Mixed Topology of DF Relayed Terrestrial Optical Wireless Links with Generalized Pointing Errors over Turbulence Channels

Abstract

This study investigated the outage performance of a terrestrial FSO communication system that uses mixed series and parallel decode-and-forward (DF) relay-assisted (i.e., cooperative diversity) configurations, taking into account the influence of both atmospheric turbulence and pointing error effects. Turbulence-induced optical signal fading is modeled by gamma-gamma or the negative exponential distribution for weak to strong and saturated turbulence conditions, respectively. Additionally, weak to strong non-zero boresight misalignment-induced optical signal fading is modeled by the generalized Beckmann distribution. Under these conditions, an outage analysis of the examined FSO system is performed, in terms of both outage probability and mean outage duration metrics. Thus, fairly accurate closed-form mathematical expressions for both performance metrics are derived, while their corresponding analytical results demonstrate concrete performance and availability improvements for the total FSO system, especially when the number of the connected in parallel DF relays increases. Moreover, the obtained results are verified through the corresponding simulation results.

Serial DF Relayed FSO Links over Mixture Gamma Turbulence Channels and Nonzero Boresight Spatial Jitter

“…In this work, a DF FSO relay-assisted system is considered, in which the source transmits the information signal towards the receiver across H serial paths, and consequently, across the (H-1) DF relay nodes. All of the H paths have the same length, D, and each relay node, after receiving the signal, decodes it and retransmits it to the next relay, or to the final node, i.e., the receiver [15,38] of the FSO system. Furthermore, we consider an OOK with IM/DD scheme, and the received signal at the h-th hop, y h , is given as [15,35,38]:…”

“…Many statistical distribution models have been proposed for the description of the intensity fluctuations which arise from the scintillation effect. Each properly describes the scintillation effect caused by different turbulence strength, i.e., weak, moderate or strong, [12,[14][15][16][17]. More precisely, lognormal and gamma statistical distributions are useful for describing the scintillations caused by weak turbulence, while GG, Malaga (M) and I-K are commonly used for a range from weak to strong turbulence conditions; finally, K and NE are suitable for strong and saturated conditions, respectively, [11,12,14,[18][19][20][21][22][23][24][25][26][27][28][29][30].…”

“…It may therefore be concluded that the obtained performance equations for the FSO link can be easily used in order to produce results for the design and implementation of workable FSO links. Additionally, the sways of high-rise buildings, in which the FSO terminals are usually located, due to wind loads, weak earthquakes, or thermal expansions, result in misalignment-induced fading of the received irradiance, which is known as the pointing errors effect [15,31,32]. The pointing errors effect consists of two components; the first is the boresight, which describes the fixed displacement between the beam center and the center of the detector, while the second is jitter.…”

“…In order to combat the limitations associated with fading, relay-assisted FSO communication is an effective method to extend coverage and performance [15,35]. In [36], the MG model is adopted for the estimation of the performance of a SIMO FSO system with receivers' diversity, operating under the composite impact of nonzero boresight pointing errors and turbulence-induced scintillation fading.…”

Transdermal Optical Wireless Links with Multiple Receivers in the Presence of Skin-Induced Attenuation and Pointing Errors

“…Nevertheless, NZB pointing errors had never been examined in TOW literature, just as no method had been proposed in order to enhance the TOW outage performance and availability. Only, very recently, authors demonstrated for the first time, in [39], that a diversity method-i.e., in space, in time, or in wavelength-is an effective technique to enhance the outage performance of a typical TOW in terms of outage probability metric, by considering the joint impact of both attenuation-induced fading and misalignment-induced fading with NZB, modeled by the accurate Beckmann distribution [3,[41][42][43][44][45][46]. In basic terms, diversity refers to the consideration of multiple copies of the propagated signals in an attempt to overcome a poor transmission media state so as to reinforce the communication link's availability and robustness.…”