Visible light communication (VLC) technology offers unregulated, unlicensed and huge bandwidth to meet the growing demand in future indoor communication system. One of the major challenge in VLC system is in improving transmission speed with optimize the bandwidth capacity. The method to improve spectral usage is using advanced modulation formats such as orthogonal frequency division multiplexing (OFDM). In this work, a new approach for modulation technique based on multiband OFDM has been developed which capable to improve the spectral efficiency and optimize the data rate. A proposed technique is then adapted in OCDMA-VLC environment to analyse the reliability of the proposed scheme in high capacity network. Different selection of parameter values such as bit rates, number of bands and effective received power will have different effect on the system performance. Numerical result shown that the catenated-OFDM outperforms conventional OFDM by five times spectral efficiency improvement and eight times spectral efficiency improvement at their five and eight number of bands respectively. It is also shown that the proposed catenated-OFDM design is working well even at very high bit rate of 15 Gbps. Moreover, there are enhancement in receiver sensitivity with 7.3 dB power penalty compared to previous work.

In this paper, the analysis of comparison between proposed detection called as Wavelength Filtrate Detection with existing detection have been analyzed to determine the best system performance in term of power received and bit error rate (BER). The analysis focus on the geometrical effect of aperture receiver and beam divergence. The performance of Free Space Optics is validated through simulation analysis using parameter 10Gbps data rate and in 14dB/km atmospheric attenuation. This analysis shows that Wavelength Filtrate Detection increase the power received of 6dBm and improve the absolute value of error rate 10-9 in acceptable threshold required by (ITR-U) as much as 50% compare to others existing detection