On the performance of OCDMA/SDM PON based on FSO under atmospheric turbulence and pointing errors

Abstract

This paper proposes and analyzes an optical code-division multiple-access (OCDMA) network based on free-space optical (FSO) links for broadband access provisioning in areas where laying down optical fiber is difficult or even impossible. Spectral-amplitude coding (SAC) category generated by a compact encoder is adopted as a coding scheme with binary ON-OFF keying (OOK) modulation and direct detection. Moreover, we employ spatial multiplexing scheme to increase the capacity of the proposed network by exploiting the unused already generated (by compact encoder) codewords at a certain acceptable bit error rate (BER) level. A closed-form average BER expression is derived under the joint impact of both turbulence-induced fading modeled by the Gamma-Gamma (ΓΓ) distribution and misalignment-induced fading, in the presence of beat noise, shot noise, and thermal noise. In addition, the data link layer performance modeled by Markov chain is evaluated in terms of achieved throughput and average packet delay by considering the effects of atmospheric turbulence and pointing errors. Our results show that both the atmospheric turbulence and the pointing errors impose a detrimental impact on the achievable throughput and average delay of FSO-based OCDMA passive optical network (PON).