Visible Light Communication using C-OFDM

Abstract

In recent years, new difficulties have been faced in data transmission rates due to advances in next-generation communications. New spectrum resources, including terahertz, millimetre, and visible light, have gained prominence as research topics. Visible light communication (VLC) has a lower deployment cost than the other resources because it allows for concurrent illumination and communication. Unlike conventional wireless communications, VLC operates in the 400-800 THz band and has unique physical characteristics, including superior resistance to electromagnetic interference, secure confidentiality, and high data throughput. This suggests that VLC can be developed as a powerful wireless technique for next-generation communication. VLC utilises light-emitting diodes (LEDs) to modulate the intensity of optical power at the transmitter before transmission over the channel and direct detection at the receiver via a photodetector. The critical challenge in VLC systems is the modulation bandwidth limitation experienced by commercial LEDs, which causes severe reductions in overall throughput. To overcome this challenge, one of the most promising solutions is the adoption of advanced modulation formats such as orthogonal frequency division multiplexing (OFDM). OFDM is a specific case of frequency division multiplexing (FDM) and a popular candidate technology for VLC systems because of its robustness against multipath propagation and high spectral efficiency. Due to the division of available bandwidth into several subcarriers. Moreover, it allows for more extensive data rates without the need for sophisticated equalisers at the receiver. These exceptional features of OFDM mean that it is deemed to be a robust modulation technique capable of significantly improving VLC systems. Although conventional OFDM modulation has been considered a successful modulation technique for wired and wireless communications systems in several applications, there are still various areas that need to be developed. The large peak to-average power ratio (PAPR) of the signal is thought to be the main barrier to the achievement of high performance by OFDM systems. In particular, the addition of DC bias to OFDM symbols and then passing them via the restricted linear dynamic range of the LED renders these schemes unsuitable for some VLC applications where energy economy is paramount. The primary emphasis of this research is the development of a unique method for OFDM with application to visible light communication (VLC). It is dedicated to improving OFDM performance by reducing the PAPR and computational complexity, thereby enhancing the non-linear region and broadening the limited bandwidth associated with LEDs. In order to address such negative elements of OFDM systems, a novel technique based on an OFDM scheme is proposed in this thesis. Here, the C transform which combines the Walsh-Hadamard transform (WHT) and discrete cosine transform (DCT) into an orthogonal signal. The proposed transform uses a novel type of optical orthogonal frequency division multiplexing called C-OFDM.