1 / 31

Advisor: Yung-An Kao Student: Chi-An Young

嶄新的一階頻域 RLS 等化器 結合通道資訊輔助 Viterbi 解碼器應用於 OFDM 系統中 A Novel one-tap frequency domain RLS equalizer combined with Viterbi decoder using channel state information in OFDM systems. Advisor: Yung-An Kao Student: Chi-An Young. Outline . Introduction Motivation OFDM system

nyoko
Télécharger la présentation

Advisor: Yung-An Kao Student: Chi-An Young

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. 嶄新的一階頻域RLS等化器結合通道資訊輔助Viterbi解碼器應用於OFDM系統中A Novel one-tap frequency domain RLS equalizer combined with Viterbi decoder using channel state information in OFDM systems Advisor: Yung-An Kao Student: Chi-An Young

  2. Outline • Introduction • Motivation • OFDM system • Novel one-tap frequency domain RLS equalizer • Conventional LMS and RLS algorithm • Novel equalizer structure • Viterbi decoding with channel state information • Simulation results • Conclusion & Future work

  3. Motivation • To design a receiver in OFDM systems with following consideration: • Channel effects & frequency offset • complexity • performance

  4. Introduction • The advantage of OFDM’s parallel transmission scheme: • makes the bandwidth more effective

  5. Receive Spectrum Transmit Spectrum Channel Spectrum Channel Training Tone Data Tone Introduction • strongly against multi-path channel • frequency selective channel multiple flat fading sub-channels the sub-channel equalization in frequency domain is simple

  6. Carrier frequency offset (CFO) • CFO is due to the oscillator mismatch from up converter and down converter QPSK, IEEE802.11a spec. no noise CFO=0.01x312.5kHz 43 OFDM symbols

  7. Sampling frequency offset (SFO) • SFO is caused by the oscillator mismatch between A/D & D/A converter QPSK, IEEE802.11a spec. no noise SFO=800Hz 43 OFDM symbols

  8. A modified version of RLS algorithm is used an inner receiver structure from[*] CSI is obtain from 1-tap FEQ [*] Y. A. Kao, C. H. Su, S. K. Lee, C. L. Hsiao and P. L. Chio, 2005, “A robust design of inner receiver structure for OFDM systems,” Digest of technical papers, ICCE, pp.377-378. OFDM receiver block signal affect by channel residual frequency offset , noise, etc.. In the proposed FEQ structure, the scale of the signal constellation must be adjusted

  9. Parameter definition • X : transmitted signal in frequency domain • Y : received signal in frequency domain • Z : equalized signal • Z’ : equalized signal (proposed equalizer) • H : channel response • w : weight coefficient of equalizer • e : error signal • d : desired signal • : LMS step size • : RLS forgetting factor • : correlation matrix • k, l : k-th subcarrier and l-th OFDM symbol • n : n-th de-interleaver output

  10. Inner receiver structure The advantage of this structure is the phase compensation.

  11. One-tap frequency domain LMS equalizer • filtering equation: • weight adaptation

  12. One-tap frequency domain LMS equalizer • filtering equation: • weight adaptation: [**]張晉銓, 2005, “一階遞迴最小平方頻域等化器應用於正交分頻多工系 統之特性分析,” 長庚大學電機工程研究所碩士論文.

  13. Division is used in NLMS and RLS algorithm • NLMS: • RLS:

  14. Novel one-tap frequency domain RLS equalizer(1/6) • filtering equation: • definition of θk,l • update ofθk,l

  15. magnitude: phase Novel one-tap frequency domain RLS equalizer(2/6) • Definition of wk,l: • Rewrite RLS filtering equation:

  16. Novel one-tap frequency domain RLS equalizer(3/6) • From the magnitude part of distorted signal is not fully compensated (QPSK modulation is assumed, CNR=15dB): 1-tap FEQ input 1-tap FEQ output

  17. constellation size multiply by Φk,ltimes : signalequalized by conventional RLS FEQ Φk,l Φk,l 1 -Φk,l Φk,l -1 Φk,l Φk,l 1 -1 -Φk,l Φk,l : signal equalized by proposed RLS FEQ Novel 1-tap frequency domain RLS equalizer(4/6) Im Im 3 3 1 Re Re -3 -1 1 3 -3 3 -1 -3 -3

  18. Novel 1-tap frequency domain RLS equalizer(5/6) • The update equation for Φk,l :

  19. Novel 1-tap frequency domain RLS equalizer(6/6) • division operation is not required • calculation of error signal is not used • must adjust the scale of constellation at symbol de-mapping device Proposed 1-tap FEQ P/S Symbol De-mapping … …

  20. decoding error probability may increase Viterbi Decoding with CSI(1/6) • Basic concept of Viterbi decoding: to select the path on code trellis with the minimum Euclidean distance • Viterbi decoding in OFDM system: • in presence of channel fading, each subcarrier is experiencing different channel condition • if we view each subcarrier with the same reliability, except for that the situation will not be reflected

  21. Viterbi Decoding with CSI(2/6) • We use channel state information (CSI) to reflect different sub-channel fading • Concept: • Adding CSI when calculating the Euclidean distance improve reliability on calculating the Euclidean distance

  22. Viterbi decoding using CSI(3/6) • CSI aided Viterbi decoder block diagram[***] BMC: Branch Metric Calculation SAM: State Accumulate Metric SPM: Survival Path Matrix [***]W. C. Lee, H. M. Park, K. J. Kang and K. B. Kim, “Performance analysis of Viterbi decoder using channel state information in COFDM system,” IEEE Transactions on Broadcasting, Vol. 44, no.4, pp.488-496, Dec. 1998.

  23. Viterbi decoding using CSI(4/6) • The calculation of the Euclidean distance: • When SNR is high enough: :possible transmitted signal

  24. the signal constellation that has been adjusted equalized signal: Viterbi decoding using CSI(5/6) • Adding CSI to D :

  25. Viterbi decoding using CSI(6/6) • Considering: • system complexity • system performance • We use to reflect channel condition

  26. Simulation environments & parameters • IEEE 802.11a standard • Transmission packets = 1000 packets • Transmission data per packets = PSDU 256 Bytes • Exponentially decaying Rayleigh fading with sampling period and RMS time • CFO = 3125 Hz • SFO = 800 Hz • = 0.85 • 6-bit soft decision Viterbi decoding

  27. Simulation result PER performance for IEEE 802.11a (no CSI aided) PER performance for IEEE 802.11a (CSI aided)

  28. conclusion • Division in the proposed algorithm is no longer used • By applying this FEQ structure, we can improve the system performance by CSI aided Viterbi decoder

  29. Future work • Apply the equalizer structure to time-variant channel • The optimal solution of CSI • Hardware implementation

  30. Reference • Y. A. Kao, C. H. Su, S. K. Lee, C. L. Hsiao and P. L. Chio, 2005, “A robust design of inner receiver structure for OFDM systems,” Digest of technical papers, ICCE, pp.377-378. • W. C. Lee, H. M. Park, K. J. Kang and K. B. Kim, “Performance analysis of Viterbi decoder using channel state information in COFDM system,” IEEE Transactions on Broadcasting, Vol. 44, no.4, pp.488-496, Dec. 1998. • 張晉銓, 2005, “一階遞迴最小平方頻域等化器應用於正交分頻多工系統之特性分析,”長庚大學電機工程研究所碩士論文.

  31. Thanks for your attention!

More Related