Abstract
With the growth of global communication and internet in recent years, the requirements for signal transmission speed, quality and information security are increasing; those above issues have been generally discussed for communication researchers. Therefore, by using fiber as the transmission medium, this not only increases transmission capacity but also reduces the signal loss and less susceptible to electromagnetic interference since the environment is simpler. In addition, information security can be upgraded because the signal transmit in the fiber is point to point. Thus, fiber communication is widely used in long-distance transmission and important infrastructure in the backbone of the network. In the traditional optical fiber communication system, the transmission channel compensation methods are mostly via optical way since the DSP (digital signal processing) technology has not yet been mature. The disadvantage of traditional way is expensive, with complicated structure and poor dynamic compensation effect. We don’t turn to take advantage of this compensation technique with lower cost till DSP technology matures. In this thesis, we will introduce our direct-detection OFDM system first and the OFDM signal will be generated by DSP. DDO-OFDM signal transmission in the optical field requires an optical carrier, which enable to convert the signal to electrical field via the photo detector at the receiver. However, when signal is converted to electrical field, the SSBI (Signal-Signal Beating Interference) will be generated simultaneously; we need to set aside one gap to avoid this interference. Because we need one gap between optical carrier, OFDM signal will decrease the signal spectrum efficiency. Therefore, in this thesis, we propose iteration algorithm which is used in DSP at the receiver. By using this algorithm, we are able to effectively eliminate SSBI and decrease the gap further; furthermore, to increase the signal spectrum efficiency and system performance. We implement iteration algorithm in the experiment and use VPI to discuss the impact of changing the system parameter.