1 / 20

Channel Estimation in OFDM Systems

Channel Estimation in OFDM Systems. Zhibin Wu Yan Liu Xiangpeng Jing. OUTLINE. OFDM System Introduction Channel Estimation Techniques Performance Evaluation Conclusion. OFDM Overview. Divides high-speed serial information signal into multiple lower-speed sub-signals:

willem
Download Presentation

Channel Estimation in OFDM Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Channel Estimation in OFDM Systems Zhibin WuYan LiuXiangpeng Jing

  2. OUTLINE • OFDM System Introduction • Channel Estimation Techniques • Performance Evaluation • Conclusion

  3. OFDM Overview • Divides high-speed serial information signal into multiple lower-speed sub-signals: • Transmits simultaneously at different frequencies in parallel. • Modulation ( BPSK, PSK,QPSK,16QAM, …). • Pilot sub-carriers used to prevent frequency and phase shift errors. • Usage of cyclic prefix for lower multi-path distortion • Controlled overlapping of bands in one channel • Max spectral efficiency (Nyquist rate) • Easy implementation using inverse FFTs • Easy time-freq. Synchronization • Modulate by switching between time and frequency domain

  4. Introduction to OFDM Systems

  5. Time-Frequency View

  6. Some Assumptions • Usage of cyclic Prefix • Impulse response of the channel shorter than Cyclic Prefix • Slow fading effects so that the channel is time-invariant over the symbol interval • Rectangular Windowing of the transmitted pulses • Perfect Synchronization of transmitter and receiver • Additive, white, Gaussian channel noise

  7. System Architecture

  8. System Architecture (cont’d) • Input to time domain • Guard Interval • Channel • Guard Removal • Output to frequency domain • Output • Channel Estimation Channel ICI AWGN Estimated Channel

  9. Pilot for Channel Estimation • Comb Type: • Part of the sub-carriers are always reserved as pilot for each symbol • Block Type: • All sub-carriers is used as pilot in a specific period Time Carriers Time Carriers

  10. Block-type Channel Estimation • LS: Least Square Estimation

  11. Comb-type Estimation Np pilot signals uniformly inserted in X(k) L=Number of Carriers/Np xp(m) is the mth pilot carrier value {Hp(k) k=0,1,…,Np} , channel at pilot sub-carriers Xp input at the kth pilot sub-carrier Yp output at the kth pilot sub-carrier LS Estimate LMS Estimate Yp(k) Xp(k) - e(k) LMS +

  12. Interpolation for Comb-type • Linear Interpolation • Second Order Interpolation

  13. Simulation Parameters

  14. System structure in MATLAB Simulation

  15. OFDM Transmitter OFDM Receiver

  16. Received and Recovered Signals Received signal phases are distorted by multi-path fading

  17. Comb-LS Estimation • Combating multipath rayleigh fading with RLS adaptive equalization • A detail simulation with MATLAB • 20 multipath, random phase, and weibull distribution of amplitutde Symbol Error Rate

  18. Comb-LS Estimation

  19. Filter length .vs. Sample Rate Observed Symbol error rate with F ( filter length ) and S ( samples per symbol) • Keep the ratio of F/S, increase S • Keep S, increase F.

  20. Conclusion • OFDM System Introduction • Block Type • Direct or Decision Feedback • Comb Type • LS or LMS estimation at pilot frequencies • Interpolation Techniques • Linear • Second Order • Time Domain • Modulation • BPSK,QPSK,16QAM,DQPSK • Some Results: • Comb Type performs better since it tracks fast fading channels. • RLS algorithm vs. LMS algorithm

More Related