Flexible Free-Space Optical CDMA Networks

In this paper, we propose a novel hybrid network solution using optical code-division multiple-access and free-space optics (OCDMA-FSO) to support multiple data rates and quality-of-service according to user requirements. The proposed OCDMA-FSO network classifies users into diverse classes based on their requirements and allows for signal transmission in a fully asynchronous manner. The new hybrid network employs 2-D OCDMA codes as well as a variable aperture FSO receiver together with an equal gain combining (EGC) technique. We derive completely new analytical formalisms to evaluate the network performance in terms of average bit error rate (ABER), outage probability, effective data rate during outages, and ergodic capacity. The derived ABER expressions are validated via Monte-Carlo simulations. These new analytical formalisms are derived considering several atmospheric turbulence conditions such as uncorrelated, totally correlated, and partially correlated turbulence. To model this atmospheric turbulence, we derive the gamma-gamma (GG) distribution, which allows us to consider both the scintillation effect and the EGC technique. Finally, we carry out a comprehensive performance evaluation of the proposed hybrid network. Analytical results show that as the number of FSO receiver apertures increases, there is an improvement in overall performance levels. However, the ergodic capacity exhibits minimal improvement even as the number of FSO receiver apertures increases, regardless of the user requirements and turbulence conditions. The proposed network is a potential solution for scenarios that demand flexibility in bandwidth and data rate allocation.