###### Abstract  
FSO is one of the most widespread, low-cost, wireless, optical communicational technologies with sufficiently high throughput, transmission reliability, and high-level security. Nevertheless, many fading effects act on the optical pulses used, during their propagation, causing performance degradation. In this work, group velocity dispersion and time jitter, modeled by the truncated normal distribution, are jointly investigated analytically and numerically. The availability of the studied model is expressed in terms of outage probability, while its reliability is given in terms of its average bit error rate, through the derived novel mathematical expressions. To the best of authors' knowledge, this is the first time that the outage and the BER performance are estimated analytically, through specific approximations, taking into account the abovementioned physical effects. Furthermore, using the obtained mathematical forms, the corresponding numerical results are presented by assuming typical parameter values for realistic FSO links.  
FSO links; longitudinal Gaussian pulses; availability and reliability performance; chirp; group velocity dispersion; time jitter; truncated normal distribution; outage probability; signal-to-noise ratio; average bit error rate +
Footnote †: journal: Electronics Letters  
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In particular, the GVD is a known effect acting on signals consisting of many frequency (or wavelength equivalently) components, which travel at different speeds, resulting in a pulse shape flattening in the time domain, implying a signal degradation, along its propagation [21; 22]. Hence, in this context, the link's length is an important parameter. The bit rate is also important, because the corresponding detection timeslot sets a tolerance limit, beyond which adjacent pulses are overlapped, inducing inter-symbol interference (ISI) [23; 24; 25].  
Furthermore, the TJ can be caused by any kind of transmission or detection delays that keep the transmitter and receiver out of sync. Under these circumstances, the peak of the incoming pulse does not coincide with the center of the dedicated timeslot. In other words, supposing that the detection is ideally performed at the center of timeslot, the amplitude of the instantly receiving signal is surely lower than the pulse's peak, inferring a fading effect. Again, the timeslot duration is especially critical in the case of a strong TJ effect, where the leading or lagging incoming pulse can be misdetected even in adjacent timeslots, causing eventual bit flips, which could disorder the bit-stream [26; 27; 28; 29]. Such problems can be efficiently solved by employing forward error correction (FEC) coding techniques [7; 30].  
In this study, the FSO link was assumed to be implemented via longitudinal Gaussian pulses, subject to GVD and a weak-to-moderate TJ effect, modeled by the truncated normal distribution, implying that the TJ effect creates uncertainty at the bit detection time, which is assumed to remain on its own timeslot. Studies and techniques facing strong TJ cases have been analyzed (e.g., in [31]). The availability of the studied model is expressed in terms of outage probability (OP), while its reliability is obtained in terms of its average bit error rate (ABER) performance.  
The remainder of this work is organized as follows: Section 2 contains the model analysis toward the generation of a compact mathematical expression of a joint probability density function (PDF) of the involved phenomena. In Section 3, the mathematical expressions for the performance quantities are derived, while the numerical results from the obtained equations are discussed in Section 4, and the study conclusions are hosted in Section 5.