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Vincent Savaux - Pilot-Aided and Blind Equalization in FBMC Modulation for PMR Networks

SCEE Team
February 12, 2015

Vincent Savaux - Pilot-Aided and Blind Equalization in FBMC Modulation for PMR Networks

SCEE Team

February 12, 2015
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  1. Pilot-Aided and
    Blind Equalization
    in FBMC Modulation
    for PMR Networks
    Séminaire SCEE
    CentraleSupélec,
    Campus de Rennes
    12 Février 2015
    Vincent Savaux

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  2. Outline
    • PMR Networks
    • FBMC Modulation Scheme
    • OFDM/OQAM
    • OFDM/OQAM
    • Pilot-Aided Estimation/Equalization
    • Blind Equalization

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  3. Foreword …
    What is the PROFIL project ?
    PROFIL: Evolution de la PROfessional Mobile Radio large bande basée sur la
    modulation FILter Bank MultiCarrier
    Evolution of the Wideband Professional Mobile Radio Based on the Filter
    Bank MultiCarrier Modulation
    • ANR Project with Cassidian, CEA-Leti, TeamCast and CentraleSupélec
    • CentraleSupélec’s part: Blind equalization in FBMC for PMR Networks

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  4. PMR Networks
    PMR : Professional Mobile Radio
    • Emergency Networks for police, firefighters, ambulances …
    • Transmission of 2G-like data
    TV GSM WiFi
    Currently:
    frequency
    380 - 395 MHz
    radio
    Standard TETRA -TETRAPOL
    TV GSM WiFi

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  5. PMR Networks
    • Specificities
    UL
    DL
    P to P
    mobility
    Narrowband channels

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  6. PMR Networks
    Goal: transmission of broadband signal in the 380 – 395 MHz band
    OFDM
    Low rate
    PMR
    Broadband PMR
    frequency
    Applications

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  7. FBMC Modulation Scheme
    x0,n
    SFB
    x1,n
    xm,n
    Transmission
    channel
    H
    w

    +
    +
    I
    F
    F PPN




    P/S
    AFB
    F
    F
    T
    PPN




    S/P

    y0,n
    y1,n
    ym,n
    - OFDM/OQAM Modem
    xm,n
    xM-1,n
    H

    +
    T


    T



    ym,n
    yM-1,n

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  8. FBMC Modulation Scheme
    Bellanger’s filter frequency response [1]:
    The subcarriers are orthogonal only in the real field

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  9. FBMC Modulation Scheme
    m
    m-1
    m+1
    n-1 n n+1 time
    m+1
    Surrounding interference part
    xm,n
    frequency
    The channel induces complex interferences from neighboring subcarriers and symbols

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  10. FBMC Modulation Scheme
    Comparison with OFDM:
    Advantages Drawbacks
    • Modem more complex
    • Intrinsic interferences
    • No cyclic prefix
    higher spectral efficiency
    • Low out-of-band interferences
    better coexistence
    • Specific processes at receiver
    better coexistence
    properties

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  11. Pilot-Aided Equalization
    Reminder: Channel equalization in OFDM/OQAM
    Transmitted signal x Received signal y
    Equalizer F
    Equalized signal a

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  12. Pilot-Aided Equalization
    First solution: pilots are multiplexed in the data stream (1/2)
    t
    pilot, help pilot
    data
    Loss of spectral
    efficiency
    Transmitted data known
    at the receiver
    f
    efficiency
    BUT
    Simple Equalization
    process

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  13. Pilot-Aided Equalization
    Pilot positions
    First solution: pilots are multiplexed in the data stream (2/2)
    2 steps:
    1) The channel H is estimated on pilot tones
    2) The signal is equalized with a one-tap per-carrier channel inversion
    F = 1/Ĥ
    Unknown
    channel

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  14. Pilot-Aided Equalization
    Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (1/4)
    p 0
    m
    n
    Simple implementation
    POP
    Pair of pilots (POP) [3]
    Simple implementation
    Good spectral efficiency (same as OFDM)
    Weak performance [c1]
    noise
    variance
    interference
    variance
    channel
    variance

