Technology training (Session 4) Long Term Evolution Technology training (Session 4)

Outline LTE major interfaces Physical, transport and logical channels Physical channel supporting DL transmission

Part 1 LTE major interfaces

SAE-Architecture LTE Network layout SAE – flat architecture Core network, RAN RAN consist of single elements: eNode B Single element simplifies RAN No single point of failure Core network provides two planes User plane (through SGSN) Control plane (through MME) Interfaces S1-UP (eNode B to SGSN) S1-CP (eNode B to MME) X2 between two eNode Bs (required for handover) Uu (UE to eNode B) LTE Network layout UE – user equipment (i.e. mobile) eNode B – base station SGSN – Support GPRS Serving Node GGSN – Gateway GPRS Serving Node MME – Mobility Management Entity PCRF - Policy and Charging Rules function SAE = System Architecture Evolution

OSI Communication model LTE interfaces described using OSI model OSI = Open System Interconnect Developed by ISO as a general model for computer communication Used as a framework for development and presentation of most contemporary communication standards Each layer communicates only with two adjacent layers and its peer on the other side Each layer receives services from the layer below and provides services to the layer above Intermediate communication nodes require layers 1 through 3 Internal operation within each layer is independent of the internal operation in any other layer Note: LTE covers Layers 1-3 of OSI Model

LTE protocol-control plane NAS – Non Access Stratum RRC – Radio Resource Control PDCP – Packet Data Convergence Protocol RLC – Radio Link Control MAC – Medium Access Control S1-AP – S1 Application SCTP – Stream Control Transmission Prot. IP – Internet Protocol Note: LTE control plane is almost the same as WCDMA (PDCP did not exist in WCDMA control plane)

LTE protocol- user plane PDCP – Packet Data Convergence Protocol RLC – Radio Link Control MAC – Medium Access Control GTP-U - GPRS Tunneling Protocol Note: LTE user plane is identical to UMTS PS side. There is no CS in LTE – user plane is simplified.

LTE protocol – X2 Connects all eNodeB’s that are supporting end user active mobility (handover) Supports both user plane and control plane Control plane – signaling required for handover execution User plane – packet forwarding during handover Control plane GTP-U: GPRS tunneling protocol STCP: Stream Transmission Control Protocol User plane

Part 2 LTE Uu channelization

Channel structure Channels – defined on Uu Logical channels Formed by RLC Characterized by type of information Transport channels Formed by MAC Characterized by how the data are organized Physical channels Formed by PHY Consist of a group of assignable radio resource elements Uu interface Note: LTE defines same types of channels as WCDMA/HSPA

LTE - channel mapping

Channels: common, shared, dedicated Channel – way of organizing information Common channel Received by all UEs Decoded by all UEs Information of interest to all UEs Shared Only portion of information of interest to a given UE Dedicated Decoded only if of interest to a given UE

Logical channels (“what channels”) BCCH – Broadcast Control CH System information sent to all UEs PCCH – Paging Control CH Paging information when addressing UE CCCH – Common Control CH Access information during call establishment DCCH – Dedicated Control CH User specific signaling and control DTCH – Dedicated Traffic CH User data MCCH – Multicast Control CH Signaling for multi-cast MTCH – Multicast Traffic CH Multicast data Red – common, green – shared, blue - dedicated LTE Channels

Transport channels(“how channels”) BCH – Broadcast CH (DL) Transport for BCCH PCH – Paging CH (DL) Transport for PCH DL-SCH – Downlink Shared CH (DL) Transport of user data and signaling. Used by many logical channels UL-SCH – Uplink Shared CH (UL) Transport for user data and signaling RACH – Random Access CH (UL) Used for UE’s accessing the network MCH – Multicast channel Used for multicast transmission Red – common, green – shared LTE Channels

PHY Channels LTE Channels Red – common, green – shared PBCH – Physical Broadcast CH Broadcast information necessary for accessing the network PDSCH – Physical DL Shared CH Uni-cast transmission and paging PDCCH – Physical Downlink Control CH Only PHY: Carries mainly scheduling information PCIFIC – Physical Control Format Indicator Only PHY: Information required by UE so that PDSCH can be demodulated (format of PDSCH) PHICH – Physical Hybrid ARQ Indicator Only PHY: Reports status of Hybrid ARQ PUSCH – Physical Uplink Shared Channel Uplink user data and signaling PUCCH – Physical Uplink Control Channel Only PHY: Reports Hybrid ARQ acknowledgements PRACH – Physical Random Access Channel Used for random access PMCH – Physical Multicast Channel Data and signaling for multicast LTE Channels Red – common, green – shared

Review Name major elements of E-UTRAN Name major elements of EPS What is the interface between UE and eNodeB? Name the interface between eNodeBs Name the interface between eNodeB and MME What are the properties of common channels? Are there any common channels on the UL? What is a shared channel? Give an example of a shared channel? What PHY channels are used for broadcast information?

