3GPP Long Term Evolution LTE

Chapter 27 3GPP Long Term Evolution LTE Slides for Wireless Communications Edfors, Molisch, Tufvesson 630

Goals of IMT-Advanced Category 1 2 3 4 5 peak data rate DL / Mbit/s 10 50 100 150 300 max DL modulation 64 QAM 64 QAM 64 QAM 64 QAM 64 QAM peak data rate UL / Mbit/s 5 25 50 50 75 max UL modulation 16 QAM 16 QAM 16 QAM 16 QAM 64 QAM max no. layers for DL MIMO 1 2 2 2 4 Slides for Wireless Communications Edfors, Molisch, Tufvesson 631

Bands for FDD Operation Operating band UL DL ba nd w i d th 1.4 3 5 10 15 20 1 1920-1980 2110-2170 Europe, Asia 2 1850-1910 1930-1990 America 3 1710-1785 1805-1880 Europe, Asia 4 1710-1755 2110-2155 America 5 824-849 869-894 America 6 830-840 875-885 Japan 7 2500-2570 2620-2690 Europe, Asia 8 880-915 925-960 Europe, Asia 9 1750-1785 1845-1880 Japan 10 1710-1770 2110-2170 Americas 11 1428-1453 1476-1501 Japan 12 698-716 728-746 Americas 13 777-787 746-756 Americas 14 788-798 758-768 Americas 17 704-716 734-746 Americas Slides for Wireless Communications Edfors, Molisch, Tufvesson 632

Bands for TDD Operation Operating band band ba nd w i d th 1.4 3 5 10 15 20 33 1900-1920 Europe, Asia 34 2010-2025 Europe, Asia 35 1850-1910 36 1930-1990 37 1910-1930 38 2570-2620 Europe 39 1880-1920 China 40 2300-2400 Europe, Asia Slides for Wireless Communications Edfors, Molisch, Tufvesson 633

Network structure Slides for Wireless Communications Edfors, Molisch, Tufvesson 634

Key Physical Layer Aspects Downlink: OFDMA Uplink: DFT spread OFDMA or SC-FDMA MIMO: DL: 2-4 Tx antennas, 2-4 Rx antennas UL: 1 Tx antenna (or antenna selection), 2-4 Rx antennas Both SU-MIMO and MU-MIMO supported Modulation schemes: QPSK, 16QAM, and 64QAM In both downlink and uplink spread spectrum Slides for Wireless Communications Edfors, Molisch, Tufvesson 635

Frames, slots, and symbols Slot: 7 consecutive OFDMA symbols (0.5ms) 1 OFDMA symbol = 71.4 μs Sub-frame: 2 slots (1 ms) Frame: 20 slots (10 ms) Slot = 0.5 ms Most basic time unit T s = 1/ (2048*15) ms (30.72 MHz sample rate for 20 MHz, 2048 point FFT) CP LB#0 CP LB #1 CP LB #2 CP LB #3 CP LB #4 CP LB #5 CP LB#6 T CP = 160 T S 144 T S 66.7 μs = 2048 T S Normal cyclic prefix mode CP LB#0 CP LB#5 T CP = 512 T Extended cyclic prefix mode (e.g., MBSFN operation) S Slides for Wireless Communications Edfors, Molisch, Tufvesson 636

Uplink/Downlink Resource Grid N subcarriers RB sc UL RB N RB N sc subcarriers N UL symb One uplink slot Tslot SC-FDMA symbols k N Resource block N UL RB N UL symb RB sc N 1 RB sc resource elements Resource element ( k, l) Same numerology for both downlink and uplink One resource block = 6*12 = 84 resource elements (RE) 7 REs used for DM RS per slot Assignment: Resource blocks (contiguous or distributed subcarriers) UL l 0 l N symb 1 k 0 Slides for Wireless Communications Edfors, Molisch, Tufvesson 637

UL SC-FDMA Transmit Chain 0 d S/P M-point DFT Subcarrier mapping N-point IFFT P / S Add CP To DAC & RF 0 0 Can view M-point DFT also as spreading across subcarriers DFT-Spread FDMA Slides for Wireless Communications Edfors, Molisch, Tufvesson 638

Mapping to physical resources in DL Two-step procedure Map symbols onto virtual resource blocks (VRB) Map VRB onto physical resource blocks (PRBs) Mapping of PRB to VRB can be Continuous (for obtaining best channel) Distributed (for frequency diversity) Slides for Wireless Communications Edfors, Molisch, Tufvesson 639

LTE Uplink Reference Signals: 2 Types Data Mod Resource: One per slot for accurate estimates for demodulation Sounding RS: Once every 2-10ms. Occupies a larger bandwidth than data to enable BS to estimate frequency response over a large portion of system bandwidth 1. Data demodulation RS 2. Sounding RS Subcarrier 0 1 2 3 4 5 6 Data BW System BW Time Slides for Wireless Communications Edfors, Molisch, Tufvesson 640

