The inner receiver structure applied to OFDM system Advisor: Yung-an kao Student: Chian Young

outline OFDM system block OFDM baseband signal model Inner receiver structure Simulink Demo Future work

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

CFO in OFDM system CFO is due to the oscillator mismatch from up convert and down convert

SFO in OFDM system RX is faster than TX. TX is faster than RX. SFO is caused by the oscillator mismatch between A/D & D/A converter

OFDM baseband signal model OFDM baseband signal after IFFT at the transmitter side The received OFDM baseband signal after FFT n: n-th sample point k: k-th subcarrier l: l-th subcarrier

The received OFDM signal is influenced by channel effect, residual CFO, SFO, initial symbol timing offset T d : initial symbol timing offset H k : frequency response of channel : residual CFO : initial phase offset T s : sampling clock period at the transmitter T s ’: sampling clock period at the receiver OFDM baseband signal model CFO SFO

OFDM baseband signal model The ICI produced by residual CFO is much smaller compared to Gaussian noise.  combine I k,l and N k,l to (4)

Inner receiver structure Input signal FFT

Inner receiver structure FFTInitial coefficient Frequency Domain Equalizer Pilot-based phase estimator Phase compensation Outer receiver Hard decision Update coefficient of equalizer Phase compensation Training sequence DataData Pilot

One-tap RLS equalizer Recursive Least Square (RLS) algorithm: One tap λ: forgetting factor 0<λ <1. ξ: estimation error

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

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

Inner receiver structure FFTInitial coefficient Frequency Domain Equalizer Pilot-based phase estimator Phase compensation Outer receiver Hard decision Update coefficient of equalizer Phase compensation Training sequence DataData Pilot Re Im ∠2∠2 A’ B’ O C’

Future work New algorithm Combine CSI