Part 3 DL Phy channels

PHY channels/signals for DL TX Service to MAC Only at PHY PBCH – used to broadcast static portion of the BCCH PDSCH – carries user information and signaling from upper layers of protocol stack SCH – allows mobile to synchronize to the DL TX during acquisition PDCCH – channel used by MAC scheduler to configure L1/L2 and assign resources (DL scheduling and UL grants) PCFICH – explains to the UE the format of the DL transmission PHICH – support for HARQ on the uplink PUCCH – support for HARQ on the downlink Channels required for DL transmission

Time/Frequency location of PBCH and SS - FDD PBCH = Physical Broadcast Channel Used for BCH transport channel SS = Synchronization Signal P-SS = Primary Synchronization Signal S-SS = Secondary Synchronization Signal SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity Note: PBCH and SS use innermost part of the spectrum. This way the system acquisition is the same regardless of deployed bandwidth

Time/Frequency location of PBCH and SS - TDD PBCH = Physical Broadcast Channel Used for BCH transport channel SS = Synchronization Signal P-SS = Primary Synchronization Signal S-SS = Secondary Synchronization Signal SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity Note: The position of the P-SS is different in TDD and FDD. By acquiring P-SS, the UE already knows if the system is FDD or TDD.

LTE resource grid – detailed view (FDD) Note: DC subcarrier 0 not represented. See also: http://dhagle.in/LTE

Synchronization Channel (SCH) SCH – first channel acquired by UE Based on SCH, UE determines eNode B PHY cell identity (PCI) 504 possible PHY layer cell IDs (PCI = 0,.., 503) 168 groups with 3 identities per group SCH consist of 2 signals PSS (Primary Synchronization Signal) SSS (Secondary Synchronization Signal) 3 possible PSS sequences: NID(2) = 0,1, 2 168 possible SSS sequences: NID(1) = 0,1, …, 167 Cell ID: NIDcell = 3* NID(1) + NID(2) For FDD (frame type 1) PSS is transmitted on OFDM symbol 7 in the first time slot of subframe 0 and 5 SSS is transmitted on OFDM symbol 6 in the first time slot of subframe 0 and 5 For TDD (frame type 2) PSS is transmitted on OFDM symbol 3 in the first time slot of subframe 1 and 6

Mapping of the BCCH information PBCH PBCH = PHY Broadcast Channel PBCH provides PHY channel for static part of Broadcast Control Channel (BCCH) BCCH carriers RRC System Information (SI) messages SI messages carry System Information Blocks (SIBs) SI-M is a special SI that carrier Master Information Block (MIB) In LTE BCCH is split into two parts Primary broadcast: Carriers MIB and provides UE with fast access to vital system broadcast information. Primary broadcast is mapped to PBCH Dynamic broadcast: Carries all SIBs that contain quasi-static information on system operating parameters. Dynamic broadcast is mapped to PDSCH Mapping of the BCCH information See also: http://www.rfwireless-world.com/Terminology/LTE-MIB-SIB-system-information-blocks.html

PCH PCH = Paging Channel Transmitted over PDSCH (messages), PDCCH (paging indicator) LTE support DRX (UE sleeps between paging occasions) LTE defines DRX cycle UE is assigned to P-RNTI (Paging – Radio Network Temporary Identifier) P-RNTI is set on PDCCH UE that finds set P-RNTI reads PCH on PDSCH to determine if it is being paged DRX cycle compromise Long cycle: good battery life, higher paging delay Short cycle: faster paging response, shorter UE battery life DRX and paging Mapping of PCCH

Downlink L1/L2 signaling Signaling that supports DL transmission Originates at L1/L2 (no higher layer data or messaging) Consists of Scheduling assignments and associated information required for demodulation and decoding of DL-SCH Uplink scheduling grants for UL-SCH HARQ acknowledgements Power control commands L1/L2 signaling is transmitting in first 1-3 symbols of a subframe – control region Size of control region may vary dynamically – always whole number of OFDM symbols (1,2,3) Signaling – beginning of the subframe Reduces delay for scheduled mobiles Improves power consumption for non-scheduled mobiles Three different PHY channel types PCFIC (PHY Control Format Indicator Channel) PHICH (PHY – Hybrid ARQ Channel) PDCCH (PHY Downlink Control Channel)

