| Summary: | 碩士 === 國立中山大學 === 光電工程學系研究所 === 101 === In the information explosion era, people are desired to receive messages anywhere and anytime. The traditional wireless communication transmits messages via radiofrequency (RF) electromagnetic wave, but it cannot be used for some special cases. For instance, due to the health concerns raised about exposure to RF fields, it cannot be used in hospitals. In addition, considering low information security, it cannot be used in highly confidential situations, such as military applications. Alternative to RF wireless technologies, visible light communication (VLC) based on white light emitting diodes (LEDs) has attracted global attention, because of its advantages of worldwide availability, high security, and immunity to RF interference.
In the thesis, we use commercially available LEDs as our emission source. Because the LEDs adopted in VLC are designed for illumination, so the modulation bandwidth is generally limited to about tens MHz. Accordingly, we used the carrier-less amplitude and phase (CAP) modulation, which has high bandwidth efficiency, to transmit signals over the limited bandwidth, and the pre-compensation is also employed in our high-speed VLC experiments to improve signal performance. On the other hand, how to increase the transmitted distance is also one of our major topics. At the receiver, we use the high photoelectric conversion efficiency avalanche photo-detectors (APDs) to increase our transmission distance and to improve signal quality. We insert unique word (UW) into CAP signals, in order to apply both frequency domain equalization (FDE) and decision feedback equalization (DFE) to overcome the uneven frequency response of the VLC channel. Moreover, 2×1 multiple-input-single-output (MISO) VLC system is also experimentally demonstrated, and Alamouti space-time block coding (STBC) is employed to CAP or orthogonal frequency division multiplexing (OFDM) signals to deal with the problem of multipath interference.
|
|---|
