System-level benefit of variable data rate in optical LEO direct-to-earth links

Abstract

The paper investigates the benefits of employing a Variable Data Rate (VDR) scheme in optical Low Earth Orbit (LEO) Direct-to-Earth (DTE) links at system level. In contrast to the Constant Data Rate (CDR) transmission approach adopted in current systems of the kind, the VDR scheme allows to optimize the data rate of the optical link within a satellite pass. Indeed, both the link budget and the atmospheric effects heavily depend on the satellite elevation angle, which varies significantly within a satellite pass. In order to thoroughly carry out the system level comparison between VDR and CDR, the paper first addresses all necessary aspects involved, including channel modeling, waveform and interleaver dimensioning, and link budget issues. For the scenario evaluated in the paper, the average throughput improvement of VDR versus CDR is found to be 100%. The paper also addresses interesting trade-offs concerning possible concepts of operations (ConOps) of the link once the VDR is in place. This preliminary work will be followed up by the Agency with further industrialized technology developments and system refinements.

Link budget calculation in optical LEO satellite downlinks with on/off‐keying and large signal divergence: A simplified methodology

“…Therefore, techniques of variable coding and modulation, or just symbol rate adaptation (variable data rate [VDR]), are required 71 . Such proceeding can already be found in according standardization approaches 12 …”

“…Besides optical inter‐satellite links, the direct‐to‐Earth transmission scenario of optical LEO downlinks (OLEODL) is of major interest 3–10 . Standardization and optimization efforts are ongoing to enable international use between different satellite missions and optical ground station (OGS) 11–13 . The carrier wavelengths employed today for optical Direct‐to‐Earth (DTE) links are in the 1550 nm region (or around 193.4 THz) using intensity‐modulation direct‐detection (IM/DD) signal formats.…”

Universal High-Throughput and Low-Complexity LDPC Decoder for Laser Communications

“…Traditional radio frequency (RF) communications are nearing their bandwidth limit, driving the demand for laser communications, which offer higher bandwidth (up to multigigabit per second), reduced weight, enhanced flexibility, and improved security. However, the propagation channel of laser communications is less than ideal due to environmental factors such as free space loss, atmospheric attenuation, and turbulence of the refraction index, resulting in channel fading [1], [2]. Therefore, channel coding is essential to protect the transmitted signal against the effects of propagation channel impairments [3].…”