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Synchronization Aspects in LTE

Synchronization Aspects in LTE

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Synchronization Aspects in LTE

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  1. Synchronization Aspects in LTE 389.075 Mobile Communication Seminar Qi Wang July 3rd, 2008

  2. Outline • LTE PHY • Synchronization in OFDM • From WiMAX to LTE • Synchronization in WiMAX • LTE Frame Structure • Conclusion

  3. LTE Physical Layer • New Features to Cellular Application • Orthogonal Frequency Division Multiplexing (OFDM) • Multiple Input Multiple Output (MIMO) • OFDMA on downlink • SC-FDMA on uplink • Frequency domain scheduling

  4. LTE Physical Layer slot

  5. Outline • LTE PHY • Synchronization in OFDM • From WiMAX to LTE • Synchronization in WiMAX • LTE Frame Structure • Conclusion

  6. Carrier Frequency Error in OFDM Received signal: e.g. subcarrier spacing = 15kHz, 10ppm.Osc at 2.5GHz, Fractional Frequency Offset (~0.665) + Integer Frequency Offset (1) + Residual Frequency Offset (~0.002) : Carrier Frequency Offset normalized in subcarrier spacing N: FFT size Carrier Frequency Offset (~1.667)

  7. OFDM Synchronization 2.Fractional Frequency Offset Estimation 3.Integer Frequency Offset Estimation Frequency Offset Correction 1. Frame Start Detection Remove CP FFT 4. Residual Frequency Offset Tracking

  8. Outline • LTE PHY • Synchronization in OFDM • From WiMAX to LTE • Synchronization in WiMAX • LTE Frame Structure • Conclusion

  9. WiMAX Frame Structure 1st Preamble: frame start detection, fractional frequency offset estimation 0 0 255 0 0 0 2nd Preamble: Integer frequency offset estimation 0 0 0 0 0 0 0 0 13 0 0 8 pilots on subcarriers {13 38 63 88 114 139 164 189}: Residual frequency offset tracking 0 0 0 frequency 0 0 0 time

  10. 1. Frame Detection 2.Fractional Frequency Offset Estimation 3.Integer Frequency Offset Estimation preamble preamble Frequency Offset Correction 1. Frame Start Detection Remove CP FFT pilot tones 4. Residual Frequency Offset Tracking

  11. 1. Frame Detection 1st Preamble in time domain: Estimated Frame Start CP 64 64 64 64

  12. 2. Fractional Frequency Offset 2.Fractional Frequency Offset Estimation 3.Integer Frequency Offset Estimation preamble preamble Frequency Offset Correction 1. Frame Start Detection Remove CP FFT pilot tones 4. Residual Frequency Offset Tracking

  13. 2. Fractional Frequency Offset 1st Preamble in time domain: Calculate the phase difference:

  14. 3. Integer Frequency Offset 2.Fractional Frequency Offset Estimation 3.Integer Frequency Offset Estimation preamble preamble Frequency Offset Correction 1. Frame Start Detection Remove CP FFT pilot tones 4. Residual Frequency Offset Tracking

  15. 3. Integer Frequency Offset ReceivedPreambleshiftedby 2i DefinedPreamble DefinedPreamble: Estimated integer frequency offset ReceivedPreamble:

  16. 4. Residual Frequency Offset 2.Fractional Frequency Offset Estimation 3.Integer Frequency Offset Estimation preamble preamble Frequency Offset Correction 1. Frame Start Detection Remove CP FFT pilot tones 4. Residual Frequency Offset Tracking

  17. 4. Residual Frequency Offset 0 average over l OFDM symbols average over k pilot subcarriers 0 255 FFT size 0 0 0 0 0 0 Cyclic Prefix length 0 0 • : received pilot in th • OFDM symbol • : pre-defined pilot in • th OFDM symbol 0 0 0 13 0 0 0 0 0 frequency 0 0 0 time

  18. Outline • LTE PHY • Synchronization in OFDM • From WiMAX to LTE • Synchronization in WiMAX • LTE Frame Structure • Conclusion

  19. LTE Frame Structure Resource Block Resource Element

  20. Synchronization Signals • Primary Synchronization Signals • identical in slot 0 and 10 • mapped to 72 centre subcarriers • Secondary Synchronization Signals • Different in slot 0 and 10 • Mapped to 62 centre subcarriers 72 subcarrier

  21. Reference Signals 1 Subframe 1ms 2 Resource Blocks Antenna Port 0 Antenna Port 1 Antenna Port 1

  22. Reference Signals Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 2

  23. Reference Signals Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3 Antenna Port 3

  24. Reference Signals Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3

  25. Conclusion: Synchronization in LTE DL 2.Fractional Frequency Offset Estimation 3.Integer Frequency Offset Estimation Primary & Secondary Synchronization Signals Primary Synchronization Signals Frequency Offset Correction 1. Frame Start Detection Remove CP FFT 4. Residual Frequency Offset Tracking Reference Signals Primary & Secondary Synchronization Signals

  26. Reference 3GPP TS 36.211 V8.2.0 3rd Generation Prtnership Project; Technical Specification group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8), March 2008 Freescale, ”Overview of the 3GPP Long Term Evolution Physical Layer,” 2007. E. Dahlman, S. Parkvall, J. Sköld, P. Beming: “3G Evolution: HSPA and LTE for Mobile Broadband“, Elsevier 2007. M. Morelli, C.-C Jay Guo, M. Pun: “Synchronization Techniques for Orthogonal Frequency Division Multiple Access (OFDMA): A Tutorial Review“, Proc. IEEE, vol. 95, No.7, July 2007. T. M. Schmidl, D. C. Cox: “Robust Frequency and Timing Synchronization for OFDM“, IEEE Tran. Comm. Vol. 45, No. 12, Dec. 1997. Y. Yan, M. Tomisawa, Y. gong, Y. Guan, G. Wang, C. Law, Joint timing and frequency synchronization for IEEE 802.16 OFDM systems, Mobile WiMAX Symposium, 2007. IEEE

  27. Thanks!

  28. Simulation Result WiMAX SISO throughputwith Timing Offset = 89, Carrier Frequency Offset = pi, in the Pedestrian B Channel, 500 frame simulation Perfectsynchronized Both Timing Offset andFrequency Offset Corrected OnlyFrequency Offset Corrected Only Timing Offset Corrected

  29. Simulation Result WiMAX SISO throughput, Carrier Frequency Offset = = 3.1416, Pedestrian B Channel, 500 frames simulation Symbol-wise Residual Frequency Offset Estimation Without Residual Frequency Offset Correction Frame-wise Residual Frequency Offset Estimation PerfectlyCorrected WithoutCarrierFrequency Offset Correction