Enhancing VDE-SAT capacity: the advantage of distinct transmit and receive satellite architectures through high electromagnetic isolation and SIC

This article focuses on the VDE-SAT service and analyses the possibility of using distinct satellites for signal transmission and reception. This application scenario can increase aggregate system capacity by sharing time and frequency resources between the uplink and downlink channels relaxing the need to implement full duplex radio on a single satellite. The uplink budget is studied to determine the maximum Self-Interference (SI) level on the receiving satellite, provided by the Tx satellite, that does not degrade communication performance. The level of SI on the receiving satellite is then analysed for various inter-satellite distances and orbital altitudes. It is concluded that, without additional isolation methods, the minimum distance between the transmitting and receiving satellites could be incompatible with application services in which the uplink and downlink frequencies are fully overlapping. In such scenarios, the introduction of a Self-Interference Cancellation (SIC) block on the receiving satellite is proposed, which provides an insufficient 16.5 dB improvement. An additional enhancement, which proves to be sufficient alone, can be provided by the polarization diversity that is able to ensure 26.9dB of electromagnetic isolation. An application solution was formulated with a near-polar Walker Star ~90°:28/4/2 constellation, designed with a geometric approach. The minimum elevation angle for communication is identified as a factor that can highly impact the constellation.