62 Uplink Numerology Number of symbols per slot Bandwidth and number of RBs UL symbN SC-FDMA symbols One uplink slot slotT 0l 1 UL symb Nl RB sc UL RBNNsubcarriers RB scNsubcarriers RB sc UL symb NN Resource block resource elements Resource element ),( lk
- 39. 39/62 Uplink Basic Mapping Structure Resource block (RB) PUSCH mapping
- 40. 40/62 Uplink Physical Channels and Signals Physical Channels (Uplink) Physical Uplink Shared Channel (PUSCH) Physical Uplink Control Channel (PUCCH) Physical Random Access Channel (PRACH) Physical Signals (Uplink) Demodulation Reference Signal Sounding Reference Signal
- 41. 41/62 Mapping of Uplink Physical Channels PUCCH: frequency edge PUSCH: between PUCCH RBs Demodulation reference signal : center symbol in each slot Sounding reference signal : last symbol in a subframe Frequency Sub-frame (1ms) Slot (0.5ms) SC-FDMA symbol PUSCH PUSCH RS SRS One example configuration for normal CP PUCCH RB
- 42. 42/62 SC-FDMA for LTE UL Equivalent to DFT-Precoded OFDMA Low PAPR It‟s proper to Uplink Overall spectrum size Lower symbol rate Higher symbol rate
- 43. 43/62 PUSCH Transmission Localized transmission Hopping transmission
- 44. 44/62 PUCCH Format 1 (SR only with On-off Keying (OOK)) Format 1a and 1b (ACK/NACK only) Format 1a: BPSK ACK/NACK for 1 Codeword Format 1b: QPSK ACK/NACK for 2 Codewords Format 2 (CQI only) Format 2a and 2b (CQI + ACK/NACK) PUCCH (format 1) PUCCH (format 1) PUCCH (format 2) PUCCH (format 2) PUSCH
- 45. 45/62 PUCCH format 1 PUCCH format 1 in RB (normal CP) Cyclic shifts : 12 EA Orthogonal cover sequence : 3 EA Total available PUCCH format 1 resource in 1 RB = 36 EA Decide available PUCCH format 1 resource as the value of Ex) = 2 , can be used 18 PUCCH format 1 resources in 1 RB
- 46. 46/62 PUCCH format 2 PUCCH format 2 resources in RB (normal CP) Cyclic shifts : 12 EA No orthogonal cover sequence for PUCCH format 2 Total available PUCCH format 2 resource in 1 RB = 12 EA Decide available PUCCH format 2 resource as the value of Ex) = 2, can be used 6 PUCCH format 2 resources in 1 RB
- 47. 47/62 Sounding Reference Signal (SRS) UE is periodically upload to eNB for checking the uplink channel status. Use checking of UL channel status for the bandwidth transmitted SRS to UE. SRS cell-specific Configuration Configuration Binary Configuration Period (subframes) Transmission offset (subframes) 0 0000 1 {0} 1 0001 2 {0} 2 0010 2 {1} 3 0011 5 {0} 4 0100 5 {1} 5 0101 5 {2} 6 0110 5 {3} 7 0111 5 {0,1} 8 1000 5 {2,3} 9 1001 10 {0} 10 1010 10 {1} 11 1011 10 {2} 12 1100 10 {3} 13 1101 10 {0,1,2,3,4,6,8} 14 1110 10 {0,1,2,3,4,5,6,8} 15 1111 Inf N/A
- 48. 48/62 Sounding Reference Signal (SRS) SRS transmission bandwidths Multiple SRS BW trees are predefined for each uplink system operating bandwidth Cell-specific 3 bits are used to indicate one of 8 SRS BW configurations One SRS BW configuration has Max. SRS BW and predefined SRS BW trees UE specific 2 bits are given via higher layers to indicate one of 4 SRS BWs For each SRS BW configurations, there exist 1~4 SRS BWs SRS bandwidth configuration and SRS bandwidth for 40~60 RB uplink system BW SRS bandwidth configuration SRSC SRS-Bandwidth 0SRS B SRS-Bandwidth 1SRS B SRS-Bandwidth 2SRS B SRS-Bandwidth 3SRS B 0SRS,m 0N 1SRS,m 1N 2SRS,m 2N 3SRS,m 3N 0 48 1 24 2 12 2 4 3 1 48 1 16 3 8 2 4 2 2 40 1 20 2 4 5 4 1 3 36 1 12 3 4 3 4 1 4 32 1 16 2 8 2 4 2 5 24 1 4 6 4 1 4 1 6 20 1 4 5 4 1 4 1 7 16 1 4 4 4 1 4 1
- 49. 49/62 Sounding Reference Signal (SRS) Configuration Cell-specific SRS SRS bandwidth configuration SRS subframe configuration Report the possibility for simultaneously transmission ACK/NACK and SRS SRS Configuration per UE SRS Transmission bandwidth SRS hopping bandwidth Cyclic shift Frequency domain position Comb SRS Periods and offset per UE
- 50. 50/62 PRACH Structure The number of RB for PRACH transmission = 6 RB Transmit the subframe and frequency offset of PRACH using system information Preamble format SequenceCP CPT SEQT Preamble format CPT SEQT 0 s3168 T s24576 T 1 s21024 T s24576 T 2 s6240 T s245762 T 3 s21024 T s245762 T 4 (frame structure type 2 only) s448 T s4096 T
