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

Abstract

Over the past few years, terrestrial free space optical (FSO) communication systems have demonstrated increasing research and commercial interest. However, due the signal’s propagation path, the operation of FSO links depends strongly on atmospheric conditions and related phenomena. One such significant phenomenon is the scintillation caused by atmospheric turbulence effects; in order to address the significant performance degradation that this causes, several statistical models have been proposed. Here, turbulence-induced fading of the received optical signal is investigated through the recently presented mixture Gamma distribution, which accurately describes the irradiance fluctuations at the receiver’s input of the FSO link. Additionally, at the same time, it significantly reduces the mathematical complexity of the expressions used for the description of composite channels with turbulence along with nonzero boresight pointing error-induced fading. In order to counterbalance the performance mitigation due to these effects, serial decode-and-forward relays are employed, and the performance of the system is estimated through derived mathematical expressions.

Α dual‐hop equivalent structure of a generalised multi‐hop free‐space optics network

“…In this section, the overall performance of the multi-hop network in terms of the OP and ABER, with OOK modulation, is assumed. OP is a significant quantity in order to evaluate the reliability of a communication system and represents the probability that the instantaneous SNR falls below a critical threshold γ th , while the ABER is a crucial metric for the reliability and performance estimation of such communication systems [3].…”

“…Finally, the total ABER of the approximated system is calculated by the following equation [3, 20, 21]: …”

“…Free-space-optics (FSO) has attracted increasing research and commercial interest mostly due to the benefits against other wireless technologies, including radiofrequency or millimetre wave systems, in cases where point-to-point connections are required [1][2][3][4]. The most important of them is the high bandwidth access, the operation in the unlicensed spectrum, the low installation and operation cost, the enhanced security provision and the immunity to the electromagnetic interference [5][6][7].…”

“…DF relays, which re‐modulate and retransmit the received signals, are often used in FSO transmission since they are more reliable, although they require more processing compared to AF relaying. To this end, we consider intensity modulation/direct detection with on‐off keying (OOK) modulation technique, which is the most commonly adopted and straightforward modulation scheme that has been used for experimental or commercial FSO systems [3]. The approximation process leads to a significant simplification of the complicated and widely adopted expressions for the outage probability (OP) and the average bit error rate (ABER) used for the performance evaluation of multi‐hop networks.…”