1. Long-Range Channel Prediction for Adaptive OFDM Systems
I. C. Wong, A. Forenza,
R. W. Heath and B. L. Evans
April 21, 2019

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Problem: Outdated CSI [Souryal & Pickholtz, 2001]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?
April 21, 2019

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
April 21, 2019

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
April 21, 2019

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 e )
Use the same Wiener predictor for the subcarriers nearest to the pilot carrier
Pilot … …
Data Carriers
April 21, 2019

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
April 21, 2019

7. Simulation Parameters (IEEE 802.16e)
Value N
256 BW
5 MHz
Guard Carriers (7)
[0-27] &
[201:256]
Fcarrier
2600 MHz
Channel Model
ETSI Vehicular A
Mobile Velocity
75 kph
Prediction Order 75
Downsampling rate 25
(4*fd)
April 21, 2019

8. Channel Prediction Example
April 21, 2019

9. Performance comparisons
April 21, 2019

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
April 21, 2019