Spectrum Efficiency Improvement for Quasi-Constant Envelope OFDM

Benefiting from low peak-to-average power ratio, constant envelope orthogonal frequency division multiplexing (CE-OFDM) is a promising technique in coherent optical communication. However, the spectrum efficiency of CE-OFDM is only half of the conventional coherent optical OFDM, which restricts its application. We proposed a novel quasi-CE-OFDM scheme with in-phase/quadrature modulator. Furthermore, a phase demodulation scheme based on Taylor series expansion is performed to reduce calculation complexity and avoid phase ambiguity. Simulation results show that the proposed scheme could double the spectrum efficiency effectively without losing the advantage of high nonlinearity tolerance.