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

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  • Problem: Outdated CSI [Souryal & Pickholtz, 2001]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


Simulation parameters ieee 802 16e

Simulation Parameters(IEEE 802.16e)

July 31, 2014


Channel prediction example

Channel Prediction Example

July 31, 2014


Performance comparisons

Performance comparisons

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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