  Cohesive Distributed Satellite Systems (CDSS) is a key enabling technology
for the future of remote sensing and communication missions. However, they have
to meet strict synchronization requirements before their use is generalized.
When clock or local oscillator signals are generated locally at each of the
distributed nodes, achieving exact synchronization in absolute phase,
frequency, and time is a complex problem. In addition, satellite systems have
significant resource constraints, especially for small satellites, which are
envisioned to be part of the future CDSS. Thus, the development of precise,
robust, and resource-efficient synchronization techniques is essential for the
advancement of future CDSS. In this context, this survey aims to summarize and
categorize the most relevant results on synchronization techniques for DSS.
First, some important architecture and system concepts are defined. Then, the
synchronization methods reported in the literature are reviewed and
categorized. This article also provides an extensive list of applications and
examples of synchronization techniques for DSS in addition to the most
significant advances in other operations closely related to synchronization,
such as inter-satellite ranging and relative position. The survey also provides
a discussion on emerging data-driven synchronization techniques based on ML.
Finally, a compilation of current research activities and potential research
topics is proposed, identifying problems and open challenges that can be useful
for researchers in the field.
