Potentials and Limitations of CDMA Networks for Combined Inter-Satellite Communication and Relative Navigation

Abstract—Precision formation flying missions require formation acquisition and maintenance through the interactions among spacecraft by the inter-satellite communication and relative navigation. This paper analyses the dedicated system constraints of the network architecture for precision formation flying missions. The critical time issue and the operational flexibility are found to be two main constraints. Potentially applicable architectures are discussed and evaluated, which combine different multiple access technologies, half-duplex/full-duplex configurations and network topologies. It is proven that the most suitable and efficient architecture for PFF mission is the use of the half-duplex CDMA with the topology that allows the role of being reference rotating from one spacecraft to another in different time slots. The capability of CDMA is also investigated in terms of the multiple access interference. The paper verifies that this interference can limit the maximum number of spacecraft and bounds the inter-satellite range diversity. The interference exhibits a Doppler dependency and suffers as well from the near-far problem. Inter-satellite navigation accuracy will easily drop down below meter level at the moments of zero- or n-kHz Doppler crossovers, and also in case of the signals being corrupted by the near-by interferences. Two realistic mission scenarios are provided to verify the severe effects of the interference. Operational considerations and interference mitigation methods are also recommended. Keywords-precision formation flying; communication; relative navigation; CDMA; Multiple access interference I