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  15. Pilot-Aided Equalization
    p a
    Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (2/4)
    m
    n
    AP
    Auxiliary pilot (AP) [4]
    Good spectral efficiency
    Cancellation of the interference
    (elegantly)
    High complexity at transmitter

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  16. Pilot-Aided Equalization
    p b
    a
    p-
    Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (3/4)
    m
    n
    IAM
    IAM-R [2]: p- = ±1, p = ±1, p+ = -p- and a = 0,b = 0.
    p+
    Interference approximation
    method (IAM) [2]

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  17. Pilot-Aided Equalization
    p b
    a
    p-
    Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (4/4)
    m
    n
    IAM
    Reduction of the noise and interference energy
    p+
    Interference approximation
    method (IAM) [2]
    Reduction of the noise and interference energy
    Simple implementation
    Loss of spectral efficiency
    Good performance [c1]

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  18. Pilot-Aided Equalization
    LMMSE in OFDM/OQAM [c2], [c3]
    ? ? ?
    ?
    OFDM-like

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  19. Pilot-Aided Equalization
    Some results: Typical urban (TU) channel, 3 km.h-1, no channel coding

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  20. Pilot-Aided Equalization
    Application to PMR band: some changes in the LTE PHY parameters [c4] (1/3)
    From LTE parameters …
    … to proposed LTE-like parameters
    More flexibility

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  21. Pilot-Aided Equalization
    time
    frequency
    Nt
    Nf


    1 RB
    in LTE


    1 RB in
    proposed
    scheme
    Application to PMR band: some changes in the LTE PHY parameters [c4] (2/3)


    2τ0







    TOFDM
    15 KHz 5 KHz
    added
    subcarrier
    a. LTE pilot distribution b. Proposed rectangular distribution

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  22. Pilot-Aided Equalization
    Application to PMR band: some changes in the LTE PHY parameters [c4] (3/3)
    1 RB
    Channel estimation
    along the whole band
    pilot
    time
    frequency
    frequency
    PMR signals
    BB BB
    PMR signal
    added
    carriers
    frequency
    More flexibility
    Good channel estimation
    over each sub-band

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  23. Pilot-Aided Equalization
    Some results (1/2): achieved bit rate
    - 4-QAM symbols, 3 MHz bandwidth
    - reference in OFDM in LTE: 4.8 Mbits.s-1
    - Proposed scheme:
    Similar to LTE
    Enable high bit rate applications, as video streaming

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  24. Pilot-Aided Equalization
    Some results (1/2): achieved BER
    - 4-QAM, no channel coding

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  25. Blind Equalization
    Second solution: blind equalization
    Iterative processus, without pilot
    Transmitted
    signal
    Received
    signal
    Recovered
    signal
    H F
    x y
    w
    z a
    +
    AFB
    Channel Blind
    equalizer
    - Goal: achieve H.F =1
    - Constraint : limited knowledge of the signal feature
    H F
    +
    AFB

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  26. Blind Equalization
    Second solution: blind equalization
    H.F H.F H.F
    Itération 0 Initial state Transient Steady state
    Gain in terms of bit rate
    Requires a convergence delay
    state

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  27. Blind Equalization
    Basics (1/2), [5], [6], [7]: AFB
    F
    F
    T
    PPN




    y0,n
    y1,n
    ym,n
    yM-1,n
    INPUT
    Equal.
    am,n
    Fm,n
    - Goal: Solve the optimization
    problem
    yM-1,n
    - How? Use the stochastic gradient
    with
    - µ is the step-size parameter
    - J a given cost function
    2 degrees of freedom

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  28. Blind Equalization
    Basics (2/2), [5], [6], [7]:
    Cost function: Constant modulus algorithm [5], [6]
    with p: another degree of freedom
    Transient state = 1000 OFDM/OQAM
    symbols !

