The Research Of Several Key Technologies Of Hybrid Access Network Based On ROF-PON Integration

The vigorous development of access network has promoted the update of wireless and wired access technologies. Wired access technologies such as fiber access and wireless access technologies such as long term evolution (LTE), wireless-fidelity (WiFi), worldwide interoperability for microwave access (WiMax) are the development trend of the future broadband access network. However, the wireless frequency sources at the low-frequency GHz band are much more crowded. The millimeter-wave (mm-wave) band signal has huge and free bandwidth resources, but the transmission loss is serious. Using the characteristics of low attenuation and rich bandwidth resources of the optical fiber, radio over fiber (ROF) technology can solve the transmission problem of mm-wave signal, so as to reduce the difficulty to realize the broadband wireless access system. As a wired access technology, passive optical network (PON) is developing fast to realize the future "last mile" access because of the characteristics of low price, easy to operate, maintain and administrate. The compatibility of PON network and ROF wireless access backhaul network has promoted the integration of wired and wirelesss access networks. And this hybrid access network has many obvious advantages.In this thesis, firstly we give an overview of the concept of the access network, the structure, feature and application of ROF and the process of development of PON. Then we elaborate the research of integration of the two access networks. Moreover, we analyze the theory of ROF and the method to generate different spectrum structure mm-wave signals using the external modulation technology in detail. We also research the influence of fiber transmission to the mm-wave signal. Then we introduce the theory, structure and key techniques of different PON systems and in the end we proposed the alternative access network theory of the integration of ROF and PON. Secondly, we propose a novel full-duplex ROF-PON link based on SSB optical mm-wave with4-pulse amplitude modulation (PAM) signal. This system can provide alternative wired and wireless accesses for the user terminals using two fiber Bragg gratings (FBGs) in the hybrid optical network unit (HONU). Through the pre-distortion of the transmitted multilevel PAM signals with the square-root law in the central station (CS), we obtain an equal level spacing signal for both wired and wireless access at the user terminals. Since the optical carrier of uplink is obtained by abstracting it from the downlink signal, no laser source is required at the HONU. The uplink for wired and wireless accesses can be co-shared through a process of the uplink wireless signal. The calculated error vector magnitude (EVMs) and eye diagrams based on the simulation link of this scheme demonstrate that both the down-and up-links for the wired and wireless accesses can keep good performance even if the transmission link is extended to40km. Thirdly, we proposed another ROF-PON system based on polarization multiplexing. The alternative wired/wireless access in the user terminals can be realized by a polarization controller (PC) in the HONU to control the polarization state of the downlink mm-wave signal. In this scheme, the polarization state of two sidebands of the OCS mm-wave signal is orthogonal and the downlink signal is carried by the upper sideband. In the HONU, the orthogonal polarization state downlink mm-wave signal can be converted to optical baseband signal for wired access and optical mm-wave signal for wireless access by PC and polarization beam splitter (PBS). The photodiode (PD) can be co-shared to convert the optical signals to electrical ones to realize the downlink access. The uplink can also be co-shared as the SSB-PAM system and this can simplify the structure of the system greatly. We also setup a duplex simulation link to prove the feasibility of our proposed system. The analysis of the bit error rate (BER) curves and eye diagrams of the duplex link demonstrates that our proposed.polarization multiplexing system can realize alternative wired and wireless access and the transmission performance of the system is good. Lastly, conclusions and prospect of the future research on integrated network are given in the last chapter.