Time Synchronization for Anchorless Satellite Networks

Abstract

In this thesis, we propose a new class of pairwise frequency, multi-domain time synchronization and ranging algorithms for anchorless mobile networks of asynchronous nodes. We apply these techniques and study network and mission level aspects of time synchronization to Orbiting Low Frequency Array for Radio astronomy (OLFAR), a proposed distributed radio interferometer. In the first step, the Frequency Pairwise Least Squares (FPLS) that estimates clock skew and relative velocity in a pairwise setup using only frequency measurements is formulated. In the second step, we extend this method to a motion model with constant acceleration. Since frequency domain methods do not estimate clock offset and pairwise range, relying purely on frequency domain estimates is not feasible for various applications. To harness the potential of frequency domain synchronization and ranging, the Combined Pairwise Least Squares (CPLS) has been proposed. The combined method reduces the number of minimum required messages from 4 to 3 compared to current methods and decreases the computational complexity. Using a generic simulation with nodes in pairwise non-linear motion, we show that frequency domain methods can outperform time domain methods in clock skew and relative velocity estimation and that the proposed multi-domain method delivers better clock offset and pairwise range estimation in low to medium SNR conditions. In the second part of our work, we apply the proposed methods to OLFAR –— a space-borne large aperture radio interferometric array platform. We address network level and mission level aspects, proposing network path planning for pairwise synchronization algorithms and determining the required resynchronization period.