Direct-detection OFDM-QPSK system performance improvement enabled by DFT spread and receiver-based ISFA algorithm

We experimentally demonstrate a direct-detection orthogonal-frequency-division-multiplexing quadrature-phase-shift-keying (OFDM-QPSK) system that is capable of delivering a 32 Gbaud OFDM-QPSK signal over 7 km single-mode fiber-28 (SMF-28). Intra-symbol frequency-domain averaging (ISFA) channel response estimation is applied to suppress in-band noise, while discrete Fourier transform-spread (DFT-spread) is used to reduce the peak-to-average power ratio (PAPR) of the transmitted OFDM signal. With