Qi Wang July 3rd, Mobile Communication Seminar

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

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 3

LTE Physical Layer 4 slot

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

Carrier Frequency Error in OFDM 6 Received signal: : Carrier Frequency Offset normalized in subcarrier spacing N: FFT size 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 (~1.667)

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

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

9 WiMAX Frame Structure 1st Preamble: frame start detection, fractional frequency offset estimation 8 pilots on subcarriers { }: Residual frequency offset tracking 2nd Preamble: Integer frequency offset estimation

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

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

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

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

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

15 3. Integer Frequency Offset Estimated integer frequency offset Received Preamble shifted by 2i Defined Preamble Defined Preamble: Received Preamble:

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

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

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

LTE Frame Structure 19 Resource Block Resource Element

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 Synchronization Signals subcarrier

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

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

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

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

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

Reference 3GPP TS V rd 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,” E. Dahlman, S. Parkvall, J. Sköld, P. Beming: “3G Evolution: HSPA and LTE for Mobile Broadband“, Elsevier 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 T. M. Schmidl, D. C. Cox: “Robust Frequency and Timing Synchronization for OFDM“, IEEE Tran. Comm. Vol. 45, No. 12, Dec Y. Yan, M. Tomisawa, Y. gong, Y. Guan, G. Wang, C. Law, Joint timing and frequency synchronization for IEEE OFDM systems, Mobile WiMAX Symposium, IEEE 26

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Simulation Result 28 WiMAX SISO throughput with Timing Offset = 89, Carrier Frequency Offset = pi, in the Pedestrian B Channel, 500 frame simulation Perfect synchronized Both Timing Offset and Frequency Offset Corrected Only Timing Offset Corrected Only Frequency Offset Corrected

Simulation Result 29/17 WiMAX SISO throughput, Carrier Frequency Offset = = , Pedestrian B Channel, 500 frames simulation Perfectly Corrected Frame-wise Residual Frequency Offset Estimation Symbol-wise Residual Frequency Offset Estimation Without Residual Frequency Offset Correction Without Carrier Frequency Offset Correction