DF Relayed Subcarrier FSO Links over Malaga Turbulence Channels with Phase Noise and Non-Zero Boresight Pointing Errors

Abstract

Subcarrier free-space optical (FSO) systems using coherent recovery techniques at the receiver have acquired growing research interest in recent times. However, their optimal performance is diminished by the non-perfect synchronization of carrier frequency and phase, which is mainly due to phase noise problems. Moreover, turbulence and pointing error effects further deteriorate the overall performance. However, relay transmission schemes can extend the coverage distance and offer substantial improvements over fading conditions. In this respect, we consider a serially relayed network using decode-and-forward relays, and investigate its performance by means of average symbol error probability and mean outage duration. Turbulence is modeled by the recently unified M(alaga) distribution, which constitutes a very general statistical model that accurately describes the irradiance fluctuations from weak-to-strong turbulence conditions. Additionally, the presence of non-zero boresight pointing errors due to misalignment between the transmitter-receiver pair is considered, while the effect of phase noise is specified by a Tikhonov distribution. A comparison between single line-of-sight and serially relayed FSO configurations is provided as well. Novel approximated mathematical expressions are deduced, which are proved to be accurate enough over a wide range of turbulence strengths and signal-to-noise values. Finally, proper numerical results are presented and validated by Monte Carlo simulations.

Time Jitter, Turbulence and Chromatic Dispersion in Underwater Optical Wireless Links

“…The normalized irradiance, I, depends on both the effects of the water turbulence, I t , along with the influence of the time jitter effect, I j . Thus, the total normalized irradiance of (1), is expressed as [35][36][37][38]:…”

“…with I l being the signal losses due to the medium's attenuation, but without loss of generality, in this work, it is assumed to be equal to unity [36][37][38]. The turbulence effect plays a very significant role in the terrestrial optical wireless links [39][40][41][42].…”

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

“…where [8,9,17,19,29]. It should be noted that increased values of the parameter ψ {i,j} correspond to a weaker amount of misalignment-induced fading, while, w z,eq,{i,j} denotes the equivalent beam radius in the jth hop in the ith path, which is given…”

“…Consequently, it becomes evident, that MOD is of particular practical use for FSO systems design, since its value directly reveals whether the investigated system can meet the required outage specifications or not. More precisely, the MOD, T od for a specific period of time is calculated as [29,36]:…”

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.…”