Channel coding procedure Slides for Wireless Communications Edfors, Molisch, Tufvesson 641

Turbo Codes Generates long codewords by encoding data with two different convolutional encoders for each of the encoders, data are interleaved with different interleavers Slides for Wireless Communications Edfors, Molisch, Tufvesson 642

Turbo Codes A brief history of turbo codes: The turbo code concept was first introduced by C. Berrou in 1993, two French engineers (not mathematicians). Today, Turbo Codes are considered as the most efficient coding schemes for FEC Scheme with known components (simple convolutional or block codes, interleaver, soft-decision decoder, etc.) Performance close to the Shannon Limit (E b /N 0 = -1.6 db if R b 0) at modest complexity! With the advent of significant computer power, Turbo Codes have become the standard in wireless communications although LTE uses CRC, convolutional codes (used only for control information) in addition to Turbo Codes used for payload data

Turbo Codes: Encoder Data Source X Convolutional Encoder 1 Y 1 X Interleaving Convolutional Encoder 2 Y Y 2 (Y 1, Y2) X: Information Y i : Redundancy Information Copyright 2010, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 34

Turbo Codes: Decoder De-interleaving Y 1 Convolutional Decoder 1 Interleaver X Interleaving Convolutional Decoder 2 De-interleaving Y 2 X X : Decoded Information Copyright 2010, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 35

Turbo Codes Diagram Copyright 2010, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 36

Turbo Code Parameters LTE 1/3 rate Parallel Concatenated Convolutional Code (PCCC) Two 8-state constituent encoders: g 1 (D) = 1 + D + D 3 and g 0 (D) = 1 + D 2 + D 3 Internal interleaver based on Quadratic Permutation Polynomial (QPP) Contention-free property enables decoder parallelism LDPC codes are not used in LTE Slides for Wireless Communications Edfors, Molisch, Tufvesson 643

Space-Time Coding in LTE 2 transmit antennas: (0) y (2i) (1) y (2i) (0) y (2i 1) (1) y (2i 1) 1 2 1 0 0 1 0 1 1 0 j 0 0 j 0Re x j Re x jim x 0 Im x (0) (1) (0) (1) ( i) ( i) ( i) ( i) 4 transmit antennas: Similar mapping over 4 symbols real and imaginary parts Slides for Wireless Communications Edfors, Molisch, Tufvesson 644

Spatial Multiplexing in LTE Vertical encoding Up to 4 layers (streams) and up to 2 code words Codeword 1 Layer 1 Codeword 1 Layer 1 Layer 2 Codeword 2 Layer 2 Various options Codeword 1 Codeword 2 Layer 1 Layer 2 Layer 3 Layer 4 Codeword 1 Layer 1 Layer 2 Codeword 2 Layer 3 for spatial multiplexing in LTE Slides for Wireless Communications Edfors, Molisch, Tufvesson 645

Precoding MIMO in LTE 2 antennas 1 layer: 4 choices 2 layers: 3 choices 4 antennas Codebook not shown Up to 16 choices Codebook index 0 1 2 Number of layers 1 2 1 1 2 1 1 1 2 1 1 1 2 j 1 1 2 0 1 1 2 1 3 1 1-2 j 1 1 2 j 0 1 1 1 1 j Precoding codebook for 2 antennas (1 and 2 layers) Slides for Wireless Communications Edfors, Molisch, Tufvesson 646

Physical channels Traffic channels Dedicated Traffic Channel (DTCH) carries the user data for all uplinks, as well as for those downlink data that are not multicast/broadcast. - Multicast Traffic Channel (MTCH): carries the user data for multicast/broadcast downlink transmission Control channels Broadcast Control Channel (BCCH): carries system information data that are broadcast to the MSs in a cell Paging Control Channel (PCCH): pages MSs in multiple cells Common Control Channel (CCCH): transmits control data for the random access, Dedicated Control Channel (DCCH): is used for the transmission of control information that relates to a specific MS Multicast Control Channel (MCCH) Slides for Wireless Communications Edfors, Molisch, Tufvesson 647

Mapping of physical channels to transport channel Slides for Wireless Communications Edfors, Molisch, Tufvesson 648

Handover Handover preparation Source BS configures measurements the MS has to do; MS sends results to BS, BS makes handover decision and sends request to target BS, target BS makes admission control and (if positive) sends signal to source BS Handover execution Source BS sends handover command to MS, MS synchronizes itself with target BS, MS sends handover confirm to target BS Handover completion Target BS sends path switch message to Mobility Management Entity; serving gateway switches all routes from source BS to target BS; source BS releases resources Slides for Wireless Communications Edfors, Molisch, Tufvesson 649