Discrete Fresnel Transform Spread OFDM for Coherent Optical Fiber Communication

In the polarization-division multiplexed coherent optical fiber communication, conventional orthogonal frequency-division multiplexing (OFDM) and discrete Fourier transform spread OFDM (DFT-S-OFDM) sacrifice the baud rate with either zero-padded subcarriers in the high-frequency region to mitigate the frequency fading, or with a large cyclic prefix (CP) to eliminate the residual inter-symbol interference (ISI). In this letter, we propose a discrete Fresnel transform spread OFDM (DFnT-S-OFDM) scheme, which spreads information over both temporal and frequency dimensions. A low-complexity encoder was also developed for the proposed precoding scheme. Simulations show that DFnT-S-OFDM is more resilient against the frequency fading than OFDM and against the residual ISI than DFT-S-OFDM. Therefore, it maximizes the net data rate by reducing the CP length or increasing the useful signal bandwidth.