  We analyze the performance of a free-space optical (FSO) link affected by
atmospheric turbulence and line-of-sight (LOS) blockage. For this purpose, the
atmospheric turbulence induced fading is modeled by the M-distribution, which
includes the Gamma-Gamma distribution as special case. We exploit the fact that
the physical interpretation of the M-distribution allows to split the optical
energy through the propagation link into three different components: two
coherent components and one incoherent scatter component. Based on this
separation, we derive novel analytical expressions for the probability density
function (PDF), for the cumulative distribution function (CDF) and for the
moment generating function (MGF) of the M-distribution under the temporary
blockage of the coherent components, hereinafter referred to as LOS blockage.
Further, a new closed-form expression for the outage probability (OP) under LOS
blockage is derived in terms of the turbulence model parameters and the LOS
blockage probability. By means of an asymptotic analysis, this expression is
simplified in the high-SNR regime and the OP in terms of the diversity order
and diversity gain is then deduced. Obtained results show that the impact of
the LOS blockage on the OP strongly depends on the intensity of the turbulence
and on the LOS blockage probability.
