Long range channel prediction for adaptive ofdm systems
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Long-Range Channel Prediction for Adaptive OFDM Systems. I. C. Wong , A. Forenza, R. W. Heath and B. L. Evans. Adaptive OFDM. Adapt modulation, coding, or power in each subcarrier at the Transmitter (Tx) in order to maximize throughput

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Long-Range Channel Prediction for Adaptive OFDM Systems

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Long-Range Channel Prediction for Adaptive OFDM Systems

I. C. Wong, A. Forenza,

R. W. Heath and B. L. Evans

July 31, 2014


Adaptive OFDM

  • Adapt modulation, coding, or power in each subcarrier at the Transmitter (Tx) in order to maximize throughput

  • Adaptation based on current channel state information (CSI) being fed back to the Tx

  • Problem: Outdated CSI [Souryal & Pickholtz, 2001]

    • Effect very relevant in mobile situations

    • How do I minimize the impact of this delay?

July 31, 2014


Wireless Channel Prediction

  • Long-range prediction (LRP) [Duel-Hallen, et. al. 2000]

    • Used an FIR Weiner prediction filter

    • Designed for flat-fading channels

    • Key Idea: Downsampling the observed channel coefficients

July 31, 2014


Application of LRP to OFDM

  • Briefly investigated in [Forenza & Heath, 2002]

    • Directly predict channel for each of the N subcarriers

      • Valid since each subcarrier is a flat-fading narrowband subchannel

      • Storage needed for p*N previous channel coefficients ck and p*N prediction coefficients dk

    • Used Burg’s algorithm to compute predictor coefficients

July 31, 2014


Low-Complexity LRP for OFDM

  • Pilot-tone Prediction

    • Perform LRP on the Npilot pilot tones only

    • Since Npilot < N, less computation and storage needed (e.g. Npilot = 8; N = 256 for 802.16e )

    • Use the same Wiener predictor for the subcarriers nearest to the pilot carrier

Pilot

Data Carriers

July 31, 2014


Low-Complexity LRP for OFDM

  • Time Domain channel tap Prediction

    • Perform LRP on the L ≤ Npilot time domain channel taps, and thus further reduce complexity

    • It can be shown that MMSE predictor for the time domain taps also minimize MSE for frequency domain

t=n

t=1

t=0

July 31, 2014


Simulation Parameters(IEEE 802.16e)

July 31, 2014


Channel Prediction Example

July 31, 2014


Performance comparisons

July 31, 2014


Conclusion

  • LRP for OFDM systems can be accomplished by:

    • Prediction on all the tones

    • Prediction on pilot tones

    • Prediction on the time domain channel taps

  • Time-domain prediction gives better MSE performance, specially in the presence of channel estimation error

  • Future work: Adaptive prediction with Weiner smoothing

July 31, 2014


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