1 / 43

應用於 OFDM 系統之強健化 內部接收機架構設計

應用於 OFDM 系統之強健化 內部接收機架構設計. 指導老師:高永安 學 生:蘇家弘. A Robust Inner Receiver Structure Design for OFDM Systems. Outline. OFDM system block diagram OFDM baseband signal model Inner receiver structure Channel estimation LMS algorithm Selection of  Pilot-based phase estimator

oded
Télécharger la présentation

應用於 OFDM 系統之強健化 內部接收機架構設計

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. 應用於OFDM 系統之強健化內部接收機架構設計 指導老師:高永安 學 生:蘇家弘 A Robust Inner Receiver Structure Design for OFDM Systems

  2. Outline • OFDM system block diagram • OFDM baseband signal model • Inner receiver structure • Channel estimation • LMS algorithm • Selection of  • Pilot-based phase estimator • Dynamic simulation by Simulink 5.0 • Conclusion and future work

  3. OFDM system block diagram Eq Eq . . . Eq Up convert CFO SFO n: n-th sample point k: k-th subcarrier l: l-th subcarrier Down convert

  4. Carrier Frequency Offsets • CFO simulation • CFO is due to the oscillator mismatch from up convert and down convert f

  5. CFO calculation for IEEE 802.11a • Maximum quantity of CFO = 20ppm for 5GHz • k: k-th subcarrier, l: l-th OFDM symbol , N=64, n=80

  6. SFO is caused by the oscillator mismatch between A/D & D/A converter SFO simulation Sampling Frequency Offsets TTX TRX WhenTRX>TTX

  7. SFO calculation for IEEE 802.11a • TTX=1/(20MHz 400Hz), TRX=1/(20MHz400Hz) • k: k-th subcarrier, l: l-th OFDM symbol , N=64, n=80

  8. OFDM baseband signal model • OFDM baseband signal after IFFT at the transmitter side • The received OFDM baseband signal before FFT -------- (2) -------- (1) n: n-th sample point k: k-th subcarrier l: l-th subcarrier

  9. OFDM baseband signal model • The received OFDM signal is influenced by channel effect, residual CFO, SFO, initial symbol timing offset and before FFT we can describe (2) as follows: -------- (3) • Td :initial symbol timing offset Hk :frequency response of channel : residual CFO : initial phase offset Ts : sampling clock period at the transmitter Ts’: sampling clock period at the receiver CFO SFO

  10. OFDM baseband signal model • The ICI produced by residual CFO is much smaller compared to Gaussian noise. N’k,lcombine Ik,land Nk,l and (3) can be modified as: -------- (4)

  11. OFDM baseband signal model • The effect of CFO and SFO can be represented as : -------- (5) and

  12. The difference between inner and outer receiver • M. Speth, S. A. Fechtel, G. Fock and H. Meyr, “Optimum Receiver Design for Wireless Broad-band Systems Using OFDM-Part II,” IEEE Trans. Commun., vol. 49, pp.571-578, Apr. 2001. Decoding & demodulation

  13. Inner receiver structure Input signal FFT

  14. Inner receiver structure Training sequence Initial coefficient FFT D a t a Update coefficient of equalizer Phase compensation Frequency Domain Equalizer Pilot Pilot-based phase estimator Phase compensation Hard decision Outer receiver

  15. Channel estimation by least square error • Lk,l : transmitted training sequence Rk,l : received training sequence : equalized training sequence Hk :channel Nk,l : noise : equalizer initial coefficient • Equalized training sequence  l : 2 long training symbol k : 52 subcarrier In 802.11a

  16. Channel estimation by least square error • Error between transmitted signal and equalized signal • Find optimal Heq,k forminimum value of ek  Setting the partial derivative of ek

  17. LMS algorithm • Filtering output: Yk=wkHXk Error estimation: ek=dk-Yk • Tap-weight vector adaptation * After hard decision kis the step size that modified by channel condition

  18. selection of  • Normalized-LMS & time average Training sequence 0 <  < 1

  19. Pilot-based phase estimator Received pilots After giving the appropriate weight Maximum ratio combination (MRC) pilot C’ Im Im A’ C A B B’ ∠2 ∠1 O Re Re O

  20. Simulation by Simulink 5.0

  21. Unequalized signal spacing plot Channel A (Ts=50ns, TRMS=50ns ) SNR=10dB Residual CFO =0.01 SFO=800Hz (Ts=1/(20MHz-400), =1/(20MHz+400 ) Code rate=1/2, QPSK 44 OFDM symbol per packet 1000 packet

