Browsing by Author "Chanda, Debashis"
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- ItemOpen AccessWireless on fiber(2004) Chanda, Debashis; Sesay, Abu B.; Davies, Robert J.Combined deployment of optical fiber technology and wireless networks provides great potential for increasing the capacity and the Quality of Service. 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. The Wireless on Fiber concept means to transport information over optical fiber by modulating the light with the radio signal. This thesis discusses the effects of using fiber in conjunction with wireless local area network standard 802.11a (WLAN) to distribute RF signal. To achieve high throughput, the 802.11a LAN uses Orthogonal Frequency Division Multiplexing (OFDM) based multi-carrier wideband modulation technique. The OFDM is one of the most favored modulation techniques in WLAN scenario due to its efficient implementation and robustness against multi-path and narrowband interference. One of the biggest drawbacks of the OFDM is its high peak to average power ratio (PAPR). High PAPR of OFDM makes it unusable in non-linear systems. To transport wireless signal over a fiber, OFDM based radio signal is modulated on to an optical carrier using a Mach-Zehnder (MZ) electro-optic modulator. Mach-Zehnder modulator has a sinusoidal electrical to optical power transfer characteristic, which restricts OFDM signal to occupy a narrow dynamic range in the most linear region of its power transfer characteristic. To overcome this limitation, OFDM signal predistortion methods have been proposed which makes OFDM more suitable for transmission over an optical system. For better system performance Mach-Zehnder modulator has to be biased at a desired point on the power transfer characteristic of Mach-Zehnder modulator. However, the desired bias point of Mach-Zehnder modulator drifts over time which deteriorates overall system performance. A novel bias drift tracking and controlling mechanism has been investigated and proposed in this thesis. This method has no adverse effects on system performance. We then discuss ways of transporting wireless signal using multimode fibers. Different multi mode fibers have been investigated and a suitable model has been proposed to mitigate multimode fiber dispersion in carrying wireless signals.