Closed-Form BER Expression for OFDM with the Effect of TI-ADC's Timing Mismatch

Timing mismatch in time-interleaved analog-to-digital converters (TI-ADCs) may cause a significant performance degradation in high-speed orthogonal frequency division multiplexing (OFDM) systems. To evaluate the impact of this impairment in such systems, we first derive a mathematical expression for the output of the discrete Fourier transform (DFT) unit that is used to demodulate the received OFDM signal samples. From the obtained expression, it follows that a TI-ADC with timing mismatch causes a phase rotation of the desired symbols and generates inter-carrier interference (ICI). Building on this result, we further derive an approximate closed-form bit error rate (BER) expression for quadrature amplitude modulation (QAM) or pulse amplitude modulation (PAM), assuming an additive white Gaussian noise (AWGN) channel and binary reflected Gray code (BRGC) mapping. Numerical results are provided to demonstrate the accuracy of the presented formula.