Introduction to WCDMA and WCDMA Dimensioning for to WCDMA and WCDMA...Introduction to WCDMA and...

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Transcript of Introduction to WCDMA and WCDMA Dimensioning for to WCDMA and WCDMA...Introduction to WCDMA and...

  • 1

    Introduction to WCDMA and

    WCDMA Dimensioning for UMTS

  • 2

    Third generation services2M

    384K

    64K

    32K

    16K

    9.6K

    2.4K

    1.2K

    point to point multipoint

    bidirectional unidirectional multicast

    video

    conference

    video

    conference

    remote

    medical

    service video

    catalogue

    shopping

    video

    on

    demand

    mobile

    TV

    inte

    rn

    et

    telephone

    conference

    telephone

    voice

    mail

    electronic

    newspaper ISDN

    electronic

    publishing

    FAX

    distribution

    services

    (data)

    mobile

    radio

    distribution

    services (voice)

    pager

  • 4

    UTRAN (UMTS Terrestrial Radio Access

    Net) Architecture

    Core Network

    RNC RNC

    Site Contr

    BTS BTS BTS

    Site Contr

    BTS BTS BTS

    Site Contr

    BTS BTS BTS

    Site Contr

    BTS BTS BTS

    RNS

    UTRAN

    RNS

    Iub IubIub Iub

    Iur

    IuIu

    B-node B-node B-node B-node

  • 5

    Access techniques for mobilecommunications

    P - Power

    T - Time

    F - Frequency

    P

    T

    P

    T

    F

    P

    T

    F

    FDMA (TACS)

    TDMA,FDMA (GSM)

    CDMA (UMTS)

    F

  • 6

    W-CDMA (Wide Band CDMA)

    Key features

    Improved capacity and coverage (over second generation); thus, backward compatible

    High degree of service flexibility: multiple, parallel services per connection; efficient pkt access

  • 7

    Basics of Spread Spectrum

    and CDMA

  • 8

    Overview

    Why consider Spread Spectrum ?

    What is Spread Spectrum & CDMA ?

    Frequency Hopping Spread Spectrum

    Impact of channel

    Current systems

    Direct Sequence Spread Spectrum

    Spreading Codes

    Analytical Performance Model

    Rake Processing

    Near Far Effect (Power Control)

    Handover

  • 9

    Why Consider Spread Spectrum ?

    Spread Spectrum has been adopted as the air

    interface standard for 3rd Generation Mobile

    Systems (IMT2000):

    Europe (ETSI): UMTS (W- CDMA )

    Japan (ARIB): Wideband CDMA

    USA (TIA TR45. 5) CDMA 2000

    2nd Generation standard deployed in US and Korea

    IS95 (Qualcomm CDMA)

  • 10

    What is spread spectrum?

    Narrow Band

    Message

    Narrow Band

    Message

    Wideband

    Message

  • 11

    Frequency Hopping Spread

    Spectrum

  • 12

    Classification of Spread Spectrum

    Systems

    Frequency Hopping (FH)

    Narrow band message signal is

    modulated with a carrier frequency which

    is rapidly shifted . The hop frequency is

    indicated by a spreading function.

    This spreading function is also available

    at the receiver and enables it to retune to

    the correct channel for each hop.

  • 13

    Hop rates in an FH system

    Fast frequency hopping

    Data symbol spread over several hop frequencies

    Symbol diversity

    Very resistant to jamming and interference, often used in military systems

    Slow frequency hopping

    Several data symbols on each hop frequency

    Codeword diversity with interleaving

    Less complex

  • 14

    Direct Sequence Spread

    Spectrum

  • 15

    Classification of Spread Spectrum

    Systems

    Direct Sequence (DS)

    Secondary modulation in the form of pseudo-

    noise is applied to an already modulated

    narrowband message, thereby spreading the

    spectrum.

    At the receiver, the incoming waveform is

    multiplied by an identical synchronized

    spreading waveform in order to recover the

    message.

  • 16

    Direct sequence spread spectrum

    D(t)

    C(t)fc fc C(t)

    S(t)

    Narrow Band

    Message Narrow Band

    Message

    Wide Band

    Pseudo Random

    Noise

    Up conversion

    To fixed carrier

    frequency

    Down

    conversionWide Band

    Pseudo Random

    Noise

  • 17

    Data

    Signal

    Code

    Signal

    Multiplication

  • 18

    Spreading codes

    Maximal length sequences

    good auto- and cross- correlation

    Gold codes and Kasami sequences are

    derived from M- sequences with similar

    correlation properties, and a larger code

    set.

