LTE Radio Interface - • Overview of OFDMA SC-FDMA • LTE Frame Structure • LTE Resource Grid • LTE Bandwidth/Resource Configuration • LTE Channels •

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  • LTE Radio Interface

  • Agenda

    Overview of OFDMA & SC-FDMA

    LTE Frame Structure

    LTE Resource Grid

    LTE Bandwidth/Resource Configuration

    LTE Channels

    LTE Protocol Architecture

  • User 1 User 2 User 3 User ..

    Overview of Radio Technologies

    f

    t

    TDMA

    Time Division

    t

    CDMA

    Code Division

    f

    OFDMA

    Frequency Division Orthogonal subcarriers

    f

    t

    f

    t

    FDMA

    Frequency Division

    Each user has a unique frequency

    All users transmit at the same time

    AMPS, NMT, TACS

    Each user has a unique timeslot

    Several users share the same frequency

    IS-136, GSM, PDC

    Each channel has a unique code

    Several users share the same frequency & time

    IS-95, CDMA2000, WCDMA

    Each user and channel has a unique time and frequency allocation

    Users are separated in frequency and/or time

    LTE, Wimax, 802.11

  • f0 f1 f2 f3 f4

    OFDM carriers

    n = 1,0,1,2. f = f + nf = f + n 1 n 0 s 0 T s

    OFDM carriers have no Adjacent Carrier Interference (ACI)

  • FDM vs OFDM Po

    wer

    Den

    sity

    Pow

    er D

    ensi

    ty

    Frequency (f/fs) Frequency (f/fs)

    Saved Bandwidth

    Compared to conventional FDM, OFDM allows orthogonal sub- carriers to overlap tightly

  • OFDM vs OFDMA

    OFDM allocates users in the time domain only

    OFDMA allocates users in the time and frequency domains

  • UL Allocation (SC-FDMA)

  • OFDMA vs SC-FDMA

    User 1

    User 2

    User 3

    User 1

    User 2

    User 3

    Sub-carriers

    TTI: 1ms

    Frequency

    System Bandwidth

    Sub-band12Sub-carriers Time User 1

    User 2

    User 3

    TTI: 1ms

    Frequency

    Time

    With OFDMA, the subcarriers are shared among multiple users. This results in: Different spectrum bandwidths can be utilized without impacts on system design. Transmission resources of variable bandwidth can be allocated to different users and scheduled freely in the frequency domain. Fractional frequency re-use and interference coordination between cells are facilitated.

    System Bandwidth

    With SC-FDMA, each user is assigned part of the system bandwidth

    SC-FDMA has a significantly lower PAPR, providing the advantages of multicarrier technology without excessive cost for the mobile terminal transmitter, while retaining a reasonable degree of commonality between uplink and downlink technologies.

    Sub-carriers

    Sub-band12Sub-carriers

    User 1

    User 2

    User 3

    User 1 User 2 User 3

    User 1 User 2

    User 3

  • Advantages Support flexible bandwidth operation Support FDD (Frequency Division Duplex), TDD (Time Division Duplex), and

    half duplex FDD mode (HD-FDD) Frequency Diversity Support MIMO Disadvantages Sensitivity to Doppler Overhead High PAPR; in UL, SCFDMA has much lower PAPR (Peak to Average Power

    Ratio) than OFDM

    OFDMA & SC-FDMA

  • Agenda

    Overview of OFDMA & SC-FDMA

    LTE Frame Structure

    LTE Resource Grid

    LTE Bandwidth/Resource Configuration

    LTE Channels

    LTE Protocol Architecture

  • LTE Frame Structure Two radio frame structures

    defined. Frame structure type 1 (FS1): FDD. Frame structure type 2 (FS2): TDD.

    A radio frame has duration of 10 ms.

    A resource block (RB) spans 12 subcarriers over a slot duration of 0.5 ms.

    One subcarrier has bandwidth of 15 kHz, thus 180 kHz per RB.

    TDD Frame

    FDD Frame

  • TYPE 1 FDD FRAME STRUCTURE

    Symbol Time = 66.7 sec

  • TYPE 2 - TDD Frame Structure

  • TDD Frame Configurations

    D = Downlink Subframe U = Uplink Subframe S = Special Subframe

    Uplink- downlink

    configuration

    Downlink-to-Uplink Switch-point periodicity

    Subframe number

    0 1 2 3 4 5 6 7 8 9

    0 5 ms D S U U U D S U U U

    1 5 ms D S U U D D S U U D

    2 5 ms D S U D D D S U D D

    3 10 ms D S U U U D D D D D

    4 10 ms D S U U D D D D D D

    5 10 ms D S U D D D D D D D

    6 5 ms D S U U U D S U U D

  • CYCLIC PREFIX INSERTION

  • FDD/TDD Summary

  • Agenda

    Overview of OFDMA & SC-FDMA

    LTE Frame Structure

    LTE Resource Grid

    LTE Bandwidth/Resource Configuration

    LTE Channels

    LTE Protocol Architecture

  • LTE Resource Grid

  • SUB-CARRIER TYPES

    DC Subcarriers

    Guard Subcarriers

    Data Subcarriers

    Reference Signals

  • Agenda

    Overview of OFDMA & SC-FDMA

    LTE Frame Structure

    LTE Resource Grid

    LTE Bandwidth/Resource Configuration

    LTE Channels

    LTE Protocol Architecture

  • CHANNEL BANDWITH vs BANDS

    Source: 3GPP TS 36.101 version 10.7.0 Release 10

  • Bandwidth vs RBs LTE physical layer supports any bandwidth

    from 1.4 MHz to 20 MHz in steps of 180 kHz (resource block)

