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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. 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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  1. Long-Range Channel Prediction for Adaptive OFDM Systems I. C. Wong, A. Forenza, R. W. Heath and B. L. Evans July 31, 2014

  2. 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maximize throughput • Adaptation based on current channel state information (CSI) being fed back to the Tx • Problem: Outdated CSI [Souryal & Pickholtz, 2001] • Effect very relevant in mobile situations • How do I minimize the impact of this delay?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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Simulation Parameters(IEEE 802.16e) July 31, 2014

  8. Channel Prediction Example July 31, 2014

  9. Performance comparisons July 31, 2014

  10. 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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