Hybrid satellite systems:Extending terrestrial networks using satellites

In this chapter, we review principles of hybrid radio access systems that are able to provide both terrestrial and satellite connectivity. Practical examples of the existing hybrid systems, such as digital video broadcasting-satellite services to handheld devices and TerreStar system, are also reviewed. The main focus is in the spectrum sharing challenges between the terrestrial and satellite components. Accordingly, we discuss different cognitive hybrid system proposals and the related issues. We describe also a potential hybrid satellite concept for the S-band, which enables efficient deployment of the higher IMT (International Mobile Telecommunications) frequency bands by providing coverage to rural areas where building of a terrestrial network is not economically feasible. The proposed concept consists of a terrestrial 3GPP (the 3rd Generation Partnership Project) LTE (Long-Term Evolution) network in dense populated urban areas and of cochannel satellite LTE cells in low populated areas. Simulation results of this overlay scenario are presented showing that the satellite interference to the terrestrial network can be kept at an acceptable level. Finally, future directions for the hybrid satellite systems are addressed