    Current LTE specification supports a subset of 6 different system

    All UEs must support the maximum bandwidth of 20 MHz

    Source: 3GPP TS 36.101 version 10.7.0 Release 10

  • BANDWIDTH vs SUBCARRIERS

  • LTE Frame and Bandwith

  • Adaptive Modulation Coding

  • Maximum Data Rate

    2X2 and 4X4 MIMO would provide higher data rate

    Channel Bandwith (MHz)

    1.4 3 5 10 15 20

    Data Sub-carriers 72 180 300 600 900 1,200

    Symbols per Slot (0.5 msec)

    6 6 6 6 6 6

    Symbols per Second (per Sub-carrier)

    12,000 12,000 12,000 12,000 12,000 12,000

    QPSK (max = 2 bits per Symbol) Mbps

    1.73 4.32 7.20 14.40 21.60 28.80

    16QAM (max = 4 bits per Symbol) Mbps

    3.46 8.64 14.40 28.80 43.20 57.60

    64QAM (max = 6 bits per Symbol) Mbps

    5.18 12.96 21.60 43.20 64.80 86.40

  • Agenda

    Overview of OFDMA & SC-FDMA

    LTE Frame Structure

    LTE Resource Grid

    LTE Bandwidth/Resource Configuration

    LTE Channels

    LTE Protocol Architecture

  • LTE Physical Channels DL

    Physical Broadcast Channel (PBCH): Carries system information for cell search, such as cell ID. Physical Downlink Control Channel (PDCCH) : Carries the resource allocation of PCH and DL-SCH, and

    Hybrid ARQ information. Physical Downlink Shared Channel (PDSCH) : Carries the downlink user data. Physical Control Format Indicator Channel (PCFICH) : Carriers information of the OFDM symbols

    number used for the PDCCH. Physical Hybrid ARQ Indicator Channel (PHICH) : Carries Hybrid ARQ ACK/NACK in response to uplink

    transmissions. Physical Multicast Channel (PMCH) : Carries the multicast information. Reference Signal (RS) Synchronization Signal (P-SS and S-SS)

    UL Physical Random Access Channel (PRACH) : Carries the random access preamble.

    Physical Uplink Shared Channel (PUSCH) : Carries the uplink user data. Physical Uplink Control Channel (PUCCH) : Carries the HARQ ACK/NACK, Scheduling Request (SR) and Channel Quality Indicator (CQI), ... Uplink Reference Signal

    Physical channels determine how data is processed and then mapped

    via dynamical scheduling onto resource blocks.

  • LTE Physical Channels DL

    Physical Broadcast Channel (PBCH): Carries system information for cell search, such as cell ID. Physical Downlink Control Channel (PDCCH) : Carries the resource allocation of PCH and DL-SCH, and

    Hybrid ARQ information. Physical Downlink Shared Channel (PDSCH) : Carries the downlink user data. Physical Control Format Indicator Channel (PCFICH) : Carriers information of the OFDM symbols

    number used for the PDCCH. Physical Hybrid ARQ Indicator Channel (PHICH) : Carries Hybrid ARQ ACK/NACK in response to uplink

    transmissions. Physical Multicast Channel (PMCH) : Carries the multicast information. Reference Signal (RS) Synchronization Signal (P-SS and S-SS)

    UL Physical Random Access Channel (PRACH) : Carries the random access preamble.

    Physical Uplink Shared Channel (PUSCH) : Carries the uplink user data. Physical Uplink Control Channel (PUCCH) : Carries the HARQ ACK/NACK, Scheduling Request (SR) and Channel Quality Indicator (CQI), ... Uplink Reference Signal

    Physical channels determine how data is processed and then mapped

    via dynamical scheduling onto resource blocks.

  • DL Reference Signals (RS) DL Reference Signals

    Used for downlink physical channel demodulation and channel quality measurement (CQI)

    Cell-Specific Reference Signals are generated from cell-specific RS sequence and frequency shift mapping.

    The frequency interval of RS is 6 subcarriers. RS distributes discretely in the time-frequency

    domain, sampling the channel situation which is the reference of DL demodulation.

    RS distribution leads to accurate channel estimation, at the cost of high overhead and reduced system capacity.

    Used for coherent demodulation in the UE channel-quality measurements for scheduling measurements for mobility

  • Synchronization Signals: used for time-frequency synchronization between UE and E-UTRAN during cell search procedure. synchronization signal comprise two parts:

    Primary Synchronization Signal (P-SS), used for symbol timing, frequency synchronization and part of the cell ID detection.

    Secondary Synchron