Reduction of bandwidth requirement in DRoF systems using optical duobinary modulation

Digital Radio over Fiber (DRoF) transmission requires a high optical bandwidth due to the digitalization process. In this paper, a DRoF system which uses an optical duobinary modulation scheme to reduce the spectral occupancy of the transmitted signals is proposed. In this system, a transmission of a digitized 16-Quadrature Amplitude Modulation (16-QAM) radio frequency signal with 2.5 Gb/s over a Standard Single Mode Fiber (SSMF) is presented. Optical duobinary transmission is realized with a reduced complexity using a simple differential precoder and a single-arm Mach-Zehender Modulator (MZM). The performance of the proposed system is compared with a DRoF system that utilizes a Non-Return-to-Zero (NRZ) coding scheme. Simulation results reveal that the proposed DRoF system is capable of transmitting a digital signal of 20 Gb/s over a SSMF that can reach up to 70 km distance without dispersion compensation requirement. To prove this concept, transmission figure of merits, such as the EVM and the BER are evaluated according to the limits established by the 3GPP specification. Moreover, system performance is studied according to the wavelength plan allocated to TWDM-PON by ITU-T-G.989.2 standards for (NG-PON2). As a result of improvement, this system can effectively support high data rate requirement of DRoF transmission over Common Public Radio Interface (CPRI) protocol.