- 51. 51/62 DL/UL Subframe Architecture DL Subframe Architecture UL Subframe Structure
- 52. 52/62 Basic procedure between eNB and UE
- 53. 53/62 Basic procedure between eNB and UE The procedure for synchronization and obtaining of system Info. MIB : system frame number, DL bandwidth, PHICH information are included SIB : Cell specific information are included for system operation except MIB information SIB1: cell access configuration, frequency band indicator, scheduling information for syst other SIBs and systemInfoValueTag SIB2: radio configuration information are included (PUCCH, PUSCH, SRS etc) eNB UE ID 0~2 Cell ID Group 0~167 Cell ID Detection 0~503 Cell specific RS (Using cell ID info.) System Information (MIB) System Information (SIB) Broadcast Information PSS SSS DL Reference Signal PBCH PDSCH * MIB: Master Information Block * SIB: System Information Block
- 54. 54/62 Basic procedure between eNB and UE Call-Access procedure UE specific resource allocation information in Msg 4 (RRC Connection Setup) are transmitted CQI Resorce index, Transmit period and subframe offset SR Resource index, Transmit period and subframe offset SRS Transmission bandwidth, Frequency location, comb, cyclic shift eNB UE Msg 1 (Random Access Preamble) Msg 2 (Random Access Response) RACH DATA UL Timing Advance DATA +Msg 3 allocation info. PDCCH PDSCH Msg 3 (RRC Connection Request) DATA PUSCH Msg 4 (RRC Connection Setup) PDCCH PDSCH PDCCH DATA PUSCH Msg 5 (RRC Connection Setup Complete) * CQI: Channel Quality Indicator (DL channel Quality index) * SR: Scheduling Request (Using it when UE reports that UE has transmit data to eNB) * SRS: Sounding Reference Signal (Using it when UE transmit it periodically for checking uplink-channel status data) PRACH
- 55. 55/62 Basic procedure between eNB and UE DL data-Transmission Procedure UE transmit periodically CQI(channel quality indicator) which is DL channel status after receiving CQI resource allocation per UE. eNB allocates PDSCH considering DL channel status of a UE and DL buffer status Transmit the information of PDSCH allocation per specific subframe with PDCCH. When CRC is OK on PDSCH detection result in UE, transmit ACK to eNB. Transmit ACK info. on PUSCH when PUSCH is allocated. In other cases, Transmit ACK info on PUCCH . eNB UE DL CQI Estimation DATA PUSCH or PUCCH PDCCH PDSCH PUSCH or PUCCH DL Reference Signal CQI CQI DL Scheduling and Link Adaptation DL allocation info. ACK/NACK DATA PDCCH PDSCH With there is ACK/NACK or not, HARQ retransmission or new data transmission PDSCH Detection DL allocation info.
- 56. 56/62 Basic procedure between eNB and UE UL data-Transmission Procedure UE transmit periodically SRS signal after receiving SRS resource allocation per UE. eNB allocates PUSCH resource considering UL channel status of a UE and BSR. When CRC is OK on PUSCH detection result in UE, transmit ACK to eNB. Transmit ACK using PHICH (Downlink direction) eNB UE Transmit SRS periodically0 PUSCH Transmit the buffer status of UE SRS SRS UL Channel Quality Estimation PUCCH SR PDCCH UL Scheduling and Link Adaptation UL allocation info. DATA + BSR •BSR: Buffer Status Report Transmit the buffer status of uplink data to eNB PDCCH UL allocation info. PHICH ACK PUSCH DATA HARQ
- 57. 57/62 Basic procedure between eNB and UE Handover Procedure UE sends measurement report to serving cell with the condition of comparing Neighbor‟s cell signal and Serving cell signal. If serving cell transmits “handover command” message to UE, UE orders target cell to be handover. After UE receives Handover command, UE will proceed the transmission of RACH ,Handover procedure, to target cell. Serving cell UE Measurement Report Transmission * Handover Command : RRC connection reconfiguration PUSCH MR Target cell DL RS DL RS Handover Command PDSCH RACH RAR PDSCH PUSCH Handover Complete * Handover Complete : RRC connection reconfiguration complete PRACH