On the Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels Using OOK Signaling

Abstract

A new upper bound on the capacity of power-and bandwidth-constrained optical wireless links over gamma-gamma atmospheric turbulence channels with intensity modulation and direct detection is derived when on-off keying (OOK) formats are used. In this free-space optical (FSO) scenario, unlike previous capacity bounds derived from the classic capacity of the well-known additive white Gaussian noise (AWGN) channel with uniform input distribution, a new closed-form upper bound on the capacity is found by bounding the mutual information subject to an average optical power constraint and not only to an average electrical power constraint, showing the fact that the input distribution that maximizes the mutual information varies with the turbulence strength and the signal-to-noise ratio (SNR). Additionally, it is shown that an increase of the peak-to-average optical power ratio (PAOPR) provides higher capacity values. Simulation results for the mutual information are further demonstrated to confirm the analytical results under several turbulence conditions.

Rate-Adaptive Free-Space Optical Links Over Atmospheric Turbulence and Misalignment Fading Channels

“…This superiority has been previously reported by the authors in terms of closed-form expressions corresponding to the average BER performance in several FSO scenarios [19,24,26], as well as from the point of view of information theory [22]. Following the approach here presented, this improvement can be viewed as an additional coding gain, regardless of the rate-adaptive transmission scheme employed.…”

Low SNR Capacity of FSO Links over Gamma-Gamma Atmospheric Turbulence Channels

“…For moderate-to-strong turbulence, the irradiance is modeled by a GG distribution [4], [11] whose probability density function (PDF) is given by…”

“…In order to evaluate the impact of atmospheric turbulence, various models have been proposed to describe the optical wireless channel statistical characteristics. While the log-normal distribution has been found to be the most suitable for the weak-to-moderate turbulence channels, the Gamma-Gamma (GG) distribution has been found to be the most suitable modeling of the optical channels for moderateto-strong turbulence channels [1]- [11]. This distribution is produced from the product of two Gamma random variables and is also known as the generalized K distribution.…”

“…In [6], Gappmair has derived closedform expression of the average capacity of FSO channels in turbulent atmosphere for adaptation policies other than ORA, such as the OPRA, channel inversion with fixed rate (CIFR) and truncated channel inversion with fixed rate (TIFR). In [11], a new upper bound on the capacity of power and bandwidth constrained optical wireless links over GG atmospheric turbulence channels, when on-off keying (OOK) formats are used. However, most of the proposed closed-form expressions in the literature do not give much insight because of the presence of the Meijer's G-function.…”

An Overview of the Physical Insight and the Various Performance Metrics of Fading Channels in Wireless Communication Systems

“…It is worth mentioning here, that the ergodic capacity is a very significant metric for the study of the wireless optical communication links, due to the strong influence of the atmospheric conditions in their performance, see e.g. (Andrews et al, 1999;Gappmair et al, 2010;Garcia-Zambrana, Castillo-Vasquez & Castillo-Vasquez, 2010;Garcia-Zambrana, Castillo-Vazquez & Castillo-Vazquez, 2010;Li & Uysal, 2003;Liu et al, 2010;Peppas & Datsikas, 2010;Popoola et al, 2008;Sandalidis & Tsiftsis, 2008;Tsiftsis, 2008;Vetelino et al, 2007;Zhu & Kahn, 2002). More specifically, the fast changes of the atmospheric turbulence conditions fades fast the transmitted signal and as a result, the estimation of the instantaneous channel capacity is nearly meaningless in this area of wireless communications.…”