Advisor: Yung-an Kao Student: Chian Young

1. A Novel one-tap frequency domain RLS equalizer combined with Viterbi decoder using channel state information in OFDM systems Advisor: Yung-an Kao Student: Chian Young

2. outline • Introduction • System overview • A Novel 1-tap frequency domain RLS equalizer • Viterbi Decoding with CSI • Simulation result • conclusion

3. Receive Spectrum Transmit Spectrum Channel Spectrum Channel Training Tone Data Tone Introduction(1/3) • The advantage of OFDM’s parallel transmission scheme: • frequency selective channel multiple flat fading sub-channels the sub-channel equalization in frequency domain is simple

4. Introduction(2/3) • The main factors that distort the signal in OFDM system: • Channel • Noise • Frequency offset: CFO (carrier frequency offset), SFO (sampling frequency offset)

5. Introduction(3/3) • The benefit of the proposed equalizer structure: • Compensate signal distorted by the channel, CFO and SFO at the same time • The division operation is not required • Combine with CSI to improve system performance

6. System overview (receiver) Signal affect by channel SFO, CFO, noise, etc.. A modified version of RLS algorithm is used In the proposed FEQ structure, the scale of signal constellation must be adjusted CSI is obtain from 1-tap FEQ

7. A Novel 1-tap frequency domain RLS equalizer(1/5) Yk,l :EQ output Xk,l: EQ input k : k-th sub-carrier l :l-th OFDM symbol λk : forgetting factor Φk,l: correlation matrix wk,l : equalizer weighting dk,l : desired signal • Filtering equation: • Definition of θk,l : • The update equation for θk,l:

8. phase A Novel 1-tap frequency domain RLS equalizer(2/5) • Definition of wk,l: • Rewrite RLS filtering equation: magnitude:

9. A Novel 1-tap frequency domain RLS equalizer(3/5) • From , the magnitude part of distorted signal is not totally compensated: 1-tap FEQ input 1-tap FEQ output

10. constellation size multiply by Φk,ltimes : equalized signal Φk,l Φk,l 1 -Φk,l Φk,l -1 Φk,l Φk,l 1 -1 -Φk,l Φk,l A Novel 1-tap frequency domain RLS equalizer(4/5) Im Im 3 3 1 Re Re -3 -1 1 3 -3 3 -1 -3 -3

11. A Novel 1-tap frequency domain RLS equalizer(5/5) • The update equation for Φk,l : • Division operation is not required • Error signal is not used

12. Viterbi Decoding with CSI(1/2) • Viterbi Decoding with CSI • Viterbi decoding: select the path on code trellis with the minimum Euclidean distance • We use CSI to reflect different sub-channel fading • Adding CSI when calculating the Euclidean distance improve reliability on calculating the Euclidean distance

13. “scaled” possible transmitted signal Viterbi Decoding with CSI(1/2) • The calculation of the Euclidean distance: • When SNR is high enough: • Adding CSI to D : : possible transmitted signal n : n-th de-interleaver output

14. Simulation environment & parameters • Follows IEEE 802.11a standard • CFO=3.125kHz,SFO=800Hz • Indoor Rayleigh fading multipath channel: Trms=50ns,Ts=50ns • 1000 packets, 256bytes/packet

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

16. conclusion • Division in the proposed algorithm is no longer used • Multiplier • Quantization

17. Thanks For your attention!!!