Long Term Evolution Protocols © Tata Consultancy Services Ltd

Objective LTE Protocol stack Layer functionalities Frame structure and Resource blocks of LTE Channel Mapping between Layers Transmission Parameters supports in LTE

LTE Protocol LTE protocol stack for User Equipment (UE). - 3 -

Physical Layer Takes care of Power control ,cell search for initial synchronization and handover - 4 -

=1ResourceElement(RE) Physical Resource Blocks in LTE OFDM Symbols 1 2 3 4 . 11 12 5 6 1Frame = 10 subframes 1 Subframe = 2 slots Subcarriers 1slot has 6<= RBs <=100 12 Subcarriers x 7symbos = 1 Resource Block (RB) 1 Subcarrier x 1 Symbol =1ResourceElement(RE) 1 frame = 10 subframes 1 subframe = 2 Slots 1 slot has 6 <= RBs <= 100 12 Subcarriers x 7 symbols = 1 Resource Block (RB) 1 Subcarrier x 1 Symbol = 1 Resource Element - 5 -

LTE Transmission Parameters Values Bandwidth (MHz) 1.4 3 5 10 15 20 Subframe duration 1ms Subcarrier spacing 15kHz Usable subcarriers 72 180 300 600 900 1200 Resource blocks 6 25 50 75 100 OFDM symbols for time slot 7 (normal CP) or 6 (extended CP) Modulation schemes BPSK or QPSK (signaling) QPSK, 16QAM or 64 QAM (data) Coding schemes 1/3 Convolutional (PDCCH) 1/3 Turbo (data and LTE messaging) - 6 -

Signals Cell-specific Reference Signals Synchronization Signals Demodulation Reference Signals There is one reference signal transmitted per downlink antenna port. The number of downlink antenna ports equals 1, 2, or 4. 504 unique physical cell identities. Uplink reference signals for channel estimation for coherent demodulation - 7 -

MAC Layer The main services and functions of the MAC(Medium Access Control): Mapping between logical channels and transport channels. - scheduling information reporting. - Error correction through HARQ. - Priority handling between UEs by means of dynamic scheduling. A general classification of logical channels is into two groups: - Control Channels (for the transfer of control plane information); - Traffic Channels (for the transfer of user plane information). - 8 -

RLC Layer The main services and functions of the RLC(Radio Link Control) : - Error Correction through ARQ. - Concatenation, segmentation and reassembly of RLC SDUs - Duplicate detection. - Protocol error detection. - 9 -

RLC Modes of Operation Modes of Operation Acknowledged Transparent (AM) Transparent (TM) Unacknowledged (UM) - 10 -

RLC Layer contd… - 11 -

PDCP Layer The main services and functions of the PDCP(Packet Data Converge Control): - Header compression and decompression: ROHC only. - Transfer of user data. -- Retransmission of PDCP SDUs at handover for RLC AM. - Ciphering and Integrity Protection. - Transfer of control plane data. - 12 -

PDCP Layer contd… - 13 -

RRC Layer The main services and functions of the RRC(Radio Resource Control): Broadcast of System Information Paging Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN including - Allocation of temporary identifiers between UE and E-UTRAN Configuration of signalling radio bearer(s) for RRC connection - mobility. - Handover; -UE cell selection and reselection and control of cell selection and reselection. Notification for MBMS services. services. - QoS management functions. - UE measurement reporting and control of the reporting. - 14 -

Layer Functionalities The RRC layer controls the lower layers in both eNB and UE, and the lower layers provide Feedback to the RRC Initiate Security Activation RRC PDCP RLC MAC PHY Configure RLC mode for DRBs Configure logical channel priorities Configure HARQ Parameters - 15 -

Radio Protocol Architecture Radio protocol architecture 2 types . User Plane Control Plane - 16 -

User Plane User plane protocol stack between UE and e-NodeB - 17 -

User Plane contd.. User Plane consists of PDCP,RLC,MAC layers Packets received by a layer are called Service Data Unit (SDU) Output of a layer is referred to by Protocol Data Unit (PDU) - 18 -

Control Plane Control Plane Between UE and MME - 19 -

Control Plane contd.. Control plane handles radio –specific functionality which depends on the state of mobile. Control plane includes RRC layer –responsible for configuring lower layers - 20 -

Interfaces - 21 -

Interfaces contd… The application layer signaling protocol S1 Application Protocol (S1AP) provides signaling services between the eNB and MME. The application layer signaling protocol X2 Application Protocol (X2AP) provides signaling services between two eNBs. The SCTP is added on top of IP for reliable transport of application layer messages. - 22 -

Stream Control Transmission Protocol (SCTP) Multi-Streaming Reliable Transmission SCTP Functions Multi-homing Message Oriented Ordered Delivery within a Stream Flow Control and Congestion Control - 23 -

S1 Application Protocol (S1AP) E-RAB Management Context Management NAS Transport Initial UE message Downlink&Uplink NAS Transport Paging Handover Signaling Path Switch Request eNB Status Transfer MME Status Transfer - 24 -

Non-Access Stratum (NAS) The NAS sub layer between the UE and the MME is transparent to the eNB. . The NAS layer takes care of two areas. 1) It handles all the procedures related to registration ,authentication and security procedure,paging procedure and mobility management of a UE 2) Session management includes creation, deletion and modification of both default and dedicated EPS bearers. - 25 -

Non-Access Stratum (NAS) contd… NAS Functions EPS Mobility Management Attach, Detach, Tracking Area Update Authentication and Security Procedures Paging Procedures EPS Session Management Default Bearer Establishment Dedicated Bearer Establishment Bearer Management - 26 -

NAS Transport MME NAS NAS Initial UE msg RRC RRC S1AP S1AP SRB1 Piggybacked to RRCConnectionSetupComplete DL NAS Transport S1-MME Bearer - 27 -

X2 Application Protocol (X2AP) Mobility Management: Start or cancel a handover, forward user plane data, transfer PDCP SN status and release UE context. Load Management: Indicate resource status, provide interference and load coordination between neighbor eNBs. The knowledge of neighbor eNB load status helps efficient scheduling. eNB Configuration Update Application level configuration data needed for two eNBs General Error Situation Report - 28 -

X2 Application Protocol (X2AP) Functions Mobility Management Handover Request & cancel SN Status Transfer UE Context Release eNB Configuration Update Load Management/Indication Resource Status Request Reporting of General Error Error Indication - 29 -

GTP (GPRS Tunneling Protocol) - 30 -

GTP contd.. used to encapsulate user data when passing through core network and also carries bearer specific signalling traffic between various core network entities - 31 -

Overview of Lte Protocol stack - 32 -

Life of packet - Downlink - 33 -

Summary Lte protocol stack contains Physical ,MAC,RLC,RRC,PDCP ,AS,NAS sub layers. Physical layer carries all the information from MAC transport channels over the interface. MAC layer is responsible for mapping between the logical channels and transport channels. RLC is responsible for error correction through ARQ RRC main service for broadcast system information related to the non- access startum(NAS). PDCP responsible for header compression and decompression of data - 34 -

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