EXPERIMENTAL IMPLEMENTATION OF COST EFFECTIVE RF-OVER-FSO BASED COMMUNICATION SYSTEM UNDER LABORATORY CONDITIONS

Abstract

The work mentioned in this thesis is carried out in two Phases. Phase-1 presents and analyzes a free-space optical (FSO) communication system under stable laboratory conditions. Phase-1 is achieved by employing a low-cost ( 140) commercial optical transmitter (OT). To further reduce the overall cost of the setup, a low cost ( 114) optical receiver (OR) is used in Phase-2. Additionally, Phase-2 involves signal transmission and reception using software defined radio (SDR), its analysis using an optical spectrum analyser (OSA), making it RF-over-FSO communication system. The experimental setup considered in Phase-1 utilizes quadrature-phase shift keying (QPSK) signaling for data transmission. To further improve the system performance, a QPSK-frequency division multiplexing (QPSK-FDM) signaling is employed. Phase-2 utilises higher modulation schemes like M-PSK and M-QAM, the algorithms for which are written in MATLAB®. During the conduct of the experimental study, all optical connections are made using a single mode fiber (SMF) only. This work includes algorithms to prepare comma-separated value (CSV) files for sample values of QPSK, QPSK-FDM, M-PSK andM-QAM signals that can be loaded to arbitrary function generator (AFG) or the SDR to generate these signals. Moreover, the decoding algorithm is also provided that consists of match filtering operation, detection criteria, and the calculation of bit error rate (SER). The entire process of signal generation, uploading to SDR, signal transmission, signal reception, downloading the sample values, detection and decoding, synchronisation and SER calculation in Phase-2 has been automated using a single MATLAB® program only. Furthermore, the performance of QPSK and QPSK-FDM is compared for the considered FSO system (Phase-1) in terms of BER performance at different optical received power. Also, the BER performance of QPSK-FDM is examined at different data rates. Additionally, in Phase-2, the performance of M-PSK and M-QAM is examined in terms of SER achieved at low power received optical signal.