Advantage of Optical Fast OFDM Over OFDM in Residual Frequency Offset Compensation

We analyze the intercarrier interference (ICI) induced by residual frequency offset (RFO) in optical fast orthogonal frequency division multiplexing (F-OFDM) and compare this scheme with conventional OFDM in two scenarios: (1) the same RFO to subcarrier spacing ratio, and (2) the same discrete cosine or Fourier transform point size. In both scenarios, the ICI on a subcarrier in F-OFDM is dominated by the adjacent subcarriers, but the contribution to that in conventional OFDM is dispersed across the subcarriers. 19.5-GBaud 16QAM and 4ASK F-OFDM systems are investigated. 16QAM F-OFDM exhibits an RFO tolerance up to six times greater than that of 16QAM OFDM, when equalizers with the same tap number are used for the RFO compensation. 4ASK F-OFDM using 1-tap equalizers can achieve an RFO tolerance of up to four times greater than that of five-tap equalizer-based 4ASK OFDM.