Architectures and Synchronization Techniques for Coherent Distributed Remote Sensing Systems

Abstract

Phase, frequency and time synchronization is a crucial requirement for many applications as such as multi-static remote sensing and distributed beamforming for communications. The literature on the field is very wide, and in some cases, the requirements of the proposed synchronization solution may surpass the ones set by the application itself. Moreover, the synchronization solution becomes even more challenging when the nodes are flying or hovering on aerial or space platforms. In this work, we compare and classify the synchronization technologies available in the literature according to a common proposed framework, and we discuss the considerations of an implementation for distributed remote sensing applications. The general framework considered is based on a distributed collection of autonomous nodes that try to synchronize their clocks with a common reference. Moreover, they can be classified in non-overlapping, adjacent and overlapping frequency band scenarios.

Satellite Communications in the New Space Era: A Survey and Future Challenges

“…In these applications the designers can make use of sensor fusion and offline processing. However, the implementation of data link communications using [189].…”

“…This configuration allows the use of cheaper and smaller spacecraft and to enlarge the number of array elements. Recently, the concept of cohesive swarms was coined [189] to describe the swarm implementations that do not require to have an accurate controllability of the array relative positions and attitudes but has an accurate monitoring of these parameters. The cohesive swarm use the parameters observations to compensate them in the signals transmitted or received by the whole array.…”

“…For this reason, the development of space missions from swarms have not been contemplated in the past for data communications applications, but for science missions where the nature of the distributed space system is crucial or strictly required to fulfil the mission objectives. Some examples, from proposed concept to actual missions, can be found in the remote sensing literature [189]. One example of synchronization and formation flying is performed in the Tandem-X mission from the German Aerospace Center.…”

A Remote Carrier Synchronization Technique for Coherent Distributed Remote Sensing Systems

“…The master reference is selected to be the one with the best frequency stability and phase noise performance. To establish such a reference lock, every combination of the radio nodes (n,m) transmit a waveform modulated with a known and controlled amplitude and phase [18]. Allowing every node to have a possible communication with other nodes will increase the SNR and, therefore, the quality of the synchronization of each node while avoiding the challenging requirements of big directive antennas and their accurate pointing.…”