Influence of Beam Divergence on the Performance of Underwater Wireless Spatial/Spectral OCDMA System

In this paper, the effect of beam divergence angle on the bit error rate (BER) performance of underwater wireless spatial/spectral optical code division multiple access (OCDMA) system using two dimensional perfect difference codes (2D-PDCs) is analyzed. In order to calculate BER of the proposed system, thermal noise, shot noise and phase-induce-intensity noise (PIIN) are considered. It is noted that Multiuser interference (MUI) and PIIN can be effectively suppressed by the proposed system. Beam divergence angle of optical source is an important parameter and the effect of different beam divergence angle for various water channels (i.e., pure sea water, clear ocean water and coastal ocean water) is investigated. A 532nm central wavelength LED is chosen as optical source and p-i-n photodiode is utilized as optical detector in the proposed underwater wireless optical system. The effect of beam divergence angle on the proposed system is investigated for different system parameters such as link distance, transmitter power, inclination angle and number of simultaneous users. From numerical results it is observed that best BER performance is achieved for narrower beam divergence angle in pure sea water channel among all water channels.