Current satellite communication solutions propose a network solution that is compatible with the existing network and 6G architecture in order to provide global coverage for rural areas and emergency applications worldwide. Therefore, integrated satellite-terrestrial technologies will enable ubiquitous connectivity for any type of end user. In this paper, we propose cooperative communication in which the satellite station transmits its information to the ground base station. The signal is then transmitted to the receiver using a decode-and-forward relaying protocol. The satellite link is presumed to be shadowed Rician, whereas the terrestrial link is referred to as Generalized-K fading since it is the generalized representation of conventional small-scale channel models in cellular communications. Alternatively, assuming a special case in which the end user is a vehicular node, the appropriate channel is selected as double Rayleigh fading on the terrestrial link. Due to the mobility of the ground user, it is assumed that the distance over the terrestrial link is uniformly distributed. In addition, several system parameters are considered when evaluating system performance, including outage probability and bit-error probability. In order to confirm the derived mathematical formulas, computer-based Monte Carlo simulations are conducted. The results indicate that the shadowing parameter of the satellite link and the distance of the terrestrial link has a significant impact on the proposed system performance.