Study On The Radio Over Fiber Transmission System And The Application In Wireless Local Area Network

As the continuously development of telecommunication technology, future telecommunication system will have to provide network service anytime anywhere. This requires wireless communication system support higher bit rate and wider coverage, especially for short range access in buildings. How to provide high bit rate wireless transmission and access is a problem yet to be deal with. Radio over Fiber combines deployment of optical fiber technology and wireless networks provide great potential for increasing the capacity and the quality of service for network access. By using Wireless on Fiber technology, the capacity of optical networks can be combined with the flexibility and mobility of wireless access networks without significant cost increment. This thesis discusses the effects of using fiber in conjunction with wireless local area network to distribute RF signal. The main contributions of this paper are as follow:(1) An OFDM based wireless LAN(802.11a) was described in this paper. Basic theory and working mechanism of OFDM technology was presented. We discussed in detail about the characteristic of OFDM signal and architecture of 802.11a wireless LAN MAC layer. We established the simulation model for the transmitter and receiver of 802.11a wireless LAN system.(2) Techniques for sending wireless signal over fiber were described. We discussed different optical link components and their role in analog optical link. Merits and demerits of each component were also discussed. We have described signal modulation techniques using Mach-Zehnder electro-optic modulator and provided figures obtained from optical spectrum analyzer to shown optical double side band and optical single side band modulation. Wireless over fiber simulation system was setup.(3) Nonlinear distortion of Mach-Zehnder modulator was discussed in detail. A mathematical upper bound of the modulation index for nonlinear distortionless transmission of wireless signal over fiber was derived according to the speciality of analog optical link modulation process.(4) The high peak to average power ratio problem of OFDM signal and its adverse effects on system performance was analyzed. An OFDM signal predistortion method was proposed, which perform a soft envelope clipping to the OFDM signal to mitigate nonlinear distortions of MZ modulator. Experimental results shown that the proposed method could successfully minish the dynamic range of OFDM signal and restrain both inband and out of band noise of the wireless over fiber system and make OFDM signal more suitable in case of transmission over fiber.(5) A novel Mach-Zehnder modulator bias control mechanism was proposed, which tracks quadrature bias point drift of MZ modulator by monitoring the second harmonic component of short training sequence in OFDM frame. According to the mechanism proposed, a Mach-Zehnder modulator bias point feedback control system was established. Evaluation performance of the proposed system from different aspects like optical power tap ratio, Laser RIN photo diode responsivity etc were give. Experimental results show excellent performance of the proposed system in MZ modulator bias drift tracking in different adverse conditions.(6) EPON broadband wireless access system was designed. The architecture and function-partition of the system was described. Hardware design and implementation of ONU-BS was discussed in detail. Wirelss data transmission throughtput of the system was tested. According to the experimental results, the system has great performance in wireless data transmission. The proposed system combined EPON and 802.11a WLAN technology and realized broadband optical transmission wireless access system for the next generation access network.