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  29. Blind Equalization
    Some results: blind equalization in mobile environment (1/2)
    MSE = (1/M).Σ(|x|-|a|)²
    SNR = 20
    dB
    Fast
    increase

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  30. Blind Equalization
    Some results: blind equalization in mobile environment (2/2)
    Blind equalization does not track the channel variations

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  31. Blind Equalization
    Any solutions ? … Yes !
    Several ways are investigated:
    Can be reconsidered [c5]
    Can be adapted to OFDM/OQAM [c6], [c7]
    New blind receiver design
    AFB
    F
    F
    T
    PPN




    y0,n
    y1,n
    ym,n
    yM-1,n
    INPUT
    Equal.
    am,n
    Fm,n

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  32. Bibliography
    [1] M. Bellanger, “Specification and Design of a Prototype Filter for Filter Bank Based
    Multicarrier Transmission,” in proc. Of ICASSP, vol. 4, Salt Lake City, UT, May 2001,
    pp. 2417 – 2420.
    [2] E. Kofidis, D. Katselis, A.Rontogiannis, and S. Theodoridis, “Preamble-based
    channel estimation in OFDM/OQAM systems: A review,” Signal Processing, Elsevier,
    vol. 93, pp. 2038 – 2054, January 2013.
    [3] C. Lélé, J.-P. Javaudin, R. Legouable, A. Skrzypczak, and P. Siohan, “Channel
    estimation methods for preamble-based OFDM/OQAM modulations,” European
    Transactions on Telecommunications, vol. 19, no. 7, pp. 741 –750, November 2008.
    Transactions on Telecommunications, vol. 19, no. 7, pp. 741 –750, November 2008.
    [4] J.-P. Javaudin, D. Lacroix, and A. Rouxel, “Pilot-Aided Channel Estimation for
    OFDM/OQAM,” in VTC’03 - Spring, vol. 3, Jeju, Korea, April 2003, pp. 1581 – 1585.
    [5] D. N. Godard, “Self-Recovering Equalization and Carrier Tracking in Two-
    Dimensional Data Communication Systems,” IEEE Transactions on Communications,
    vol. com-28, no. 11, pp. 1867 – 1875, November 1980.
    [6] B. Farhang-Boroujeny, “Multicarrier Modulation With Blind Detection Capability
    Using Cosine Modulated Filter Banks,” IEEE Transactions on Communications, vol.
    51, no. 12, pp. 2057 – 2070, December 2003.
    [7] A. Goupil and J. Palicot, “New Algorithms for Blind Equalization: The Constant
    Norm Algorithm Family,” IEEE Transactions on Signal Processing, vol. 55, no. 4, pp.
    1436 – 1444, April 2007.

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  33. Bibliography
    Contributions:
    [c1] V. Savaux, F. Bader, “Mean Square Error Analysis and LMMSE Application for
    Preamble-Based Channel Estimation in OFDM/OQAM Systems,”
    [c2] V. Savaux, F. Bader, Y. Louët “A Joint MMSE Channel and Noise Variance
    Estimation for OFDM/OQAM Modulation,”
    [c3] L. Caro, V. Savaux, D. Boiteau, M. Djoko-Kouam, Y. Louët “Preamble-Based
    LMMSE Channel Estimation in OFDM/OQAM Modulation,” in proc of VTC’15 Spring,
    Glasgow, May 2015
    Glasgow, May 2015
    [c4] V. Savaux, F. Bader “Pilot Adaptation for Broadband LTE-Like FBMC System in
    PMR Band,” in proc of VTC’15 Spring, Glasgow, May 2015
    [c5] V. Savaux, F. Bader, J. Palicot “Frequency Blind Equalization Using Constant
    Norm Algorithm for OFDM Systems,”
    [c6] V. Savaux, F. Bader “Sub-Optimal Initialization for Blind Equalization with Fast
    Convergence in OFDM/OQAM Modulation,”
    [c7] V. Savaux, F. Bader “Enhancing the Constant Modulus Algorithm for Blind
    Equalization in OFDM/OQAM Modulation,”

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  34. Thanks for your attention !
    Merci de votre attention !
    Des questions ?

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