LTE systems: overview

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1 LTE systems: overview Luca Reggiani LTE overview 1

2 Outline 1. Standard status 2. Signal structure 3. Signal generation 4. Physical layer procedures 5. System architecture 6. References LTE overview 2

Standard status 1/1 Long Term Evolution Release 8: Dec. 2009 www.3gpp.

3 Standard status 1/1 Long Term Evolution Release 8: Dec GPP - Series 36: RF processing aspects Physical layer [layer 1] MAC, RRC [layer 2,3] 1xx 2xx 3xx Peak rate: 150, 300 Mbps (MIMO Downlink), 75 Mbps (Uplink) LTE overview 3

4 Signal structure 1/3 FDD (Half or Full duplex): (time)frame structure 1 TDD: (time)frame structure 2 Bandwidths: MHz Carriers for FDD and TDD: several bandwidths in MHz, 1.4 GHz, GHz, GHz Downlink resource allocation: OFDMA x frame Uplink resource allocation: SC-OFDM x frame The downlink and uplink (time, frequency) grids are composed by resource blocks of 12 sub-carriers (frequency spacing of 15 khz 180 khz) x 0.5 ms, equal to 1 (time)slot. A user is assigned a rectangular set of resource blocks. LTE overview 4

5 Signal structure Downlink / Uplink Frame - FDD 2/3 Radio frame 1 = 10 ms Subframe Slot number resource block (RB).. N subcarriers.. resource element = 1 sub-carrier x 1 OFDMA symbol time LTE overview 5

6 Signal structure Downlink / Uplink Frame - TDD 3/3 Subframe Radio frame 2 = 2 half-frames = 2 x 5 ms Slot number 0 1 resource block (RB) resource element = 1 sub-carrier x 1 SC-OFDM symbol time Several uplink/downlink divisions of subframes N subcarriers Subframe number 0 DwPTS, GP, UpPTS 4 9 DwPTS, GP, UpPTS.. LTE overview 6

7 Signal generation Downlink OFDMA 1/2 Main operations for downlink signal generation (multiple antennas) Encoding Scrambling Modulation Element mapper OFDM modulator.. Layer mapper Precoder.. Encoding Scrambling Modulation Element mapper OFDM modulator LTE overview 7

8 Signal generation 2/2 Encoding Channels UL-SCH, DL-SCH (UL-, DL- Shared) PCH (Paging), MCH (Multicast) BCH (Broadcast) Code Turbo parallel code, R = 1/3 Tailbiting convolutional code, R = 1/3 Modulation: QPSK, 16-QAM, 64-QAM LTE overview 8

9 Physical layer procedures 1/1 Synchronization Power control Random access Cell search Timing Downlink: Uplink: energy per resource element average power over an SC-FDMA symbol Reporting of several measurements / indicators: e.g. channel quality indication (CQI) Link adaptation: AMC (adaptive modulation and coding). LTE overview 9

10 System architecture 1/5 Network MME / S-GW MME / S-GW enb #1 UE E-UTRAN: enbs providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol for the UEs. enb #1 enb #2 UE enbs are interconnected with each other by means of X2 interface. enbs are connected by means of the S1- MME interface to the MME (Mobility Management Entity) and to the Serving Gateway (S-GW) by means of the S1-U (EPC, Evolved Packet Core). LTE overview 10

11 System architecture 2/5 Protocol stack enb MME Inter cell RRM NAS security RBC CMC Idle state mobility RAC Measurements EPS BC UE PDCP RLC MAC PHY Scheduler RRC PDCP RLC MAC PHY Layer 3 Layer 2 Layer 1 S-GW Mobility P-GW UE IP address allocation Packet filtering LTE overview 11

12 System architecture 3/5 Main functions enb downlink MME) Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility, Control, Dynamic allocation of resources to UEs in both uplink and (scheduling); Routing of User Plane data towards Serving Gateway; Scheduling and transmission of paging, broadcast and ETWS messages (originated from the Measurement and reporting configuration for mobility and scheduling; RRC sublayer Broadcast of System Information related to the non-access stratum (NAS) or access stratum (AS); Paging; Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN Security functions including key management; Establishment, configuration, maintenance and release of point to point Radio Bearers; Mobility functions including handover; QoS management functions; UE measurement reporting and control of the reporting; RLC sublayer Error Correction through ARQ, concatenation, segmentation and reassembly of RLC SDUs Protocol error detection and recovery; LTE overview 12

13 System architecture 4/5 Network MME NAS signalling; Inter CN node signalling for mobility between 3GPP access networks; Idle mode UE Reachability (including control and execution of paging retransmission); MME selection for handovers with MME change; Roaming; Authentication; Bearer management functions including dedicated bearer establishment; Support for ETWS message transmission. Serving Gateway (S-GW) The local Mobility Anchor point for inter-enb handover; Mobility anchoring for inter-3gpp mobility; Lawful Interception; Packet routing and forwarding; PDN Gateway (P-GW) Per-user based packet filtering (by e.g. deep packet inspection); Lawful Interception; UE IP address allocation; LTE overview 13

14 System architecture 5/5 RRM The purpose of radio resource management (RRM) is to ensure the efficient use the available radio resources. It includes Radio Bearer Control (RBC) Radio Admission Control (RAC) Connection Mobility Control (CMC) Dynamic Resource Allocation (DRA) - Packet Scheduling (PS) Inter-cell Interference Coordination (ICIC) Load Balancing (LB) LTE overview 14

15 References [1] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; General description". [2] 3GPP TS :"Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation " [3] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding" [4] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures" [5] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Services provided by the physical layer" [6] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio access capabilities" [7] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Acces Control (MAC) protocol specification" [8] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) protocol specification" [9] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification" [10] 3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC) protocol specification". LTE overview 15

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