Comprehensive Performance Analysis of Hovering UAV-Based FSO Communication System

Abstract

Unmanned-aerial-vehicle (UAV)-based communications are expected to play an important role in the future generation wireless communication networks. It is a promising solution to enhance the wireless connectivity of devices without infrastructure. As compared to the terrestrial communications, UAVs offer various advantages such as line-of-sight (LoS) connectivity, dynamic deployment and flexible reconfiguration. Further, free space optics (FSO) communication is considered as a possible solution to enable UAV-based communication links due to its cost effective and high bandwidth nature. However, despite offering large bandwidth, UAV-based FSO links are marred by atmospheric path loss, atmospheric turbulence, non-zero boresight pointing errors, and angle-of-arrival (AoA) fluctuations. In this paper, the performance of a hovering UAV-based FSO communication system is investigated. The closed-form expressions for outage probability, average symbol error rate (SER), and ergodic capacity are derived taking into account both heterodyne (HD) and direct detection (DD) techniques for ground-to-UAV (G2U), UAV-to-UAV (U2U), and UAV-to-ground (U2G) links over the generalized Málaga distribution. Moreover, the asymptotic expressions for the above performance metrics are also derived to get the diversity gain of the system.

Review on UAV-based FSO links: recent advances, challenges, and performance metrics

“…where R is the responsivity of the detector, h is the overall channel impulse response, x t is transmitted symbol ∈ f0;1g, P t is the average source transmit power, n represents the AWGN with zero mean and variance, σ 2 n , which is independent of the signal and the value of the parameter, c, is 1 for heterodyne detection (HD) and its 2 for intensity modulation/direct detection (IM/DD). 60 Therefore, the instantaneous SNR for the case of IM/DD receiver can be given as γ ¼…”

“…This NLoS component is totally independent of the other two. The PDF of M random variable is given as 60 fht(ht)=AM∑m=1βamhtα+m2−1kα−m(2αβhtgβ+Ω′),where AM=2αα/2g1+α/2Γ(α)(gβgβ+Ω′)β+α/2 and am=(β−1Cm−1)(<...…”

“…Beckmann distribution is a useful distribution but it is not in closed form. Therefore, a general Beckmann distribution approximation is used, known as modified Rayleigh distribution given as 60 frd(rd)≈rdσm2 exp(−rd22σm2),rd≥0,where the total displacement variance, σm2, for different scenarios is given in Table 4. Here, σdx2=σxt2+σxr2+Z2σtx2 and σdy2=σyt2+σyr2+Z2σty2 denote the variances in x-z and …”

“…The channel coefficient, ho, can be simply defined as above due to the fact that the main lobe width of the airy pattern is approximately equal to 2.4λ 37 that is very small as compared to the detector size, which is in the order of millimeters. As, θtx, θty, θrx, and θry are all Gaussian random variables with non-zero means and variances, AoA will have Beckmann distribution that can be nearly represented by the modified Rayleigh distribution as 60 fθa(θa)≈θaσa2 exp(−θa22σa2),θa≥0.…”

“…Channel state information is an essential requirement for determining the SNR at the receiver, which ultimately leads to the computation of the various performance metrics of the optical link. The signal at the destination can be expressed as y=(RhPtxt)c/2+n,where R is the responsivity of the detector, h is the overall channel impulse response, xt is transmitted symbol ∈{0,1}, Pt is the average source transmit power, n represents the AWGN with zero mean and variance, σn2, which is independent of the signal and the value of the parameter, c, is 1 for heterodyne detection (HD) and its 2 for intensity modulation/direct detection (IM/DD) 60 . Therefore, the instantaneous SNR for the case of IM/DD receiver can be given as γ=2Pt2R2h2σn2 and thus, the average SNR in absence of fading is given by γ¯=Pt2R22σ…”