| Nowadays our human society has arrived in the era of advanced information age. Along with the rapid development of novel ultra broadband multimedia business such as video conference, telemedicine,online teaching, three-dimensional (3D) display, Augmented Reality (AR)and ultra-high definition television (HDTV)/blue-ray television and the continuous emerging of mobile application platforms such as mobile video live, online shopping, broadband games, cloud service,navigation/positioning, electronic bank, etc., the demand for information transmission bandwidth of human society grows at an alarming rate,which leads to an dramatic increase in the communication capacity of wired and wireless access network. Meanwhile, with the fast construction and development of wisdom city, people are increasingly dependent on network, and then at any place (fixed and mobile location) people hope to connect with the ubiquitous network at any desired time. Thus higher requirements of flexible selective for network access way are proposed.The fiber optical access network, using the large bandwidth and low loss of the fiber, can realize the high speed optical millimeter-wave's long distance transmission. The current fiber-based passive optical network(PON) has become the main solution to solve the bottleneck of the optical network, and is one of the effective methods to address the issue of "the last mile" access. It can provide huge bandwidth resource to meet the current and future bandwidth requirement of the ultra-wideband new business, but its flexibility is limited by laying optical fiber link. While the wireless access network can realize the flexible and convenient access,to meet the need of the diversity access for the terminal user. But the transmission rate of the current wireless access communication, such as the long term evolution (LTE) and global microwave interconnect(WiMax), is far less than that of the fiber access communication.Moreover, the low frequency spectrum used in these narrow-band wireless access communication has been quite congestion. Therefore, the radio-over-fiber (RoF) technology, integrating the advantages of fiber-based optical access and wireless access communications, comes to being. On the one hand, the RoF technology reveals the compatibility between the fiber optical access and wireless access communications on the network distribution, namely, they all use the fiber to transmit the optical signal. On the other hand, it further promotes the fusion between them. In the future broadband access network, both the optical wired access and wireless access communications will play a huge role. They are complement with each other, together to meet the requirements of the bandwidth, transmission rate and access flexibility, driven by new communication business The hybrid access network, based on the fusion of the current optical fiber access network based on wavelength division multiplexing-passive optical network (WDM-PON) and the wireless access network based on RoF, has the advantages of the low loss and large broadband of the fiber, and the flexible and convenient access of the wireless access network. It not only can simplify the network structure by the layer fusion of the wired and wireless access networks, but also can meet the requirements of the bandwidth, transmission rate and access way for the new business. Moreover, it is gaining more and more attentions and researches.The network architectures of the wired access network based on WDM-PON and the wireless access network based on RoF, as well as the spectrum characteristics of the baseband and mm-wave optical signals,have been studied in this paper. Moreover, it mainly focuses on analyzing and solving several key techniques in broadband hybrid wired/wireless access network based on the fusion of PON and RoF. That will provide an important reference for the architecture design and practical application of the actual hybrid access network. The main innovations are summarized as follows:I . About the network architectures for alternatively providing wired and wireless accessesUnder the analysis of the time-frequency characteristics of the baseband and mm-wave optical signals, the idea of the signal fusion is proposed. And by combining the baseband optical signal used in PON with the mm-wave optical signal used in RoF into an unified optical signal, it can realize the deeper integration of the wired and wireless access networks.(1) A novel full-duplex fiber-wireless system based on homodyne/heterodyne coherent detection has been proposed to provide alternative wired and wireless accesses. The optical spectrum structure of the unified optical signal is used as that of the baseband optical signal which is used in fiber-based optical access network. Since the unified optical signal has a simple structure, the spectrum efficiency is greatly improved. At the same time, a tunable laser at the hybrid optical network unit (HONU) is used to provide optical local oscillator (LO) for homodyne/heterodyne coherent detection and the optical carrier for uplink, so the downlink vector signal's wired or wireless access and the full-duplex transmission are realized.(2) To improve the (1),another full-duplex fiber-wireless system for alternative wired and wireless accesses based on differential quaternary phase-shift (DQPSK) optical sideband mm-wave signal has been proposed. The single sideband (SSB) modulation format is used, which can effectively reduce the influence on the millimeter-wave (MMW)signal induced by the fiber dispersion, and thus increase the transmission distance. Moreover, the blank optical carrier included in downlink optical signal is used as the uplink optical carrier. So unlike the (1), the HONU no longer need an extra light source. The structure and cost of the HONU are substantially simplified and reduced.(3) Based on the study of optical frequency multiplication (OFM)technique using Mach-Zehnder Modulator (MZM), a full-duplex hybrid PON/RoF system for alternative wired and wireless accesses using OFM has been proposed. In this scheme, for the wired access, a 20GHz radio frequency (RF) LO and a 20GHz quaternary quadrature amplitude modulation (4QAM) signal are simultaneously generated by heterodyne beating. Then the former is used as the RF LO to coherently demodulate the latter, to realize the wired access. Meanwhile, the former can also be used as the LO to down-convert the wireless access uplink RF signal,which reduces the bandwidth requirement of the uplink modulator.(4) Based on the study of the direct detection-orthogonal frequency division multiplexing (DD-OFDM) technique, a bidirectional system with a unified optical OFDM signal for alternative wired and MMW wireless accesses based on direct detection has been proposed. The important feature of this system is that at the HONU, a RF LO generated by direct detection is transmitted with the downlink RF-OFDM signal to wireless user terminal. So at the wireless user terminal it can be used as the RF LO to down-convert the downlink RF-OFDM signal into an intermediate frequency (IF) OFDM signal based on power detection, which makes the wireless user terminal free from the RF source. Moreover, the RF LO can also be used as the uplink RF carrier. As a result, the structure of the wireless user terminal is effectively simplified.(5) Through the studies of the phase information periodicity of the binary phase-shift keying (BPSK) signal and the modulation characteristics of the optical phase modulator (OPM), a simple bidirectional hybrid optical system for alternatively providing wired and wireless accesses based on an OPM has been proposed. The difference of this scheme is that, the network structure for downlink optical signal generation is simple and the required optical devices are less. Only an OPM along with an optical band-pass filter (OBPF) is used to generate the MMW optical signal at the optical line terminal (OLT) and only one tone of the MMW optical signal carries the downlink BPSK signal.Moreover, only a photodiode (PD) at the HONU is used to generate the downlink wired and wireless access electrical signals.?. The methods of the multi-band wireless access(6) A multi-band access RoF system based on SSB and optical carrier suppression (OCS) modulations has been proposed. At the base station (BS), by using two tunable fiber Bragg grating (FBGs), the multi-tone optical signal can be decomposed as different SSB optical signals. These SSB optical signals are formed by different optical frequency components. After heterodyne beating, these SSB optical signals are down-converted into electrical MMW signals with different frequencies, to realize the alternative multi-band wireless access. Since only one tone of the multi-tone downlink MMW optical signal is modulated by the data, the impairment induced by fiber dispersion is mitigated, and the optical spectrum structure of the downlink MMW optical signal is simplified. |
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