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Study Of Ultra-Wideband Radio-over-Fiber System's Design And Application

Posted on:2011-12-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:J YinFull Text:PDF
GTID:1118360308461135Subject:Electromagnetic field and microwave technology
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The rapid increase of network bandwidth demand and more convenient access environment are two driving forces for radio over fiber research and development. On one hand, although high bandwidth efficiency modulation formats are available, with the emergence of a lot of new wireless services, the remained wireless resource becomes much scarcer. In order to supply high bit-rate services, researchers gradually turned to higher frequency such as millimeter waveband. On the other hand, with the optical access network's high speed growth, optical access demonstrates its advantages of broad bandwidth, low devices cost, simple and reliable structure. However, compared with wireless access, the wired access network has the disadvantages of high installation cost, inflexible access to mobile users. Under this background, the research of radio over fiber which combines both advantages of wireless access and wired access is attracting attentions both from academia and industry all over the world. This issue which transmits wireless signals in the fiber, called radio-over-fiber, has a lot of key problems to be solved. In this dissertation, several design issues of ROF systems have been intensively investigated for broadband wireless access applications under the sponsorship of national 863 programs and national natural science foundation in China.The main works of this dissertation are summarized as follows:1. Firstly, a novel approach of the UWB monocycle and doublet pulses generation based on dual-in dual-out LiNbO3 modulator is proposed, whose spectrum matches the FCC standard. Employing two lasers of different wavelengths and two modulators, the pulse shape modulation can be achieved, which is simpler than the existed proposals.2. Secondly, two novel ROF system schemes based on the LiNbO3 phase modulator are accomplished. Employing one MZM(Mach-Zenhder modulator) and one PM(phase modulator), the scheme of generating frequency-diversity binary phase shift keying(BPSK) millimeter wave signals at 20GHz/40GHz with the frequency multiplication technique is completed. The optical phase modulator does not suffer from the bias drifting problem as it does not need DC bias. The envelope of output optical signal after the phase modulator keeps stable and the optical signal can be used to carry uplink data back to the base-station. The system can generate two frequencies, which will decrease frequency selective fading effect. The second scheme generates binary phase shift keying(BPSK) millimeter wave signals at 30GHz. Two sidebands are filtered into two paths and are modulated by two phase modulators with complementary data. To obtain the same effect of using one phase modulator, the amplitude of the drivers on the two phase modulators can decrease to half of that in one phase modulator scheme. Thus, more stable amplifiers of lower magnification can be used to increase the system's reliability.3. Thirdly, the intensive research of Radio-over-Fiber system and the demonstration of HDTV service application based on heterodyne detection are completed, which includes theoretical analysis and experiments. In the experiment, the optical signal carrying DPSK information is coupled with the high power laser at the base station and the RF signal is demodulated by the delaying-multiplying structure at the terminal. The scheme has high dispersion tolerance and excellent receiver sensitivity of better than 10-30dBm. The second scheme of 2.5Gb/s optical PSK signals transmission and ASK wireless signals generation with 15GHz carrier based on heterodyne detection is demonstrated, which can realize polarization diversity and has excellent receiver sensitivity. Based on that ROF testbed, the first domestic demonstration of 1.3Gb/s uncompressed HDTV service is achieved with more than 20km wired(single mode fiber) and 5m wireless transmission. The video stream is smooth and fluent for the low bit-error-rate (<10-9).4. Finally, the scheme of the broad bandwidth wired and wireless hybrid access network with the integration of EPON and 60G ROF system is proposed. The wired and wireless signals are transmitted in one optical link. Through employment of the multi-antenna technology, the drawback of millimeter waveband signal's straight line radiation can be overcome. For different applications environment, an intelligent gateways including star and tree topologies are designed, which can achieve the distribution of wireless down link stream and the convergence of the uplink data.
Keywords/Search Tags:Millimeter Waveband Radio-over-fiber, Ultra Wideband, Binary Phase Shift Keying, Differential Phase Shift Keying, Optical Heterodyne Detection, Sensitivity, BER(bit error rate), Frequency Multiplexing, Polarization Diversity
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