The Research Of Key Technologies On Optical Access Network Based On OFDM

Driven by exponentially growing demand for ever-increasing multimedia services、IPTV and HDTV, broadband wired and wireless access networks will migrate to40-Gb/s or above per channel in the near future. Thus, it is attractive to simultaneously distribute both wired and wireless access signals in an integrated platform. Wavelength division multiplexed passive optical network (WDM-PON) for wired access networks has been widely investigated for its advantages of high capacity, large coverage range, upgradeability, and cost-effective configuration, but it is inconvenient and fixed by the cable. With respect to wireless access networks,60-GHz mm-wave wireless access system has garners considerable research momentum to offer huge unlicensed bandwidth (-7GHz), and radio-over-fiber (RoF) technology in millimeter(mm)-wave band is considered as an effective solution to upgrade the capacity of the current mobile cell network. Moreover, OFDM has shown its robust dispersion tolerance and high spectrum efficiency that rivals single carrier system in both wired and wireless fields. The OFDM modulation format has been widely employed in wireless system and has shown great potentials in wired system. Combining the advantages of large bandwidth and coverage range in fiber communication with the advantages of high flexibility in wireless communication, the convergence of OFDM based WDM-PON and RoF technologies on an integrated platform is promising to provide broadband and ubiquitous access with cost-effective configuration.In this paper, firstly, we summarize the generation of OFDM signal and discrete Fourier transform(DFT) implementation for OFDM. We highlight the generation of optical millimeter-wave OFDM signal, and compare the difference between double sideband modulation (DSB) and single sideband modulation (SSB) OFDM signal of external modulation technology. Secondly, we propose an OFDM-RoF system based on SSB modulation and direct detection. The simulation results demonstrate that the EVMs of the4QAM-and16QAM-OFDM signals are much below the FEC limits. Meanwhile, the theoretical analysis and simulation is preformed to verify that an optimum modulation index exists which can bring on an optimum transmission performance regardless of the fiber length. Thirdly, we propose A novel lightwave centralized full-duplex WDM-PON access network based on SSB-OOFDM for providing wired and60-GHz band wireless accesses alternately. At the OLT, the multi-channels with10-Gb/s4-QAM-RF-OFDM signals are SSB modulated on the optical local oscillators (OLOs). At the RN, one OOFDM signal along with two OLOs is abstracted and switched to the corresponding HONU, where the signal can be downconverted to the10-GHz or60-GHz band RF-OFDM signal by one OLO for wired or wireless access, while the other one is used to bear the uplink signal. Since the HONU is free from the light sources, the system complexity and cost are reduced. Full duplex transmission over25km fiber have been demonstrated that the error vector magnitude (EVM) of the down-and up-link signals are much below the FEC limit for both the wired and60-GHz band wireless access services.