Sensitivity of FFT-equalised zero-padded OFDM systems to time and frequency synchronisation errors

A detailed analysis of the performance of FFT-equalised (FFT-EQ) zero-padded OFDM (ZP-OFDM) systems in the presence of time and frequency synchronisation errors is given. In order to achieve low-complexity in equalisation, FFT-based demodulation and per subcarrier channel equalisation is considered for ZP-OFDM. It is shown that, unlike in cyclic-prefix OFDM (CP-OFDM), FFT-equalised ZP-OFDM is sensitive to time synchronisation error causing ICI. An exact expression for ICI is derived in terms of time and frequency synchronisation errors for both AWGN and frequency-selective Rayleigh fading channels. Moreover, based on the Gaussian approximation for the ICI noise, expressions are derived for the symbol-error-probability (SEP) of a FFT-EQ-ZP-OFDM system with time and frequency synchronisation errors in both AWGN and frequency-selective Rayleigh fading channels. Numerical results demonstrate the sensitivity of FFT-EQ-ZP-OFDM systems to synchronisation errors.