One-Tap Frequency Domain LMS Equalizer for OFDM Systems

1. One-Tap Frequency Domain LMS Equalizer for OFDM Systems 指導教授 : 高永安 博士 報告學生 : 黃凡維 2003/11/14

2. Outline • Introduction • One-Tap Frequency Domain LMS Equalizer • Simulation • Conclusion

3. Introduction(1/2)

4. Introduction(2/2)

5. One-tap frequency domain LMS equalizer • LMS :

6. 1st order IIR filter • convergence constraint

7. One-tap frequency domain LMS equalizer

8. One-tap frequency domain LMS equalizer • ideal : 

9. One-tap frequency domain LMS equalizer • The magnitudes of U(ej) for different k|Hk|2

10. One-tap frequency domain LMS equalizer • The phases of U(ej) for different k|Hk|2.

11. One-Tap Frequency Domain LMS Equalizer • The effect of noise to LMS algorithm • LMS

12. One-Tap Frequency Domain LMS Equalizer

13. One-Tap Frequency Domain LMS Equalizer

14. One-Tap Frequency Domain LMS Equalizer • LMS • Transfer Function

15. One-Tap Frequency Domain LMS Equalizer • Convergence constraint • We expect the system can compensate and also blockadeX*k,lNk,l • is a lowpass filter when

16. Simulation(1/8) Example 1. IEEE 802.11a standard. • The maximal tolerance of sampling clock offset shall be ±20 ppm. • The maximal sampling clock offset equals ±800Hz when sampling clock is 20MHz. • Ts=1/(20106) and Ts=1/(±800+20106). • Assume that the carrier frequency offset can be completely compensated. • Let k=27 and then 27 = 227(Ts-Ts)(64+16)/(Ts64) = ±0.00848 • Let =0.1, Hk=1, and Xk be modulated by QPSK with |Xk,l|=1, then SNR=10dB. • For one-run simulation, the simulated number of OFDM symbols is 1000. • The simulation results are the average of 100-run simulations.

17. Simulation(2/8) • MSE with different step size 27

18. Simulation(3/8) • Mean of absolute phase error with different step size 27

19. Simulation(4/8) • Constellation of compensated signal (27=0.2)

20. Simulation(5/8) • Example 2. All parameters are same as example 1except • Xk is modulated by 16 QAM with average magnitude being oneand SNR=20dB .

21. Simulation(6/8) • MSE with different step size 27

22. Simulation(7/8) • Mean of absolute phase error with different step size 27

23. Simulation(8/8) • Constellation of compensated signal (27=0.25)

24. Conclusion • 1st order IIR filter • Step size