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Robust communication is required to provide a safe airspace for the large numbers of unmanned aerial systems that are coming to the National Airspace System (NAS). This thesis explores methods for providing robust communication to large numbers of vehicles in the NAS. Automatic dependent surveillance-broadcast (ASD-B) is a transmission system that can transmit to and is currently required on all manned aircraft. Unfortunately, ADS-B suffers connectivity problems when supporting large numbers of unmanned aerial systems (UAS). The 5G Cellular protocol can support large numbers of UAS, but connectivity suffers with an increase in distance and interference. Using a 5G cellular and an ADS-B simulator we evaluate the advantages of a combined ADS-B and 5G Cellular transmission system compared to a 5G or ADS-B exclusive system. We also offer hybrid system recommendations that clarify the appropriate operation strategies or triggers that should prompt transitions between transmission systems in different environmental situations. The simulation results show message success and vehicle collision rates, with each messaging method investigated to show the case for a combined communication system. This study shows that a hybrid transmission system is a possible communication solution for UAS operating in beyond visual line of sight (BVLOS) environments.