With the rapid growth in the internet applications, pressure is observed on the optical communication systems. Free space optical communication (FSO) is very important alternative to the optical fiber because of elimination of licenses, trenching, and no cost of ways and saves the time of installation. Wavelength division is capacity enhancement multiplexing but due to large number of laser requirements, it becomes expensive. Mode division multiplexing (MDM) is suitable multiplexing technique because it needs only single laser and can support high data rates. Optical code division multiplexing and MDM is demonstrated in this work at 100 Gbps over FSO supporting 10 users. Multiple access interference is prominent issue in OCDMA codes and in order to suppress MAI, zero cross correlation codes are used and use of Laguerre Gaussian modes has been done. Different fog conditions are analyzed and two different OCDMA cods are incorporated as well as compared in the proposed system such as shift zero cross correlation codes and multi diagonal codes in terms of Q factor and BER.
Optical Communication system consists of three main blocks, such as a transmitter, a transmission channel and a receiver. The modulation and demodulation techniques are the most important for the transmitter and receiver, respectively, to transmit and receive the useful information to the longer distance without compromising the minimum error, maximum Q factor and also maintaining sufficient power and other parameters at the receiver to reproduce the original signal with minimum noise and distortion. A hybrid modulation technique is used which will optimize the merits of both digital and analogue modulation. Moreover, the impact of amplification at the transmitter and receiver has been studied and analyzed. The present paper highlights the design of various hybrid modulation techniques mainly DPSK-FM and QAM-FM in this context. Furthermore, the evaluation and performance analysis of various designed systems in terms of Q factor, bit error rate and the number of users and received power has been done.
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