International Journal of Satellite Communications and Networking最新文献

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.

Optical space communications has long been considered the most efficient means for transferring information and keeping high-rate connection to various space assets, from Low-Earth Orbit via GEO and Moon towards the planets in our solar system. While technological boundaries prevented its use in the first place after the invention of the laser, initial evaluations of interorbit links for data repatriation in the 2000s proved its advantages (SILEX, OICETS, LCTSX). After that, Space Data High Way has demonstrated operational service provision with the EDRS constellation. Also, in deep space communication scenarios, LLCD and currently Psyche confirmed the advantages of optical communication in reaching the farther spots of our Solar System.

Nowadays, optical intersatellite links are already the technology of choice for network interconnects in LEO Mega-Constellations. In future, in Very-High-Throughput Satellite Systems (VHTS), the RF-feeder link will be replaced by optical feeders providing several Terabit/s in one beam instead of requiring a multitude of RF ground stations spread over several countries.

Furthermore, quantum key exchange and network securing by discrete particle states are already in early application phase on ground and in space applications, and finally, the application of deep space optical communications for Planetary Exploration promises not only extreme increase in data throughput but also new sensing and observation opportunities, up to the interplanetary internet as is required for human settling on other planets and asteroids, allowing to finally overcome the frontier of our terrestrial legacy.

Concluding, we would like to cordially thank all the authors for their excellent contributions and their perseverance during the long reviewing and publication process. We also compliment the reviewers for their valuable comments and suggestions which helped to further refine the quality of all papers. We trust that the readership will perceive this special issue beneficial and will take it as a reference for future developments in the field of Optical Space Communications and their scientific application.

The authors declare no conflicts of interest.

Optical satellite communications provide high-data rates with compact and power efficient payloads that can solve the bottlenecks of RF technologies. Photonic integrated circuits have the potential to reduce the cost, size, weight, and power consumption of satellite laser communications terminals, by integrating all the required photonic components on a chip. This can be achieved by leveraging on the mature technology for fiber communications. In this article, the technology status of photonic integrated circuits for optical satellite link is reviewed. Different material platforms are compared, with a focus on high-speed coherent optical communications. The integration of the photonic chip into a communications payload is discussed, together with possible challenges and opportunities. The impact of the space environment, especially the one of radiation, on the performance of the integrated photonic devices is reviewed and discussed.

Satellite-based laser communication is an emerging technology that is finding its way from research to industry. Compared to radio frequency (RF) systems, it has a more efficient size, weight, and power budget and, furthermore, is license free. The required space laser terminals can be designed in different sizes, depending on the mission needs. Data rate requirements range from CubeSats with Mb/s to large satellites with Gb/s data rates and sometimes even Tb/s. This enables, for example, the use of high-resolution imagers even in CubeSats or mega-constellation networks with high-rate intersatellite links. Space laser terminals are also necessary for satellite-based Quantum Key Distribution (QKD), which is increasingly important for the development of future quantum-safe networks. In contrast to classical optical links for data transmission, link budget constraints cannot be overcome by simply amplifying the power, but the end-to-end loss needs to be minimized. This is possible with high antenna gains defined by the transmit and receive optics size. Therefore, the optics size of the laser terminal is one of the most important parameters. Building optical terminals with large apertures for use in space is expensive and requires at least a small satellite platform, increasing the cost of development and launch. The New Space approach using a CubeSat platform is a cost-effective alternative because many components can be selected off-the-shelf. This paper reviews developments of laser communication terminals for CubeSats in space to ground and intersatellite scenarios with applications in quantum communications and telecommunications. The systems are selected with respect to clear space deployment, and their core parameters are compared. Special focus and detailed insight are given for the development OSIRIS4CubeSat (O4C).

Delay- and disruption-tolerant networking (DTN) enables communication in networks afflicted by long propagation delays and sporadic connectivity. DTN routing techniques such as schedule-aware bundle routing (SABR) exist to route data bundles in deterministic networks, such as those found in deep-space environments, where node contacts are predictable. This article begins with an overview of DTN architecture and SABR. SABR's method of final route selection (forwarding rules) is closely examined. The article then addresses a limitation of SABR whereby the algorithm may overlook parallel channels, leading to network congestion. To mitigate this, an enhancement is proposed. This enhancement aims to optimize data bundle distribution across candidate routes in networks with parallel channels, thus alleviating congestion and enhancing overall network performance. This is achieved with simple modifications to SABR's forwarding rules to avoid the concentration of data bundles on a minority of node contacts. The enhancement is demonstrated through simulations in a reference scenario implemented in DtnSim.

Direct-to-satellite communication for the Internet of Things (IoT) has attracted significant interest from both the scientific community and major telecommunications players. The integration of satellite connectivity in smartphones and IoT devices promises a transformative impact on critical applications such as environmental monitoring, asset tracking, agriculture, and nature conservation. These applications require reliable and energy-efficient technologies for transmitting sensor data from regions without terrestrial networks, necessitating robust design of waveforms and protocols. This work investigates the most suitable IoT protocols for direct-to-satellite communication, emphasizing overhead, spectral, and energy efficiency. By introducing a framework and evaluation metrics that incorporate physical layer overhead into the evaluation, a comprehensive analysis of the effective energy efficiency in satellite IoT systems is conducted. Our findings highlight substantial differences among the Low Power Wide Area Network (LPWAN) protocols. Consequently, we propose a new classification for the most energy-efficient protocols, termed Massive Multiple Access very Low Power Wide Area Networks (MMA-vLPWANs). This classification aims to streamline the selection process for energy-conscious satellite IoT waveforms for deployments in remote areas. The results not only advance the understanding of protocol efficiency in satellite IoT communications but also offer a guideline for optimizing power usage in IoT devices, extending their operational life and enhancing their utility in inaccessible regions.