PCFICH PCFICH – PHY Channel Format Indicator Channel Indicates to UE the size of the control region (1,2 or 3 OFDM symbols) PCFICH value may be 1, 2 or 3 (0 is reserved for future use) Decoding of PCFICH is essential for UE operation Encoded with 1/16 repetition code Uses QPSK modulation Mapped to the first symbol of each subframe 16 resource elements in 4 groups of 4 (RE Groups) Location of the resource elements depends on cell identity Processing of PCFICH Note: REGs of the PCFICH are spread in frequency domain to achieve frequency diversity

PHICH Processing of PHICH PHICH = PHY Hybrid-ARQ Indicator Channel HARQ acknowledgements for UL-SCH transmission As many PHICH channels as the number of UEs in the cell A set of PHICH channels is multiplexed on the same resource elements (8 normal CP, 4 extended CP) Transmitted in the first OFDM symbol of the subframe Occupies 3 resource element groups (REGs) = 12 resource elements (RE) PHICH response comes 4 sub-frames after PU-SCH Processing of PHICH

PDCCH PDCCH = Physical Downlink Control Channel Used for DL scheduling assignments UL scheduling grants Power control commands PDCCH message occupies 1,2,4 or 8 Control Channel Elements (CCEs) CCE = 9 Resource Element groups (REGs) = 36 Resource Elements (REs) One PDCCH carrier one message with a specific Downlink Control Information (DCI) Multiple UE-s scheduled simultaneously -> Multiple PDCCH transmissions in a subframe

PDCCH DCIs DCI formats of PDCCH PDCCH carrier Downlink Control Information (DCI) Multiple DCI formats are defined based on type of information DCI formats of PDCCH Format Purpose Content # of bits (FDD) UL PUSCH grant RB assignment, MCS, hopping flag, NDI, cyclic shift of DM-RS, CQI, … 44 1 DL PDSCH grant for single code word Resource allocation header, RB allocation, MCS, HARQ, HARQ PID, … 55 1A Compact DL PDSCH grant of single code word Similar to format 1, but with smaller flexibility RACH initiated by PDCCH order Localized/distributed VRB assignment flag, preamble index, PRACH message mask index 1B Compact DL PDSCH grant with pre-coding information Similar to 1, but with distributed VRB flag, reduced RB allocation flexibility, transmit PMI and pre-coding 49 1C Very compact DL PDSCH grant Reduced payload for improved coverage, always uses QPSK on associated PDSCH, restricted RB assignment, No HARQ, … 31 1D Compact DL PDSCH grant with pre-coding information and power offset Same as 1, but with reduced RB allocation flexibility and addition of distributed VRB transmission flag. Transmit PMI information for pre-coding, DL power offset 2 MIMO DL grant Same as 1, but for MIMO transmission 76 2A Compact MIMO DL grant Same as 1A, but for MIMO transmission 68 3 2-bit UL power control TPC for 14 UEs plus 16 bit CRC 3A 1-bit UL power control TPC for 28 UEs plus 16 bit CRC

PDSCH DL-SCH = DL Shared channel Used for user data coming from upper layers (both signaling and payload) Optimized for low latency and high data rate Individual steps in the processing chain operate on data blocks – enables parallel processing Many different adaptation modes Modulation Coding Transport block size Antenna mapping (TX diversity, beam forming, spatial multiplexing)

Summary of PHY DL channels L1/L2 signaling L1/L2 Control Coding scheme PHY Channel Modulation CFI (Channel format Indicator) Block code R=1/16 PCFICH QPSK HI (HARQ information) Repetition 1/3 PHICH BPSK DCI (Downlink control Information) Convolutional 1/3 with rate matching PDCCH Services to upper layers Transport channel Coding scheme PHY Channel Modulation DL-SCH Turbo 1/3 PDSCH QPSK, 16-QAM, 64-QAM BCH Convolutional 1/3 PBCH QPSK PCH MCH PMCH

Section review What are two PHY channels providing service to MAC layer? What are the two signals used in SCH? What is PCI? How many PCIs are defined in LTE? Explain discontinuous reception (DRX) What is L1/L2 signaling? Which LTE OFDM symbols are used for L1/L2 signaling? What is the use of PDCCH? What is the use of PCFICH? What type of error control coding is implemented on PDSCH? Use website http://dhagle.in/LTE to explore different formats of the LTE DL resource grid.