Investigation of rain and haze attenuations impact on proposed SCM˗SAC˗OCDMA˗FSO system with optical amplifier

Free space optics (FSO) is a new modern communication technique, which allows users to transmit their data in secure state where line-of-sight (LOS) mechanism used to ensure successful transmission of optical laser signal through free space. While optical laser beam travel through unguided medium where no fixed medium allocate to each user to transmit its data, so large atmosphere phenomena like (rain, fog/haze, etc.) can effect on the transmission signal. Over the years, many techniques were implemented in system design of FSO to reduce the effect of multiple access interference (MAI) and weather phenomena on the optical laser beam attenuation. Therefore, this study proposed sub-carrier multiplexing (SCM)-spectral-amplitude coding (SAC)-optical code division multiple access (OCDMA) FSO system with operational amplifier to reduce the effect of rain and haze on laser beam attenuations. This study, conducted in three different regions of Iraqi cities, which are Baghdad, Basra, and Mosul. The FSO system proposed consists of the combination of three techniques. OCDMA technique start using in system design to support a large number of users that share the same single laser beam and provide multiple access to the system. SCM and SAC also used to decrease the effect of MAI on the signal quality to decrease the external effect and increase network capability. Type of code used in the system called multi-diagonal (MD) code to support better in signal quality, providing zero cross correlation even if the number of user increase in the system. An additional component added to the system in order to enhance the signal quality called ''optical amplifier'' that used to add more energy to the signal to allow user signal travels through long distance. Based on these techniques, signal can travel through the rain and the haze weather state in three different regions of Iraqi cities [BAGHDAD, BASRA and MOSUL] which are with less bit error rate (BER) in final point and acceptable distance (reach to 1.35 km in rain state and 1.85 km in haze weather state). In addition to that, this paper shows a new laboratory method to study the effect of free space particles (rain and haze) on laser signal by using the glass room that must have the ability to perform rain and haze weather effect. Then, using an ocean optic device to collect the light from the room and translate it to the PC. The practical part ensures that rain largely attenuate wireless signal than haze particles. The results of practical part indicate the relation between the intensity count of light in the receiver side and the different types of wavelength (670 nm, 785 nm) that used in the laboratory experiment.