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Förslaget inkom 2007-03-20

Performance of Coded OFDM in Hybrid Radio-over-Fiber Links


The increasing demand for more bandwidth and high capacity is growing exponentially since the wireless communication is entering a new phase where the focus is shifting from voice to multimedia services which makes the next generation of the wireless networks tend to extensively use microcells or picocells. Using more microcells and picocells leads to improved spectral efficiency through increased frequency reuse, but at the same time, smaller cell sizes means larger number of base stations (BS) or remote antenna units (RAUs) are needed in order to achieve the wide coverage required of ubiquitous communication systems. Furthermore, extensive feeder networks are needed to service large number of base stations and RAUs. The usage of more microcells will result in an increasing number of base stations which will make the cost of the system increase highly. This is where radio-over-fiber (RoF) technology comes in. It achieves the simplification of the base stations and RAUs through consolidation of radio system functionalities at a centralized head end, which are then shared by multiple RAUs. By using fiber based wireless access schemes such as RoF, high-speed multimedia can easily be supported. RoF refers to a fiber optic link where the optical signal is modulated at radio frequencies and transmitted via optical fiber. Hybrid fiber-radio technology is found to be a hot topic of the recent discussions on the wireless local area network (WLAN) in the next generation for broadband applications.
Employing RoF system into OFDM based WLAN will introduce the distortion from the RoF link, such as dispersion, attenuation, nonlinearity and so on that will affect the whole system performance; especially the nonlinearity will cause intercarrier interference (ICI) which could make harmful impairment to the OFDM signals. Since the RoF system can provide many advantages such as cost, power and capacity it is necessarily to find out if the hybrid RoF transmission link can achieve the required performance in an OFDM based system such as IEEE 802.11a. The AM/AM and AM/PM nonlinearities of the fiber link and the fading multipath channel will be considered as the two critical factors that limit the performance.


This master thesis work will investigate uplink and downlink performance of coded OFDM signals in Radio-over-Fiber links. Interesting questions to be answered is how much improvement can be achieved to combat the nonlinear distortion under a certain coding complexity.


- Fundamental knowledge in error control techniques and digital communication.
- Candidates for the thesis work should have major in electrical engineering.
- Knowledge in Matlab.


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