Ee359 lecture 19 outline
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EE359 – Lecture 19 Outline. Announcements Final Exam Announcements HW 8 (last HW) due Friday 5pm (no late HWs) 10 bonus points for course evaluations online Projects due Dec. 6 Direct Sequence Spread Spectrum ISI and Inteference Rejection Spreading Codes and Maximal Linear Codes

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EE359 – Lecture 19 Outline

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Ee359 lecture 19 outline

EE359 – Lecture 19Outline

  • Announcements

    • Final Exam Announcements

    • HW 8 (last HW) due Friday 5pm (no late HWs)

    • 10 bonus points for course evaluations online

    • Projects due Dec. 6

  • Direct Sequence Spread Spectrum

  • ISI and Inteference Rejection

  • Spreading Codes and Maximal Linear Codes

  • Synchronization

  • RAKE Receivers

  • Multiuser Spread Spectrum


Final exam announcements

Final Exam Announcements

  • Final Friday, 12/13, 12:15-3:15

  • Covers Chapters 9, 10, 12, 13.1-13.2 (+ earlier chps)

  • Similar format to MT, but longer: open book, notes.

  • Practice finals posted next week(10 bonus points)

    • Turn in to Pat or Mainakfor solns, by exam for bonus pts

    • Course summary Dec 6 12:30-2:05 here ([email protected])

    • Final review (Mainak) : Mon 12/9, 6 pm to 7 pm?

    • OHs next 3 weeks:

      • Me: next MTW by appt, 12/2 9-10am, 12/6 2-3pm, 12/9 by appt, 12/12 6:30-7:30pm (pls confirm), 12/13 9-10am, Skype

      • Mainak: Please respond to Piazza poll (see last slide)


  • Review of last lecture fft implementation of ofdm

    cos(2pfct)

    cos(2pfct)

    LPF

    A/D

    D/A

    Serial

    To

    Parallel

    Converter

    x

    x

    +

    Review of Last LectureFFT Implementation of OFDM

    X0

    x0

    n(t)

    TX

    R bps

    Add cyclic

    prefix and

    Parallel

    To Serial

    Convert

    • Design Issues

      • PAPR, frequency offset, fading, complexity

      • MIMO-OFDM

      • Pulse shaping

        v

    QAM

    Modulator

    IFFT

    h(t)

    +

    Pulse

    shaping

    XN-1

    xN-1

    m=sTm/Tsamp

    RX

    Y0

    y0

    Remove

    cyclic

    prefix and

    Serial to

    Parallel

    Convert

    R bps

    QAM

    Modulator

    Parallel

    To Serial

    Convert

    FFT

    yN-1

    YN-1

    Yi=HiXi+ni


    Review of last lecture intro to spread spectrum

    Tc

    Review of Last Lecture:Intro. to Spread Spectrum

    • Modulation that increases signal BW to combat narrowband interference and ISI

      • Also used as a multiple access technique

    • Two types: Frequency Hopping and DSSS

      • FH:Hops info. signals over a wide bandwidth

      • DSSS: modulates info signal by chip sequence

    S(f)

    s(t)

    sc(t)

    Sc(f)

    S(f)*Sc(f)

    1/Tb

    1/Tc

    Tb=KTc


    Isi and interference rejection

    S(f)

    I(f)

    S(f)

    S(f)*Sc(f)

    I(f)*Sc(f)

    Despread Signal

    Receiver Input

    Info. Signal

    ISI and Interference Rejection

    • Narrowband Interference Rejection (1/K)

    • Multipath Rejection (Autocorrelation r(t))

    aS(f)

    S(f)*Sc(f)[ad(t)+b(t-t)]

    S(f)

    brS’(f)

    Despread Signal

    Receiver Input

    Info. Signal


    Maximal linear codes

    1

    -Tc

    Tc

    -1

    N

    Maximal Linear Codes

    • Autocorrelation determines ISI rejection

      • Ideally equals delta function

    • Maximal Linear Codes

      • No DC component

      • Large period (2n-1)Tc

      • Linear autocorrelation

      • Recorrelates every period

      • Short code for acquisition, longer for transmission

      • In SS receiver, autocorrelation taken over Tb

      • Poor cross correlation (bad for MAC)


    Synchronization

    1

    -Tc

    Tc

    -1

    2n-1

    Synchronization

    • Adjusts delay of sc(t-t) to hit peak value of autocorrelation.

      • Typically synchronize to LOS component

    • Complicated by noise, interference, and MP

    • Synchronization offset of Dt leads to signal attenuation by r(Dt)

    r(Dt)

    Dt


    Rake receiver

    x

    x

    x

    RAKE Receiver

    • Multibranch receiver

      • Branches synchronized to different MP components

    • These components can be coherently combined

      • Use SC, MRC, or EGC

    Demod

    sc(t)

    y(t)

    ^

    dk

    Diversity

    Combiner

    Demod

    sc(t-iTc)

    Demod

    sc(t-NTc)


    Multiuser dsss

    Multiuser DSSS

    • Each user assigned a unique spreading code; transmit simultaneously over same bandwidth

    • Interference between users mitigated by code cross correlation

    • In downlink, signal and interference have same received power

    • In uplink, “close” users drown out “far” users (a1>>a2: near-far problem)

    a

    a1

    a2

    a


    Main points

    Main Points

    • Spread spectrum increases signal bandwidth above that required for information transmission

      • Benefits include ISI and interference rejection, multiuser technique

    • DSSS rejects ISI by code autocorrelation

      • Maximal linear codes have good autocorrelation properties but poor cross correlation

    • Synchronization depends on autocorrelation properties of spreading code.

    • RAKE receivers combine energy of all MP

      • Use same diversity combining techniques as before


    Proposed days times for mainak s ohs final review and discussion

    Proposed days/times for Mainak’s OHs, final review, and discussion

    Please respond to

    Piazza poll on this

    proposal

    12/2 (8:30 am to 10:30 am): Discussion session for Homework 8 + Office hour (to replace Tuesday DH and Wednesday OH)

    12/6 (11 am to 12 noon): OH (instead of Thursday OH)

    12/9 (6 pm to 7 pm): Final review session

    12/10 (7 pm to 8 pm): Extra

    12/11 (7 pm to 8 pm): OH

    12/12 (7 pm to 8 pm): OH


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