DFT-Spread Hybrid OFDM-DFMA PONs Incorporating Directly Modulated DFB Laser-Based ONUs

OFDM is widely used in 4G mobile networks and is also expected to play a vital role in future 5G and beyond networks. Recently, we have reported new hybrid OFDM-DFMA PONs [1], where DSP-based digital filtering is employed for individual OFDM signals from various ONUs, and a single FFT operation and following data recovery processes are implemented in the OLT. Hybrid OFDM-DFMA PONs not only support good backward compatibility to OFDM-based 4G networks, but also offers various DSP-enabled SDN solutions of low complexity to meet the stringent requirements of 5G networks. However, due to multiple subcarrier modulation, OFDM suffers from a large peak-to-average power ratio (PAPR), which requires highly linear dynamic ranges of certain properties of modulators and amplifiers. To mitigate this problem, discrete-Fourier-transform (DFT)-spread OFDM is widely considered, which decreases the probability of independently modulated subcarriers being added up coherently by the IFFT [2]. DFT-spread OFDM has been applied in 4G standards [3]. In this paper, utilizing low-cost direct modulated DFB laser (DML)-based ONUs, DFT-spread hybrid OFDM-DFMA PONs is proposed and numerically explored, for the first time, to further enhance low-cost device-enabled network transmission performance.