Why Optical Wireless in Satellite Communications
By Hossein Safi (PhD Student)
Satellite communication links utilizing conventional commercial bandwidth allocations, such as the X, Ku, and Ka bands, are grappling with the escalating demand for data-intensive services in 6G and beyond systems. This growing discrepancy has compelled satellite operators to explore alternatives that can offer higher bandwidth capacity. Optical wireless communication is emerging as a key solution for satellite systems due to its inherent advantages. Offering higher data rates, lower latency, a license-free spectrum band, and increased bandwidth compared to traditional radio frequency (RF) communication, optical wireless presents a compelling response to the evolving needs of satellite-based communications.
Credit: SpaceX’s Starlink
Recent Projects and current trends
The current landscape of satellite-based optical wireless communications is characterized by several noteworthy trends, reflecting advancements in technology and emerging standards.
Recent developments showcase an increasing preference for optical wireless in satellite communication links [1]. Indeed, the integration of optical communication in satellite constellations has gained momentum. Projects like SpaceX’s Starlink [2] and Telesat’s Lightspeed [3] employing constellations of satellites, demonstrate the feasibility and advantages of optical wireless communication in providing global coverage and enabling high-throughput data delivery.
Commercial applications are witnessing increased interest, with satellite operators exploring partnerships and collaborations to deploy optical communication solutions. This trend is indicative of the growing confidence in the capabilities of optical wireless communication to meet the evolving requirements of satellite networks. The current trends highlight the dynamic nature of satellite-based optical wireless communications, with ongoing advancements poised to transform the way we approach satellite connectivity. This shift towards optical solutions positions the field as a key player in shaping the future of satellite communications.
For instance, Starlink, utilizes optical wireless communication via lasers to deliver remarkable results. According to the latest report from Starlink [4], the system is delivering over 42 petabytes of data for customers per day. The lasers employed in this system are capable of sustaining a 100 Gbps connection per link. This capability is especially crucial in scenarios where no SpaceX ground station is near, such as over the ocean or Antarctic, enabling the satellites to fetch data efficiently.
This innovative approach exemplifies the potential of optical wireless communication in satellite systems, providing not only high data rates but also robust connectivity in challenging environments.
Ongoing Research at the LiFi Research Centre
Within the LiFi Research Centre, our commitment to advancing optical wireless communication in satellite systems is evident through several ongoing research projects addressing key challenges and opportunities in the field. One project focuses on establishing a comprehensive channel model for ground-to-satellite optical links utilizing an array of avalanche photodiodes (APDs) at the satellite receiver. Particularly, there are limitations to consider, such as fluctuations in the angle of arrival caused by satellite vibrations, which are often the result of using commercially available products with imperfect stabilization mechanisms. Motivated by this, our primary objective is to present a channel model that integrates various parameters affecting the communication link. This research aims to enhance our understanding of the optical communication channel, paving the way for improved performance and reliability. In parallel, we are dedicated to proposing low complex data detection schemes tailored for newly announced, compact satellite architectures, such as CubeSats. These architectures, characterized by constraints in size, weight, and power (SWaP), present unique challenges that require innovative solutions for efficient optical communication. In particular, as the mission lifetime of a satellite is mainly determined by its battery life, maximizing a satellite’s battery life is critical for minimizing the replacement cost of the satellites. In this regard, we aim to keep power consumption by the communication system as low as possible to increase the battery lifetime. This strategic approach not only contributes to the sustainability of satellite missions but also aligns with the broader objective of optimizing operational costs and ensuring prolonged functionality in space environments. Additionally, our endeavours extend to the development of fast and accurate approaches for the acquisition and tracking of CubeSats in low Earth orbits (LEO).
By addressing these challenges, we aim to contribute to the advancement of optical communication technologies, pushing the boundaries to improve data rates, signal reliability, and overall performance.
References
[1] J. Liang et al., “Free-Space Optical (FSO) Satellite Networks Performance Analysis: Transmission Power, Latency, and Outage Probability,” in IEEE Open Journal of Vehicular Technology, doi: 10.1109/OJVT.2023.3341409.
[2] https://www.starlink.com/technology
[3] Telesat Canada FCC update, May 2020, “Application for Modification of Market Access Authorization,” [Online]. Available: https: //fcc.report/IBFS/SATMPL-20200526-00053/2378318.pdf, Accessed: November 2, 2023.
[4] https://uk.pcmag.com/networking/150673/starlinks-laser-system-is-beaming-42-million-gb-of-data-per-day