LTE Radio Interface Architecture Sherif A. Elgohari (selgohari@ieee.org)
Agenda Overall System Architecture Radio Protocol Architecture Radio Link Control Medium Access Control Physical Layer Control Plan Protocols
Overall System Architecture (EPC) Evolved Packet Core (Logical Functions): PS domain only MME: Mobility Management Entity Connection/Release Handling IDLE/ACTIVE transitions Handling Security Keys Non Access Stratum Functionality S-GW: Serving Gateway User Plan connecting RAN to EPC Mobility Anchor (Inter and Intra system) Information for Charging P-GW: Packet Data Network Gateway Connect the core to the Internet Allocation of IP addresses QoS implementation from PCRF Mobility with non-3gpp systems HSS: Home Subscriber Service Database contains subscriber Information
Overall System Architecture (RAN) S1-u: User Plan Part S1-c: Control Plan Part X2 Interface: Support Active Mode Mobility, MultiCell RRM, Inter- Cell Interference Coordination, Packet forwarding
RAN Protocol Architecture
RAN Protocol Architecture (2) RoHC header compression Ciphering/deciphering Data integrity and in sequence delivery of packets Segmentation/concatenation Retransmission/duplicate detection Multiplexing of logical channels HARQ, UL/DL scheduling Provide service to RLC in form of logical channels Encoding/decoding modulation./demodulation Multiple antenna mapping Other physical functions
Radio Link Control (RLC) Segmentation of RLC SDU (Service Data unit) into RLC PDU (Packet Data Unit) Retransmission of erroneous PDU Removal of Duplicate PDUs In Sequence delivery of SDUs to upper layers RLC PDU size varies dynamically according to scheduler (higher PDU size for high data rate => less overhead)
Medium Access Control Downlink Logical and Transport Channels RLC MAC{ PHY
Medium Access Control (2) Downlink Logical Channels The Broadcast Control Channel (BCCH): transmission of system information. The Paging Control Channel (PCCH): paging of terminals whose location on a cell level is not known to the network. The Common Control Channel (CCCH) : transmission of control information in conjunction with random access. The Dedicated Control Channel (DCCH): transmission of control information to/from a terminal. The Multicast Control Channel (MCCH): transmission of control information required for reception of the MTCH. The Dedicated Traffic Channel (DTCH): transmission of user data to/from a terminal. The Multicast Traffic Channel (MTCH): downlink transmission of MBMS services.
Medium Access Control (3) Downlink Transport Channels The Broadcast Channel (BCH) : transmission of parts of the BCCH system information, more specifically the so-called Master Information Block (MIB) The Paging Channel (PCH): transmission of paging information from the PCCH logical channel. The Downlink Shared Channel (DL-SCH) is the main transport channel used for transmission of downlink data in LTE. It supports key LTE features such as dynamic rate adaptation and channel dependent scheduling, hybrid ARQ with soft combining, and spatial multiplexing. There can be multiple DL-SCHs in a cell, one per terminal scheduled in this TTI, and, in some subframes, one DL-SCH carrying system information. The Multicast Channel (MCH) is used to support MBMS.
Medium Access Control (4) Uplink logical and Transport Channels
Medium Access Control (5) MAC Header and SDU Multiplexing To each RLC PDU there is associated Sub-header contains the identity of logical channel Mac Control Elements is used for inband control signaling (e.g. Timing Advance, Random Access response, etc)
Medium Access Control (6) MAC Multiplexing Functionality Carrier Aggregation is invisible to PDCP and RLC Logical Channels are multiplexed to form one transport block per component carrier
Medium Access Control (7) Scheduling Controls the assignment of DL/UL resource in terms of Radio-block Pairs (time frequency unit of 1ms times 180Khz) The enodeb every 1ms takes a scheduling decisions and sends scheduling information to terminals Coordinated scheduling decision is supported using the X2 Interface. Also Interference Coordination is part of the scheduler Transport format selection (transport block size, modulation and antenna mapping)
Medium Access Control (8) Hybrid ARQ with Soft Combining
Physical Channels Overview The Physical Downlink Shared Channel (PDSCH) : unicast data transmission, and transmission of paging information. The Physical Broadcast Channel (PBCH) carries part of the system information The Physical Multicast Channel (PMCH) is used for MBSFN operation. The Physical Downlink Control Channel (PDCCH) is used for downlink control information, mainly scheduling decisions and for scheduling grants enabling transmission on the PUSCH. The Physical Hybrid-ARQ Indicator Channel (PHICH) carries the hybrid-arq acknowledgement. The Physical Control Format Indicator Channel (PCFICH) Per carrier information necessary to decode the set of PDCCHs. The Physical Uplink Shared Channel (PUSCH) is the uplink counterpart to the PDSCH. The Physical Uplink Control Channel (PUCCH) is used by the terminal to send hybrid-arq, to send channel-state reports, and for requesting resources to transmit uplink data upon. The Physical Random-Access Channel (PRACH) is used for random access.
Control Plan protocols NAS control plan functionality (MME) EPS bearer management Authentication Security Idle Mode procedures IP address assignment RRC in the enodeb (transmitted using SRBs) Broadcast System information Transmission of Paging messages Connection Management Mobility Functions Measurement Configuration and Reporting Handling of UE Capabilities
Control Plan protocols (State Machines) Two states for the Terminal RRC_Connected Cell is known Each terminal has identifieer (C-RNTI) Data Transfer with/without DRX Two states: IN_SYNC, OUT_OF_SYNC (Uplink synchronization) RRC_Idle Terminal Periodically wake up to receive Paging Messages
Thank You (selgohari@ieee.org)