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The Study Of Transmission Baseband Signal Base On The Radio-Over-Fiber System

Posted on:2011-12-11Degree:MasterType:Thesis
Country:ChinaCandidate:Q ZhangFull Text:PDF
GTID:2178360305461234Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
ROF (Radio-over-fiber) transmission system is a new technology which combines wireless communications with optical communications, using the mobility of wireless technology instead of optical communications with fibers, and transmitting wireless signals, which have high loss in the air, with high-capacity fibers. With the increase of customers' information, more and more transmission systems transmit baseband signals to meet people's needs. Therefore, the technology of transmitting ROF uplink and downlink signals and baseband signals simultaneously in a system will be widely used in the future high-capacity system.Firstly, carrier suppression millimeter-wave transmission systems using intensity modulation and phase modulation with FBG at the central station are simulated with MATLAB, and the spectrogram, system bit error rate, eye diagrams at the receiver and power penalty of the two systems are analyzed and compared. Two systems using carrier-suppressed sideband technique to transmit downlink signal are analyzed based on Optisystem. The first system uses the Mach-Zehnder modulator to generate carrier-suppressed sideband signal in the center station, which uses the upper sideband to carry downlink signal to the base station system. Two different types of baseband signals, OOK signal and DPSK signal, are added to the system to transmit with the uplink signal. OOK baseband signal is coupled to the central frequency of the laser to transmit to the base station with downlink signal over a single mode fiber (SMF), and the low sideband is reused to transmit uplink signal. While DPSK baseband signal is modulated to the sideband of the unmodulated signal of the carrier-suppressed sideband signal, and then transmitted to the base station with downlink signal over a SMF, and the sideband which carries DPSK baseband signal is reused to transmit uplink signal. The uplink signals of the two systems are modulated and demodulated at the base station. The spectrogram, bit error rate curve, power penalty, modulation depth of the modulator and sensitivity of the receiver are analyzed. The second system uses Four-Wave Mixing(FWM) effect of highly nonlinear fiber and filters to generate carrier-suppressed sideband signal. Single channel system transmitting downlink signal is verified, and dual channel system transmitting baseband signal and uplink signal are analyzed based on it. The spectrogram, bit error rate curve, and power penalty of the dual channel system are analyzed.The results show that the ROF system with carrier-suppressed sideband signal generated by phase modulation is better than that generated by intensity modulation. By adding baseband signal in the two systems, and for the first improved system, the power penalty of baseband signal, uplink signal and downlink signal are reduced when the OOK baseband signal is transmitted for 40 km, but the receiver sensitivity is weakened, and the influence of the central station on the receiver sensitivity becomes larger. With the addition of DPSK baseband signal, the anti-dispersion capability of uplink signal and baseband signal is enhanced, the downlink transmission performance and receiver sensitivity become better. Besides, the influence of modulator at the central station on the receiver sensitivity is reduced. The transmission performance of downlink signal is not changed in the second improved system, but the receiver sensitivity is enhanced. The added uplink signal and baseband signal have good anti-dispersion capability. Therefore, the improved systems achieve the purpose of mixed-signal transmission.
Keywords/Search Tags:ROF, Carrier suppression, Baseband signal, Down-link signal, Up-link signal, Four-wave mixing(FWM)
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