An improved combined symbol and sampling clock synchronization method for OFDM systems 指導老師 : 黃文傑, 高永安 姓名 : 吳政修

outline Synchronization Proposed Simulation Conclusion

synchronization Carrier frequency synchronization Timing recovery 1.symbol synchronization (coarse) short training symbol 2.sampling clock synchronization (fine) align the RX sampling clock frequency to that of the transmitter.

Carrier frequency synchronization error phase rotation Symbol timing error ISI Sampling clock frequency error ICI and ISI.

Ex. If the sampling clock specification of 10 parts per million and the sampling frequency is 5MHz, then the symbol timing has a drift of about 50 samples per second.

Proposed Use the correlation method based on GI to do the coarse synchronization. A path time delayed estimation is employed to improve the accuracy of coarse symbol synchronization. Finally use a delay-locked loop to do the sampling clock synchronization and maintain the symbol timing.

System model Signal and channel models N: subcarrier M: pilot subcarrier symbols multipath fading channel the FFT output within perfect synchronization

Synchronization error effects Symbol timing error Sampling clock errors

Combined symbol and sampling clock synchronization Coarse synchronization ML estimate

Fine synchronization: symbol timing acquisition the estimates of the channel frequency response The channel power delay profiles

The estimated first path time delay The path energy threshold

DLL tracking The output of the NCO The integer part adjusts the FFT window position. The fraction part adjust the sampling instant of the ADC.

Fine synchronization: DLL tracking

DLL tracking jitter the received pilot The received pilots are cross-correlated with the early reference pilot the output is

The tracking error The variance of the loop tracking error

Simulation www

we

Conclusion The symbol synchronization and the sampling clock adjustment are important in OFDM systems.