Inter-Satellite Radio Frequency Ranging in a Hybrid OFDM Communication-Metrology System

Precision Formation Flying (PFF) is an approach that enables the deployment of large-scale scientific instruments in future space missions. In PFF, multiple smaller satellites cooperate and interact with each other in order to accomplish objectives that are typically fulfilled by a much larger satellite. PFF missions require accurate knowledge regarding the relative positioning of the satellites in terms of distance and orientation. This paper presents a radio frequency ranging technique used in a hybrid Orthogonal Frequency Division Multiplexing (OFDM) communication-metrology system for a formation of two satellites. The technique, called the frequency correlation method, estimates the inter-satellite distance using an OFDM training symbol. We show how the precision of the estimation worsens as the bandwidth of the OFDM signal becomes narrower or the number of data subcarriers is reduced and we propose an improvement by performing a linear regression on multiple symbols. The basic and improved estimators are evaluated using MATLAB simulations and a real-time functioning test bed implemented with National Instruments Universal Software Radio Peripheral (USRP) platforms. The test parameters comply with the requirements of the physical layer of an inter-satellite link (ISL). The results show that the linear regression significantly improves the precision of the distance estimation at low SNRs and narrow bandwidth.