  • 19

    Orthogonal spreading Codes

    Walsh and Hadamard sequences

    zero correlation between codes when aligned

    cross- correlation non- zero when time shifted

    fixed spreading factor (codes of different length are not orthogonal)

    Orthogonal Variable Spreading Factor (OVSF) codes

    permit orthogonal codes for different rate services

    Both types of code lose orthogonality when shifted due to channel dispersion

    e. g. 40% loss of orthogonality in a large macrocell

  • Orthogonal Variable Spreading Factor

    c4,1

    = (1,1,1,1)

    c2,1 = (1,1)

    c4,2 = (1,1,-1,-1)

    c4,3 = (1,-1,1,-1)c2,2 = (1,-1)

    c4,4 = (1,-1,-1,1)

  • 21

  • 22

  • 23

  • 24

    DS-SS Application for CDMA

    Mod.

    g1(t)

    S1(t)

    Coswt

    S1(t)g1(t)

    S2(t)g2(t)

    g1(t)

    SN(t)gN(t)

    X1(t)

  • 25

    Theoretical CDMA capacity

    DS- CDMA capacity is inversely proportional to the energy per bit per noise power density which is tolerated

    A standard DS- CDMA system is interference limited by

    - intra- cell interference

    - Therefore increase capacity by:

    - voice activity detection

    - antenna sectorisation

    - adaptive antennas

    - interference cancellation

  • 26

    The Multipath Environment

    The received signal

    is made up of a sum

    of attenuated, phase-

    shifted and time

    delayed versions of

    the transmitted signal.

    Propagation modes

    include diffraction,

    transmission and

    reflection.

  • 27

    Path diversity in the multipath Path

    diversity

    Path diversity can be exploited by

    separating out the multipath components,

    co- phasing and summing them.

    Number of paths resolved (Lm) depends

    on the total multipath delay (Tm) and the

    chip period (Tc) Lm< Tm/Tc +1

  • 28

    RAKE Receiver

    One method of realising path diversity is with a RAKE and a bank of correlators

    tc tc tc

    Int. Int Int

    Diversity Combiner

    Out

    Put

    C(t) C(t-tc) C(t-LTc)

  • 29

    Diversity and diversity combinig

    Diversity: providing multiple versions of the transmitted signal. Commonly:

    multiple antennas

    multiple paths

    Diversity combining

    selection: best branch is chosen

    equal gain: equal combining: all branch summed

    maximal ratio: branches summed and weighted

    depending on their quality

  • 30

    The near-far effect in CDMA

    Everyone on same

    frequency at the same

    time.

    A MS close to the BS will drown out other MSs unless it reduces its power.

    Power control is required.

  • 31

    CDMA Power Control

    Power control required on uplink, desired on

    downlink.

    Open loop control can be used to remove shadowing (as the channel is reciprocal).

    Closed loop control is required to remove the

    fast fading

    BS receives MS signal and calculates the SIR

    BS sends MS a transmit power control (TPC)

    signal to increase or decrease its power

    TPC issues include rate and step size

  • 32

    Uplink closed loop power

    control algorithms

    Sigma- delta scheme used

    Command rate must be sufficient to track

    channel changes

    Trade- off in step size between tracking

    and accuracy

  • 33

    Handover and Mobility

    BS1 BS2

  • 34

    W-CDMA in UMTS

    W- CDMA is used in FDD mode in UMTS

    On the downlink it is possible to use orthogonal

    reading codes to reduce interference. A

    scrambling code is used to separate the cells

    On the uplink, low cross correlation codes are

    used to separate the mobiles. A single mobile

    can use multi-code transmission: each service is

    mapped onto several bearers, each of which is

    spread by an orthogonal code.

  • 35

    WCDMA Air Interface

  • 36

    RLCRLC

    LACLAC

    Radio Interface - protocol

    architecture

    RLC

    RRC

    LAC

    MAC

    Physical Layer

    L3

    L2/LAC

    L2/MAC

    L1

    C-plane U-plane

    Logicalchannels

    Transportchannels

    RLC

  • 37

    Layer 1 - up link physical

    channels

    (W-CDMA example)Data

    Pilot

    Dedicated PhysicalData Channel

    Dedicated PhysicalControl Channel

    Transmitpower control

    Transportformat ind.

    Slot#1Slot#2 Slot#i Slot#15

    Frame#1Frame#2 Frame#i Frame#72

    0.667 ms

    10 ms

    Feedbackindicator

  • 38

    Layer 1 - down link physical

    channels

    (W-CDMA example)

    Data

    Slot#1Slot#2 Slot#i Slot#15

    Frame#1Frame#2 Frame#i Frame#72

    Pilot TPC TFI

    DPCCH DPDCH

    frame

    superframe

    0.667 ms

    10 ms

  • 39

    Transport channels (example)

    Dedicated Channel (DCH): fast change of bit rate (10ms)fast power controlinherent MS addressing

    Random Access Channel (RACH) - up link: collisionopen loop power cont