  22. After channel equalization Applied the proposed inner receiver structure

  23. IEEE 802.11a PER v.s. SNR =0.15 =0.3 Channel A (Ts=50ns, TRMS=50ns ) Residual CFO =0.01 SFO=800Hz (Ts=1/(20MHz-400), =1/(20MHz+400 ) PSDU=256 bytes 1000 packet

  24. Channel B (Ts=50ns, TRMS=100ns ) Channel C (Ts=50ns, TRMS=150ns ) IEEE 802.11a PER v.s. SNR

  25. Channel D (Ts=50ns, TRMS=200ns ) Channel E (Ts=50ns, TRMS=250ns ) IEEE 802.11a PER v.s. SNR

  26. PER v.s. SNR with different  =0.3 Channel A (Ts=50ns, TRMS=50ns ) Residual CFO =0.01 SFO=800Hz (Ts=1/(20MHz-400), =1/(20MHz+400 ) 44 OFDM symbol per packet 1000 packet

  27. Channel C (Ts=50ns, TRMS=150ns ) Channel E (Ts=50ns, TRMS=250ns ) PER v.s. SNR with different 

  28. PER v.s. SNR with different  =0.3 Channel A (Ts=50ns, TRMS=50ns ) Residual CFO =0.01 SFO=800Hz (Ts=1/(20MHz-400), =1/(20MHz+400 ) 200 OFDM symbol per packet 1000 packet

  29. Channel C (Ts=50ns, TRMS=150ns ) Channel E (Ts=50ns, TRMS=250ns ) PER v.s. SNR with different 

  30. PER v.s.  with different channel =0.3 Channel A (Ts=50ns, TRMS=50ns ) Channel C (Ts=50ns, TRMS=150ns ) Channel E (Ts=50ns, TRMS=250ns ) SNR=10dB Residual CFO =0.01 SFO=800Hz (Ts=1/(20MHz-400), =1/(20MHz+400 ) 44 OFDM symbol per packet 1000 packet

  31. PER v.s.  with different channel =0.3 Channel A (Ts=50ns, TRMS=50ns ) Channel C (Ts=50ns, TRMS=150ns ) Channel E (Ts=50ns, TRMS=250ns ) SNR=10dB Residual CFO =0.01 SFO=800Hz (Ts=1/(20MHz-400), =1/(20MHz+400 ) 200 OFDM symbol per packet 1000 packet

  32. Conclusion • A Robust Inner Receiver Structure • Simulink 5.0  pilot-based phase estimator 1. Compensate the residual CFO 2. Assist the LMS equalizer in phase tracking  Dynamic simulation

  33. Future work • At present • Frequency selective fading channel • LMS algorithm • The future work • Slow fading channel • Other adaptive algorithms • Decoding block of Simulink 5.0

  34. Reference • IEEE Std 802.11a-1999, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High Speed Physical Layer in the 5GHz Band. • Yung-An Kao; Chia-Hung Su; Shih-Kai Lee; Chung-Lung Hsiao; Po-Lin Chio, “A robust design of inner receiver structure for OFDM systems,” IEEE Conference. on Consumer Electronics, pp. 377-378, Jan. 2005. • S. Haykin, Adaptive Filter Theory, Englewood Cliffs, NJ: Prentice-Hall, 2002, 4th Ed. • M. Speth, S. A. Fechtel, G. Fock and H. Meyr, “Optimum Receiver Design for Wireless Broad-band Systems Using OFDM-Part I,” IEEE Trans. Commun., vol. 47, pp. 1668-1677, Nov. 1999. • M. Speth, S. A. Fechtel, G. Fock and H. Meyr, “Optimum Receiver Design for Wireless Broad-band Systems Using OFDM-Part II,” IEEE Trans. Commun., vol. 49, pp.571-578, Apr. 2001. • Doufexi, A.; Armour, S.; Butler, M.; Nix, A.; Bull, D.; McGeehan, J.; Karlsson, P., “A comparison of the HIPERLAN/2 and IEEE 802.11a wireless LAN standards,” IEEE Magazine on Comm. Vol. 40, pp.172-180, May 2002. • 黃凡維, 2004, “一揭最小均方差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

  35. Any Questions?

  36. Channel estimation by LSE

  37. Channel estimation by LSE • Applying we obtain and R:real part I:imaginary part

  38. Channel estimation by LSE

  39. Comparison between the MRC pilot and the original pilot multiplication • MRC pilot Only add MRC pilot

  40. Comparison between the MRC pilot and the original pilot addition • Original pilot multiplication After mutual multiplying

  41. MRC pilot 4 pilot multiplying Channel A

More Related