Review and Analysis of Digital Signal Processing Algorithms for Coherent Optical Satellite Links

Coherent optical satellite links enable high-throughput communication and high accuracy ranging to and between satellites. Due to the ever-increasing demand for throughput, wavelength division multiplexing of polarization multiplexed optical signals is being considered as a solution to provide high-speed optical satellite links. Fiber-optic systems solve the implementation scalability problem of these systems by shifting design complexity to integrated circuits, thereby massively reducing the system footprint. As a result of the major advances in complementary metal-oxide-semiconductor (CMOS) technology, the implementation scalability of such systems in terrestrial fiber systems has been solved by shifting the system complexity to digital hardware, enabling intradyne reception and complex signal recovery algorithms. While the use of fiber-optic transceivers provides a fast path to high-speed coherent optical satellite links (OSLs), it requires additional mitigation techniques to combat the effects of both the OSL channel and the space environment. To support future satellite networks with Tbit/s optical links, it will be critical to further minimize the size, weight, and power (SWaP), cost and reliability of the transceivers. Thus, the development of custom intradyne optical transceivers for OSLs is emerging as an attractive option as the demand for throughput in satellite networks continues to grow. This would not only enable the use of a more optimized signal processing chain but also enable the use of radiation mitigation techniques optimized for the signal processing architecture and the use of soft-decision forward error correction (FEC) optimized for OSLs. The signal processing of coherent optical satellite receivers can be divided into three key subsystems: timing recovery, carrier synchronization, and equalization. This paper reviews state-of-the-art digital signal processing for optical communication to identify suitable algorithms for timing recovery, carrier frequency and phase compensation, equalization, and polarization demultiplexing with emphasis on high-throughput optical satellite links. Finally, the performance of different digital signal processing algorithms is assessed by numerical simulations considering different optical satellite link scenarios.