Abstract:
Optical wireless communication (OWC) is becoming popular nowadays due to high data rate and more security features than the radio frequency (RF) communication. One of the major branches of OWC is optical camera communication (OCC) which can be categorized into visible light communication (VLC) and pixelated communication. The screen of a digital gadget like smartphones/tablets/laptops is used as transmitter and camera of any of those digital gadgets is used as receiver to transfer images in pixelated OWC. A pixelated system is susceptible to different spatial impairments such as motion blur, defocus blur, rotational misalignment and perspective distortion. This thesisanalyses the impact of motion blur in the context of pixelated systems for the first time and also finds the combined impact of all spatial impairments mathematically. At first the effect of stand-alone motion blur is derived and it is found that the impact of motion blur depends on motion length and subcarrier index. Next, the joint impacts of defocus and motion blur are modeled which show that the impact of both blurs are independent to each other and the attenuation due to defocus blur depends on point spread function (PSF) of defocus blur and subcarrier index. Finally the combined effect of all the impairments are modeled which indicate that the impact of each impairment does not depend on others and the combined effect is the joint attenuation due to motion blur, defocus blur, linear fractional misalignment (LFM), and vignetting. On the other hand, the performance of non-DC biased optical OFDM (NDC-OFDM) and LED index modulation optical OFDM (LIM-OFDM) areevaluated and compared with different forms of spatial orthogonal frequency division multiplexing (spatial OFDM) including spatial DC biased optical OFDM (SDCO-OFDM), spatial asymmetrically clipped optical OFDM (SACO-OFDM) and spatial asymmetrically clipped DC biased optical OFDM (SADO-OFDM) for both VLC and pixelated OWC systems to find out the best candidate in terms of electrical and optical power efficiency. Simulation results show that without the presence of impairments, SLIM shows better optical power efficiency than SNDC when only AWGN is present. On the other hand, SNDC performs better than SLIM, SACO and SDCO when channel is modeled with different spatial impairments like motion blur, linear fractional misalignment, vignetting along with channel noise. Practical experiments are also conducted for SDCO-OFDM modulation to realize the practical impact of these impairments and some techniques are followed to reduce the impact from practically impaired received images.
