Study On Fronthaul Scheme Based On WDM-PON

Mobile communication technology has developed into the 5G era,with the massive data transmission,the access of a large number of mobile devices,and the emergence of new application scenarios,the fronthaul network is facing enormous pressure.The fronthaul network is defined as a network where active antenna unit（AAU）and distributed unit（DU）are connected.It is very important to choose a suitable fronthaul network bearing scheme to meet the needs of 5G communication.Wavelength division multiplexing passive optical network（WDM-PON）has a large bandwidth and supports higher-speed data transmission,and it is one of the best scheme for 5G fronthaul network.This thesis studies the fronthaul network bearer scheme based on WDM-PON.Firstly,the working principle,advantages and disadvantages of several bearing schemes of 5G fronthaul network are analyzed and compared:optical fiber direct-drive,passive wavelength division multiplexing（WDM）,active wavelength division multiplexing/optical transmission network（WDM/OTN）and WDM-PON.Among them,WDM-PON can save fiber resources and support large-capacity,high-speed data transmission,becomes one of the options for 5G fronthaul networks.Analyzes the working principle and advantages of WDM-PON system,principle,advantages and disadvantages of four common colorless ONU technologies:wavelength tunable laser,broadband light source spectrum division,FP-LD laser and remodulation technology,and finally choose reflective semiconductor optical amplifier（RSOA）is used as a light source on the ONU side of the WDM-PON fronthaul network bearer scheme to realize a colorless ONU.Secondly,the WDM-PON fronthaul bearer scheme based on multi-carrier modulation orthogonal frequency division multiplexing（OFDM）is studied.The modulation,demodulation principle,advantages and disadvantages of OFDM signal and NRZ signal are studied.The OFDM signal is used as a downlink modulation format in the WDM-PON fronthaul network.The downlink transmits 10Gb/s OFDM signal,the uplink transmits 10Gb/s NRZ signal to form a symmetrical two-way transmission system.The system is built on the optical communication simulation software,the performance changes of the system under different optical fiber transmission distances are simulated and analyzed.The results show that after20km of optical fiber transmission,the downlink OFDM signal constellation is neatly distributed,the uplink NRZ signal has a large eye opening,the Q value is 20.6,which meets the transmission requirements of the fronthaul network,and the OFDM-based WDM-PON system can become the bearer scheme of the fronthaul network to serve the fronthaul network.Finally,the D-band RoF-WDM-PON fusion system based on RSOA remodulation is studied.The working principle,characteristics of RoF system,three millimeter wave modulation types are introduced in detail:SSB,OCS,DSB,and these three modulation types are simulated,and SSB is selected as the generation method of OFDM optical millimeter wave signal.The advantages of RoF technology are high transmission bandwidth and large transmission capacity.The integration of RoF technology and WDM-PON system can make the carrying capacity of the fronthaul network stronger,provide users with wired and wireless access services at the same time,and realize the diversity of access methods.Then,the modulation principle and generation method of PAM4 signal are introduced;D-band（110-170GHz）has high frequency and large bandwidth in the millimeter wave,it can allow higher rate data transmission and reduce the signal attenuation in the atmosphere and rainfall.Therefore,this thesis combines D-band RoF wireless access and PAM4-WDM-PON wired access to form a RoF-WDM-PON wired and wireless converged access system fronthaul network.The downlink transmits 25Gb/s 120GHz OFDM millimeter wave wireless signal and PAM4 wired signal,uplink transmits 10Gb/s NRZ signal,RSOA is used as uplink laser source to achieve colorless ONU,and the system is simulated and verified by optical communication simulation software.The results show that under the fiber transmission distance of 20km,the constellation points of the downlink OFDM signal are evenly distributed,the eye diagram of the PAM4 signal is complete,and the bit error rate of the uplink signal is 2.76×10^-22.The transmission of downlink OFDM wireless signals and PAM4 wired signals is realized,this system can enhance the carrying capacity of the fronthaul network,serve wired and wireless users at the same time.