Research On Key Technologies For High-Speed Broadband Radio-over-Fiber Access Network Based On FTTx

With the rapid development and application of mobile communications,big data and cloud services,the demand for data and diversified services of wireless networks is increasing dramatically.The transmission bandwidth for subscribers will reach the Gbps level in the future fifth-generation(5G)mobile communications system,as well as the carrier frequency will move toward a higher microwave bands.Radio-over-fiber(RoF)technology has become a key technology to realize low loss long-distance transmission of high-frequency carriers and effective coverage of denser cellular with low costs owing to its unique advantages.In view of the rapid development and wide application of the fiber to the X(FTTx)access network,it can not only significantly improve the performance of RoF systems for an efficient coverage by combining the RoF technology with the FTTx network,but also can make full use of the existing fiber resources for a further reduction of the system construction cost,maintenance and operation cost,which is more consistent with the development trend of future diversified network and of great scientific significance and practical value for the promotion of future 5G systems,especially for the high-band communications.On the basis of the adequate investigation of the present status of the national and international research,this dissertation has carried out a detailed theoretical,technical and experimental investigation of several key scientific and technical issues for the application of RoF systems,especially in future 5G communications system.The main innovative contributions of this dissertation are listed as follows.(1)In the experiment of the high-frequency RoF system,it is found that the eye diagram of the recovered signal at the receiver terminal has a cyclic phenomenon of "opening decreasing-closing-reopening" due to influence of ambient factors such as the temperature,which causes the system unable to work properly.The reason for this phase-shift characteristics of the high-band radio frequency(RF)signal transmission through an optical fiber is theoretically analyzed.A system implementation scheme by means of the carrier recovery technique is proposed and verified experimentally to solve the phase-shift phenomenon.(2)A RoF system structure of central station(CS)-subcentral station(SCS)-base station(BS),and a full-duplex WDM-RoF communication technique are proposed.A 10-GHz full-duplex RoF experimental system is established to verify the performance of this system.The proposed technique and structure can improve the system performance against the chromatic dispersion and phase-shift characteristics,and realize an effective compatibility between the RoF system and the FTTx network.Structure of base station without local light sources is achieved by the centralized allocation of the upstream optical carriers,which leads a reduction of the cost and complexity of base stations.Thus the cost of future 5G network construction can be greatly reduced.(3)A TWDM-RoF technique on the basis of CS-SCS-BS structure is proposed.A 26-GHz TWDM-RoF experimental system with data rate at 1.25Gbps over a 40-km standard single mode optical fiber,as an example,is established to verify the validity of this technical scheme.In this scheme,the separation cost of the upstream optical carrier and downstream signal at each base station can be reduced as well as a higher spectrum utilization of single wavelength.By the additional optical cross-connect unit at the SCS,flexible configuration of downstream and upstream carrier resources can be realized,which improves the system efficiency and reduces energy consumption.(4)An adaptive multi-rates optical transceiver and a real-time bit error rate tester(BERT)module for 5G bearer network are designed and developed.The adaptive optical transceiver with small size,low cost and low power consumption can operates form 100Mbps?10.709Gbps.The BERT module can realize the bit error test at any rate between 10Mbps and 11 Gbps.Compared with the existing expensive BERT(Anritsu,MP1800A),the error detection results of this BERT module are consistent.It can also be placed into the OLT,ONU and OADM to implement a real-time monitoring of BER performance,which has a wide application prospect.