Flexible and fast multi-level modulation format identification using optical orthogonal frequency division multiplexing redundancy subcarriers

Compared with the orthogonal frequency division multiplexing (OFDM) communication system, the subcarrier-index modulation OFDM communication system can alleviate the problem of peak-to-average power ratio and the frequency offset sensitivity. Therefore, the problem of inter carrier interference (ICI) and low power of the radio frequency amplifier in OFDM communication system can be solved to some extent. A fast and flexible modulation format recognition (MFR) scheme utilizing OFDM redundancy subcarriers is proposed in order to solve the MFR problem in coherent optical OFDM transmission. The scheme uses the silent subcarrier position of OFDM to carry modulation format information (MFI) and the receiving end decodes the MFI index by comparing the modulus values of the redundant symbols. It can recognize the phase shift keying (PSK) and multiple quadrature amplitude modulation (M-QAM) modulation formats block by block. The number of symbols required by the proposed MFR is equal to the number of OFDM subcarriers, and the average time to get the recognition result in a block is O(1). We numerically investigate the proposed MFR among 20 Gbaud 4/16/32/64 QAM and 8/16 PSK. The results show that the correct recognition rate of the proposed scheme is not affected by the modulation formats. In particular, the proposed MFR is a potential solution for future flexible optical networks.