A.N. Stassinakis

Capacity analysis of dual amplify-and-forward relayed free-space optical communication systems over turbulence channels with pointing errors

This paper elaborates on the end-to-end capacity of dual-hop free-space optical (FSO) communication systems employing amplify-and-forward (AF) relaying, assuming channel state information is only known at the receiving terminals. The relay is assumed to either possess perfect channel state information or have a fixed gain. The performance of the considered system is affected by the combined effects of atmospheric turbulence-induced fading, pointing errors (i.e., misalignment fading), and path loss. Atmospheric turbulence conditions are modeled using the gamma-gamma distribution. For the system under consideration, accurate analytical approximations as well as upper bounds to the ergodic capacity are derived. In addition, bound approximations in the high signal-to-noise ratio regime are deduced that provide valuable insights into the impact of model parameters on the capacity of AF FSO dual-hop relaying systems. Numerically evaluated and computer simulation results are further provided to demonstrate the validity of the proposed mathematical analysis.

Average capacity of optical wireless communication systems over I-K atmospheric turbulence channels

The optical wireless communication systems are rapidly gaining popularity as effective means of transferring data at high rates over short distances. These systems facilitate rapidly deployable, lightweight, high-capacity communication without licensing fees and tariffs. On the other hand, the performance of this new technology depends strongly on the atmospheric conditions and the parameters of the link such as the length and the operation wavelength. In this work, we extract closed form mathematical expression for the evaluation of the average (ergodic) capacity of such a system, using the log-normal and gamma-gamma distribution, in order to model the atmospheric turbulence conditions and we study the influence of the above parameters on it.

K modeled turbulence and nonlinear clipping for QAM OFDM with FSO and fiber serially linked

The free space optical (FSO) and more specifically the radio on free space optical (RoFSO) communication systems are becoming very popular because they can achieve high bit rate transmission with low operational and installation cost. The main disadvantage of such systems is their dependence on the atmospheric conditions and more specifically the randomly time varying characteristics of the propagation path through the atmosphere which is, mainly, caused by the turbulence effect and affects significantly the systems availability and performance. On the other hand, the use of optical fiber systems, offer higher bit-rates and security level but their cost is larger. In this work, the performance of a hybrid dual hop optical communication system is investigated. This system consists of a RoFSO communication link which is connected with an optical fiber link part using a regenerator between them. In both links, the modulation technique that is used is the orthogonal frequency division multiplexing (OFDM) with either a 4 or 16 QAM format. The main phenomena that are taken into account are the atmospheric turbulence, which is modelled with K distribution, the nonlinearities of the laser diode which could be modelled by Volterra series and the biasing with the nonlinear clipping at the optical fiber segment. For this system, closed form mathematical expression for the estimation of its BER is derived and numerical results are presented for realistic parameter values.

Wavelength diversity/or Free Space Optical Systems: Performance evaluation over log normal turbulence channels

The scientific area of Free Space Optical (FSO) communication systems have attracted significant research and commercial attention in recent years. This is due to their cost-effective and license-free high bandwidth access characteristics. On the other hand, this technology is using the atmosphere as transmission media and thus the performance of an FSO system depends strongly on the atmospheric conditions in the area of the link. One phenomenon which may significantly degrade the performance of the associated communication system is the atmospheric turbulence. Many techniques have been used in order to overcome this degradation and particular attention has been given to diversity methods. In this work, we consider the use of wavelength diversity in FSO systems that operate under weak to moderate atmospheric turbulence conditions modeled by the log normal distribution. We derive mathematical expressions for the estimation of the outage probability and the average bit error rate of the system and using these expressions we present numerical results referred to common practical FSO cases, showing that the use of wavelength diversity results in considerable performance improvement at a moderate increase of the overall systems complexity and cost.

Block error rate estimation for wireless optical communication links over strong turbulence channels with pointing errors

Free-space optical communication systems are gaining popularity as a high-capacity, cost-effective and license-free wireless technology, addressing the bandwidth demands of existing and future wireless networks. The deployment scenarios of free pace optical links usually concern secure, fast and reliable connections. Thus, in this work, the performance of optical wireless communication systems is studied in terms of the average block error rate which constitutes a very significant metric for their reliability. The optical signal transmission is assumed to be hampered by the joint effects of strong atmospheric turbulence, modeled by the Negative Exponential and the pointing errors effect which affects the alignment between the transmitter and the receiver. Accurate closed-form expression for the evaluation of the average block error rate is obtained, including the aforementioned effects, while finally the corresponding numerical results, for realistic optical wireless links, are presented.