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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

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
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  • Problem: Outdated CSI [Souryal & Pickholtz, 2001]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
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
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
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 ofdm1
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

conclusion
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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