On the performance of a UAV-based Malaga-distributed FSO/FSO communication system with NOMA

Abstract

Non-Orthogonal Multiple Access (NOMA) is an efficient communication technique that can offer improved spectral efficiency, ultra-low latency and massive connectivity and its integration with Free Space Optical (FSO) communication can improve the network capacity to a great extent. In this manuscript, an Unmanned Aerial Vehicle (UAV) is employed as a relay in an FSO/FSO downlink network, comprising of two users, user 1, U1 and user 2, U2, using Amplify-and-Forward (AF) protocol. UAVs can prove to be assets in disaster-struck situations (during natural disasters such as earthquakes, floods, etc.), when all terrestrial communication is at halt. The performance of this system is determined in the presence of atmospheric attenuation, Malaga (M) turbulence fading, pointing errors and Angle-of-Arrival (AoA) fluctuations. Heterodyne detection (HD) technique is used for information detection at the users for providing improved sensitivity and Signal-to-Noise Ratio (SNR). The closed-form expressions for Outage Probability (OP), Ergodic Capacity and Bit Error Rate (BER) are derived in terms of Meijer-G function and OP is analyzed with respect to different weather conditions, turbulence levels, pointing error coefficients, NOMA coefficients and Field-of-View (FoV) angles. It is observed that at an SNR of 0 dB, the outage at U1 and U2 is 0.5489 and 0.7423, respectively. A comparison of OP is presented for the cases of HD and Intensity Modulation/Direct Detection (IM/DD) techniques and for NOMA and Orthogonal Multiple Access (OMA) technologies. Ergodic Capacity is analyzed for different turbulence strengths and pointing error values and it can be noticed that it is enhanced by reducing the turbulence strength and pointing error impairment. BER is observed for different modulation schemes and it is found to be 7.7×10−3, 1.9×10−2, 7.9×10−2 and 2.8×10−2, for QPSK, 8-PSK, 16-PSK and 16-QAM, respectively, at an SNR of 30 dB. In addition, BER is analyzed for clear, rainy and foggy weather along with different pointing errors and turbulence regimes. Monte-Carlo simulations are also carried out in order to validate the correctness of the obtained analytical results.